1config DEFCONFIG_LIST
2 string
3 depends on !UML
4 option defconfig_list
5 default "/lib/modules/$(shell,uname -r)/.config"
6 default "/etc/kernel-config"
7 default "/boot/config-$(shell,uname -r)"
8 default ARCH_DEFCONFIG
9 default "arch/$(ARCH)/defconfig"
10
11config CC_IS_GCC
12 def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc)
13
14config GCC_VERSION
15 int
16 default $(shell,$(srctree)/scripts/gcc-version.sh -p $(CC) | sed 's/^0*//') if CC_IS_GCC
17 default 0
18
19config CC_IS_CLANG
20 def_bool $(success,$(CC) --version | head -n 1 | grep -q clang)
21
22config CLANG_VERSION
23 int
24 default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
25
26config CONSTRUCTORS
27 bool
28 depends on !UML
29
30config IRQ_WORK
31 bool
32
33config BUILDTIME_EXTABLE_SORT
34 bool
35
36config THREAD_INFO_IN_TASK
37 bool
38 help
39 Select this to move thread_info off the stack into task_struct. To
40 make this work, an arch will need to remove all thread_info fields
41 except flags and fix any runtime bugs.
42
43 One subtle change that will be needed is to use try_get_task_stack()
44 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
45
46menu "General setup"
47
48config BROKEN
49 bool
50
51config BROKEN_ON_SMP
52 bool
53 depends on BROKEN || !SMP
54 default y
55
56config INIT_ENV_ARG_LIMIT
57 int
58 default 32 if !UML
59 default 128 if UML
60 help
61 Maximum of each of the number of arguments and environment
62 variables passed to init from the kernel command line.
63
64config COMPILE_TEST
65 bool "Compile also drivers which will not load"
66 depends on !UML
67 default n
68 help
69 Some drivers can be compiled on a different platform than they are
70 intended to be run on. Despite they cannot be loaded there (or even
71 when they load they cannot be used due to missing HW support),
72 developers still, opposing to distributors, might want to build such
73 drivers to compile-test them.
74
75 If you are a developer and want to build everything available, say Y
76 here. If you are a user/distributor, say N here to exclude useless
77 drivers to be distributed.
78
79config LOCALVERSION
80 string "Local version - append to kernel release"
81 help
82 Append an extra string to the end of your kernel version.
83 This will show up when you type uname, for example.
84 The string you set here will be appended after the contents of
85 any files with a filename matching localversion* in your
86 object and source tree, in that order. Your total string can
87 be a maximum of 64 characters.
88
89config LOCALVERSION_AUTO
90 bool "Automatically append version information to the version string"
91 default y
92 depends on !COMPILE_TEST
93 help
94 This will try to automatically determine if the current tree is a
95 release tree by looking for git tags that belong to the current
96 top of tree revision.
97
98 A string of the format -gxxxxxxxx will be added to the localversion
99 if a git-based tree is found. The string generated by this will be
100 appended after any matching localversion* files, and after the value
101 set in CONFIG_LOCALVERSION.
102
103 (The actual string used here is the first eight characters produced
104 by running the command:
105
106 $ git rev-parse --verify HEAD
107
108 which is done within the script "scripts/setlocalversion".)
109
110config BUILD_SALT
111 string "Build ID Salt"
112 default ""
113 help
114 The build ID is used to link binaries and their debug info. Setting
115 this option will use the value in the calculation of the build id.
116 This is mostly useful for distributions which want to ensure the
117 build is unique between builds. It's safe to leave the default.
118
119config HAVE_KERNEL_GZIP
120 bool
121
122config HAVE_KERNEL_BZIP2
123 bool
124
125config HAVE_KERNEL_LZMA
126 bool
127
128config HAVE_KERNEL_XZ
129 bool
130
131config HAVE_KERNEL_LZO
132 bool
133
134config HAVE_KERNEL_LZ4
135 bool
136
137config HAVE_KERNEL_UNCOMPRESSED
138 bool
139
140choice
141 prompt "Kernel compression mode"
142 default KERNEL_GZIP
143 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
144 help
145 The linux kernel is a kind of self-extracting executable.
146 Several compression algorithms are available, which differ
147 in efficiency, compression and decompression speed.
148 Compression speed is only relevant when building a kernel.
149 Decompression speed is relevant at each boot.
150
151 If you have any problems with bzip2 or lzma compressed
152 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
153 version of this functionality (bzip2 only), for 2.4, was
154 supplied by Christian Ludwig)
155
156 High compression options are mostly useful for users, who
157 are low on disk space (embedded systems), but for whom ram
158 size matters less.
159
160 If in doubt, select 'gzip'
161
162config KERNEL_GZIP
163 bool "Gzip"
164 depends on HAVE_KERNEL_GZIP
165 help
166 The old and tried gzip compression. It provides a good balance
167 between compression ratio and decompression speed.
