Version:  2.0.40 2.2.26 2.4.37 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6

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 #
866 # Architectures with an unreliable sched_clock() should select this:
867 #
868 config HAVE_UNSTABLE_SCHED_CLOCK
869         bool
870 
871 config GENERIC_SCHED_CLOCK
872         bool
873 
874 #
875 # For architectures that want to enable the support for NUMA-affine scheduler
876 # balancing logic:
877 #
878 config ARCH_SUPPORTS_NUMA_BALANCING
879         bool
880 
881 #
882 # For architectures that prefer to flush all TLBs after a number of pages
883 # are unmapped instead of sending one IPI per page to flush. The architecture
884 # must provide guarantees on what happens if a clean TLB cache entry is
885 # written after the unmap. Details are in mm/rmap.c near the check for
886 # should_defer_flush. The architecture should also consider if the full flush
887 # and the refill costs are offset by the savings of sending fewer IPIs.
888 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
889         bool
890 
891 #
892 # For architectures that know their GCC __int128 support is sound
893 #
894 config ARCH_SUPPORTS_INT128
895         bool
896 
897 # For architectures that (ab)use NUMA to represent different memory regions
898 # all cpu-local but of different latencies, such as SuperH.
899 #
900 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
901         bool
902 
903 config NUMA_BALANCING
904         bool "Memory placement aware NUMA scheduler"
905         depends on ARCH_SUPPORTS_NUMA_BALANCING
906         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
907         depends on SMP && NUMA && MIGRATION
908         help
909           This option adds support for automatic NUMA aware memory/task placement.
910           The mechanism is quite primitive and is based on migrating memory when
911           it has references to the node the task is running on.
912 
913           This system will be inactive on UMA systems.
914 
915 config NUMA_BALANCING_DEFAULT_ENABLED
916         bool "Automatically enable NUMA aware memory/task placement"
917         default y
918         depends on NUMA_BALANCING
919         help
920           If set, automatic NUMA balancing will be enabled if running on a NUMA
921           machine.
922 
923 menuconfig CGROUPS
924         bool "Control Group support"
925         select KERNFS
926         help
927           This option adds support for grouping sets of processes together, for
928           use with process control subsystems such as Cpusets, CFS, memory
929           controls or device isolation.
930           See
931                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
932                 - Documentation/cgroups/ (features for grouping, isolation
933                                           and resource control)
934 
935           Say N if unsure.
936 
937 if CGROUPS
938 
939 config PAGE_COUNTER
940        bool
941 
942 config MEMCG
943         bool "Memory controller"
944         select PAGE_COUNTER
945         select EVENTFD
946         help
947           Provides control over the memory footprint of tasks in a cgroup.
948 
949 config MEMCG_SWAP
950         bool "Swap controller"
951         depends on MEMCG && SWAP
952         help
953           Provides control over the swap space consumed by tasks in a cgroup.
954 
955 config MEMCG_SWAP_ENABLED
956         bool "Swap controller enabled by default"
957         depends on MEMCG_SWAP
958         default y
959         help
960           Memory Resource Controller Swap Extension comes with its price in
961           a bigger memory consumption. General purpose distribution kernels
962           which want to enable the feature but keep it disabled by default
963           and let the user enable it by swapaccount=1 boot command line
964           parameter should have this option unselected.
965           For those who want to have the feature enabled by default should
966           select this option (if, for some reason, they need to disable it
967           then swapaccount=0 does the trick).
968 
969 config BLK_CGROUP
970         bool "IO controller"
971         depends on BLOCK
972         default n
973         ---help---
974         Generic block IO controller cgroup interface. This is the common
975         cgroup interface which should be used by various IO controlling
976         policies.
977 
978         Currently, CFQ IO scheduler uses it to recognize task groups and
979         control disk bandwidth allocation (proportional time slice allocation)
980         to such task groups. It is also used by bio throttling logic in
981         block layer to implement upper limit in IO rates on a device.
982 
983         This option only enables generic Block IO controller infrastructure.
984         One needs to also enable actual IO controlling logic/policy. For
985         enabling proportional weight division of disk bandwidth in CFQ, set
986         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
987         CONFIG_BLK_DEV_THROTTLING=y.
988 
989         See Documentation/cgroups/blkio-controller.txt for more information.
990 
991 config DEBUG_BLK_CGROUP
992         bool "IO controller debugging"
993         depends on BLK_CGROUP
994         default n
995         ---help---
996         Enable some debugging help. Currently it exports additional stat
997         files in a cgroup which can be useful for debugging.
998 
999 config CGROUP_WRITEBACK
1000         bool
1001         depends on MEMCG && BLK_CGROUP
1002         default y
1003 
1004 menuconfig CGROUP_SCHED
1005         bool "CPU controller"
1006         default n
1007         help
1008           This feature lets CPU scheduler recognize task groups and control CPU
1009           bandwidth allocation to such task groups. It uses cgroups to group
1010           tasks.
