Version:  2.0.40 2.2.26 2.4.37 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18

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"
276         select EXPORTFS
277         help
278           If you say Y here, a user level program will be able to map
279           file names to handle and then later use the handle for
280           different file system operations. This is useful in implementing
281           userspace file servers, which now track files using handles instead
282           of names. The handle would remain the same even if file names
283           get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
284           syscalls.
285 
286 config USELIB
287         bool "uselib syscall"
288         default y
289         help
290           This option enables the uselib syscall, a system call used in the
291           dynamic linker from libc5 and earlier.  glibc does not use this
292           system call.  If you intend to run programs built on libc5 or
293           earlier, you may need to enable this syscall.  Current systems
294           running glibc can safely disable this.
295 
296 config AUDIT
297         bool "Auditing support"
298         depends on NET
299         help
300           Enable auditing infrastructure that can be used with another
301           kernel subsystem, such as SELinux (which requires this for
302           logging of avc messages output).  Does not do system-call
303           auditing without CONFIG_AUDITSYSCALL.
304 
305 config HAVE_ARCH_AUDITSYSCALL
306         bool
307 
308 config AUDITSYSCALL
309         bool "Enable system-call auditing support"
310         depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
311         default y if SECURITY_SELINUX
312         help
313           Enable low-overhead system-call auditing infrastructure that
314           can be used independently or with another kernel subsystem,
315           such as SELinux.
316 
317 config AUDIT_WATCH
318         def_bool y
319         depends on AUDITSYSCALL
320         select FSNOTIFY
321 
322 config AUDIT_TREE
323         def_bool y
324         depends on AUDITSYSCALL
325         select FSNOTIFY
326 
327 source "kernel/irq/Kconfig"
328 source "kernel/time/Kconfig"
329 
330 menu "CPU/Task time and stats accounting"
331 
332 config VIRT_CPU_ACCOUNTING
333         bool
334 
335 choice
336         prompt "Cputime accounting"
337         default TICK_CPU_ACCOUNTING if !PPC64
338         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
339 
340 # Kind of a stub config for the pure tick based cputime accounting
341 config TICK_CPU_ACCOUNTING
342         bool "Simple tick based cputime accounting"
343         depends on !S390 && !NO_HZ_FULL
344         help
345           This is the basic tick based cputime accounting that maintains
346           statistics about user, system and idle time spent on per jiffies
347           granularity.
348 
349           If unsure, say Y.
350 
351 config VIRT_CPU_ACCOUNTING_NATIVE
352         bool "Deterministic task and CPU time accounting"
353         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
354         select VIRT_CPU_ACCOUNTING
355         help
356           Select this option to enable more accurate task and CPU time
357           accounting.  This is done by reading a CPU counter on each
358           kernel entry and exit and on transitions within the kernel
359           between system, softirq and hardirq state, so there is a
360           small performance impact.  In the case of s390 or IBM POWER > 5,
361           this also enables accounting of stolen time on logically-partitioned
362           systems.
363 
364 config VIRT_CPU_ACCOUNTING_GEN
365         bool "Full dynticks CPU time accounting"
366         depends on HAVE_CONTEXT_TRACKING
367         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
368         select VIRT_CPU_ACCOUNTING
369         select CONTEXT_TRACKING
370         help
371           Select this option to enable task and CPU time accounting on full
372           dynticks systems. This accounting is implemented by watching every
373           kernel-user boundaries using the context tracking subsystem.
374           The accounting is thus performed at the expense of some significant
375           overhead.
376 
377           For now this is only useful if you are working on the full
378           dynticks subsystem development.
379 
380           If unsure, say N.
381 
382 config IRQ_TIME_ACCOUNTING
383         bool "Fine granularity task level IRQ time accounting"
384         depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
385         help
386           Select this option to enable fine granularity task irq time
387           accounting. This is done by reading a timestamp on each
388           transitions between softirq and hardirq state, so there can be a
389           small performance impact.
390 
391           If in doubt, say N here.
392 
393 endchoice
394 
395 config BSD_PROCESS_ACCT
396         bool "BSD Process Accounting"
397         help
398           If you say Y here, a user level program will be able to instruct the
399           kernel (via a special system call) to write process accounting
400           information to a file: whenever a process exits, information about
401           that process will be appended to the file by the kernel.  The
402           information includes things such as creation time, owning user,
403           command name, memory usage, controlling terminal etc. (the complete
404           list is in the struct acct in <file:include/linux/acct.h>).  It is
405           up to the user level program to do useful things with this
406           information.  This is generally a good idea, so say Y.
407 
408 config BSD_PROCESS_ACCT_V3
409         bool "BSD Process Accounting version 3 file format"
410         depends on BSD_PROCESS_ACCT
411         default n
412         help
413           If you say Y here, the process accounting information is written
414           in a new file format that also logs the process IDs of each
415           process and it's parent. Note that this file format is incompatible
416           with previous v0/v1/v2 file formats, so you will need updated tools
417           for processing it. A preliminary version of these tools is available
418           at <http://www.gnu.org/software/acct/>.
419 
420 config TASKSTATS
421         bool "Export task/process statistics through netlink"
422         depends on NET
423         default n
424         help
425           Export selected statistics for tasks/processes through the
426           generic netlink interface. Unlike BSD process accounting, the
427           statistics are available during the lifetime of tasks/processes as
428           responses to commands. Like BSD accounting, they are sent to user
429           space on task exit.
430 
431           Say N if unsure.
432 
433 config TASK_DELAY_ACCT
434         bool "Enable per-task delay accounting"
435         depends on TASKSTATS
436         help
437           Collect information on time spent by a task waiting for system
438           resources like cpu, synchronous block I/O completion and swapping
439           in pages. Such statistics can help in setting a task's priorities
440           relative to other tasks for cpu, io, rss limits etc.
441 
442           Say N if unsure.
443 
444 config TASK_XACCT
445         bool "Enable extended accounting over taskstats"
446         depends on TASKSTATS
447         help
448           Collect extended task accounting data and send the data
449           to userland for processing over the taskstats interface.
450 
451           Say N if unsure.
452 
453 config TASK_IO_ACCOUNTING
454         bool "Enable per-task storage I/O accounting"
455         depends on TASK_XACCT
456         help
457           Collect information on the number of bytes of storage I/O which this
458           task has caused.
459 
460           Say N if unsure.
461 
462 endmenu # "CPU/Task time and stats accounting"
463 
464 menu "RCU Subsystem"
465 
466 choice
467         prompt "RCU Implementation"
468         default TREE_RCU
469 
470 config TREE_RCU
471         bool "Tree-based hierarchical RCU"
472         depends on !PREEMPT && SMP
473         select IRQ_WORK
474         help
475           This option selects the RCU implementation that is
476           designed for very large SMP system with hundreds or
477           thousands of CPUs.  It also scales down nicely to
478           smaller systems.
479 
480 config TREE_PREEMPT_RCU
481         bool "Preemptible tree-based hierarchical RCU"
482         depends on PREEMPT
483         select IRQ_WORK
484         help
485           This option selects the RCU implementation that is
486           designed for very large SMP systems with hundreds or
487           thousands of CPUs, but for which real-time response
488           is also required.  It also scales down nicely to
489           smaller systems.
490 
491           Select this option if you are unsure.
492 
493 config TINY_RCU
494         bool "UP-only small-memory-footprint RCU"
495         depends on !PREEMPT && !SMP
496         help
497           This option selects the RCU implementation that is
498           designed for UP systems from which real-time response
499           is not required.  This option greatly reduces the
500           memory footprint of RCU.
