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

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