1011 
1012 if CGROUP_SCHED
1013 config FAIR_GROUP_SCHED
1014         bool "Group scheduling for SCHED_OTHER"
1015         depends on CGROUP_SCHED
1016         default CGROUP_SCHED
1017 
1018 config CFS_BANDWIDTH
1019         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1020         depends on FAIR_GROUP_SCHED
1021         default n
1022         help
1023           This option allows users to define CPU bandwidth rates (limits) for
1024           tasks running within the fair group scheduler.  Groups with no limit
1025           set are considered to be unconstrained and will run with no
1026           restriction.
1027           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1028 
1029 config RT_GROUP_SCHED
1030         bool "Group scheduling for SCHED_RR/FIFO"
1031         depends on CGROUP_SCHED
1032         default n
1033         help
1034           This feature lets you explicitly allocate real CPU bandwidth
1035           to task groups. If enabled, it will also make it impossible to
1036           schedule realtime tasks for non-root users until you allocate
1037           realtime bandwidth for them.
1038           See Documentation/scheduler/sched-rt-group.txt for more information.
1039 
1040 endif #CGROUP_SCHED
1041 
1042 config CGROUP_PIDS
1043         bool "PIDs controller"
1044         help
1045           Provides enforcement of process number limits in the scope of a
1046           cgroup. Any attempt to fork more processes than is allowed in the
1047           cgroup will fail. PIDs are fundamentally a global resource because it
1048           is fairly trivial to reach PID exhaustion before you reach even a
1049           conservative kmemcg limit. As a result, it is possible to grind a
1050           system to halt without being limited by other cgroup policies. The
1051           PIDs controller is designed to stop this from happening.
1052 
1053           It should be noted that organisational operations (such as attaching
1054           to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1055           since the PIDs limit only affects a process's ability to fork, not to
1056           attach to a cgroup.
1057 
1058 config CGROUP_FREEZER
1059         bool "Freezer controller"
1060         help
1061           Provides a way to freeze and unfreeze all tasks in a
1062           cgroup.
1063 
1064           This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1065           controller includes important in-kernel memory consumers per default.
1066 
1067           If you're using cgroup2, say N.
1068 
1069 config CGROUP_HUGETLB
1070         bool "HugeTLB controller"
1071         depends on HUGETLB_PAGE
1072         select PAGE_COUNTER
1073         default n
1074         help
1075           Provides a cgroup controller for HugeTLB pages.
1076           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1077           The limit is enforced during page fault. Since HugeTLB doesn't
1078           support page reclaim, enforcing the limit at page fault time implies
1079           that, the application will get SIGBUS signal if it tries to access
1080           HugeTLB pages beyond its limit. This requires the application to know
1081           beforehand how much HugeTLB pages it would require for its use. The
1082           control group is tracked in the third page lru pointer. This means
1083           that we cannot use the controller with huge page less than 3 pages.
1084 
1085 config CPUSETS
1086         bool "Cpuset controller"
1087         help
1088           This option will let you create and manage CPUSETs which
1089           allow dynamically partitioning a system into sets of CPUs and
1090           Memory Nodes and assigning tasks to run only within those sets.
1091           This is primarily useful on large SMP or NUMA systems.
1092 
1093           Say N if unsure.
1094 
1095 config PROC_PID_CPUSET
1096         bool "Include legacy /proc/<pid>/cpuset file"
1097         depends on CPUSETS
1098         default y
1099 
1100 config CGROUP_DEVICE
1101         bool "Device controller"
1102         help
1103           Provides a cgroup controller implementing whitelists for
1104           devices which a process in the cgroup can mknod or open.
1105 
1106 config CGROUP_CPUACCT
1107         bool "Simple CPU accounting controller"
1108         help
1109           Provides a simple controller for monitoring the
1110           total CPU consumed by the tasks in a cgroup.
1111 
1112 config CGROUP_PERF
1113         bool "Perf controller"
1114         depends on PERF_EVENTS
1115         help
1116           This option extends the perf per-cpu mode to restrict monitoring
1117           to threads which belong to the cgroup specified and run on the
1118           designated cpu.
1119 
1120           Say N if unsure.
1121 
1122 config CGROUP_DEBUG
1123         bool "Example controller"
1124         default n
1125         help
1126           This option enables a simple controller that exports
1127           debugging information about the cgroups framework.
1128 
1129           Say N.
1130 
1131 endif # CGROUPS
1132 
1133 config CHECKPOINT_RESTORE
1134         bool "Checkpoint/restore support" if EXPERT
1135         select PROC_CHILDREN
1136         default n
1137         help
1138           Enables additional kernel features in a sake of checkpoint/restore.
1139           In particular it adds auxiliary prctl codes to setup process text,
1140           data and heap segment sizes, and a few additional /proc filesystem
1141           entries.
1142 
1143           If unsure, say N here.
1144 
1145 menuconfig NAMESPACES
1146         bool "Namespaces support" if EXPERT
1147         depends on MULTIUSER
1148         default !EXPERT
1149         help
1150           Provides the way to make tasks work with different objects using
1151           the same id. For example same IPC id may refer to different objects
1152           or same user id or pid may refer to different tasks when used in
1153           different namespaces.
1154 
1155 if NAMESPACES
1156 
1157 config UTS_NS
1158         bool "UTS namespace"
1159         default y
1160         help
1161           In this namespace tasks see different info provided with the
1162           uname() system call
1163 
1164 config IPC_NS
1165         bool "IPC namespace"
1166         depends on (SYSVIPC || POSIX_MQUEUE)
1167         default y
1168         help
1169           In this namespace tasks work with IPC ids which correspond to
1170           different IPC objects in different namespaces.
