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Linux/init/Kconfig

  1 config ARCH
  2         string
  3         option env="ARCH"
  4 
  5 config KERNELVERSION
  6         string
  7         option env="KERNELVERSION"
  8 
  9 config DEFCONFIG_LIST
 10         string
 11         depends on !UML
 12         option defconfig_list
 13         default "/lib/modules/$UNAME_RELEASE/.config"
 14         default "/etc/kernel-config"
 15         default "/boot/config-$UNAME_RELEASE"
 16         default "$ARCH_DEFCONFIG"
 17         default "arch/$ARCH/defconfig"
 18 
 19 config CONSTRUCTORS
 20         bool
 21         depends on !UML
 22 
 23 config IRQ_WORK
 24         bool
 25 
 26 config BUILDTIME_EXTABLE_SORT
 27         bool
 28 
 29 config THREAD_INFO_IN_TASK
 30         bool
 31         help
 32           Select this to move thread_info off the stack into task_struct.  To
 33           make this work, an arch will need to remove all thread_info fields
 34           except flags and fix any runtime bugs.
 35 
 36           One subtle change that will be needed is to use try_get_task_stack()
 37           and put_task_stack() in save_thread_stack_tsk() and get_wchan().
 38 
 39 menu "General setup"
 40 
 41 config BROKEN
 42         bool
 43 
 44 config BROKEN_ON_SMP
 45         bool
 46         depends on BROKEN || !SMP
 47         default y
 48 
 49 config INIT_ENV_ARG_LIMIT
 50         int
 51         default 32 if !UML
 52         default 128 if UML
 53         help
 54           Maximum of each of the number of arguments and environment
 55           variables passed to init from the kernel command line.
 56 
 57 
 58 config CROSS_COMPILE
 59         string "Cross-compiler tool prefix"
 60         help
 61           Same as running 'make CROSS_COMPILE=prefix-' but stored for
 62           default make runs in this kernel build directory.  You don't
 63           need to set this unless you want the configured kernel build
 64           directory to select the cross-compiler automatically.
 65 
 66 config COMPILE_TEST
 67         bool "Compile also drivers which will not load"
 68         depends on !UML
 69         default n
 70         help
 71           Some drivers can be compiled on a different platform than they are
 72           intended to be run on. Despite they cannot be loaded there (or even
 73           when they load they cannot be used due to missing HW support),
 74           developers still, opposing to distributors, might want to build such
 75           drivers to compile-test them.
 76 
 77           If you are a developer and want to build everything available, say Y
 78           here. If you are a user/distributor, say N here to exclude useless
 79           drivers to be distributed.
 80 
 81 config LOCALVERSION
 82         string "Local version - append to kernel release"
 83         help
 84           Append an extra string to the end of your kernel version.
 85           This will show up when you type uname, for example.
 86           The string you set here will be appended after the contents of
 87           any files with a filename matching localversion* in your
 88           object and source tree, in that order.  Your total string can
 89           be a maximum of 64 characters.
 90 
 91 config LOCALVERSION_AUTO
 92         bool "Automatically append version information to the version string"
 93         default y
 94         depends on !COMPILE_TEST
 95         help
 96           This will try to automatically determine if the current tree is a
 97           release tree by looking for git tags that belong to the current
 98           top of tree revision.
 99 
100           A string of the format -gxxxxxxxx will be added to the localversion
101           if a git-based tree is found.  The string generated by this will be
102           appended after any matching localversion* files, and after the value
103           set in CONFIG_LOCALVERSION.
104 
105           (The actual string used here is the first eight characters produced
106           by running the command:
107 
108             $ git rev-parse --verify HEAD
109 
110           which is done within the script "scripts/setlocalversion".)
111 
112 config HAVE_KERNEL_GZIP
113         bool
114 
115 config HAVE_KERNEL_BZIP2
116         bool
117 
118 config HAVE_KERNEL_LZMA
119         bool
120 
121 config HAVE_KERNEL_XZ
122         bool
123 
124 config HAVE_KERNEL_LZO
125         bool
126 
127 config HAVE_KERNEL_LZ4
128         bool
129 
130 choice
131         prompt "Kernel compression mode"
132         default KERNEL_GZIP
133         depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
134         help
135           The linux kernel is a kind of self-extracting executable.
136           Several compression algorithms are available, which differ
137           in efficiency, compression and decompression speed.
138           Compression speed is only relevant when building a kernel.
139           Decompression speed is relevant at each boot.
140 
141           If you have any problems with bzip2 or lzma compressed
142           kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
143           version of this functionality (bzip2 only), for 2.4, was
144           supplied by Christian Ludwig)
145 
146           High compression options are mostly useful for users, who
147           are low on disk space (embedded systems), but for whom ram
148           size matters less.
149 
150           If in doubt, select 'gzip'
151 
152 config KERNEL_GZIP
153         bool "Gzip"
154         depends on HAVE_KERNEL_GZIP
155         help
156           The old and tried gzip compression. It provides a good balance
157           between compression ratio and decompression speed.
158 
159 config KERNEL_BZIP2
160         bool "Bzip2"
161         depends on HAVE_KERNEL_BZIP2
162         help
163           Its compression ratio and speed is intermediate.
164           Decompression speed is slowest among the choices.  The kernel
165           size is about 10% smaller with bzip2, in comparison to gzip.
166           Bzip2 uses a large amount of memory. For modern kernels you
167           will need at least 8MB RAM or more for booting.
168 
169 config KERNEL_LZMA
170         bool "LZMA"
171         depends on HAVE_KERNEL_LZMA
172         help
173           This compression algorithm's ratio is best.  Decompression speed
174           is between gzip and bzip2.  Compression is slowest.
175           The kernel size is about 33% smaller with LZMA in comparison to gzip.
176 
177 config KERNEL_XZ
178         bool "XZ"
179         depends on HAVE_KERNEL_XZ
180         help
181           XZ uses the LZMA2 algorithm and instruction set specific
182           BCJ filters which can improve compression ratio of executable
183           code. The size of the kernel is about 30% smaller with XZ in
184           comparison to gzip. On architectures for which there is a BCJ
185           filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
186           will create a few percent smaller kernel than plain LZMA.
187 
188           The speed is about the same as with LZMA: The decompression
189           speed of XZ is better than that of bzip2 but worse than gzip
190           and LZO. Compression is slow.
191 
192 config KERNEL_LZO
193         bool "LZO"
194         depends on HAVE_KERNEL_LZO
195         help
196           Its compression ratio is the poorest among the choices. The kernel
197           size is about 10% bigger than gzip; however its speed
198           (both compression and decompression) is the fastest.
199 
200 config KERNEL_LZ4
201         bool "LZ4"
202         depends on HAVE_KERNEL_LZ4
203         help
204           LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
205           A preliminary version of LZ4 de/compression tool is available at
206           <https://code.google.com/p/lz4/>.
207 
208           Its compression ratio is worse than LZO. The size of the kernel
209           is about 8% bigger than LZO. But the decompression speed is
210           faster than LZO.
211 
212 endchoice
213 
214 config DEFAULT_HOSTNAME
215         string "Default hostname"
216         default "(none)"
217         help
218           This option determines the default system hostname before userspace
219           calls sethostname(2). The kernel traditionally uses "(none)" here,
220           but you may wish to use a different default here to make a minimal
221           system more usable with less configuration.
222 
223 config SWAP
224         bool "Support for paging of anonymous memory (swap)"
225         depends on MMU && BLOCK
226         default y
227         help
228           This option allows you to choose whether you want to have support
229           for so called swap devices or swap files in your kernel that are
230           used to provide more virtual memory than the actual RAM present
231           in your computer.  If unsure say Y.
232 
233 config SYSVIPC
234         bool "System V IPC"
235         ---help---
236           Inter Process Communication is a suite of library functions and
237           system calls which let processes (running programs) synchronize and
238           exchange information. It is generally considered to be a good thing,
239           and some programs won't run unless you say Y here. In particular, if
240           you want to run the DOS emulator dosemu under Linux (read the
241           DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
242           you'll need to say Y here.
243 
244           You can find documentation about IPC with "info ipc" and also in
245           section 6.4 of the Linux Programmer's Guide, available from
246           <http://www.tldp.org/guides.html>.
247 
248 config SYSVIPC_SYSCTL
249         bool
250         depends on SYSVIPC
251         depends on SYSCTL
252         default y
253 
254 config POSIX_MQUEUE
255         bool "POSIX Message Queues"
256         depends on NET
257         ---help---
258           POSIX variant of message queues is a part of IPC. In POSIX message
259           queues every message has a priority which decides about succession
260           of receiving it by a process. If you want to compile and run
261           programs written e.g. for Solaris with use of its POSIX message
262           queues (functions mq_*) say Y here.
263 
264           POSIX message queues are visible as a filesystem called 'mqueue'
265           and can be mounted somewhere if you want to do filesystem
266           operations on message queues.
267 
268           If unsure, say Y.
269 
270 config POSIX_MQUEUE_SYSCTL
271         bool
272         depends on POSIX_MQUEUE
273         depends on SYSCTL
274         default y
275 
276 config CROSS_MEMORY_ATTACH
277         bool "Enable process_vm_readv/writev syscalls"
278         depends on MMU
279         default y
280         help
281           Enabling this option adds the system calls process_vm_readv and
282           process_vm_writev which allow a process with the correct privileges
283           to directly read from or write to another process' address space.