501 
502 endchoice
503 
504 config PREEMPT_RCU
505         def_bool TREE_PREEMPT_RCU
506         help
507           This option enables preemptible-RCU code that is common between
508           TREE_PREEMPT_RCU and, in the old days, TINY_PREEMPT_RCU.
509 
510 config TASKS_RCU
511         bool "Task_based RCU implementation using voluntary context switch"
512         default n
513         help
514           This option enables a task-based RCU implementation that uses
515           only voluntary context switch (not preemption!), idle, and
516           user-mode execution as quiescent states.
517 
518           If unsure, say N.
519 
520 config RCU_STALL_COMMON
521         def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
522         help
523           This option enables RCU CPU stall code that is common between
524           the TINY and TREE variants of RCU.  The purpose is to allow
525           the tiny variants to disable RCU CPU stall warnings, while
526           making these warnings mandatory for the tree variants.
527 
528 config CONTEXT_TRACKING
529        bool
530 
531 config RCU_USER_QS
532         bool "Consider userspace as in RCU extended quiescent state"
533         depends on HAVE_CONTEXT_TRACKING && SMP
534         select CONTEXT_TRACKING
535         help
536           This option sets hooks on kernel / userspace boundaries and
537           puts RCU in extended quiescent state when the CPU runs in
538           userspace. It means that when a CPU runs in userspace, it is
539           excluded from the global RCU state machine and thus doesn't
540           try to keep the timer tick on for RCU.
541 
542           Unless you want to hack and help the development of the full
543           dynticks mode, you shouldn't enable this option.  It also
544           adds unnecessary overhead.
545 
546           If unsure say N
547 
548 config CONTEXT_TRACKING_FORCE
549         bool "Force context tracking"
550         depends on CONTEXT_TRACKING
551         default y if !NO_HZ_FULL
552         help
553           The major pre-requirement for full dynticks to work is to
554           support the context tracking subsystem. But there are also
555           other dependencies to provide in order to make the full
556           dynticks working.
557 
558           This option stands for testing when an arch implements the
559           context tracking backend but doesn't yet fullfill all the
560           requirements to make the full dynticks feature working.
561           Without the full dynticks, there is no way to test the support
562           for context tracking and the subsystems that rely on it: RCU
563           userspace extended quiescent state and tickless cputime
564           accounting. This option copes with the absence of the full
565           dynticks subsystem by forcing the context tracking on all
566           CPUs in the system.
567 
568           Say Y only if you're working on the development of an
569           architecture backend for the context tracking.
570 
571           Say N otherwise, this option brings an overhead that you
572           don't want in production.
573 
574 
575 config RCU_FANOUT
576         int "Tree-based hierarchical RCU fanout value"
577         range 2 64 if 64BIT
578         range 2 32 if !64BIT
579         depends on TREE_RCU || TREE_PREEMPT_RCU
580         default 64 if 64BIT
581         default 32 if !64BIT
582         help
583           This option controls the fanout of hierarchical implementations
584           of RCU, allowing RCU to work efficiently on machines with
585           large numbers of CPUs.  This value must be at least the fourth
586           root of NR_CPUS, which allows NR_CPUS to be insanely large.
587           The default value of RCU_FANOUT should be used for production
588           systems, but if you are stress-testing the RCU implementation
589           itself, small RCU_FANOUT values allow you to test large-system
590           code paths on small(er) systems.
591 
592           Select a specific number if testing RCU itself.
593           Take the default if unsure.
594 
595 config RCU_FANOUT_LEAF
596         int "Tree-based hierarchical RCU leaf-level fanout value"
597         range 2 RCU_FANOUT if 64BIT
598         range 2 RCU_FANOUT if !64BIT
599         depends on TREE_RCU || TREE_PREEMPT_RCU
600         default 16
601         help
602           This option controls the leaf-level fanout of hierarchical
603           implementations of RCU, and allows trading off cache misses
604           against lock contention.  Systems that synchronize their
605           scheduling-clock interrupts for energy-efficiency reasons will
606           want the default because the smaller leaf-level fanout keeps
607           lock contention levels acceptably low.  Very large systems
608           (hundreds or thousands of CPUs) will instead want to set this
609           value to the maximum value possible in order to reduce the
610           number of cache misses incurred during RCU's grace-period
611           initialization.  These systems tend to run CPU-bound, and thus
612           are not helped by synchronized interrupts, and thus tend to
613           skew them, which reduces lock contention enough that large
614           leaf-level fanouts work well.
615 
616           Select a specific number if testing RCU itself.
617 
618           Select the maximum permissible value for large systems.
619 
620           Take the default if unsure.
621 
622 config RCU_FANOUT_EXACT
623         bool "Disable tree-based hierarchical RCU auto-balancing"
624         depends on TREE_RCU || TREE_PREEMPT_RCU
625         default n
626         help
627           This option forces use of the exact RCU_FANOUT value specified,
628           regardless of imbalances in the hierarchy.  This is useful for
629           testing RCU itself, and might one day be useful on systems with
630           strong NUMA behavior.
631 
632           Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
633 
634           Say N if unsure.
635 
636 config RCU_FAST_NO_HZ
637         bool "Accelerate last non-dyntick-idle CPU's grace periods"
638         depends on NO_HZ_COMMON && SMP
639         default n
640         help
641           This option permits CPUs to enter dynticks-idle state even if
642           they have RCU callbacks queued, and prevents RCU from waking
643           these CPUs up more than roughly once every four jiffies (by
644           default, you can adjust this using the rcutree.rcu_idle_gp_delay
645           parameter), thus improving energy efficiency.  On the other
646           hand, this option increases the duration of RCU grace periods,
647           for example, slowing down synchronize_rcu().
648 
649           Say Y if energy efficiency is critically important, and you
650                 don't care about increased grace-period durations.
651 
652           Say N if you are unsure.
653 
654 config TREE_RCU_TRACE
655         def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
656         select DEBUG_FS
657         help
658           This option provides tracing for the TREE_RCU and
659           TREE_PREEMPT_RCU implementations, permitting Makefile to
660           trivially select kernel/rcutree_trace.c.
661 
662 config RCU_BOOST
663         bool "Enable RCU priority boosting"
664         depends on RT_MUTEXES && PREEMPT_RCU
665         default n
666         help
667           This option boosts the priority of preempted RCU readers that
668           block the current preemptible RCU grace period for too long.
669           This option also prevents heavy loads from blocking RCU
670           callback invocation for all flavors of RCU.
671 
672           Say Y here if you are working with real-time apps or heavy loads
673           Say N here if you are unsure.
674 
675 config RCU_BOOST_PRIO
676         int "Real-time priority to boost RCU readers to"
677         range 1 99
678         depends on RCU_BOOST
679         default 1
680         help
681           This option specifies the real-time priority to which long-term
682           preempted RCU readers are to be boosted.  If you are working
683           with a real-time application that has one or more CPU-bound
684           threads running at a real-time priority level, you should set
685           RCU_BOOST_PRIO to a priority higher then the highest-priority
686           real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
687           of 1 is appropriate in the common case, which is real-time
688           applications that do not have any CPU-bound threads.
689 
690           Some real-time applications might not have a single real-time
691           thread that saturates a given CPU, but instead might have
692           multiple real-time threads that, taken together, fully utilize
693           that CPU.  In this case, you should set RCU_BOOST_PRIO to
694           a priority higher than the lowest-priority thread that is
695           conspiring to prevent the CPU from running any non-real-time
696           tasks.  For example, if one thread at priority 10 and another
697           thread at priority 5 are between themselves fully consuming
698           the CPU time on a given CPU, then RCU_BOOST_PRIO should be
699           set to priority 6 or higher.