1171 
1172 config USER_NS
1173         bool "User namespace"
1174         default n
1175         help
1176           This allows containers, i.e. vservers, to use user namespaces
1177           to provide different user info for different servers.
1178 
1179           When user namespaces are enabled in the kernel it is
1180           recommended that the MEMCG option also be enabled and that
1181           user-space use the memory control groups to limit the amount
1182           of memory a memory unprivileged users can use.
1183 
1184           If unsure, say N.
1185 
1186 config PID_NS
1187         bool "PID Namespaces"
1188         default y
1189         help
1190           Support process id namespaces.  This allows having multiple
1191           processes with the same pid as long as they are in different
1192           pid namespaces.  This is a building block of containers.
1193 
1194 config NET_NS
1195         bool "Network namespace"
1196         depends on NET
1197         default y
1198         help
1199           Allow user space to create what appear to be multiple instances
1200           of the network stack.
1201 
1202 endif # NAMESPACES
1203 
1204 config SCHED_AUTOGROUP
1205         bool "Automatic process group scheduling"
1206         select CGROUPS
1207         select CGROUP_SCHED
1208         select FAIR_GROUP_SCHED
1209         help
1210           This option optimizes the scheduler for common desktop workloads by
1211           automatically creating and populating task groups.  This separation
1212           of workloads isolates aggressive CPU burners (like build jobs) from
1213           desktop applications.  Task group autogeneration is currently based
1214           upon task session.
1215 
1216 config SYSFS_DEPRECATED
1217         bool "Enable deprecated sysfs features to support old userspace tools"
1218         depends on SYSFS
1219         default n
1220         help
1221           This option adds code that switches the layout of the "block" class
1222           devices, to not show up in /sys/class/block/, but only in
1223           /sys/block/.
1224 
1225           This switch is only active when the sysfs.deprecated=1 boot option is
1226           passed or the SYSFS_DEPRECATED_V2 option is set.
1227 
1228           This option allows new kernels to run on old distributions and tools,
1229           which might get confused by /sys/class/block/. Since 2007/2008 all
1230           major distributions and tools handle this just fine.
1231 
1232           Recent distributions and userspace tools after 2009/2010 depend on
1233           the existence of /sys/class/block/, and will not work with this
1234           option enabled.
1235 
1236           Only if you are using a new kernel on an old distribution, you might
1237           need to say Y here.
1238 
1239 config SYSFS_DEPRECATED_V2
1240         bool "Enable deprecated sysfs features by default"
1241         default n
1242         depends on SYSFS
1243         depends on SYSFS_DEPRECATED
1244         help
1245           Enable deprecated sysfs by default.
1246 
1247           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1248           option.
1249 
1250           Only if you are using a new kernel on an old distribution, you might
1251           need to say Y here. Even then, odds are you would not need it
1252           enabled, you can always pass the boot option if absolutely necessary.
1253 
1254 config RELAY
1255         bool "Kernel->user space relay support (formerly relayfs)"
1256         help
1257           This option enables support for relay interface support in
1258           certain file systems (such as debugfs).
1259           It is designed to provide an efficient mechanism for tools and
1260           facilities to relay large amounts of data from kernel space to
1261           user space.
1262 
1263           If unsure, say N.
1264 
1265 config BLK_DEV_INITRD
1266         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1267         depends on BROKEN || !FRV
1268         help
1269           The initial RAM filesystem is a ramfs which is loaded by the
1270           boot loader (loadlin or lilo) and that is mounted as root
1271           before the normal boot procedure. It is typically used to
1272           load modules needed to mount the "real" root file system,
1273           etc. See <file:Documentation/initrd.txt> for details.
1274 
1275           If RAM disk support (BLK_DEV_RAM) is also included, this
1276           also enables initial RAM disk (initrd) support and adds
1277           15 Kbytes (more on some other architectures) to the kernel size.
1278 
1279           If unsure say Y.
1280 
1281 if BLK_DEV_INITRD
1282 
1283 source "usr/Kconfig"
1284 
1285 endif
1286 
1287 config CC_OPTIMIZE_FOR_SIZE
1288         bool "Optimize for size"
1289         help
1290           Enabling this option will pass "-Os" instead of "-O2" to
1291           your compiler resulting in a smaller kernel.
1292 
1293           If unsure, say N.
1294 
1295 config SYSCTL
1296         bool
1297 
1298 config ANON_INODES
1299         bool
1300 
1301 config HAVE_UID16
1302         bool
1303 
1304 config SYSCTL_EXCEPTION_TRACE
1305         bool
1306         help
1307           Enable support for /proc/sys/debug/exception-trace.
1308 
1309 config SYSCTL_ARCH_UNALIGN_NO_WARN
1310         bool
1311         help
1312           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1313           Allows arch to define/use @no_unaligned_warning to possibly warn
1314           about unaligned access emulation going on under the hood.