284           See the man page for more details.
285 
286 config FHANDLE
287         bool "open by fhandle syscalls" if EXPERT
288         select EXPORTFS
289         default y
290         help
291           If you say Y here, a user level program will be able to map
292           file names to handle and then later use the handle for
293           different file system operations. This is useful in implementing
294           userspace file servers, which now track files using handles instead
295           of names. The handle would remain the same even if file names
296           get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
297           syscalls.
298 
299 config USELIB
300         bool "uselib syscall"
301         def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
302         help
303           This option enables the uselib syscall, a system call used in the
304           dynamic linker from libc5 and earlier.  glibc does not use this
305           system call.  If you intend to run programs built on libc5 or
306           earlier, you may need to enable this syscall.  Current systems
307           running glibc can safely disable this.
308 
309 config AUDIT
310         bool "Auditing support"
311         depends on NET
312         help
313           Enable auditing infrastructure that can be used with another
314           kernel subsystem, such as SELinux (which requires this for
315           logging of avc messages output).  System call auditing is included
316           on architectures which support it.
317 
318 config HAVE_ARCH_AUDITSYSCALL
319         bool
320 
321 config AUDITSYSCALL
322         def_bool y
323         depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
324 
325 config AUDIT_WATCH
326         def_bool y
327         depends on AUDITSYSCALL
328         select FSNOTIFY
329 
330 config AUDIT_TREE
331         def_bool y
332         depends on AUDITSYSCALL
333         select FSNOTIFY
334 
335 source "kernel/irq/Kconfig"
336 source "kernel/time/Kconfig"
337 
338 menu "CPU/Task time and stats accounting"
339 
340 config VIRT_CPU_ACCOUNTING
341         bool
342 
343 choice
344         prompt "Cputime accounting"
345         default TICK_CPU_ACCOUNTING if !PPC64
346         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
347 
348 # Kind of a stub config for the pure tick based cputime accounting
349 config TICK_CPU_ACCOUNTING
350         bool "Simple tick based cputime accounting"
351         depends on !S390 && !NO_HZ_FULL
352         help
353           This is the basic tick based cputime accounting that maintains
354           statistics about user, system and idle time spent on per jiffies
355           granularity.
356 
357           If unsure, say Y.
358 
359 config VIRT_CPU_ACCOUNTING_NATIVE
360         bool "Deterministic task and CPU time accounting"
361         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
362         select VIRT_CPU_ACCOUNTING
363         help
364           Select this option to enable more accurate task and CPU time
365           accounting.  This is done by reading a CPU counter on each
366           kernel entry and exit and on transitions within the kernel
367           between system, softirq and hardirq state, so there is a
368           small performance impact.  In the case of s390 or IBM POWER > 5,
369           this also enables accounting of stolen time on logically-partitioned
370           systems.
371 
372 config VIRT_CPU_ACCOUNTING_GEN
373         bool "Full dynticks CPU time accounting"
374         depends on HAVE_CONTEXT_TRACKING
375         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
376         select VIRT_CPU_ACCOUNTING
377         select CONTEXT_TRACKING
378         help
379           Select this option to enable task and CPU time accounting on full
380           dynticks systems. This accounting is implemented by watching every
381           kernel-user boundaries using the context tracking subsystem.
382           The accounting is thus performed at the expense of some significant
383           overhead.
384 
385           For now this is only useful if you are working on the full
386           dynticks subsystem development.
387 
388           If unsure, say N.
389 
390 endchoice
391 
392 config IRQ_TIME_ACCOUNTING
393         bool "Fine granularity task level IRQ time accounting"
394         depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
395         help
396           Select this option to enable fine granularity task irq time
397           accounting. This is done by reading a timestamp on each
398           transitions between softirq and hardirq state, so there can be a
399           small performance impact.
400 
401           If in doubt, say N here.
402 
403 config BSD_PROCESS_ACCT
404         bool "BSD Process Accounting"
405         depends on MULTIUSER
406         help
407           If you say Y here, a user level program will be able to instruct the
408           kernel (via a special system call) to write process accounting
409           information to a file: whenever a process exits, information about
410           that process will be appended to the file by the kernel.  The
411           information includes things such as creation time, owning user,
412           command name, memory usage, controlling terminal etc. (the complete
413           list is in the struct acct in <file:include/linux/acct.h>).  It is
414           up to the user level program to do useful things with this
415           information.  This is generally a good idea, so say Y.
416 
417 config BSD_PROCESS_ACCT_V3
418         bool "BSD Process Accounting version 3 file format"
419         depends on BSD_PROCESS_ACCT
420         default n
421         help
422           If you say Y here, the process accounting information is written
423           in a new file format that also logs the process IDs of each
424           process and it's parent. Note that this file format is incompatible
425           with previous v0/v1/v2 file formats, so you will need updated tools
426           for processing it. A preliminary version of these tools is available
427           at <http://www.gnu.org/software/acct/>.
428 
429 config TASKSTATS
430         bool "Export task/process statistics through netlink"
431         depends on NET
432         depends on MULTIUSER
433         default n
434         help
435           Export selected statistics for tasks/processes through the
436           generic netlink interface. Unlike BSD process accounting, the
437           statistics are available during the lifetime of tasks/processes as
438           responses to commands. Like BSD accounting, they are sent to user
439           space on task exit.
440 
441           Say N if unsure.
442 
443 config TASK_DELAY_ACCT
444         bool "Enable per-task delay accounting"
445         depends on TASKSTATS
446         select SCHED_INFO
447         help
448           Collect information on time spent by a task waiting for system
449           resources like cpu, synchronous block I/O completion and swapping
450           in pages. Such statistics can help in setting a task's priorities
451           relative to other tasks for cpu, io, rss limits etc.
452 
453           Say N if unsure.
454 
455 config TASK_XACCT
456         bool "Enable extended accounting over taskstats"
457         depends on TASKSTATS
458         help
459           Collect extended task accounting data and send the data
460           to userland for processing over the taskstats interface.
461 
462           Say N if unsure.
463 
464 config TASK_IO_ACCOUNTING
465         bool "Enable per-task storage I/O accounting"
466         depends on TASK_XACCT
467         help
468           Collect information on the number of bytes of storage I/O which this
469           task has caused.
470 
471           Say N if unsure.
472 
473 endmenu # "CPU/Task time and stats accounting"
474 
475 menu "RCU Subsystem"
476 
477 config TREE_RCU
478         bool
479         default y if !PREEMPT && SMP
480         help
481           This option selects the RCU implementation that is
482           designed for very large SMP system with hundreds or
483           thousands of CPUs.  It also scales down nicely to
484           smaller systems.
485 
486 config PREEMPT_RCU
487         bool
488         default y if PREEMPT
489         help
490           This option selects the RCU implementation that is
491           designed for very large SMP systems with hundreds or
492           thousands of CPUs, but for which real-time response
493           is also required.  It also scales down nicely to
494           smaller systems.
495 
496           Select this option if you are unsure.
497 
498 config TINY_RCU
499         bool
500         default y if !PREEMPT && !SMP
501         help
502           This option selects the RCU implementation that is
503           designed for UP systems from which real-time response
504           is not required.  This option greatly reduces the
505           memory footprint of RCU.
506 
507 config RCU_EXPERT
508         bool "Make expert-level adjustments to RCU configuration"
509         default n
510         help
511           This option needs to be enabled if you wish to make
512           expert-level adjustments to RCU configuration.  By default,
513           no such adjustments can be made, which has the often-beneficial
514           side-effect of preventing "make oldconfig" from asking you all
515           sorts of detailed questions about how you would like numerous
516           obscure RCU options to be set up.
517 
518           Say Y if you need to make expert-level adjustments to RCU.
519 
520           Say N if you are unsure.
521 
522 config SRCU
523         bool
524         help
525           This option selects the sleepable version of RCU. This version
526           permits arbitrary sleeping or blocking within RCU read-side critical
527           sections.
528 
529 config TASKS_RCU
530         bool
531         default n
532         depends on !UML
533         select SRCU
534         help
535           This option enables a task-based RCU implementation that uses
536           only voluntary context switch (not preemption!), idle, and
537           user-mode execution as quiescent states.
538 
539 config RCU_STALL_COMMON
540         def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
541         help
542           This option enables RCU CPU stall code that is common between
543           the TINY and TREE variants of RCU.  The purpose is to allow
544           the tiny variants to disable RCU CPU stall warnings, while
545           making these warnings mandatory for the tree variants.
546 
547 config CONTEXT_TRACKING
548        bool
549 
550 config CONTEXT_TRACKING_FORCE
551         bool "Force context tracking"
552         depends on CONTEXT_TRACKING
553         default y if !NO_HZ_FULL
554         help
555           The major pre-requirement for full dynticks to work is to
556           support the context tracking subsystem. But there are also
557           other dependencies to provide in order to make the full
558           dynticks working.
559 
560           This option stands for testing when an arch implements the
561           context tracking backend but doesn't yet fullfill all the
562           requirements to make the full dynticks feature working.