700 
701           Specify the real-time priority, or take the default if unsure.
702 
703 config RCU_BOOST_DELAY
704         int "Milliseconds to delay boosting after RCU grace-period start"
705         range 0 3000
706         depends on RCU_BOOST
707         default 500
708         help
709           This option specifies the time to wait after the beginning of
710           a given grace period before priority-boosting preempted RCU
711           readers blocking that grace period.  Note that any RCU reader
712           blocking an expedited RCU grace period is boosted immediately.
713 
714           Accept the default if unsure.
715 
716 config RCU_NOCB_CPU
717         bool "Offload RCU callback processing from boot-selected CPUs"
718         depends on TREE_RCU || TREE_PREEMPT_RCU
719         default n
720         help
721           Use this option to reduce OS jitter for aggressive HPC or
722           real-time workloads.  It can also be used to offload RCU
723           callback invocation to energy-efficient CPUs in battery-powered
724           asymmetric multiprocessors.
725 
726           This option offloads callback invocation from the set of
727           CPUs specified at boot time by the rcu_nocbs parameter.
728           For each such CPU, a kthread ("rcuox/N") will be created to
729           invoke callbacks, where the "N" is the CPU being offloaded,
730           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
731           "s" for RCU-sched.  Nothing prevents this kthread from running
732           on the specified CPUs, but (1) the kthreads may be preempted
733           between each callback, and (2) affinity or cgroups can be used
734           to force the kthreads to run on whatever set of CPUs is desired.
735 
736           Say Y here if you want to help to debug reduced OS jitter.
737           Say N here if you are unsure.
738 
739 choice
740         prompt "Build-forced no-CBs CPUs"
741         default RCU_NOCB_CPU_NONE
742         help
743           This option allows no-CBs CPUs (whose RCU callbacks are invoked
744           from kthreads rather than from softirq context) to be specified
745           at build time.  Additional no-CBs CPUs may be specified by
746           the rcu_nocbs= boot parameter.
747 
748 config RCU_NOCB_CPU_NONE
749         bool "No build_forced no-CBs CPUs"
750         depends on RCU_NOCB_CPU
751         help
752           This option does not force any of the CPUs to be no-CBs CPUs.
753           Only CPUs designated by the rcu_nocbs= boot parameter will be
754           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
755           kthreads whose names begin with "rcuo".  All other CPUs will
756           invoke their own RCU callbacks in softirq context.
757 
758           Select this option if you want to choose no-CBs CPUs at
759           boot time, for example, to allow testing of different no-CBs
760           configurations without having to rebuild the kernel each time.
761 
762 config RCU_NOCB_CPU_ZERO
763         bool "CPU 0 is a build_forced no-CBs CPU"
764         depends on RCU_NOCB_CPU
765         help
766           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
767           callbacks are invoked by a per-CPU kthread whose name begins
768           with "rcuo".  Additional CPUs may be designated as no-CBs
769           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
770           All other CPUs will invoke their own RCU callbacks in softirq
771           context.
772 
773           Select this if CPU 0 needs to be a no-CBs CPU for real-time
774           or energy-efficiency reasons, but the real reason it exists
775           is to ensure that randconfig testing covers mixed systems.
776 
777 config RCU_NOCB_CPU_ALL
778         bool "All CPUs are build_forced no-CBs CPUs"
779         depends on RCU_NOCB_CPU
780         help
781           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
782           boot parameter will be ignored.  All CPUs' RCU callbacks will
783           be executed in the context of per-CPU rcuo kthreads created for
784           this purpose.  Assuming that the kthreads whose names start with
785           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
786           on the remaining CPUs, but might decrease memory locality during
787           RCU-callback invocation, thus potentially degrading throughput.
788 
789           Select this if all CPUs need to be no-CBs CPUs for real-time
790           or energy-efficiency reasons.
791 
792 endchoice
793 
794 endmenu # "RCU Subsystem"
795 
796 config BUILD_BIN2C
797         bool
798         default n
799 
800 config IKCONFIG
801         tristate "Kernel .config support"
802         select BUILD_BIN2C
803         ---help---
804           This option enables the complete Linux kernel ".config" file
805           contents to be saved in the kernel. It provides documentation
806           of which kernel options are used in a running kernel or in an
807           on-disk kernel.  This information can be extracted from the kernel
808           image file with the script scripts/extract-ikconfig and used as
809           input to rebuild the current kernel or to build another kernel.
810           It can also be extracted from a running kernel by reading
811           /proc/config.gz if enabled (below).
812 
813 config IKCONFIG_PROC
814         bool "Enable access to .config through /proc/config.gz"
815         depends on IKCONFIG && PROC_FS
816         ---help---
817           This option enables access to the kernel configuration file
818           through /proc/config.gz.
819 
820 config LOG_BUF_SHIFT
821         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
822         range 12 21
823         default 17
824         depends on PRINTK
825         help
826           Select the minimal kernel log buffer size as a power of 2.
827           The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
828           parameter, see below. Any higher size also might be forced
829           by "log_buf_len" boot parameter.
830 
831           Examples:
832                      17 => 128 KB
833                      16 => 64 KB
834                      15 => 32 KB
835                      14 => 16 KB
836                      13 =>  8 KB
837                      12 =>  4 KB
838 
839 config LOG_CPU_MAX_BUF_SHIFT
840         int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
841         depends on SMP
842         range 0 21
843         default 12 if !BASE_SMALL
844         default 0 if BASE_SMALL
845         depends on PRINTK
846         help
847           This option allows to increase the default ring buffer size
848           according to the number of CPUs. The value defines the contribution
849           of each CPU as a power of 2. The used space is typically only few
850           lines however it might be much more when problems are reported,
851           e.g. backtraces.
852 
853           The increased size means that a new buffer has to be allocated and
854           the original static one is unused. It makes sense only on systems
855           with more CPUs. Therefore this value is used only when the sum of
856           contributions is greater than the half of the default kernel ring
857           buffer as defined by LOG_BUF_SHIFT. The default values are set
858           so that more than 64 CPUs are needed to trigger the allocation.
859 
860           Also this option is ignored when "log_buf_len" kernel parameter is
861           used as it forces an exact (power of two) size of the ring buffer.
862 
863           The number of possible CPUs is used for this computation ignoring
864           hotplugging making the compuation optimal for the the worst case
865           scenerio while allowing a simple algorithm to be used from bootup.
866 
867           Examples shift values and their meaning:
868                      17 => 128 KB for each CPU
869                      16 =>  64 KB for each CPU
870                      15 =>  32 KB for each CPU
871                      14 =>  16 KB for each CPU
872                      13 =>   8 KB for each CPU
873                      12 =>   4 KB for each CPU
874 
875 #
876 # Architectures with an unreliable sched_clock() should select this:
877 #
878 config HAVE_UNSTABLE_SCHED_CLOCK
879         bool
880 
881 config GENERIC_SCHED_CLOCK
882         bool
883 
884 #
885 # For architectures that want to enable the support for NUMA-affine scheduler
886 # balancing logic:
887 #
888 config ARCH_SUPPORTS_NUMA_BALANCING
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_DEFAULT_ENABLED
904         bool "Automatically enable NUMA aware memory/task placement"
905         default y
906         depends on NUMA_BALANCING
907         help
908           If set, automatic NUMA balancing will be enabled if running on a NUMA
909           machine.
910 
911 config NUMA_BALANCING
912         bool "Memory placement aware NUMA scheduler"
913         depends on ARCH_SUPPORTS_NUMA_BALANCING
914         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
915         depends on SMP && NUMA && MIGRATION
916         help
917           This option adds support for automatic NUMA aware memory/task placement.
918           The mechanism is quite primitive and is based on migrating memory when
919           it has references to the node the task is running on.