1315 
1316 config SYSCTL_ARCH_UNALIGN_ALLOW
1317         bool
1318         help
1319           Enable support for /proc/sys/kernel/unaligned-trap
1320           Allows arches to define/use @unaligned_enabled to runtime toggle
1321           the unaligned access emulation.
1322           see arch/parisc/kernel/unaligned.c for reference
1323 
1324 config HAVE_PCSPKR_PLATFORM
1325         bool
1326 
1327 # interpreter that classic socket filters depend on
1328 config BPF
1329         bool
1330 
1331 menuconfig EXPERT
1332         bool "Configure standard kernel features (expert users)"
1333         # Unhide debug options, to make the on-by-default options visible
1334         select DEBUG_KERNEL
1335         help
1336           This option allows certain base kernel options and settings
1337           to be disabled or tweaked. This is for specialized
1338           environments which can tolerate a "non-standard" kernel.
1339           Only use this if you really know what you are doing.
1340 
1341 config UID16
1342         bool "Enable 16-bit UID system calls" if EXPERT
1343         depends on HAVE_UID16 && MULTIUSER
1344         default y
1345         help
1346           This enables the legacy 16-bit UID syscall wrappers.
1347 
1348 config MULTIUSER
1349         bool "Multiple users, groups and capabilities support" if EXPERT
1350         default y
1351         help
1352           This option enables support for non-root users, groups and
1353           capabilities.
1354 
1355           If you say N here, all processes will run with UID 0, GID 0, and all
1356           possible capabilities.  Saying N here also compiles out support for
1357           system calls related to UIDs, GIDs, and capabilities, such as setuid,
1358           setgid, and capset.
1359 
1360           If unsure, say Y here.
1361 
1362 config SGETMASK_SYSCALL
1363         bool "sgetmask/ssetmask syscalls support" if EXPERT
1364         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1365         ---help---
1366           sys_sgetmask and sys_ssetmask are obsolete system calls
1367           no longer supported in libc but still enabled by default in some
1368           architectures.
1369 
1370           If unsure, leave the default option here.
1371 
1372 config SYSFS_SYSCALL
1373         bool "Sysfs syscall support" if EXPERT
1374         default y
1375         ---help---
1376           sys_sysfs is an obsolete system call no longer supported in libc.
1377           Note that disabling this option is more secure but might break
1378           compatibility with some systems.
1379 
1380           If unsure say Y here.
1381 
1382 config SYSCTL_SYSCALL
1383         bool "Sysctl syscall support" if EXPERT
1384         depends on PROC_SYSCTL
1385         default n
1386         select SYSCTL
1387         ---help---
1388           sys_sysctl uses binary paths that have been found challenging
1389           to properly maintain and use.  The interface in /proc/sys
1390           using paths with ascii names is now the primary path to this
1391           information.
1392 
1393           Almost nothing using the binary sysctl interface so if you are
1394           trying to save some space it is probably safe to disable this,
1395           making your kernel marginally smaller.
1396 
1397           If unsure say N here.
1398 
1399 config KALLSYMS
1400          bool "Load all symbols for debugging/ksymoops" if EXPERT
1401          default y
1402          help
1403            Say Y here to let the kernel print out symbolic crash information and
1404            symbolic stack backtraces. This increases the size of the kernel
1405            somewhat, as all symbols have to be loaded into the kernel image.
1406 
1407 config KALLSYMS_ALL
1408         bool "Include all symbols in kallsyms"
1409         depends on DEBUG_KERNEL && KALLSYMS
1410         help
1411            Normally kallsyms only contains the symbols of functions for nicer
1412            OOPS messages and backtraces (i.e., symbols from the text and inittext
1413            sections). This is sufficient for most cases. And only in very rare
1414            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1415            names of variables from the data sections, etc).
1416 
1417            This option makes sure that all symbols are loaded into the kernel
1418            image (i.e., symbols from all sections) in cost of increased kernel
1419            size (depending on the kernel configuration, it may be 300KiB or
1420            something like this).
1421 
1422            Say N unless you really need all symbols.
1423 
1424 config KALLSYMS_ABSOLUTE_PERCPU
1425         bool
1426         default X86_64 && SMP
1427 
1428 config KALLSYMS_BASE_RELATIVE
1429         bool
1430         depends on KALLSYMS
1431         default !IA64 && !(TILE && 64BIT)
1432         help
1433           Instead of emitting them as absolute values in the native word size,
1434           emit the symbol references in the kallsyms table as 32-bit entries,
1435           each containing a relative value in the range [base, base + U32_MAX]
1436           or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1437           an absolute value in the range [0, S32_MAX] or a relative value in the
1438           range [base, base + S32_MAX], where base is the lowest relative symbol
1439           address encountered in the image.
1440 
1441           On 64-bit builds, this reduces the size of the address table by 50%,
1442           but more importantly, it results in entries whose values are build
1443           time constants, and no relocation pass is required at runtime to fix
1444           up the entries based on the runtime load address of the kernel.
1445 
1446 config PRINTK
1447         default y
1448         bool "Enable support for printk" if EXPERT
1449         select IRQ_WORK
1450         help
1451           This option enables normal printk support. Removing it
1452           eliminates most of the message strings from the kernel image
1453           and makes the kernel more or less silent. As this makes it
1454           very difficult to diagnose system problems, saying N here is
1455           strongly discouraged.