563           Without the full dynticks, there is no way to test the support
564           for context tracking and the subsystems that rely on it: RCU
565           userspace extended quiescent state and tickless cputime
566           accounting. This option copes with the absence of the full
567           dynticks subsystem by forcing the context tracking on all
568           CPUs in the system.
569 
570           Say Y only if you're working on the development of an
571           architecture backend for the context tracking.
572 
573           Say N otherwise, this option brings an overhead that you
574           don't want in production.
575 
576 
577 config RCU_FANOUT
578         int "Tree-based hierarchical RCU fanout value"
579         range 2 64 if 64BIT
580         range 2 32 if !64BIT
581         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
582         default 64 if 64BIT
583         default 32 if !64BIT
584         help
585           This option controls the fanout of hierarchical implementations
586           of RCU, allowing RCU to work efficiently on machines with
587           large numbers of CPUs.  This value must be at least the fourth
588           root of NR_CPUS, which allows NR_CPUS to be insanely large.
589           The default value of RCU_FANOUT should be used for production
590           systems, but if you are stress-testing the RCU implementation
591           itself, small RCU_FANOUT values allow you to test large-system
592           code paths on small(er) systems.
593 
594           Select a specific number if testing RCU itself.
595           Take the default if unsure.
596 
597 config RCU_FANOUT_LEAF
598         int "Tree-based hierarchical RCU leaf-level fanout value"
599         range 2 64 if 64BIT
600         range 2 32 if !64BIT
601         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
602         default 16
603         help
604           This option controls the leaf-level fanout of hierarchical
605           implementations of RCU, and allows trading off cache misses
606           against lock contention.  Systems that synchronize their
607           scheduling-clock interrupts for energy-efficiency reasons will
608           want the default because the smaller leaf-level fanout keeps
609           lock contention levels acceptably low.  Very large systems
610           (hundreds or thousands of CPUs) will instead want to set this
611           value to the maximum value possible in order to reduce the
612           number of cache misses incurred during RCU's grace-period
613           initialization.  These systems tend to run CPU-bound, and thus
614           are not helped by synchronized interrupts, and thus tend to
615           skew them, which reduces lock contention enough that large
616           leaf-level fanouts work well.
617 
618           Select a specific number if testing RCU itself.
619 
620           Select the maximum permissible value for large systems.
621 
622           Take the default if unsure.
623 
624 config RCU_FAST_NO_HZ
625         bool "Accelerate last non-dyntick-idle CPU's grace periods"
626         depends on NO_HZ_COMMON && SMP && RCU_EXPERT
627         default n
628         help
629           This option permits CPUs to enter dynticks-idle state even if
630           they have RCU callbacks queued, and prevents RCU from waking
631           these CPUs up more than roughly once every four jiffies (by
632           default, you can adjust this using the rcutree.rcu_idle_gp_delay
633           parameter), thus improving energy efficiency.  On the other
634           hand, this option increases the duration of RCU grace periods,
635           for example, slowing down synchronize_rcu().
636 
637           Say Y if energy efficiency is critically important, and you
638                 don't care about increased grace-period durations.
639 
640           Say N if you are unsure.
641 
642 config TREE_RCU_TRACE
643         def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
644         select DEBUG_FS
645         help
646           This option provides tracing for the TREE_RCU and
647           PREEMPT_RCU implementations, permitting Makefile to
648           trivially select kernel/rcutree_trace.c.
649 
650 config RCU_BOOST
651         bool "Enable RCU priority boosting"
652         depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
653         default n
654         help
655           This option boosts the priority of preempted RCU readers that
656           block the current preemptible RCU grace period for too long.
657           This option also prevents heavy loads from blocking RCU
658           callback invocation for all flavors of RCU.
659 
660           Say Y here if you are working with real-time apps or heavy loads
661           Say N here if you are unsure.
662 
663 config RCU_KTHREAD_PRIO
664         int "Real-time priority to use for RCU worker threads"
665         range 1 99 if RCU_BOOST
666         range 0 99 if !RCU_BOOST
667         default 1 if RCU_BOOST
668         default 0 if !RCU_BOOST
669         depends on RCU_EXPERT
670         help
671           This option specifies the SCHED_FIFO priority value that will be
672           assigned to the rcuc/n and rcub/n threads and is also the value
673           used for RCU_BOOST (if enabled). If you are working with a
674           real-time application that has one or more CPU-bound threads
675           running at a real-time priority level, you should set
676           RCU_KTHREAD_PRIO to a priority higher than the highest-priority
677           real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO
678           value of 1 is appropriate in the common case, which is real-time
679           applications that do not have any CPU-bound threads.
680 
681           Some real-time applications might not have a single real-time
682           thread that saturates a given CPU, but instead might have
683           multiple real-time threads that, taken together, fully utilize
684           that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
685           a priority higher than the lowest-priority thread that is
686           conspiring to prevent the CPU from running any non-real-time
687           tasks.  For example, if one thread at priority 10 and another
688           thread at priority 5 are between themselves fully consuming
689           the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
690           set to priority 6 or higher.
691 
692           Specify the real-time priority, or take the default if unsure.
693 
694 config RCU_BOOST_DELAY
695         int "Milliseconds to delay boosting after RCU grace-period start"
696         range 0 3000
697         depends on RCU_BOOST
698         default 500
699         help
700           This option specifies the time to wait after the beginning of
701           a given grace period before priority-boosting preempted RCU
702           readers blocking that grace period.  Note that any RCU reader
703           blocking an expedited RCU grace period is boosted immediately.
704 
705           Accept the default if unsure.
706 
707 config RCU_NOCB_CPU
708         bool "Offload RCU callback processing from boot-selected CPUs"
709         depends on TREE_RCU || PREEMPT_RCU
710         depends on RCU_EXPERT || NO_HZ_FULL
711         default n
712         help
713           Use this option to reduce OS jitter for aggressive HPC or
714           real-time workloads.  It can also be used to offload RCU
715           callback invocation to energy-efficient CPUs in battery-powered
716           asymmetric multiprocessors.
717 
718           This option offloads callback invocation from the set of
719           CPUs specified at boot time by the rcu_nocbs parameter.
720           For each such CPU, a kthread ("rcuox/N") will be created to
721           invoke callbacks, where the "N" is the CPU being offloaded,
722           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
723           "s" for RCU-sched.  Nothing prevents this kthread from running
724           on the specified CPUs, but (1) the kthreads may be preempted
725           between each callback, and (2) affinity or cgroups can be used
726           to force the kthreads to run on whatever set of CPUs is desired.
727 
728           Say Y here if you want to help to debug reduced OS jitter.
729           Say N here if you are unsure.
730 
731 choice
732         prompt "Build-forced no-CBs CPUs"
733         default RCU_NOCB_CPU_NONE
734         depends on RCU_NOCB_CPU
735         help
736           This option allows no-CBs CPUs (whose RCU callbacks are invoked
737           from kthreads rather than from softirq context) to be specified
738           at build time.  Additional no-CBs CPUs may be specified by
739           the rcu_nocbs= boot parameter.
740 
741 config RCU_NOCB_CPU_NONE
742         bool "No build_forced no-CBs CPUs"
743         help
744           This option does not force any of the CPUs to be no-CBs CPUs.
745           Only CPUs designated by the rcu_nocbs= boot parameter will be
746           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
747           kthreads whose names begin with "rcuo".  All other CPUs will
748           invoke their own RCU callbacks in softirq context.
749 
750           Select this option if you want to choose no-CBs CPUs at
751           boot time, for example, to allow testing of different no-CBs
752           configurations without having to rebuild the kernel each time.
753 
754 config RCU_NOCB_CPU_ZERO
755         bool "CPU 0 is a build_forced no-CBs CPU"
756         help
757           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
758           callbacks are invoked by a per-CPU kthread whose name begins
759           with "rcuo".  Additional CPUs may be designated as no-CBs
760           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
761           All other CPUs will invoke their own RCU callbacks in softirq
762           context.
763 
764           Select this if CPU 0 needs to be a no-CBs CPU for real-time
765           or energy-efficiency reasons, but the real reason it exists
766           is to ensure that randconfig testing covers mixed systems.
767 
768 config RCU_NOCB_CPU_ALL
769         bool "All CPUs are build_forced no-CBs CPUs"
770         help
771           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
772           boot parameter will be ignored.  All CPUs' RCU callbacks will
773           be executed in the context of per-CPU rcuo kthreads created for
774           this purpose.  Assuming that the kthreads whose names start with
775           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
776           on the remaining CPUs, but might decrease memory locality during
777           RCU-callback invocation, thus potentially degrading throughput.
778 
779           Select this if all CPUs need to be no-CBs CPUs for real-time
780           or energy-efficiency reasons.
781 
782 endchoice
783 
784 config RCU_EXPEDITE_BOOT
785         bool
786         default n
787         help
788           This option enables expedited grace periods at boot time,
789           as if rcu_expedite_gp() had been invoked early in boot.
790           The corresponding rcu_unexpedite_gp() is invoked from
791           rcu_end_inkernel_boot(), which is intended to be invoked
792           at the end of the kernel-only boot sequence, just before
793           init is exec'ed.