920 
921           This system will be inactive on UMA systems.
922 
923 menuconfig CGROUPS
924         boolean "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 CGROUP_DEBUG
940         bool "Example debug cgroup subsystem"
941         default n
942         help
943           This option enables a simple cgroup subsystem that
944           exports useful debugging information about the cgroups
945           framework.
946 
947           Say N if unsure.
948 
949 config CGROUP_FREEZER
950         bool "Freezer cgroup subsystem"
951         help
952           Provides a way to freeze and unfreeze all tasks in a
953           cgroup.
954 
955 config CGROUP_DEVICE
956         bool "Device controller for cgroups"
957         help
958           Provides a cgroup implementing whitelists for devices which
959           a process in the cgroup can mknod or open.
960 
961 config CPUSETS
962         bool "Cpuset support"
963         help
964           This option will let you create and manage CPUSETs which
965           allow dynamically partitioning a system into sets of CPUs and
966           Memory Nodes and assigning tasks to run only within those sets.
967           This is primarily useful on large SMP or NUMA systems.
968 
969           Say N if unsure.
970 
971 config PROC_PID_CPUSET
972         bool "Include legacy /proc/<pid>/cpuset file"
973         depends on CPUSETS
974         default y
975 
976 config CGROUP_CPUACCT
977         bool "Simple CPU accounting cgroup subsystem"
978         help
979           Provides a simple Resource Controller for monitoring the
980           total CPU consumed by the tasks in a cgroup.
981 
982 config RESOURCE_COUNTERS
983         bool "Resource counters"
984         help
985           This option enables controller independent resource accounting
986           infrastructure that works with cgroups.
987 
988 config MEMCG
989         bool "Memory Resource Controller for Control Groups"
990         depends on RESOURCE_COUNTERS
991         select EVENTFD
992         help
993           Provides a memory resource controller that manages both anonymous
994           memory and page cache. (See Documentation/cgroups/memory.txt)
995 
996           Note that setting this option increases fixed memory overhead
997           associated with each page of memory in the system. By this,
998           8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
999           usage tracking struct at boot. Total amount of this is printed out
1000           at boot.
1001 
1002           Only enable when you're ok with these trade offs and really
1003           sure you need the memory resource controller. Even when you enable
1004           this, you can set "cgroup_disable=memory" at your boot option to
1005           disable memory resource controller and you can avoid overheads.
1006           (and lose benefits of memory resource controller)
1007 
1008 config MEMCG_SWAP
1009         bool "Memory Resource Controller Swap Extension"
1010         depends on MEMCG && SWAP
1011         help
1012           Add swap management feature to memory resource controller. When you
1013           enable this, you can limit mem+swap usage per cgroup. In other words,
1014           when you disable this, memory resource controller has no cares to
1015           usage of swap...a process can exhaust all of the swap. This extension
1016           is useful when you want to avoid exhaustion swap but this itself
1017           adds more overheads and consumes memory for remembering information.
1018           Especially if you use 32bit system or small memory system, please
1019           be careful about enabling this. When memory resource controller
1020           is disabled by boot option, this will be automatically disabled and
1021           there will be no overhead from this. Even when you set this config=y,
1022           if boot option "swapaccount=0" is set, swap will not be accounted.
1023           Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
1024           size is 4096bytes, 512k per 1Gbytes of swap.
1025 config MEMCG_SWAP_ENABLED
1026         bool "Memory Resource Controller Swap Extension enabled by default"
1027         depends on MEMCG_SWAP
1028         default y
1029         help
1030           Memory Resource Controller Swap Extension comes with its price in
1031           a bigger memory consumption. General purpose distribution kernels
1032           which want to enable the feature but keep it disabled by default
1033           and let the user enable it by swapaccount=1 boot command line
1034           parameter should have this option unselected.
1035           For those who want to have the feature enabled by default should
1036           select this option (if, for some reason, they need to disable it
1037           then swapaccount=0 does the trick).
1038 config MEMCG_KMEM
1039         bool "Memory Resource Controller Kernel Memory accounting"
1040         depends on MEMCG
1041         depends on SLUB || SLAB
1042         help
1043           The Kernel Memory extension for Memory Resource Controller can limit
1044           the amount of memory used by kernel objects in the system. Those are
1045           fundamentally different from the entities handled by the standard
1046           Memory Controller, which are page-based, and can be swapped. Users of
1047           the kmem extension can use it to guarantee that no group of processes
1048           will ever exhaust kernel resources alone.
1049 
1050           WARNING: Current implementation lacks reclaim support. That means
1051           allocation attempts will fail when close to the limit even if there
1052           are plenty of kmem available for reclaim. That makes this option
1053           unusable in real life so DO NOT SELECT IT unless for development
1054           purposes.
1055 
1056 config CGROUP_HUGETLB
1057         bool "HugeTLB Resource Controller for Control Groups"
1058         depends on RESOURCE_COUNTERS && HUGETLB_PAGE
1059         default n
1060         help
1061           Provides a cgroup Resource Controller for HugeTLB pages.
1062           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1063           The limit is enforced during page fault. Since HugeTLB doesn't
1064           support page reclaim, enforcing the limit at page fault time implies
1065           that, the application will get SIGBUS signal if it tries to access
1066           HugeTLB pages beyond its limit. This requires the application to know
1067           beforehand how much HugeTLB pages it would require for its use. The
1068           control group is tracked in the third page lru pointer. This means
1069           that we cannot use the controller with huge page less than 3 pages.
1070 
1071 config CGROUP_PERF
1072         bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1073         depends on PERF_EVENTS && CGROUPS
1074         help
1075           This option extends the per-cpu mode to restrict monitoring to
1076           threads which belong to the cgroup specified and run on the
1077           designated cpu.
1078 
1079           Say N if unsure.
1080 
1081 menuconfig CGROUP_SCHED
1082         bool "Group CPU scheduler"
1083         default n
1084         help
1085           This feature lets CPU scheduler recognize task groups and control CPU
1086           bandwidth allocation to such task groups. It uses cgroups to group
1087           tasks.
1088 
1089 if CGROUP_SCHED
1090 config FAIR_GROUP_SCHED
1091         bool "Group scheduling for SCHED_OTHER"
1092         depends on CGROUP_SCHED
1093         default CGROUP_SCHED
1094 
1095 config CFS_BANDWIDTH
1096         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1097         depends on FAIR_GROUP_SCHED
1098         default n
1099         help
1100           This option allows users to define CPU bandwidth rates (limits) for
1101           tasks running within the fair group scheduler.  Groups with no limit
1102           set are considered to be unconstrained and will run with no
1103           restriction.
1104           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1105 
1106 config RT_GROUP_SCHED
1107         bool "Group scheduling for SCHED_RR/FIFO"
1108         depends on CGROUP_SCHED
1109         default n
1110         help
1111           This feature lets you explicitly allocate real CPU bandwidth
1112           to task groups. If enabled, it will also make it impossible to
1113           schedule realtime tasks for non-root users until you allocate
1114           realtime bandwidth for them.
1115           See Documentation/scheduler/sched-rt-group.txt for more information.
1116 
1117 endif #CGROUP_SCHED
1118 
1119 config BLK_CGROUP
1120         bool "Block IO controller"
1121         depends on BLOCK
1122         default n
1123         ---help---
1124         Generic block IO controller cgroup interface. This is the common
1125         cgroup interface which should be used by various IO controlling
1126         policies.
1127 
1128         Currently, CFQ IO scheduler uses it to recognize task groups and
1129         control disk bandwidth allocation (proportional time slice allocation)
1130         to such task groups. It is also used by bio throttling logic in
1131         block layer to implement upper limit in IO rates on a device.