1456 
1457 config BUG
1458         bool "BUG() support" if EXPERT
1459         default y
1460         help
1461           Disabling this option eliminates support for BUG and WARN, reducing
1462           the size of your kernel image and potentially quietly ignoring
1463           numerous fatal conditions. You should only consider disabling this
1464           option for embedded systems with no facilities for reporting errors.
1465           Just say Y.
1466 
1467 config ELF_CORE
1468         depends on COREDUMP
1469         default y
1470         bool "Enable ELF core dumps" if EXPERT
1471         help
1472           Enable support for generating core dumps. Disabling saves about 4k.
1473 
1474 
1475 config PCSPKR_PLATFORM
1476         bool "Enable PC-Speaker support" if EXPERT
1477         depends on HAVE_PCSPKR_PLATFORM
1478         select I8253_LOCK
1479         default y
1480         help
1481           This option allows to disable the internal PC-Speaker
1482           support, saving some memory.
1483 
1484 config BASE_FULL
1485         default y
1486         bool "Enable full-sized data structures for core" if EXPERT
1487         help
1488           Disabling this option reduces the size of miscellaneous core
1489           kernel data structures. This saves memory on small machines,
1490           but may reduce performance.
1491 
1492 config FUTEX
1493         bool "Enable futex support" if EXPERT
1494         default y
1495         select RT_MUTEXES
1496         help
1497           Disabling this option will cause the kernel to be built without
1498           support for "fast userspace mutexes".  The resulting kernel may not
1499           run glibc-based applications correctly.
1500 
1501 config HAVE_FUTEX_CMPXCHG
1502         bool
1503         depends on FUTEX
1504         help
1505           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1506           is implemented and always working. This removes a couple of runtime
1507           checks.
1508 
1509 config EPOLL
1510         bool "Enable eventpoll support" if EXPERT
1511         default y
1512         select ANON_INODES
1513         help
1514           Disabling this option will cause the kernel to be built without
1515           support for epoll family of system calls.
1516 
1517 config SIGNALFD
1518         bool "Enable signalfd() system call" if EXPERT
1519         select ANON_INODES
1520         default y
1521         help
1522           Enable the signalfd() system call that allows to receive signals
1523           on a file descriptor.
1524 
1525           If unsure, say Y.
1526 
1527 config TIMERFD
1528         bool "Enable timerfd() system call" if EXPERT
1529         select ANON_INODES
1530         default y
1531         help
1532           Enable the timerfd() system call that allows to receive timer
1533           events on a file descriptor.
1534 
1535           If unsure, say Y.
1536 
1537 config EVENTFD
1538         bool "Enable eventfd() system call" if EXPERT
1539         select ANON_INODES
1540         default y
1541         help
1542           Enable the eventfd() system call that allows to receive both
1543           kernel notification (ie. KAIO) or userspace notifications.
1544 
1545           If unsure, say Y.
1546 
1547 # syscall, maps, verifier
1548 config BPF_SYSCALL
1549         bool "Enable bpf() system call"
1550         select ANON_INODES
1551         select BPF
1552         default n
1553         help
1554           Enable the bpf() system call that allows to manipulate eBPF
1555           programs and maps via file descriptors.
1556 
1557 config SHMEM
1558         bool "Use full shmem filesystem" if EXPERT
1559         default y
1560         depends on MMU
1561         help
1562           The shmem is an internal filesystem used to manage shared memory.
1563           It is backed by swap and manages resource limits. It is also exported
1564           to userspace as tmpfs if TMPFS is enabled. Disabling this
1565           option replaces shmem and tmpfs with the much simpler ramfs code,
1566           which may be appropriate on small systems without swap.
1567 
1568 config AIO
1569         bool "Enable AIO support" if EXPERT
1570         default y
1571         help
1572           This option enables POSIX asynchronous I/O which may by used
1573           by some high performance threaded applications. Disabling
1574           this option saves about 7k.
1575 
1576 config ADVISE_SYSCALLS
1577         bool "Enable madvise/fadvise syscalls" if EXPERT
1578         default y
1579         help
1580           This option enables the madvise and fadvise syscalls, used by
1581           applications to advise the kernel about their future memory or file
1582           usage, improving performance. If building an embedded system where no
1583           applications use these syscalls, you can disable this option to save
1584           space.
1585 
1586 config USERFAULTFD
1587         bool "Enable userfaultfd() system call"
1588         select ANON_INODES
1589         depends on MMU
1590         help
1591           Enable the userfaultfd() system call that allows to intercept and
1592           handle page faults in userland.
1593 
1594 config PCI_QUIRKS
1595         default y
1596         bool "Enable PCI quirk workarounds" if EXPERT
1597         depends on PCI
1598         help
1599           This enables workarounds for various PCI chipset
1600           bugs/quirks. Disable this only if your target machine is
1601           unaffected by PCI quirks.
1602 
1603 config MEMBARRIER
1604         bool "Enable membarrier() system call" if EXPERT
1605         default y
1606         help
1607           Enable the membarrier() system call that allows issuing memory
1608           barriers across all running threads, which can be used to distribute
1609           the cost of user-space memory barriers asymmetrically by transforming
1610           pairs of memory barriers into pairs consisting of membarrier() and a
1611           compiler barrier.