794 
795           Accept the default if unsure.
796 
797 endmenu # "RCU Subsystem"
798 
799 config BUILD_BIN2C
800         bool
801         default n
802 
803 config IKCONFIG
804         tristate "Kernel .config support"
805         select BUILD_BIN2C
806         ---help---
807           This option enables the complete Linux kernel ".config" file
808           contents to be saved in the kernel. It provides documentation
809           of which kernel options are used in a running kernel or in an
810           on-disk kernel.  This information can be extracted from the kernel
811           image file with the script scripts/extract-ikconfig and used as
812           input to rebuild the current kernel or to build another kernel.
813           It can also be extracted from a running kernel by reading
814           /proc/config.gz if enabled (below).
815 
816 config IKCONFIG_PROC
817         bool "Enable access to .config through /proc/config.gz"
818         depends on IKCONFIG && PROC_FS
819         ---help---
820           This option enables access to the kernel configuration file
821           through /proc/config.gz.
822 
823 config LOG_BUF_SHIFT
824         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
825         range 12 25
826         default 17
827         depends on PRINTK
828         help
829           Select the minimal kernel log buffer size as a power of 2.
830           The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
831           parameter, see below. Any higher size also might be forced
832           by "log_buf_len" boot parameter.
833 
834           Examples:
835                      17 => 128 KB
836                      16 => 64 KB
837                      15 => 32 KB
838                      14 => 16 KB
839                      13 =>  8 KB
840                      12 =>  4 KB
841 
842 config LOG_CPU_MAX_BUF_SHIFT
843         int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
844         depends on SMP
845         range 0 21
846         default 12 if !BASE_SMALL
847         default 0 if BASE_SMALL
848         depends on PRINTK
849         help
850           This option allows to increase the default ring buffer size
851           according to the number of CPUs. The value defines the contribution
852           of each CPU as a power of 2. The used space is typically only few
853           lines however it might be much more when problems are reported,
854           e.g. backtraces.
855 
856           The increased size means that a new buffer has to be allocated and
857           the original static one is unused. It makes sense only on systems
858           with more CPUs. Therefore this value is used only when the sum of
859           contributions is greater than the half of the default kernel ring
860           buffer as defined by LOG_BUF_SHIFT. The default values are set
861           so that more than 64 CPUs are needed to trigger the allocation.
862 
863           Also this option is ignored when "log_buf_len" kernel parameter is
864           used as it forces an exact (power of two) size of the ring buffer.
865 
866           The number of possible CPUs is used for this computation ignoring
867           hotplugging making the computation optimal for the worst case
868           scenario while allowing a simple algorithm to be used from bootup.
869 
870           Examples shift values and their meaning:
871                      17 => 128 KB for each CPU
872                      16 =>  64 KB for each CPU
873                      15 =>  32 KB for each CPU
874                      14 =>  16 KB for each CPU
875                      13 =>   8 KB for each CPU
876                      12 =>   4 KB for each CPU
877 
878 config NMI_LOG_BUF_SHIFT
879         int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
880         range 10 21
881         default 13
882         depends on PRINTK_NMI
883         help
884           Select the size of a per-CPU buffer where NMI messages are temporary
885           stored. They are copied to the main log buffer in a safe context
886           to avoid a deadlock. The value defines the size as a power of 2.
887 
888           NMI messages are rare and limited. The largest one is when
889           a backtrace is printed. It usually fits into 4KB. Select
890           8KB if you want to be on the safe side.
891 
892           Examples:
893                      17 => 128 KB for each CPU
894                      16 =>  64 KB for each CPU
895                      15 =>  32 KB for each CPU
896                      14 =>  16 KB for each CPU
897                      13 =>   8 KB for each CPU
898                      12 =>   4 KB for each CPU
899 
900 #
901 # Architectures with an unreliable sched_clock() should select this:
902 #
903 config HAVE_UNSTABLE_SCHED_CLOCK
904         bool
905 
906 config GENERIC_SCHED_CLOCK
907         bool
908 
909 #
910 # For architectures that want to enable the support for NUMA-affine scheduler
911 # balancing logic:
912 #
913 config ARCH_SUPPORTS_NUMA_BALANCING
914         bool
915 
916 #
917 # For architectures that prefer to flush all TLBs after a number of pages
918 # are unmapped instead of sending one IPI per page to flush. The architecture
919 # must provide guarantees on what happens if a clean TLB cache entry is
920 # written after the unmap. Details are in mm/rmap.c near the check for
921 # should_defer_flush. The architecture should also consider if the full flush
922 # and the refill costs are offset by the savings of sending fewer IPIs.
923 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
924         bool
925 
926 #
927 # For architectures that know their GCC __int128 support is sound
928 #
929 config ARCH_SUPPORTS_INT128
930         bool
931 
932 # For architectures that (ab)use NUMA to represent different memory regions
933 # all cpu-local but of different latencies, such as SuperH.
934 #
935 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
936         bool
937 
938 config NUMA_BALANCING
939         bool "Memory placement aware NUMA scheduler"
940         depends on ARCH_SUPPORTS_NUMA_BALANCING
941         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
942         depends on SMP && NUMA && MIGRATION
943         help
944           This option adds support for automatic NUMA aware memory/task placement.
945           The mechanism is quite primitive and is based on migrating memory when
946           it has references to the node the task is running on.
947 
948           This system will be inactive on UMA systems.
949 
950 config NUMA_BALANCING_DEFAULT_ENABLED
951         bool "Automatically enable NUMA aware memory/task placement"
952         default y
953         depends on NUMA_BALANCING
954         help
955           If set, automatic NUMA balancing will be enabled if running on a NUMA
956           machine.
957 
958 menuconfig CGROUPS
959         bool "Control Group support"
960         select KERNFS
961         help
962           This option adds support for grouping sets of processes together, for
963           use with process control subsystems such as Cpusets, CFS, memory
964           controls or device isolation.
965           See
966                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
967                 - Documentation/cgroup-v1/ (features for grouping, isolation
968                                           and resource control)
969 
970           Say N if unsure.
971 
972 if CGROUPS
973 
974 config PAGE_COUNTER
975        bool
976 
977 config MEMCG
978         bool "Memory controller"
979         select PAGE_COUNTER
980         select EVENTFD
981         help
982           Provides control over the memory footprint of tasks in a cgroup.
983 
984 config MEMCG_SWAP
985         bool "Swap controller"
986         depends on MEMCG && SWAP
987         help
988           Provides control over the swap space consumed by tasks in a cgroup.
989 
990 config MEMCG_SWAP_ENABLED
991         bool "Swap controller enabled by default"
992         depends on MEMCG_SWAP
993         default y
994         help
995           Memory Resource Controller Swap Extension comes with its price in
996           a bigger memory consumption. General purpose distribution kernels
997           which want to enable the feature but keep it disabled by default
998           and let the user enable it by swapaccount=1 boot command line
999           parameter should have this option unselected.
1000           For those who want to have the feature enabled by default should
1001           select this option (if, for some reason, they need to disable it
1002           then swapaccount=0 does the trick).
1003 
1004 config BLK_CGROUP
1005         bool "IO controller"
1006         depends on BLOCK
1007         default n
1008         ---help---
1009         Generic block IO controller cgroup interface. This is the common
1010         cgroup interface which should be used by various IO controlling
1011         policies.
1012 
1013         Currently, CFQ IO scheduler uses it to recognize task groups and
1014         control disk bandwidth allocation (proportional time slice allocation)
1015         to such task groups. It is also used by bio throttling logic in
1016         block layer to implement upper limit in IO rates on a device.
1017 
1018         This option only enables generic Block IO controller infrastructure.
1019         One needs to also enable actual IO controlling logic/policy. For
1020         enabling proportional weight division of disk bandwidth in CFQ, set
1021         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1022         CONFIG_BLK_DEV_THROTTLING=y.
1023 
1024         See Documentation/cgroup-v1/blkio-controller.txt for more information.
1025 
1026 config DEBUG_BLK_CGROUP
1027         bool "IO controller debugging"
1028         depends on BLK_CGROUP
1029         default n
1030         ---help---
1031         Enable some debugging help. Currently it exports additional stat
1032         files in a cgroup which can be useful for debugging.
1033 
1034 config CGROUP_WRITEBACK
1035         bool
1036         depends on MEMCG && BLK_CGROUP
1037         default y
1038 
1039 menuconfig CGROUP_SCHED
1040         bool "CPU controller"
1041         default n
1042         help
1043           This feature lets CPU scheduler recognize task groups and control CPU
1044           bandwidth allocation to such task groups. It uses cgroups to group
1045           tasks.
1046 
1047 if CGROUP_SCHED
1048 config FAIR_GROUP_SCHED
1049         bool "Group scheduling for SCHED_OTHER"
1050         depends on CGROUP_SCHED
1051         default CGROUP_SCHED
1052 
1053 config CFS_BANDWIDTH
1054         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1055         depends on FAIR_GROUP_SCHED
1056         default n
1057         help
1058           This option allows users to define CPU bandwidth rates (limits) for
1059           tasks running within the fair group scheduler.  Groups with no limit
1060           set are considered to be unconstrained and will run with no
1061           restriction.