1132 
1133         This option only enables generic Block IO controller infrastructure.
1134         One needs to also enable actual IO controlling logic/policy. For
1135         enabling proportional weight division of disk bandwidth in CFQ, set
1136         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1137         CONFIG_BLK_DEV_THROTTLING=y.
1138 
1139         See Documentation/cgroups/blkio-controller.txt for more information.
1140 
1141 config DEBUG_BLK_CGROUP
1142         bool "Enable Block IO controller debugging"
1143         depends on BLK_CGROUP
1144         default n
1145         ---help---
1146         Enable some debugging help. Currently it exports additional stat
1147         files in a cgroup which can be useful for debugging.
1148 
1149 endif # CGROUPS
1150 
1151 config CHECKPOINT_RESTORE
1152         bool "Checkpoint/restore support" if EXPERT
1153         default n
1154         help
1155           Enables additional kernel features in a sake of checkpoint/restore.
1156           In particular it adds auxiliary prctl codes to setup process text,
1157           data and heap segment sizes, and a few additional /proc filesystem
1158           entries.
1159 
1160           If unsure, say N here.
1161 
1162 menuconfig NAMESPACES
1163         bool "Namespaces support" if EXPERT
1164         default !EXPERT
1165         help
1166           Provides the way to make tasks work with different objects using
1167           the same id. For example same IPC id may refer to different objects
1168           or same user id or pid may refer to different tasks when used in
1169           different namespaces.
1170 
1171 if NAMESPACES
1172 
1173 config UTS_NS
1174         bool "UTS namespace"
1175         default y
1176         help
1177           In this namespace tasks see different info provided with the
1178           uname() system call
1179 
1180 config IPC_NS
1181         bool "IPC namespace"
1182         depends on (SYSVIPC || POSIX_MQUEUE)
1183         default y
1184         help
1185           In this namespace tasks work with IPC ids which correspond to
1186           different IPC objects in different namespaces.
1187 
1188 config USER_NS
1189         bool "User namespace"
1190         default n
1191         help
1192           This allows containers, i.e. vservers, to use user namespaces
1193           to provide different user info for different servers.
1194 
1195           When user namespaces are enabled in the kernel it is
1196           recommended that the MEMCG and MEMCG_KMEM options also be
1197           enabled and that user-space use the memory control groups to
1198           limit the amount of memory a memory unprivileged users can
1199           use.
1200 
1201           If unsure, say N.
1202 
1203 config PID_NS
1204         bool "PID Namespaces"
1205         default y
1206         help
1207           Support process id namespaces.  This allows having multiple
1208           processes with the same pid as long as they are in different
1209           pid namespaces.  This is a building block of containers.
1210 
1211 config NET_NS
1212         bool "Network namespace"
1213         depends on NET
1214         default y
1215         help
1216           Allow user space to create what appear to be multiple instances
1217           of the network stack.
1218 
1219 endif # NAMESPACES
1220 
1221 config SCHED_AUTOGROUP
1222         bool "Automatic process group scheduling"
1223         select CGROUPS
1224         select CGROUP_SCHED
1225         select FAIR_GROUP_SCHED
1226         help
1227           This option optimizes the scheduler for common desktop workloads by
1228           automatically creating and populating task groups.  This separation
1229           of workloads isolates aggressive CPU burners (like build jobs) from
1230           desktop applications.  Task group autogeneration is currently based
1231           upon task session.
1232 
1233 config SYSFS_DEPRECATED
1234         bool "Enable deprecated sysfs features to support old userspace tools"
1235         depends on SYSFS
1236         default n
1237         help
1238           This option adds code that switches the layout of the "block" class
1239           devices, to not show up in /sys/class/block/, but only in
1240           /sys/block/.
1241 
1242           This switch is only active when the sysfs.deprecated=1 boot option is
1243           passed or the SYSFS_DEPRECATED_V2 option is set.
1244 
1245           This option allows new kernels to run on old distributions and tools,
1246           which might get confused by /sys/class/block/. Since 2007/2008 all
1247           major distributions and tools handle this just fine.
1248 
1249           Recent distributions and userspace tools after 2009/2010 depend on
1250           the existence of /sys/class/block/, and will not work with this
1251           option enabled.
1252 
1253           Only if you are using a new kernel on an old distribution, you might
1254           need to say Y here.
1255 
1256 config SYSFS_DEPRECATED_V2
1257         bool "Enable deprecated sysfs features by default"
1258         default n
1259         depends on SYSFS
1260         depends on SYSFS_DEPRECATED
1261         help
1262           Enable deprecated sysfs by default.
1263 
1264           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1265           option.
1266 
1267           Only if you are using a new kernel on an old distribution, you might
1268           need to say Y here. Even then, odds are you would not need it
1269           enabled, you can always pass the boot option if absolutely necessary.
1270 
1271 config RELAY
1272         bool "Kernel->user space relay support (formerly relayfs)"
1273         help
1274           This option enables support for relay interface support in
1275           certain file systems (such as debugfs).
1276           It is designed to provide an efficient mechanism for tools and
1277           facilities to relay large amounts of data from kernel space to
1278           user space.
1279 
1280           If unsure, say N.
1281 
1282 config BLK_DEV_INITRD
1283         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1284         depends on BROKEN || !FRV
1285         help
1286           The initial RAM filesystem is a ramfs which is loaded by the
1287           boot loader (loadlin or lilo) and that is mounted as root
1288           before the normal boot procedure. It is typically used to
1289           load modules needed to mount the "real" root file system,
1290           etc. See <file:Documentation/initrd.txt> for details.
1291 
1292           If RAM disk support (BLK_DEV_RAM) is also included, this
1293           also enables initial RAM disk (initrd) support and adds
1294           15 Kbytes (more on some other architectures) to the kernel size.
1295 
1296           If unsure say Y.
1297 
1298 if BLK_DEV_INITRD
1299 
1300 source "usr/Kconfig"
1301 
1302 endif
1303 
1304 config CC_OPTIMIZE_FOR_SIZE
1305         bool "Optimize for size"
1306         help
1307           Enabling this option will pass "-Os" instead of "-O2" to gcc
1308           resulting in a smaller kernel.
1309 
1310           If unsure, say N.
1311 
1312 config SYSCTL
1313         bool
1314 
1315 config ANON_INODES
1316         bool
1317 
1318 config HAVE_UID16
1319         bool
1320 
1321 config SYSCTL_EXCEPTION_TRACE
1322         bool
1323         help
1324           Enable support for /proc/sys/debug/exception-trace.
1325 
1326 config SYSCTL_ARCH_UNALIGN_NO_WARN
1327         bool
1328         help
1329           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1330           Allows arch to define/use @no_unaligned_warning to possibly warn
1331           about unaligned access emulation going on under the hood.
1332 
1333 config SYSCTL_ARCH_UNALIGN_ALLOW
1334         bool
1335         help
1336           Enable support for /proc/sys/kernel/unaligned-trap
1337           Allows arches to define/use @unaligned_enabled to runtime toggle
1338           the unaligned access emulation.
1339           see arch/parisc/kernel/unaligned.c for reference
1340 
1341 config HAVE_PCSPKR_PLATFORM
1342         bool
1343 
1344 # interpreter that classic socket filters depend on
1345 config BPF
1346         bool
1347 
1348 menuconfig EXPERT
1349         bool "Configure standard kernel features (expert users)"
1350         # Unhide debug options, to make the on-by-default options visible
1351         select DEBUG_KERNEL
1352         help
1353           This option allows certain base kernel options and settings
1354           to be disabled or tweaked. This is for specialized
1355           environments which can tolerate a "non-standard" kernel.