168
169config KERNEL_BZIP2
170 bool "Bzip2"
171 depends on HAVE_KERNEL_BZIP2
172 help
173 Its compression ratio and speed is intermediate.
174 Decompression speed is slowest among the choices. The kernel
175 size is about 10% smaller with bzip2, in comparison to gzip.
176 Bzip2 uses a large amount of memory. For modern kernels you
177 will need at least 8MB RAM or more for booting.
178
179config KERNEL_LZMA
180 bool "LZMA"
181 depends on HAVE_KERNEL_LZMA
182 help
183 This compression algorithm's ratio is best. Decompression speed
184 is between gzip and bzip2. Compression is slowest.
185 The kernel size is about 33% smaller with LZMA in comparison to gzip.
186
187config KERNEL_XZ
188 bool "XZ"
189 depends on HAVE_KERNEL_XZ
190 help
191 XZ uses the LZMA2 algorithm and instruction set specific
192 BCJ filters which can improve compression ratio of executable
193 code. The size of the kernel is about 30% smaller with XZ in
194 comparison to gzip. On architectures for which there is a BCJ
195 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
196 will create a few percent smaller kernel than plain LZMA.
197
198 The speed is about the same as with LZMA: The decompression
199 speed of XZ is better than that of bzip2 but worse than gzip
200 and LZO. Compression is slow.
201
202config KERNEL_LZO
203 bool "LZO"
204 depends on HAVE_KERNEL_LZO
205 help
206 Its compression ratio is the poorest among the choices. The kernel
207 size is about 10% bigger than gzip; however its speed
208 (both compression and decompression) is the fastest.
209
210config KERNEL_LZ4
211 bool "LZ4"
212 depends on HAVE_KERNEL_LZ4
213 help
214 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
215 A preliminary version of LZ4 de/compression tool is available at
216 <https://code.google.com/p/lz4/>.
217
218 Its compression ratio is worse than LZO. The size of the kernel
219 is about 8% bigger than LZO. But the decompression speed is
220 faster than LZO.
221
222config KERNEL_UNCOMPRESSED
223 bool "None"
224 depends on HAVE_KERNEL_UNCOMPRESSED
225 help
226 Produce uncompressed kernel image. This option is usually not what
227 you want. It is useful for debugging the kernel in slow simulation
228 environments, where decompressing and moving the kernel is awfully
229 slow. This option allows early boot code to skip the decompressor
230 and jump right at uncompressed kernel image.
231
232endchoice
233
234config DEFAULT_HOSTNAME
235 string "Default hostname"
236 default "(none)"
237 help
238 This option determines the default system hostname before userspace
239 calls sethostname(2). The kernel traditionally uses "(none)" here,
240 but you may wish to use a different default here to make a minimal
241 system more usable with less configuration.
242
243
244
245
246
247config ARCH_NO_SWAP
248 bool
249
250config SWAP
251 bool "Support for paging of anonymous memory (swap)"
252 depends on MMU && BLOCK && !ARCH_NO_SWAP
253 default y
254 help
255 This option allows you to choose whether you want to have support
256 for so called swap devices or swap files in your kernel that are
257 used to provide more virtual memory than the actual RAM present
258 in your computer. If unsure say Y.
259
260config SYSVIPC
261 bool "System V IPC"
262 ---help---
263 Inter Process Communication is a suite of library functions and
264 system calls which let processes (running programs) synchronize and
265 exchange information. It is generally considered to be a good thing,
266 and some programs won't run unless you say Y here. In particular, if
267 you want to run the DOS emulator dosemu under Linux (read the
268 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html
269 you'll need to say Y here.
270
271 You can find documentation about IPC with "info ipc" and also in
272 section 6.4 of the Linux Programmer's Guide, available from
273 <http://www.tldp.org/guides.html>.
274
275config SYSVIPC_SYSCTL
276 bool
277 depends on SYSVIPC
278 depends on SYSCTL
279 default y
280
281config POSIX_MQUEUE
282 bool "POSIX Message Queues"
283 depends on NET
284 ---help---
285 POSIX variant of message queues is a part of IPC. In POSIX message
286 queues every message has a priority which decides about succession
287 of receiving it by a process. If you want to compile and run
288 programs written e.g. for Solaris with use of its POSIX message
289 queues (functions mq_*) say Y here.
290
291 POSIX message queues are visible as a filesystem called 'mqueue'
292 and can be mounted somewhere if you want to do filesystem
293 operations on message queues.