1062           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1063 
1064 config RT_GROUP_SCHED
1065         bool "Group scheduling for SCHED_RR/FIFO"
1066         depends on CGROUP_SCHED
1067         default n
1068         help
1069           This feature lets you explicitly allocate real CPU bandwidth
1070           to task groups. If enabled, it will also make it impossible to
1071           schedule realtime tasks for non-root users until you allocate
1072           realtime bandwidth for them.
1073           See Documentation/scheduler/sched-rt-group.txt for more information.
1074 
1075 endif #CGROUP_SCHED
1076 
1077 config CGROUP_PIDS
1078         bool "PIDs controller"
1079         help
1080           Provides enforcement of process number limits in the scope of a
1081           cgroup. Any attempt to fork more processes than is allowed in the
1082           cgroup will fail. PIDs are fundamentally a global resource because it
1083           is fairly trivial to reach PID exhaustion before you reach even a
1084           conservative kmemcg limit. As a result, it is possible to grind a
1085           system to halt without being limited by other cgroup policies. The
1086           PIDs controller is designed to stop this from happening.
1087 
1088           It should be noted that organisational operations (such as attaching
1089           to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1090           since the PIDs limit only affects a process's ability to fork, not to
1091           attach to a cgroup.
1092 
1093 config CGROUP_FREEZER
1094         bool "Freezer controller"
1095         help
1096           Provides a way to freeze and unfreeze all tasks in a
1097           cgroup.
1098 
1099           This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1100           controller includes important in-kernel memory consumers per default.
1101 
1102           If you're using cgroup2, say N.
1103 
1104 config CGROUP_HUGETLB
1105         bool "HugeTLB controller"
1106         depends on HUGETLB_PAGE
1107         select PAGE_COUNTER
1108         default n
1109         help
1110           Provides a cgroup controller for HugeTLB pages.
1111           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1112           The limit is enforced during page fault. Since HugeTLB doesn't
1113           support page reclaim, enforcing the limit at page fault time implies
1114           that, the application will get SIGBUS signal if it tries to access
1115           HugeTLB pages beyond its limit. This requires the application to know
1116           beforehand how much HugeTLB pages it would require for its use. The
1117           control group is tracked in the third page lru pointer. This means
1118           that we cannot use the controller with huge page less than 3 pages.
1119 
1120 config CPUSETS
1121         bool "Cpuset controller"
1122         help
1123           This option will let you create and manage CPUSETs which
1124           allow dynamically partitioning a system into sets of CPUs and
1125           Memory Nodes and assigning tasks to run only within those sets.
1126           This is primarily useful on large SMP or NUMA systems.
1127 
1128           Say N if unsure.
1129 
1130 config PROC_PID_CPUSET
1131         bool "Include legacy /proc/<pid>/cpuset file"
1132         depends on CPUSETS
1133         default y
1134 
1135 config CGROUP_DEVICE
1136         bool "Device controller"
1137         help
1138           Provides a cgroup controller implementing whitelists for
1139           devices which a process in the cgroup can mknod or open.
1140 
1141 config CGROUP_CPUACCT
1142         bool "Simple CPU accounting controller"
1143         help
1144           Provides a simple controller for monitoring the
1145           total CPU consumed by the tasks in a cgroup.
1146 
1147 config CGROUP_PERF
1148         bool "Perf controller"
1149         depends on PERF_EVENTS
1150         help
1151           This option extends the perf per-cpu mode to restrict monitoring
1152           to threads which belong to the cgroup specified and run on the
1153           designated cpu.
1154 
1155           Say N if unsure.
1156 
1157 config CGROUP_DEBUG
1158         bool "Example controller"
1159         default n
1160         help
1161           This option enables a simple controller that exports
1162           debugging information about the cgroups framework.
1163 
1164           Say N.
1165 
1166 endif # CGROUPS
1167 
1168 config CHECKPOINT_RESTORE
1169         bool "Checkpoint/restore support" if EXPERT
1170         select PROC_CHILDREN
1171         default n
1172         help
1173           Enables additional kernel features in a sake of checkpoint/restore.
1174           In particular it adds auxiliary prctl codes to setup process text,
1175           data and heap segment sizes, and a few additional /proc filesystem
1176           entries.
1177 
1178           If unsure, say N here.
1179 
1180 menuconfig NAMESPACES
1181         bool "Namespaces support" if EXPERT
1182         depends on MULTIUSER
1183         default !EXPERT
1184         help
1185           Provides the way to make tasks work with different objects using
1186           the same id. For example same IPC id may refer to different objects
1187           or same user id or pid may refer to different tasks when used in
1188           different namespaces.
1189 
1190 if NAMESPACES
1191 
1192 config UTS_NS
1193         bool "UTS namespace"
1194         default y
1195         help
1196           In this namespace tasks see different info provided with the
1197           uname() system call
1198 
1199 config IPC_NS
1200         bool "IPC namespace"
1201         depends on (SYSVIPC || POSIX_MQUEUE)
1202         default y
1203         help
1204           In this namespace tasks work with IPC ids which correspond to
1205           different IPC objects in different namespaces.
1206 
1207 config USER_NS
1208         bool "User namespace"
1209         default n
1210         help
1211           This allows containers, i.e. vservers, to use user namespaces
1212           to provide different user info for different servers.
1213 
1214           When user namespaces are enabled in the kernel it is
1215           recommended that the MEMCG option also be enabled and that
1216           user-space use the memory control groups to limit the amount
1217           of memory a memory unprivileged users can use.
1218 
1219           If unsure, say N.
1220 
1221 config PID_NS
1222         bool "PID Namespaces"
1223         default y
1224         help
1225           Support process id namespaces.  This allows having multiple
1226           processes with the same pid as long as they are in different
1227           pid namespaces.  This is a building block of containers.
1228 
1229 config NET_NS
1230         bool "Network namespace"
1231         depends on NET
1232         default y
1233         help
1234           Allow user space to create what appear to be multiple instances
1235           of the network stack.
1236 
1237 endif # NAMESPACES
1238 
1239 config SCHED_AUTOGROUP
1240         bool "Automatic process group scheduling"
1241         select CGROUPS
1242         select CGROUP_SCHED
1243         select FAIR_GROUP_SCHED
1244         help
1245           This option optimizes the scheduler for common desktop workloads by
1246           automatically creating and populating task groups.  This separation
1247           of workloads isolates aggressive CPU burners (like build jobs) from
1248           desktop applications.  Task group autogeneration is currently based
1249           upon task session.
1250 
1251 config SYSFS_DEPRECATED
1252         bool "Enable deprecated sysfs features to support old userspace tools"
1253         depends on SYSFS
1254         default n
1255         help
1256           This option adds code that switches the layout of the "block" class
1257           devices, to not show up in /sys/class/block/, but only in
1258           /sys/block/.
1259 
1260           This switch is only active when the sysfs.deprecated=1 boot option is
1261           passed or the SYSFS_DEPRECATED_V2 option is set.
1262 
1263           This option allows new kernels to run on old distributions and tools,
1264           which might get confused by /sys/class/block/. Since 2007/2008 all
1265           major distributions and tools handle this just fine.
1266 
1267           Recent distributions and userspace tools after 2009/2010 depend on
1268           the existence of /sys/class/block/, and will not work with this
1269           option enabled.
1270 
1271           Only if you are using a new kernel on an old distribution, you might
1272           need to say Y here.
1273 
1274 config SYSFS_DEPRECATED_V2
1275         bool "Enable deprecated sysfs features by default"
1276         default n
1277         depends on SYSFS
1278         depends on SYSFS_DEPRECATED
1279         help
1280           Enable deprecated sysfs by default.
1281 
1282           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1283           option.
1284 
1285           Only if you are using a new kernel on an old distribution, you might
1286           need to say Y here. Even then, odds are you would not need it
1287           enabled, you can always pass the boot option if absolutely necessary.
1288 
1289 config RELAY
1290         bool "Kernel->user space relay support (formerly relayfs)"
1291         select IRQ_WORK
1292         help
1293           This option enables support for relay interface support in
1294           certain file systems (such as debugfs).
1295           It is designed to provide an efficient mechanism for tools and
1296           facilities to relay large amounts of data from kernel space to
1297           user space.
1298 
1299           If unsure, say N.
1300 
1301 config BLK_DEV_INITRD
1302         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1303         depends on BROKEN || !FRV
1304         help
1305           The initial RAM filesystem is a ramfs which is loaded by the
1306           boot loader (loadlin or lilo) and that is mounted as root
1307           before the normal boot procedure. It is typically used to
1308           load modules needed to mount the "real" root file system,
1309           etc. See <file:Documentation/initrd.txt> for details.
1310 
1311           If RAM disk support (BLK_DEV_RAM) is also included, this
1312           also enables initial RAM disk (initrd) support and adds
1313           15 Kbytes (more on some other architectures) to the kernel size.
1314 
1315           If unsure say Y.
1316 
1317 if BLK_DEV_INITRD
1318 
1319 source "usr/Kconfig"
1320 
1321 endif
1322 
1323 choice
1324         prompt "Compiler optimization level"
1325         default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
1326 
1327 config CC_OPTIMIZE_FOR_PERFORMANCE
1328         bool "Optimize for performance"
1329         help
1330           This is the default optimization level for the kernel, building
1331           with the "-O2" compiler flag for best performance and most
1332           helpful compile-time warnings.