1356           Only use this if you really know what you are doing.
1357 
1358 config UID16
1359         bool "Enable 16-bit UID system calls" if EXPERT
1360         depends on HAVE_UID16
1361         default y
1362         help
1363           This enables the legacy 16-bit UID syscall wrappers.
1364 
1365 config SGETMASK_SYSCALL
1366         bool "sgetmask/ssetmask syscalls support" if EXPERT
1367         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1368         ---help---
1369           sys_sgetmask and sys_ssetmask are obsolete system calls
1370           no longer supported in libc but still enabled by default in some
1371           architectures.
1372 
1373           If unsure, leave the default option here.
1374 
1375 config SYSFS_SYSCALL
1376         bool "Sysfs syscall support" if EXPERT
1377         default y
1378         ---help---
1379           sys_sysfs is an obsolete system call no longer supported in libc.
1380           Note that disabling this option is more secure but might break
1381           compatibility with some systems.
1382 
1383           If unsure say Y here.
1384 
1385 config SYSCTL_SYSCALL
1386         bool "Sysctl syscall support" if EXPERT
1387         depends on PROC_SYSCTL
1388         default n
1389         select SYSCTL
1390         ---help---
1391           sys_sysctl uses binary paths that have been found challenging
1392           to properly maintain and use.  The interface in /proc/sys
1393           using paths with ascii names is now the primary path to this
1394           information.
1395 
1396           Almost nothing using the binary sysctl interface so if you are
1397           trying to save some space it is probably safe to disable this,
1398           making your kernel marginally smaller.
1399 
1400           If unsure say N here.
1401 
1402 config KALLSYMS
1403          bool "Load all symbols for debugging/ksymoops" if EXPERT
1404          default y
1405          help
1406            Say Y here to let the kernel print out symbolic crash information and
1407            symbolic stack backtraces. This increases the size of the kernel
1408            somewhat, as all symbols have to be loaded into the kernel image.
1409 
1410 config KALLSYMS_ALL
1411         bool "Include all symbols in kallsyms"
1412         depends on DEBUG_KERNEL && KALLSYMS
1413         help
1414            Normally kallsyms only contains the symbols of functions for nicer
1415            OOPS messages and backtraces (i.e., symbols from the text and inittext
1416            sections). This is sufficient for most cases. And only in very rare
1417            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1418            names of variables from the data sections, etc).
1419 
1420            This option makes sure that all symbols are loaded into the kernel
1421            image (i.e., symbols from all sections) in cost of increased kernel
1422            size (depending on the kernel configuration, it may be 300KiB or
1423            something like this).
1424 
1425            Say N unless you really need all symbols.
1426 
1427 config PRINTK
1428         default y
1429         bool "Enable support for printk" if EXPERT
1430         select IRQ_WORK
1431         help
1432           This option enables normal printk support. Removing it
1433           eliminates most of the message strings from the kernel image
1434           and makes the kernel more or less silent. As this makes it
1435           very difficult to diagnose system problems, saying N here is
1436           strongly discouraged.
1437 
1438 config BUG
1439         bool "BUG() support" if EXPERT
1440         default y
1441         help
1442           Disabling this option eliminates support for BUG and WARN, reducing
1443           the size of your kernel image and potentially quietly ignoring
1444           numerous fatal conditions. You should only consider disabling this
1445           option for embedded systems with no facilities for reporting errors.
1446           Just say Y.
1447 
1448 config ELF_CORE
1449         depends on COREDUMP
1450         default y
1451         bool "Enable ELF core dumps" if EXPERT
1452         help
1453           Enable support for generating core dumps. Disabling saves about 4k.
1454 
1455 
1456 config PCSPKR_PLATFORM
1457         bool "Enable PC-Speaker support" if EXPERT
1458         depends on HAVE_PCSPKR_PLATFORM
1459         select I8253_LOCK
1460         default y
1461         help
1462           This option allows to disable the internal PC-Speaker
1463           support, saving some memory.
1464 
1465 config BASE_FULL
1466         default y
1467         bool "Enable full-sized data structures for core" if EXPERT
1468         help
1469           Disabling this option reduces the size of miscellaneous core
1470           kernel data structures. This saves memory on small machines,
1471           but may reduce performance.
1472 
1473 config FUTEX
1474         bool "Enable futex support" if EXPERT
1475         default y
1476         select RT_MUTEXES
1477         help
1478           Disabling this option will cause the kernel to be built without
1479           support for "fast userspace mutexes".  The resulting kernel may not
1480           run glibc-based applications correctly.
1481 
1482 config HAVE_FUTEX_CMPXCHG
1483         bool
1484         depends on FUTEX
1485         help
1486           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1487           is implemented and always working. This removes a couple of runtime
1488           checks.
1489 
1490 config EPOLL
1491         bool "Enable eventpoll support" if EXPERT
1492         default y
1493         select ANON_INODES
1494         help
1495           Disabling this option will cause the kernel to be built without
1496           support for epoll family of system calls.
1497 
1498 config SIGNALFD
1499         bool "Enable signalfd() system call" if EXPERT
1500         select ANON_INODES
1501         default y
1502         help
1503           Enable the signalfd() system call that allows to receive signals
1504           on a file descriptor.
1505 
1506           If unsure, say Y.
1507 
1508 config TIMERFD
1509         bool "Enable timerfd() system call" if EXPERT
1510         select ANON_INODES
1511         default y
1512         help
1513           Enable the timerfd() system call that allows to receive timer
1514           events on a file descriptor.
1515 
1516           If unsure, say Y.
1517 
1518 config EVENTFD
1519         bool "Enable eventfd() system call" if EXPERT
1520         select ANON_INODES
1521         default y
1522         help
1523           Enable the eventfd() system call that allows to receive both
1524           kernel notification (ie. KAIO) or userspace notifications.
1525 
1526           If unsure, say Y.
1527 
1528 # syscall, maps, verifier
1529 config BPF_SYSCALL
1530         bool "Enable bpf() system call" if EXPERT
1531         select ANON_INODES
1532         select BPF
1533         default n
1534         help
1535           Enable the bpf() system call that allows to manipulate eBPF
1536           programs and maps via file descriptors.
1537 
1538 config SHMEM
1539         bool "Use full shmem filesystem" if EXPERT
1540         default y
1541         depends on MMU
1542         help
1543           The shmem is an internal filesystem used to manage shared memory.
1544           It is backed by swap and manages resource limits. It is also exported
1545           to userspace as tmpfs if TMPFS is enabled. Disabling this
1546           option replaces shmem and tmpfs with the much simpler ramfs code,
1547           which may be appropriate on small systems without swap.
1548 
1549 config AIO
1550         bool "Enable AIO support" if EXPERT
1551         default y
1552         help
1553           This option enables POSIX asynchronous I/O which may by used
1554           by some high performance threaded applications. Disabling
1555           this option saves about 7k.
1556 
1557 config ADVISE_SYSCALLS
1558         bool "Enable madvise/fadvise syscalls" if EXPERT
1559         default y
1560         help
1561           This option enables the madvise and fadvise syscalls, used by
1562           applications to advise the kernel about their future memory or file
1563           usage, improving performance. If building an embedded system where no
1564           applications use these syscalls, you can disable this option to save
1565           space.
1566 
1567 config PCI_QUIRKS
1568         default y
1569         bool "Enable PCI quirk workarounds" if EXPERT
1570         depends on PCI
1571         help
1572           This enables workarounds for various PCI chipset
1573           bugs/quirks. Disable this only if your target machine is
1574           unaffected by PCI quirks.
1575 
1576 config EMBEDDED
1577         bool "Embedded system"
1578         option allnoconfig_y
1579         select EXPERT
1580         help
1581           This option should be enabled if compiling the kernel for
1582           an embedded system so certain expert options are available
1583           for configuration.
