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

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