1333 
1334 config CC_OPTIMIZE_FOR_SIZE
1335         bool "Optimize for size"
1336         help
1337           Enabling this option will pass "-Os" instead of "-O2" to
1338           your compiler resulting in a smaller kernel.
1339 
1340           If unsure, say N.
1341 
1342 endchoice
1343 
1344 config SYSCTL
1345         bool
1346 
1347 config ANON_INODES
1348         bool
1349 
1350 config HAVE_UID16
1351         bool
1352 
1353 config SYSCTL_EXCEPTION_TRACE
1354         bool
1355         help
1356           Enable support for /proc/sys/debug/exception-trace.
1357 
1358 config SYSCTL_ARCH_UNALIGN_NO_WARN
1359         bool
1360         help
1361           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1362           Allows arch to define/use @no_unaligned_warning to possibly warn
1363           about unaligned access emulation going on under the hood.
1364 
1365 config SYSCTL_ARCH_UNALIGN_ALLOW
1366         bool
1367         help
1368           Enable support for /proc/sys/kernel/unaligned-trap
1369           Allows arches to define/use @unaligned_enabled to runtime toggle
1370           the unaligned access emulation.
1371           see arch/parisc/kernel/unaligned.c for reference
1372 
1373 config HAVE_PCSPKR_PLATFORM
1374         bool
1375 
1376 # interpreter that classic socket filters depend on
1377 config BPF
1378         bool
1379 
1380 menuconfig EXPERT
1381         bool "Configure standard kernel features (expert users)"
1382         # Unhide debug options, to make the on-by-default options visible
1383         select DEBUG_KERNEL
1384         help
1385           This option allows certain base kernel options and settings
1386           to be disabled or tweaked. This is for specialized
1387           environments which can tolerate a "non-standard" kernel.
1388           Only use this if you really know what you are doing.
1389 
1390 config UID16
1391         bool "Enable 16-bit UID system calls" if EXPERT
1392         depends on HAVE_UID16 && MULTIUSER
1393         default y
1394         help
1395           This enables the legacy 16-bit UID syscall wrappers.
1396 
1397 config MULTIUSER
1398         bool "Multiple users, groups and capabilities support" if EXPERT
1399         default y
1400         help
1401           This option enables support for non-root users, groups and
1402           capabilities.
1403 
1404           If you say N here, all processes will run with UID 0, GID 0, and all
1405           possible capabilities.  Saying N here also compiles out support for
1406           system calls related to UIDs, GIDs, and capabilities, such as setuid,
1407           setgid, and capset.
1408 
1409           If unsure, say Y here.
1410 
1411 config SGETMASK_SYSCALL
1412         bool "sgetmask/ssetmask syscalls support" if EXPERT
1413         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1414         ---help---
1415           sys_sgetmask and sys_ssetmask are obsolete system calls
1416           no longer supported in libc but still enabled by default in some
1417           architectures.
1418 
1419           If unsure, leave the default option here.
1420 
1421 config SYSFS_SYSCALL
1422         bool "Sysfs syscall support" if EXPERT
1423         default y
1424         ---help---
1425           sys_sysfs is an obsolete system call no longer supported in libc.
1426           Note that disabling this option is more secure but might break
1427           compatibility with some systems.
1428 
1429           If unsure say Y here.
1430 
1431 config SYSCTL_SYSCALL
1432         bool "Sysctl syscall support" if EXPERT
1433         depends on PROC_SYSCTL
1434         default n
1435         select SYSCTL
1436         ---help---
1437           sys_sysctl uses binary paths that have been found challenging
1438           to properly maintain and use.  The interface in /proc/sys
1439           using paths with ascii names is now the primary path to this
1440           information.
1441 
1442           Almost nothing using the binary sysctl interface so if you are
1443           trying to save some space it is probably safe to disable this,
1444           making your kernel marginally smaller.
1445 
1446           If unsure say N here.
1447 
1448 config KALLSYMS
1449          bool "Load all symbols for debugging/ksymoops" if EXPERT
1450          default y
1451          help
1452            Say Y here to let the kernel print out symbolic crash information and
1453            symbolic stack backtraces. This increases the size of the kernel
1454            somewhat, as all symbols have to be loaded into the kernel image.
1455 
1456 config KALLSYMS_ALL
1457         bool "Include all symbols in kallsyms"
1458         depends on DEBUG_KERNEL && KALLSYMS
1459         help
1460            Normally kallsyms only contains the symbols of functions for nicer
1461            OOPS messages and backtraces (i.e., symbols from the text and inittext
1462            sections). This is sufficient for most cases. And only in very rare
1463            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1464            names of variables from the data sections, etc).
1465 
1466            This option makes sure that all symbols are loaded into the kernel
1467            image (i.e., symbols from all sections) in cost of increased kernel
1468            size (depending on the kernel configuration, it may be 300KiB or
1469            something like this).
1470 
1471            Say N unless you really need all symbols.
1472 
1473 config KALLSYMS_ABSOLUTE_PERCPU
1474         bool
1475         depends on KALLSYMS
1476         default X86_64 && SMP
1477 
1478 config KALLSYMS_BASE_RELATIVE
1479         bool
1480         depends on KALLSYMS
1481         default !IA64 && !(TILE && 64BIT)
1482         help
1483           Instead of emitting them as absolute values in the native word size,
1484           emit the symbol references in the kallsyms table as 32-bit entries,
1485           each containing a relative value in the range [base, base + U32_MAX]
1486           or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1487           an absolute value in the range [0, S32_MAX] or a relative value in the
1488           range [base, base + S32_MAX], where base is the lowest relative symbol
1489           address encountered in the image.
1490 
1491           On 64-bit builds, this reduces the size of the address table by 50%,
1492           but more importantly, it results in entries whose values are build
1493           time constants, and no relocation pass is required at runtime to fix
1494           up the entries based on the runtime load address of the kernel.
1495 
1496 config PRINTK
1497         default y
1498         bool "Enable support for printk" if EXPERT
1499         select IRQ_WORK
1500         help
1501           This option enables normal printk support. Removing it
1502           eliminates most of the message strings from the kernel image
1503           and makes the kernel more or less silent. As this makes it
1504           very difficult to diagnose system problems, saying N here is
1505           strongly discouraged.
1506 
1507 config PRINTK_NMI
1508         def_bool y
1509         depends on PRINTK
1510         depends on HAVE_NMI
1511 
1512 config BUG
1513         bool "BUG() support" if EXPERT
1514         default y
1515         help
1516           Disabling this option eliminates support for BUG and WARN, reducing
1517           the size of your kernel image and potentially quietly ignoring
1518           numerous fatal conditions. You should only consider disabling this
1519           option for embedded systems with no facilities for reporting errors.
1520           Just say Y.
1521 
1522 config ELF_CORE
1523         depends on COREDUMP
1524         default y
1525         bool "Enable ELF core dumps" if EXPERT
1526         help
1527           Enable support for generating core dumps. Disabling saves about 4k.
1528 
1529 
1530 config PCSPKR_PLATFORM
1531         bool "Enable PC-Speaker support" if EXPERT
1532         depends on HAVE_PCSPKR_PLATFORM
1533         select I8253_LOCK
1534         default y
1535         help
1536           This option allows to disable the internal PC-Speaker
1537           support, saving some memory.
1538 
1539 config BASE_FULL
1540         default y
1541         bool "Enable full-sized data structures for core" if EXPERT
1542         help
1543           Disabling this option reduces the size of miscellaneous core
1544           kernel data structures. This saves memory on small machines,
1545           but may reduce performance.
1546 
1547 config FUTEX
1548         bool "Enable futex support" if EXPERT
1549         default y
1550         select RT_MUTEXES
1551         help
1552           Disabling this option will cause the kernel to be built without
1553           support for "fast userspace mutexes".  The resulting kernel may not
1554           run glibc-based applications correctly.
1555 
1556 config HAVE_FUTEX_CMPXCHG
1557         bool
1558         depends on FUTEX
1559         help
1560           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1561           is implemented and always working. This removes a couple of runtime
1562           checks.
1563 
1564 config EPOLL
1565         bool "Enable eventpoll support" if EXPERT
1566         default y
1567         select ANON_INODES
1568         help
1569           Disabling this option will cause the kernel to be built without
1570           support for epoll family of system calls.
1571 
1572 config SIGNALFD
1573         bool "Enable signalfd() system call" if EXPERT
1574         select ANON_INODES
1575         default y
1576         help
1577           Enable the signalfd() system call that allows to receive signals
1578           on a file descriptor.
1579 
1580           If unsure, say Y.
1581 
1582 config TIMERFD
1583         bool "Enable timerfd() system call" if EXPERT
1584         select ANON_INODES
1585         default y
1586         help
1587           Enable the timerfd() system call that allows to receive timer
1588           events on a file descriptor.
1589 
1590           If unsure, say Y.
1591 
1592 config EVENTFD
1593         bool "Enable eventfd() system call" if EXPERT
1594         select ANON_INODES
1595         default y
1596         help
1597           Enable the eventfd() system call that allows to receive both
1598           kernel notification (ie. KAIO) or userspace notifications.