1584 
1585 config HAVE_PERF_EVENTS
1586         bool
1587         help
1588           See tools/perf/design.txt for details.
1589 
1590 config PERF_USE_VMALLOC
1591         bool
1592         help
1593           See tools/perf/design.txt for details
1594 
1595 menu "Kernel Performance Events And Counters"
1596 
1597 config PERF_EVENTS
1598         bool "Kernel performance events and counters"
1599         default y if PROFILING
1600         depends on HAVE_PERF_EVENTS
1601         select ANON_INODES
1602         select IRQ_WORK
1603         help
1604           Enable kernel support for various performance events provided
1605           by software and hardware.
1606 
1607           Software events are supported either built-in or via the
1608           use of generic tracepoints.
1609 
1610           Most modern CPUs support performance events via performance
1611           counter registers. These registers count the number of certain
1612           types of hw events: such as instructions executed, cachemisses
1613           suffered, or branches mis-predicted - without slowing down the
1614           kernel or applications. These registers can also trigger interrupts
1615           when a threshold number of events have passed - and can thus be
1616           used to profile the code that runs on that CPU.
1617 
1618           The Linux Performance Event subsystem provides an abstraction of
1619           these software and hardware event capabilities, available via a
1620           system call and used by the "perf" utility in tools/perf/. It
1621           provides per task and per CPU counters, and it provides event
1622           capabilities on top of those.
1623 
1624           Say Y if unsure.
1625 
1626 config DEBUG_PERF_USE_VMALLOC
1627         default n
1628         bool "Debug: use vmalloc to back perf mmap() buffers"
1629         depends on PERF_EVENTS && DEBUG_KERNEL
1630         select PERF_USE_VMALLOC
1631         help
1632          Use vmalloc memory to back perf mmap() buffers.
1633 
1634          Mostly useful for debugging the vmalloc code on platforms
1635          that don't require it.
1636 
1637          Say N if unsure.
1638 
1639 endmenu
1640 
1641 config VM_EVENT_COUNTERS
1642         default y
1643         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1644         help
1645           VM event counters are needed for event counts to be shown.
1646           This option allows the disabling of the VM event counters
1647           on EXPERT systems.  /proc/vmstat will only show page counts
1648           if VM event counters are disabled.
1649 
1650 config SLUB_DEBUG
1651         default y
1652         bool "Enable SLUB debugging support" if EXPERT
1653         depends on SLUB && SYSFS
1654         help
1655           SLUB has extensive debug support features. Disabling these can
1656           result in significant savings in code size. This also disables
1657           SLUB sysfs support. /sys/slab will not exist and there will be
1658           no support for cache validation etc.
1659 
1660 config COMPAT_BRK
1661         bool "Disable heap randomization"
1662         default y
1663         help
1664           Randomizing heap placement makes heap exploits harder, but it
1665           also breaks ancient binaries (including anything libc5 based).
1666           This option changes the bootup default to heap randomization
1667           disabled, and can be overridden at runtime by setting
1668           /proc/sys/kernel/randomize_va_space to 2.
1669 
1670           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1671 
1672 choice
1673         prompt "Choose SLAB allocator"
1674         default SLUB
1675         help
1676            This option allows to select a slab allocator.
1677 
1678 config SLAB
1679         bool "SLAB"
1680         help
1681           The regular slab allocator that is established and known to work
1682           well in all environments. It organizes cache hot objects in
1683           per cpu and per node queues.
1684 
1685 config SLUB
1686         bool "SLUB (Unqueued Allocator)"
1687         help
1688            SLUB is a slab allocator that minimizes cache line usage
1689            instead of managing queues of cached objects (SLAB approach).
1690            Per cpu caching is realized using slabs of objects instead
1691            of queues of objects. SLUB can use memory efficiently
1692            and has enhanced diagnostics. SLUB is the default choice for
1693            a slab allocator.
1694 
1695 config SLOB
1696         depends on EXPERT
1697         bool "SLOB (Simple Allocator)"
1698         help
1699            SLOB replaces the stock allocator with a drastically simpler
1700            allocator. SLOB is generally more space efficient but
1701            does not perform as well on large systems.
1702 
1703 endchoice
1704 
1705 config SLUB_CPU_PARTIAL
1706         default y
1707         depends on SLUB && SMP
1708         bool "SLUB per cpu partial cache"
1709         help
1710           Per cpu partial caches accellerate objects allocation and freeing
1711           that is local to a processor at the price of more indeterminism
1712           in the latency of the free. On overflow these caches will be cleared
1713           which requires the taking of locks that may cause latency spikes.
1714           Typically one would choose no for a realtime system.
1715 
1716 config MMAP_ALLOW_UNINITIALIZED
1717         bool "Allow mmapped anonymous memory to be uninitialized"
1718         depends on EXPERT && !MMU
1719         default n
1720         help
1721           Normally, and according to the Linux spec, anonymous memory obtained
1722           from mmap() has it's contents cleared before it is passed to
1723           userspace.  Enabling this config option allows you to request that
1724           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1725           providing a huge performance boost.  If this option is not enabled,
1726           then the flag will be ignored.
1727 
1728           This is taken advantage of by uClibc's malloc(), and also by
1729           ELF-FDPIC binfmt's brk and stack allocator.
1730 
1731           Because of the obvious security issues, this option should only be
1732           enabled on embedded devices where you control what is run in
1733           userspace.  Since that isn't generally a problem on no-MMU systems,
1734           it is normally safe to say Y here.
1735 
1736           See Documentation/nommu-mmap.txt for more information.
1737 
1738 config SYSTEM_TRUSTED_KEYRING
1739         bool "Provide system-wide ring of trusted keys"
1740         depends on KEYS
1741         help
1742           Provide a system keyring to which trusted keys can be added.  Keys in
1743           the keyring are considered to be trusted.  Keys may be added at will
1744           by the kernel from compiled-in data and from hardware key stores, but
1745           userspace may only add extra keys if those keys can be verified by
1746           keys already in the keyring.
1747 
1748           Keys in this keyring are used by module signature checking.
1749 
1750 config PROFILING
1751         bool "Profiling support"
1752         help
1753           Say Y here to enable the extended profiling support mechanisms used
1754           by profilers such as OProfile.
1755 
1756 #
1757 # Place an empty function call at each tracepoint site. Can be
1758 # dynamically changed for a probe function.
1759 #
1760 config TRACEPOINTS
1761         bool
1762 
1763 source "arch/Kconfig"
1764 
1765 endmenu         # General setup
1766 
1767 config HAVE_GENERIC_DMA_COHERENT
1768         bool
1769         default n
1770 
1771 config SLABINFO
1772         bool
1773         depends on PROC_FS
1774         depends on SLAB || SLUB_DEBUG
1775         default y
1776 
1777 config RT_MUTEXES
1778         boolean
1779 
1780 config BASE_SMALL
1781         int
1782         default 0 if BASE_FULL
1783         default 1 if !BASE_FULL
1784 
1785 menuconfig MODULES
1786         bool "Enable loadable module support"
1787         option modules
1788         help
1789           Kernel modules are small pieces of compiled code which can
1790           be inserted in the running kernel, rather than being
1791           permanently built into the kernel.  You use the "modprobe"
1792           tool to add (and sometimes remove) them.  If you say Y here,
1793           many parts of the kernel can be built as modules (by
1794           answering M instead of Y where indicated): this is most
1795           useful for infrequently used options which are not required
1796           for booting.  For more information, see the man pages for
1797           modprobe, lsmod, modinfo, insmod and rmmod.
1798 
1799           If you say Y here, you will need to run "make
1800           modules_install" to put the modules under /lib/modules/
1801           where modprobe can find them (you may need to be root to do
1802           this).