1612 
1613           If unsure, say Y.
1614 
1615 config EMBEDDED
1616         bool "Embedded system"
1617         option allnoconfig_y
1618         select EXPERT
1619         help
1620           This option should be enabled if compiling the kernel for
1621           an embedded system so certain expert options are available
1622           for configuration.
1623 
1624 config HAVE_PERF_EVENTS
1625         bool
1626         help
1627           See tools/perf/design.txt for details.
1628 
1629 config PERF_USE_VMALLOC
1630         bool
1631         help
1632           See tools/perf/design.txt for details
1633 
1634 menu "Kernel Performance Events And Counters"
1635 
1636 config PERF_EVENTS
1637         bool "Kernel performance events and counters"
1638         default y if PROFILING
1639         depends on HAVE_PERF_EVENTS
1640         select ANON_INODES
1641         select IRQ_WORK
1642         select SRCU
1643         help
1644           Enable kernel support for various performance events provided
1645           by software and hardware.
1646 
1647           Software events are supported either built-in or via the
1648           use of generic tracepoints.
1649 
1650           Most modern CPUs support performance events via performance
1651           counter registers. These registers count the number of certain
1652           types of hw events: such as instructions executed, cachemisses
1653           suffered, or branches mis-predicted - without slowing down the
1654           kernel or applications. These registers can also trigger interrupts
1655           when a threshold number of events have passed - and can thus be
1656           used to profile the code that runs on that CPU.
1657 
1658           The Linux Performance Event subsystem provides an abstraction of
1659           these software and hardware event capabilities, available via a
1660           system call and used by the "perf" utility in tools/perf/. It
1661           provides per task and per CPU counters, and it provides event
1662           capabilities on top of those.
1663 
1664           Say Y if unsure.
1665 
1666 config DEBUG_PERF_USE_VMALLOC
1667         default n
1668         bool "Debug: use vmalloc to back perf mmap() buffers"
1669         depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1670         select PERF_USE_VMALLOC
1671         help
1672          Use vmalloc memory to back perf mmap() buffers.
1673 
1674          Mostly useful for debugging the vmalloc code on platforms
1675          that don't require it.
1676 
1677          Say N if unsure.
1678 
1679 endmenu
1680 
1681 config VM_EVENT_COUNTERS
1682         default y
1683         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1684         help
1685           VM event counters are needed for event counts to be shown.
1686           This option allows the disabling of the VM event counters
1687           on EXPERT systems.  /proc/vmstat will only show page counts
1688           if VM event counters are disabled.
1689 
1690 config SLUB_DEBUG
1691         default y
1692         bool "Enable SLUB debugging support" if EXPERT
1693         depends on SLUB && SYSFS
1694         help
1695           SLUB has extensive debug support features. Disabling these can
1696           result in significant savings in code size. This also disables
1697           SLUB sysfs support. /sys/slab will not exist and there will be
1698           no support for cache validation etc.
1699 
1700 config COMPAT_BRK
1701         bool "Disable heap randomization"
1702         default y
1703         help
1704           Randomizing heap placement makes heap exploits harder, but it
1705           also breaks ancient binaries (including anything libc5 based).
1706           This option changes the bootup default to heap randomization
1707           disabled, and can be overridden at runtime by setting
1708           /proc/sys/kernel/randomize_va_space to 2.
1709 
1710           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1711 
1712 choice
1713         prompt "Choose SLAB allocator"
1714         default SLUB
1715         help
1716            This option allows to select a slab allocator.
1717 
1718 config SLAB
1719         bool "SLAB"
1720         help
1721           The regular slab allocator that is established and known to work
1722           well in all environments. It organizes cache hot objects in
1723           per cpu and per node queues.
1724 
1725 config SLUB
1726         bool "SLUB (Unqueued Allocator)"
1727         help
1728            SLUB is a slab allocator that minimizes cache line usage
1729            instead of managing queues of cached objects (SLAB approach).
1730            Per cpu caching is realized using slabs of objects instead
1731            of queues of objects. SLUB can use memory efficiently
1732            and has enhanced diagnostics. SLUB is the default choice for
1733            a slab allocator.
1734 
1735 config SLOB
1736         depends on EXPERT
1737         bool "SLOB (Simple Allocator)"
1738         help
1739            SLOB replaces the stock allocator with a drastically simpler
1740            allocator. SLOB is generally more space efficient but
1741            does not perform as well on large systems.
1742 
1743 endchoice
1744 
1745 config SLUB_CPU_PARTIAL
1746         default y
1747         depends on SLUB && SMP
1748         bool "SLUB per cpu partial cache"
1749         help
1750           Per cpu partial caches accellerate objects allocation and freeing
1751           that is local to a processor at the price of more indeterminism
1752           in the latency of the free. On overflow these caches will be cleared
1753           which requires the taking of locks that may cause latency spikes.