1599 
1600           If unsure, say Y.
1601 
1602 # syscall, maps, verifier
1603 config BPF_SYSCALL
1604         bool "Enable bpf() system call"
1605         select ANON_INODES
1606         select BPF
1607         default n
1608         help
1609           Enable the bpf() system call that allows to manipulate eBPF
1610           programs and maps via file descriptors.
1611 
1612 config SHMEM
1613         bool "Use full shmem filesystem" if EXPERT
1614         default y
1615         depends on MMU
1616         help
1617           The shmem is an internal filesystem used to manage shared memory.
1618           It is backed by swap and manages resource limits. It is also exported
1619           to userspace as tmpfs if TMPFS is enabled. Disabling this
1620           option replaces shmem and tmpfs with the much simpler ramfs code,
1621           which may be appropriate on small systems without swap.
1622 
1623 config AIO
1624         bool "Enable AIO support" if EXPERT
1625         default y
1626         help
1627           This option enables POSIX asynchronous I/O which may by used
1628           by some high performance threaded applications. Disabling
1629           this option saves about 7k.
1630 
1631 config ADVISE_SYSCALLS
1632         bool "Enable madvise/fadvise syscalls" if EXPERT
1633         default y
1634         help
1635           This option enables the madvise and fadvise syscalls, used by
1636           applications to advise the kernel about their future memory or file
1637           usage, improving performance. If building an embedded system where no
1638           applications use these syscalls, you can disable this option to save
1639           space.
1640 
1641 config USERFAULTFD
1642         bool "Enable userfaultfd() system call"
1643         select ANON_INODES
1644         depends on MMU
1645         help
1646           Enable the userfaultfd() system call that allows to intercept and
1647           handle page faults in userland.
1648 
1649 config PCI_QUIRKS
1650         default y
1651         bool "Enable PCI quirk workarounds" if EXPERT
1652         depends on PCI
1653         help
1654           This enables workarounds for various PCI chipset
1655           bugs/quirks. Disable this only if your target machine is
1656           unaffected by PCI quirks.
1657 
1658 config MEMBARRIER
1659         bool "Enable membarrier() system call" if EXPERT
1660         default y
1661         help
1662           Enable the membarrier() system call that allows issuing memory
1663           barriers across all running threads, which can be used to distribute
1664           the cost of user-space memory barriers asymmetrically by transforming
1665           pairs of memory barriers into pairs consisting of membarrier() and a
1666           compiler barrier.
1667 
1668           If unsure, say Y.
1669 
1670 config EMBEDDED
1671         bool "Embedded system"
1672         option allnoconfig_y
1673         select EXPERT
1674         help
1675           This option should be enabled if compiling the kernel for
1676           an embedded system so certain expert options are available
1677           for configuration.
1678 
1679 config HAVE_PERF_EVENTS
1680         bool
1681         help
1682           See tools/perf/design.txt for details.
1683 
1684 config PERF_USE_VMALLOC
1685         bool
1686         help
1687           See tools/perf/design.txt for details
1688 
1689 menu "Kernel Performance Events And Counters"
1690 
1691 config PERF_EVENTS
1692         bool "Kernel performance events and counters"
1693         default y if PROFILING
1694         depends on HAVE_PERF_EVENTS
1695         select ANON_INODES
1696         select IRQ_WORK
1697         select SRCU
1698         help
1699           Enable kernel support for various performance events provided
1700           by software and hardware.
1701 
1702           Software events are supported either built-in or via the
1703           use of generic tracepoints.
1704 
1705           Most modern CPUs support performance events via performance
1706           counter registers. These registers count the number of certain
1707           types of hw events: such as instructions executed, cachemisses
1708           suffered, or branches mis-predicted - without slowing down the
1709           kernel or applications. These registers can also trigger interrupts
1710           when a threshold number of events have passed - and can thus be
1711           used to profile the code that runs on that CPU.
1712 
1713           The Linux Performance Event subsystem provides an abstraction of
1714           these software and hardware event capabilities, available via a
1715           system call and used by the "perf" utility in tools/perf/. It
1716           provides per task and per CPU counters, and it provides event
1717           capabilities on top of those.
1718 
1719           Say Y if unsure.
1720 
1721 config DEBUG_PERF_USE_VMALLOC
1722         default n
1723         bool "Debug: use vmalloc to back perf mmap() buffers"
1724         depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1725         select PERF_USE_VMALLOC
1726         help
1727          Use vmalloc memory to back perf mmap() buffers.
1728 
1729          Mostly useful for debugging the vmalloc code on platforms
1730          that don't require it.
1731 
1732          Say N if unsure.
1733 
1734 endmenu
1735 
1736 config VM_EVENT_COUNTERS
1737         default y
1738         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1739         help
1740           VM event counters are needed for event counts to be shown.
1741           This option allows the disabling of the VM event counters
1742           on EXPERT systems.  /proc/vmstat will only show page counts
1743           if VM event counters are disabled.
1744 
1745 config SLUB_DEBUG
1746         default y
1747         bool "Enable SLUB debugging support" if EXPERT
1748         depends on SLUB && SYSFS
1749         help
1750           SLUB has extensive debug support features. Disabling these can
1751           result in significant savings in code size. This also disables
1752           SLUB sysfs support. /sys/slab will not exist and there will be
1753           no support for cache validation etc.
1754 
1755 config COMPAT_BRK
1756         bool "Disable heap randomization"
1757         default y
1758         help
1759           Randomizing heap placement makes heap exploits harder, but it
1760           also breaks ancient binaries (including anything libc5 based).
1761           This option changes the bootup default to heap randomization
1762           disabled, and can be overridden at runtime by setting
1763           /proc/sys/kernel/randomize_va_space to 2.
1764 
1765           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1766 
1767 choice
1768         prompt "Choose SLAB allocator"
1769         default SLUB
1770         help
1771            This option allows to select a slab allocator.
1772 
1773 config SLAB
1774         bool "SLAB"
1775         select HAVE_HARDENED_USERCOPY_ALLOCATOR
1776         help
1777           The regular slab allocator that is established and known to work
1778           well in all environments. It organizes cache hot objects in
1779           per cpu and per node queues.
1780 
1781 config SLUB
1782         bool "SLUB (Unqueued Allocator)"
1783         select HAVE_HARDENED_USERCOPY_ALLOCATOR
1784         help
1785            SLUB is a slab allocator that minimizes cache line usage
1786            instead of managing queues of cached objects (SLAB approach).
1787            Per cpu caching is realized using slabs of objects instead
1788            of queues of objects. SLUB can use memory efficiently
1789            and has enhanced diagnostics. SLUB is the default choice for
1790            a slab allocator.
1791 
1792 config SLOB
1793         depends on EXPERT
1794         bool "SLOB (Simple Allocator)"
1795         help
1796            SLOB replaces the stock allocator with a drastically simpler
1797            allocator. SLOB is generally more space efficient but
1798            does not perform as well on large systems.
1799 
1800 endchoice
1801 
1802 config SLAB_FREELIST_RANDOM
1803         default n
1804         depends on SLAB || SLUB
1805         bool "SLAB freelist randomization"
1806         help
1807           Randomizes the freelist order used on creating new pages. This
1808           security feature reduces the predictability of the kernel slab
1809           allocator against heap overflows.
1810 
1811 config SLUB_CPU_PARTIAL
1812         default y
1813         depends on SLUB && SMP
1814         bool "SLUB per cpu partial cache"
1815         help
1816           Per cpu partial caches accellerate objects allocation and freeing
1817           that is local to a processor at the price of more indeterminism
1818           in the latency of the free. On overflow these caches will be cleared
1819           which requires the taking of locks that may cause latency spikes.
1820           Typically one would choose no for a realtime system.
1821 
1822 config MMAP_ALLOW_UNINITIALIZED
1823         bool "Allow mmapped anonymous memory to be uninitialized"
1824         depends on EXPERT && !MMU
1825         default n
1826         help
1827           Normally, and according to the Linux spec, anonymous memory obtained
1828           from mmap() has it's contents cleared before it is passed to
1829           userspace.  Enabling this config option allows you to request that
1830           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1831           providing a huge performance boost.  If this option is not enabled,
1832           then the flag will be ignored.
1833 
1834           This is taken advantage of by uClibc's malloc(), and also by
1835           ELF-FDPIC binfmt's brk and stack allocator.
1836 
1837           Because of the obvious security issues, this option should only be
1838           enabled on embedded devices where you control what is run in
1839           userspace.  Since that isn't generally a problem on no-MMU systems,
1840           it is normally safe to say Y here.
1841 
1842           See Documentation/nommu-mmap.txt for more information.
1843 
1844 config SYSTEM_DATA_VERIFICATION
1845         def_bool n
1846         select SYSTEM_TRUSTED_KEYRING
1847         select KEYS
1848         select CRYPTO
1849         select CRYPTO_RSA
1850         select ASYMMETRIC_KEY_TYPE
1851         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1852         select ASN1
1853         select OID_REGISTRY
1854         select X509_CERTIFICATE_PARSER
1855         select PKCS7_MESSAGE_PARSER
1856         help
1857           Provide PKCS#7 message verification using the contents of the system
1858           trusted keyring to provide public keys.  This then can be used for
1859           module verification, kexec image verification and firmware blob
1860           verification.
1861 
1862 config PROFILING
1863         bool "Profiling support"
1864         help
1865           Say Y here to enable the extended profiling support mechanisms used
1866           by profilers such as OProfile.