1803 
1804           If unsure, say Y.
1805 
1806 if MODULES
1807 
1808 config MODULE_FORCE_LOAD
1809         bool "Forced module loading"
1810         default n
1811         help
1812           Allow loading of modules without version information (ie. modprobe
1813           --force).  Forced module loading sets the 'F' (forced) taint flag and
1814           is usually a really bad idea.
1815 
1816 config MODULE_UNLOAD
1817         bool "Module unloading"
1818         help
1819           Without this option you will not be able to unload any
1820           modules (note that some modules may not be unloadable
1821           anyway), which makes your kernel smaller, faster
1822           and simpler.  If unsure, say Y.
1823 
1824 config MODULE_FORCE_UNLOAD
1825         bool "Forced module unloading"
1826         depends on MODULE_UNLOAD
1827         help
1828           This option allows you to force a module to unload, even if the
1829           kernel believes it is unsafe: the kernel will remove the module
1830           without waiting for anyone to stop using it (using the -f option to
1831           rmmod).  This is mainly for kernel developers and desperate users.
1832           If unsure, say N.
1833 
1834 config MODVERSIONS
1835         bool "Module versioning support"
1836         help
1837           Usually, you have to use modules compiled with your kernel.
1838           Saying Y here makes it sometimes possible to use modules
1839           compiled for different kernels, by adding enough information
1840           to the modules to (hopefully) spot any changes which would
1841           make them incompatible with the kernel you are running.  If
1842           unsure, say N.
1843 
1844 config MODULE_SRCVERSION_ALL
1845         bool "Source checksum for all modules"
1846         help
1847           Modules which contain a MODULE_VERSION get an extra "srcversion"
1848           field inserted into their modinfo section, which contains a
1849           sum of the source files which made it.  This helps maintainers
1850           see exactly which source was used to build a module (since
1851           others sometimes change the module source without updating
1852           the version).  With this option, such a "srcversion" field
1853           will be created for all modules.  If unsure, say N.
1854 
1855 config MODULE_SIG
1856         bool "Module signature verification"
1857         depends on MODULES
1858         select SYSTEM_TRUSTED_KEYRING
1859         select KEYS
1860         select CRYPTO
1861         select ASYMMETRIC_KEY_TYPE
1862         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1863         select PUBLIC_KEY_ALGO_RSA
1864         select ASN1
1865         select OID_REGISTRY
1866         select X509_CERTIFICATE_PARSER
1867         help
1868           Check modules for valid signatures upon load: the signature
1869           is simply appended to the module. For more information see
1870           Documentation/module-signing.txt.
1871 
1872           !!!WARNING!!!  If you enable this option, you MUST make sure that the
1873           module DOES NOT get stripped after being signed.  This includes the
1874           debuginfo strip done by some packagers (such as rpmbuild) and
1875           inclusion into an initramfs that wants the module size reduced.
1876 
1877 config MODULE_SIG_FORCE
1878         bool "Require modules to be validly signed"
1879         depends on MODULE_SIG
1880         help
1881           Reject unsigned modules or signed modules for which we don't have a
1882           key.  Without this, such modules will simply taint the kernel.
1883 
1884 config MODULE_SIG_ALL
1885         bool "Automatically sign all modules"
1886         default y
1887         depends on MODULE_SIG
1888         help
1889           Sign all modules during make modules_install. Without this option,
1890           modules must be signed manually, using the scripts/sign-file tool.
1891 
1892 comment "Do not forget to sign required modules with scripts/sign-file"
1893         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1894 
1895 choice
1896         prompt "Which hash algorithm should modules be signed with?"
1897         depends on MODULE_SIG
1898         help
1899           This determines which sort of hashing algorithm will be used during
1900           signature generation.  This algorithm _must_ be built into the kernel
1901           directly so that signature verification can take place.  It is not
1902           possible to load a signed module containing the algorithm to check
1903           the signature on that module.
1904 
1905 config MODULE_SIG_SHA1
1906         bool "Sign modules with SHA-1"
1907         select CRYPTO_SHA1
1908 
1909 config MODULE_SIG_SHA224
1910         bool "Sign modules with SHA-224"
1911         select CRYPTO_SHA256
1912 
1913 config MODULE_SIG_SHA256
1914         bool "Sign modules with SHA-256"
1915         select CRYPTO_SHA256
1916 
1917 config MODULE_SIG_SHA384
1918         bool "Sign modules with SHA-384"
1919         select CRYPTO_SHA512
1920 
1921 config MODULE_SIG_SHA512
1922         bool "Sign modules with SHA-512"
1923         select CRYPTO_SHA512
1924 
1925 endchoice
1926 
1927 config MODULE_SIG_HASH
1928         string
1929         depends on MODULE_SIG
1930         default "sha1" if MODULE_SIG_SHA1
1931         default "sha224" if MODULE_SIG_SHA224
1932         default "sha256" if MODULE_SIG_SHA256
1933         default "sha384" if MODULE_SIG_SHA384
1934         default "sha512" if MODULE_SIG_SHA512
1935 
1936 config MODULE_COMPRESS
1937         bool "Compress modules on installation"
1938         depends on MODULES
1939         help
1940           This option compresses the kernel modules when 'make
1941           modules_install' is run.
1942 
1943           The modules will be compressed either using gzip or xz depend on the
1944           choice made in "Compression algorithm".
1945 
1946           module-init-tools has support for gzip format while kmod handle gzip
1947           and xz compressed modules.
1948 
1949           When a kernel module is installed from outside of the main kernel
1950           source and uses the Kbuild system for installing modules then that
1951           kernel module will also be compressed when it is installed.
1952 
1953           This option provides little benefit when the modules are to be used inside
1954           an initrd or initramfs, it generally is more efficient to compress the whole
1955           initrd or initramfs instead.
1956 
1957           This is fully compatible with signed modules while the signed module is
1958           compressed. module-init-tools or kmod handles decompression and provide to
1959           other layer the uncompressed but signed payload.
1960 
1961 choice
1962         prompt "Compression algorithm"
1963         depends on MODULE_COMPRESS
1964         default MODULE_COMPRESS_GZIP
1965         help
1966           This determines which sort of compression will be used during
1967           'make modules_install'.
1968 
1969           GZIP (default) and XZ are supported.
1970 
1971 config MODULE_COMPRESS_GZIP
1972         bool "GZIP"
1973 
1974 config MODULE_COMPRESS_XZ
1975         bool "XZ"
1976 
1977 endchoice
1978 
1979 endif # MODULES
1980 
1981 config INIT_ALL_POSSIBLE
1982         bool
1983         help
1984           Back when each arch used to define their own cpu_online_mask and
1985           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1986           with all 1s, and others with all 0s.  When they were centralised,
1987           it was better to provide this option than to break all the archs
1988           and have several arch maintainers pursuing me down dark alleys.
1989 
1990 config STOP_MACHINE
1991         bool
1992         default y
1993         depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1994         help
1995           Need stop_machine() primitive.
1996 
1997 source "block/Kconfig"
1998 
1999 config PREEMPT_NOTIFIERS
2000         bool
2001 
2002 config PADATA
2003         depends on SMP
2004         bool
2005 
2006 # Can be selected by architectures with broken toolchains
2007 # that get confused by correct const<->read_only section
2008 # mappings
2009 config BROKEN_RODATA
2010         bool
2011 
2012 config ASN1
2013         tristate
2014         help
2015           Build a simple ASN.1 grammar compiler that produces a bytecode output
2016           that can be interpreted by the ASN.1 stream decoder and used to
2017           inform it as to what tags are to be expected in a stream and what
2018           functions to call on what tags.
2019 
2020 source "kernel/Kconfig.locks"

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