1754           Typically one would choose no for a realtime system.
1755 
1756 config MMAP_ALLOW_UNINITIALIZED
1757         bool "Allow mmapped anonymous memory to be uninitialized"
1758         depends on EXPERT && !MMU
1759         default n
1760         help
1761           Normally, and according to the Linux spec, anonymous memory obtained
1762           from mmap() has it's contents cleared before it is passed to
1763           userspace.  Enabling this config option allows you to request that
1764           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1765           providing a huge performance boost.  If this option is not enabled,
1766           then the flag will be ignored.
1767 
1768           This is taken advantage of by uClibc's malloc(), and also by
1769           ELF-FDPIC binfmt's brk and stack allocator.
1770 
1771           Because of the obvious security issues, this option should only be
1772           enabled on embedded devices where you control what is run in
1773           userspace.  Since that isn't generally a problem on no-MMU systems,
1774           it is normally safe to say Y here.
1775 
1776           See Documentation/nommu-mmap.txt for more information.
1777 
1778 config SYSTEM_DATA_VERIFICATION
1779         def_bool n
1780         select SYSTEM_TRUSTED_KEYRING
1781         select KEYS
1782         select CRYPTO
1783         select CRYPTO_RSA
1784         select ASYMMETRIC_KEY_TYPE
1785         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1786         select ASN1
1787         select OID_REGISTRY
1788         select X509_CERTIFICATE_PARSER
1789         select PKCS7_MESSAGE_PARSER
1790         help
1791           Provide PKCS#7 message verification using the contents of the system
1792           trusted keyring to provide public keys.  This then can be used for
1793           module verification, kexec image verification and firmware blob
1794           verification.
1795 
1796 config PROFILING
1797         bool "Profiling support"
1798         help
1799           Say Y here to enable the extended profiling support mechanisms used
1800           by profilers such as OProfile.
1801 
1802 #
1803 # Place an empty function call at each tracepoint site. Can be
1804 # dynamically changed for a probe function.
1805 #
1806 config TRACEPOINTS
1807         bool
1808 
1809 source "arch/Kconfig"
1810 
1811 endmenu         # General setup
1812 
1813 config HAVE_GENERIC_DMA_COHERENT
1814         bool
1815         default n
1816 
1817 config SLABINFO
1818         bool
1819         depends on PROC_FS
1820         depends on SLAB || SLUB_DEBUG
1821         default y
1822 
1823 config RT_MUTEXES
1824         bool
1825 
1826 config BASE_SMALL
1827         int
1828         default 0 if BASE_FULL
1829         default 1 if !BASE_FULL
1830 
1831 menuconfig MODULES
1832         bool "Enable loadable module support"
1833         option modules
1834         help
1835           Kernel modules are small pieces of compiled code which can
1836           be inserted in the running kernel, rather than being
1837           permanently built into the kernel.  You use the "modprobe"
1838           tool to add (and sometimes remove) them.  If you say Y here,
1839           many parts of the kernel can be built as modules (by
1840           answering M instead of Y where indicated): this is most
1841           useful for infrequently used options which are not required
1842           for booting.  For more information, see the man pages for
1843           modprobe, lsmod, modinfo, insmod and rmmod.
1844 
1845           If you say Y here, you will need to run "make
1846           modules_install" to put the modules under /lib/modules/
1847           where modprobe can find them (you may need to be root to do
1848           this).
1849 
1850           If unsure, say Y.
1851 
1852 if MODULES
1853 
1854 config MODULE_FORCE_LOAD
1855         bool "Forced module loading"
1856         default n
1857         help
1858           Allow loading of modules without version information (ie. modprobe
1859           --force).  Forced module loading sets the 'F' (forced) taint flag and
1860           is usually a really bad idea.
1861 
1862 config MODULE_UNLOAD
1863         bool "Module unloading"
1864         help
1865           Without this option you will not be able to unload any
1866           modules (note that some modules may not be unloadable
1867           anyway), which makes your kernel smaller, faster
1868           and simpler.  If unsure, say Y.
1869 
1870 config MODULE_FORCE_UNLOAD
1871         bool "Forced module unloading"
1872         depends on MODULE_UNLOAD
1873         help
1874           This option allows you to force a module to unload, even if the
1875           kernel believes it is unsafe: the kernel will remove the module
1876           without waiting for anyone to stop using it (using the -f option to
1877           rmmod).  This is mainly for kernel developers and desperate users.
1878           If unsure, say N.
1879 
1880 config MODVERSIONS
1881         bool "Module versioning support"
1882         help
1883           Usually, you have to use modules compiled with your kernel.
1884           Saying Y here makes it sometimes possible to use modules
1885           compiled for different kernels, by adding enough information
1886           to the modules to (hopefully) spot any changes which would
1887           make them incompatible with the kernel you are running.  If
1888           unsure, say N.
1889 
1890 config MODULE_SRCVERSION_ALL
1891         bool "Source checksum for all modules"
1892         help
1893           Modules which contain a MODULE_VERSION get an extra "srcversion"
1894           field inserted into their modinfo section, which contains a
1895           sum of the source files which made it.  This helps maintainers
1896           see exactly which source was used to build a module (since
1897           others sometimes change the module source without updating
1898           the version).  With this option, such a "srcversion" field
1899           will be created for all modules.  If unsure, say N.