1867 
1868 #
1869 # Place an empty function call at each tracepoint site. Can be
1870 # dynamically changed for a probe function.
1871 #
1872 config TRACEPOINTS
1873         bool
1874 
1875 source "arch/Kconfig"
1876 
1877 endmenu         # General setup
1878 
1879 config HAVE_GENERIC_DMA_COHERENT
1880         bool
1881         default n
1882 
1883 config SLABINFO
1884         bool
1885         depends on PROC_FS
1886         depends on SLAB || SLUB_DEBUG
1887         default y
1888 
1889 config RT_MUTEXES
1890         bool
1891 
1892 config BASE_SMALL
1893         int
1894         default 0 if BASE_FULL
1895         default 1 if !BASE_FULL
1896 
1897 menuconfig MODULES
1898         bool "Enable loadable module support"
1899         option modules
1900         help
1901           Kernel modules are small pieces of compiled code which can
1902           be inserted in the running kernel, rather than being
1903           permanently built into the kernel.  You use the "modprobe"
1904           tool to add (and sometimes remove) them.  If you say Y here,
1905           many parts of the kernel can be built as modules (by
1906           answering M instead of Y where indicated): this is most
1907           useful for infrequently used options which are not required
1908           for booting.  For more information, see the man pages for
1909           modprobe, lsmod, modinfo, insmod and rmmod.
1910 
1911           If you say Y here, you will need to run "make
1912           modules_install" to put the modules under /lib/modules/
1913           where modprobe can find them (you may need to be root to do
1914           this).
1915 
1916           If unsure, say Y.
1917 
1918 if MODULES
1919 
1920 config MODULE_FORCE_LOAD
1921         bool "Forced module loading"
1922         default n
1923         help
1924           Allow loading of modules without version information (ie. modprobe
1925           --force).  Forced module loading sets the 'F' (forced) taint flag and
1926           is usually a really bad idea.
1927 
1928 config MODULE_UNLOAD
1929         bool "Module unloading"
1930         help
1931           Without this option you will not be able to unload any
1932           modules (note that some modules may not be unloadable
1933           anyway), which makes your kernel smaller, faster
1934           and simpler.  If unsure, say Y.
1935 
1936 config MODULE_FORCE_UNLOAD
1937         bool "Forced module unloading"
1938         depends on MODULE_UNLOAD
1939         help
1940           This option allows you to force a module to unload, even if the
1941           kernel believes it is unsafe: the kernel will remove the module
1942           without waiting for anyone to stop using it (using the -f option to
1943           rmmod).  This is mainly for kernel developers and desperate users.
1944           If unsure, say N.
1945 
1946 config MODVERSIONS
1947         bool "Module versioning support"
1948         help
1949           Usually, you have to use modules compiled with your kernel.
1950           Saying Y here makes it sometimes possible to use modules
1951           compiled for different kernels, by adding enough information
1952           to the modules to (hopefully) spot any changes which would
1953           make them incompatible with the kernel you are running.  If
1954           unsure, say N.
1955 
1956 config MODULE_SRCVERSION_ALL
1957         bool "Source checksum for all modules"
1958         help
1959           Modules which contain a MODULE_VERSION get an extra "srcversion"
1960           field inserted into their modinfo section, which contains a
1961           sum of the source files which made it.  This helps maintainers
1962           see exactly which source was used to build a module (since
1963           others sometimes change the module source without updating
1964           the version).  With this option, such a "srcversion" field
1965           will be created for all modules.  If unsure, say N.
1966 
1967 config MODULE_SIG
1968         bool "Module signature verification"
1969         depends on MODULES
1970         select SYSTEM_DATA_VERIFICATION
1971         help
1972           Check modules for valid signatures upon load: the signature
1973           is simply appended to the module. For more information see
1974           Documentation/module-signing.txt.
1975 
1976           Note that this option adds the OpenSSL development packages as a
1977           kernel build dependency so that the signing tool can use its crypto
1978           library.
1979 
1980           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1981           module DOES NOT get stripped after being signed.  This includes the
1982           debuginfo strip done by some packagers (such as rpmbuild) and
1983           inclusion into an initramfs that wants the module size reduced.
1984 
1985 config MODULE_SIG_FORCE
1986         bool "Require modules to be validly signed"
1987         depends on MODULE_SIG
1988         help
1989           Reject unsigned modules or signed modules for which we don't have a
1990           key.  Without this, such modules will simply taint the kernel.
1991 
1992 config MODULE_SIG_ALL
1993         bool "Automatically sign all modules"
1994         default y
1995         depends on MODULE_SIG
1996         help
1997           Sign all modules during make modules_install. Without this option,
1998           modules must be signed manually, using the scripts/sign-file tool.
1999 
2000 comment "Do not forget to sign required modules with scripts/sign-file"
2001         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2002 
2003 choice
2004         prompt "Which hash algorithm should modules be signed with?"
2005         depends on MODULE_SIG
2006         help
2007           This determines which sort of hashing algorithm will be used during
2008           signature generation.  This algorithm _must_ be built into the kernel
2009           directly so that signature verification can take place.  It is not
2010           possible to load a signed module containing the algorithm to check
2011           the signature on that module.
2012 
2013 config MODULE_SIG_SHA1
2014         bool "Sign modules with SHA-1"
2015         select CRYPTO_SHA1
2016 
2017 config MODULE_SIG_SHA224
2018         bool "Sign modules with SHA-224"
2019         select CRYPTO_SHA256
2020 
2021 config MODULE_SIG_SHA256
2022         bool "Sign modules with SHA-256"
2023         select CRYPTO_SHA256
2024 
2025 config MODULE_SIG_SHA384
2026         bool "Sign modules with SHA-384"
2027         select CRYPTO_SHA512
2028 
2029 config MODULE_SIG_SHA512
2030         bool "Sign modules with SHA-512"
2031         select CRYPTO_SHA512
2032 
2033 endchoice
2034 
2035 config MODULE_SIG_HASH
2036         string
2037         depends on MODULE_SIG
2038         default "sha1" if MODULE_SIG_SHA1
2039         default "sha224" if MODULE_SIG_SHA224
2040         default "sha256" if MODULE_SIG_SHA256
2041         default "sha384" if MODULE_SIG_SHA384
2042         default "sha512" if MODULE_SIG_SHA512
2043 
2044 config MODULE_COMPRESS
2045         bool "Compress modules on installation"
2046         depends on MODULES
2047         help
2048 
2049           Compresses kernel modules when 'make modules_install' is run; gzip or
2050           xz depending on "Compression algorithm" below.
2051 
2052           module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2053 
2054           Out-of-tree kernel modules installed using Kbuild will also be
2055           compressed upon installation.
2056 
2057           Note: for modules inside an initrd or initramfs, it's more efficient
2058           to compress the whole initrd or initramfs instead.
2059 
2060           Note: This is fully compatible with signed modules.
2061 
2062           If in doubt, say N.
2063 
2064 choice
2065         prompt "Compression algorithm"
2066         depends on MODULE_COMPRESS
2067         default MODULE_COMPRESS_GZIP
2068         help
2069           This determines which sort of compression will be used during
2070           'make modules_install'.
2071 
2072           GZIP (default) and XZ are supported.
2073 
2074 config MODULE_COMPRESS_GZIP
2075         bool "GZIP"
2076 
2077 config MODULE_COMPRESS_XZ
2078         bool "XZ"
2079 
2080 endchoice
2081 
2082 config TRIM_UNUSED_KSYMS
2083         bool "Trim unused exported kernel symbols"
2084         depends on MODULES && !UNUSED_SYMBOLS
2085         help
2086           The kernel and some modules make many symbols available for
2087           other modules to use via EXPORT_SYMBOL() and variants. Depending
2088           on the set of modules being selected in your kernel configuration,
2089           many of those exported symbols might never be used.
2090 
2091           This option allows for unused exported symbols to be dropped from
2092           the build. In turn, this provides the compiler more opportunities
2093           (especially when using LTO) for optimizing the code and reducing
2094           binary size.  This might have some security advantages as well.
2095 
2096           If unsure, or if you need to build out-of-tree modules, say N.
2097 
2098 endif # MODULES
2099 
2100 config MODULES_TREE_LOOKUP
2101         def_bool y
2102         depends on PERF_EVENTS || TRACING
2103 
2104 config INIT_ALL_POSSIBLE
2105         bool
2106         help
2107           Back when each arch used to define their own cpu_online_mask and
2108           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2109           with all 1s, and others with all 0s.  When they were centralised,
2110           it was better to provide this option than to break all the archs
2111           and have several arch maintainers pursuing me down dark alleys.
2112 
2113 source "block/Kconfig"
2114 
2115 config PREEMPT_NOTIFIERS
2116         bool
2117 
2118 config PADATA
2119         depends on SMP
2120         bool
2121 
2122 config ASN1
2123         tristate
2124         help
2125           Build a simple ASN.1 grammar compiler that produces a bytecode output
2126           that can be interpreted by the ASN.1 stream decoder and used to
2127           inform it as to what tags are to be expected in a stream and what
2128           functions to call on what tags.
2129 
2130 source "kernel/Kconfig.locks"

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