1900 
1901 config MODULE_SIG
1902         bool "Module signature verification"
1903         depends on MODULES
1904         select SYSTEM_DATA_VERIFICATION
1905         help
1906           Check modules for valid signatures upon load: the signature
1907           is simply appended to the module. For more information see
1908           Documentation/module-signing.txt.
1909 
1910           Note that this option adds the OpenSSL development packages as a
1911           kernel build dependency so that the signing tool can use its crypto
1912           library.
1913 
1914           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1915           module DOES NOT get stripped after being signed.  This includes the
1916           debuginfo strip done by some packagers (such as rpmbuild) and
1917           inclusion into an initramfs that wants the module size reduced.
1918 
1919 config MODULE_SIG_FORCE
1920         bool "Require modules to be validly signed"
1921         depends on MODULE_SIG
1922         help
1923           Reject unsigned modules or signed modules for which we don't have a
1924           key.  Without this, such modules will simply taint the kernel.
1925 
1926 config MODULE_SIG_ALL
1927         bool "Automatically sign all modules"
1928         default y
1929         depends on MODULE_SIG
1930         help
1931           Sign all modules during make modules_install. Without this option,
1932           modules must be signed manually, using the scripts/sign-file tool.
1933 
1934 comment "Do not forget to sign required modules with scripts/sign-file"
1935         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1936 
1937 choice
1938         prompt "Which hash algorithm should modules be signed with?"
1939         depends on MODULE_SIG
1940         help
1941           This determines which sort of hashing algorithm will be used during
1942           signature generation.  This algorithm _must_ be built into the kernel
1943           directly so that signature verification can take place.  It is not
1944           possible to load a signed module containing the algorithm to check
1945           the signature on that module.
1946 
1947 config MODULE_SIG_SHA1
1948         bool "Sign modules with SHA-1"
1949         select CRYPTO_SHA1
1950 
1951 config MODULE_SIG_SHA224
1952         bool "Sign modules with SHA-224"
1953         select CRYPTO_SHA256
1954 
1955 config MODULE_SIG_SHA256
1956         bool "Sign modules with SHA-256"
1957         select CRYPTO_SHA256
1958 
1959 config MODULE_SIG_SHA384
1960         bool "Sign modules with SHA-384"
1961         select CRYPTO_SHA512
1962 
1963 config MODULE_SIG_SHA512
1964         bool "Sign modules with SHA-512"
1965         select CRYPTO_SHA512
1966 
1967 endchoice
1968 
1969 config MODULE_SIG_HASH
1970         string
1971         depends on MODULE_SIG
1972         default "sha1" if MODULE_SIG_SHA1
1973         default "sha224" if MODULE_SIG_SHA224
1974         default "sha256" if MODULE_SIG_SHA256
1975         default "sha384" if MODULE_SIG_SHA384
1976         default "sha512" if MODULE_SIG_SHA512
1977 
1978 config MODULE_COMPRESS
1979         bool "Compress modules on installation"
1980         depends on MODULES
1981         help
1982 
1983           Compresses kernel modules when 'make modules_install' is run; gzip or
1984           xz depending on "Compression algorithm" below.
1985 
1986           module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
1987 
1988           Out-of-tree kernel modules installed using Kbuild will also be
1989           compressed upon installation.
1990 
1991           Note: for modules inside an initrd or initramfs, it's more efficient
1992           to compress the whole initrd or initramfs instead.
1993 
1994           Note: This is fully compatible with signed modules.
1995 
1996           If in doubt, say N.
1997 
1998 choice
1999         prompt "Compression algorithm"
2000         depends on MODULE_COMPRESS
2001         default MODULE_COMPRESS_GZIP
2002         help
2003           This determines which sort of compression will be used during
2004           'make modules_install'.
2005 
2006           GZIP (default) and XZ are supported.
2007 
2008 config MODULE_COMPRESS_GZIP
2009         bool "GZIP"
2010 
2011 config MODULE_COMPRESS_XZ
2012         bool "XZ"
2013 
2014 endchoice
2015 
2016 endif # MODULES
2017 
2018 config MODULES_TREE_LOOKUP
2019         def_bool y
2020         depends on PERF_EVENTS || TRACING
2021 
2022 config INIT_ALL_POSSIBLE
2023         bool
2024         help
2025           Back when each arch used to define their own cpu_online_mask and
2026           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2027           with all 1s, and others with all 0s.  When they were centralised,
2028           it was better to provide this option than to break all the archs
2029           and have several arch maintainers pursuing me down dark alleys.
2030 
2031 source "block/Kconfig"
2032 
2033 config PREEMPT_NOTIFIERS
2034         bool
2035 
2036 config PADATA
2037         depends on SMP
2038         bool
2039 
2040 # Can be selected by architectures with broken toolchains
2041 # that get confused by correct const<->read_only section
2042 # mappings
2043 config BROKEN_RODATA
2044         bool
2045 
2046 config ASN1
2047         tristate
2048         help
2049           Build a simple ASN.1 grammar compiler that produces a bytecode output
2050           that can be interpreted by the ASN.1 stream decoder and used to
2051           inform it as to what tags are to be expected in a stream and what
2052           functions to call on what tags.
2053 
2054 source "kernel/Kconfig.locks"

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