294
295 If unsure, say Y.
296
297config POSIX_MQUEUE_SYSCTL
298 bool
299 depends on POSIX_MQUEUE
300 depends on SYSCTL
301 default y
302
303config CROSS_MEMORY_ATTACH
304 bool "Enable process_vm_readv/writev syscalls"
305 depends on MMU
306 default y
307 help
308 Enabling this option adds the system calls process_vm_readv and
309 process_vm_writev which allow a process with the correct privileges
310 to directly read from or write to another process' address space.
311 See the man page for more details.
312
313config USELIB
314 bool "uselib syscall"
315 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
316 help
317 This option enables the uselib syscall, a system call used in the
318 dynamic linker from libc5 and earlier. glibc does not use this
319 system call. If you intend to run programs built on libc5 or
320 earlier, you may need to enable this syscall. Current systems
321 running glibc can safely disable this.
322
323config AUDIT
324 bool "Auditing support"
325 depends on NET
326 help
327 Enable auditing infrastructure that can be used with another
328 kernel subsystem, such as SELinux (which requires this for
329 logging of avc messages output). System call auditing is included
330 on architectures which support it.
331
332config HAVE_ARCH_AUDITSYSCALL
333 bool
334
335config AUDITSYSCALL
336 def_bool y
337 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
338
339config AUDIT_WATCH
340 def_bool y
341 depends on AUDITSYSCALL
342 select FSNOTIFY
343
344config AUDIT_TREE
345 def_bool y
346 depends on AUDITSYSCALL
347 select FSNOTIFY
348
349source "kernel/irq/Kconfig"
350source "kernel/time/Kconfig"
351source "kernel/Kconfig.preempt"
352
353menu "CPU/Task time and stats accounting"
354
355config VIRT_CPU_ACCOUNTING
356 bool
357
358choice
359 prompt "Cputime accounting"
360 default TICK_CPU_ACCOUNTING if !PPC64
361 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
362
363
364config TICK_CPU_ACCOUNTING
365 bool "Simple tick based cputime accounting"
366 depends on !S390 && !NO_HZ_FULL
367 help
368 This is the basic tick based cputime accounting that maintains
369 statistics about user, system and idle time spent on per jiffies
370 granularity.
371
372 If unsure, say Y.
373
374config VIRT_CPU_ACCOUNTING_NATIVE
375 bool "Deterministic task and CPU time accounting"
376 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
377 select VIRT_CPU_ACCOUNTING
378 help
379 Select this option to enable more accurate task and CPU time
380 accounting. This is done by reading a CPU counter on each
381 kernel entry and exit and on transitions within the kernel
382 between system, softirq and hardirq state, so there is a
383 small performance impact. In the case of s390 or IBM POWER > 5,
384 this also enables accounting of stolen time on logically-partitioned
385 systems.
386
387config VIRT_CPU_ACCOUNTING_GEN
388 bool "Full dynticks CPU time accounting"
389 depends on HAVE_CONTEXT_TRACKING
390 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
391 select VIRT_CPU_ACCOUNTING
392 select CONTEXT_TRACKING
393 help
394 Select this option to enable task and CPU time accounting on full
395 dynticks systems. This accounting is implemented by watching every
396 kernel-user boundaries using the context tracking subsystem.
397 The accounting is thus performed at the expense of some significant
398 overhead.
399
400 For now this is only useful if you are working on the full
401 dynticks subsystem development.
402
403 If unsure, say N.
404
405endchoice
406
407config IRQ_TIME_ACCOUNTING
408 bool "Fine granularity task level IRQ time accounting"
409 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
410 help
411 Select this option to enable fine granularity task irq time
412 accounting. This is done by reading a timestamp on each
413 transitions between softirq and hardirq state, so there can be a
414 small performance impact.
415
416 If in doubt, say N here.
417
418config HAVE_SCHED_AVG_IRQ
419 def_bool y
420 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
421 depends on SMP
422
423config BSD_PROCESS_ACCT
424 bool "BSD Process Accounting"
425 depends on MULTIUSER
426 help
427 If you say Y here, a user level program will be able to instruct the
428 kernel (via a special system call) to write process accounting
429 information to a file: whenever a process exits, information about
430 that process will be appended to the file by the kernel. The
431 information includes things such as creation time, owning user,
432 command name, memory usage, controlling terminal etc. (the complete
433 list is in the struct acct in <file:include/linux/acct.h>). It is
434 up to the user level program to do useful things with this
435 information. This is generally a good idea, so say Y.
436
437config BSD_PROCESS_ACCT_V3
438 bool "BSD Process Accounting version 3 file format"
439 depends on BSD_PROCESS_ACCT
440 default n
441 help
442 If you say Y here, the process accounting information is written
443 in a new file format that also logs the process IDs of each
444 process and its parent. Note that this file format is incompatible
445 with previous v0/v1/v2 file formats, so you will need updated tools
446 for processing it. A preliminary version of these tools is available
447 at <http://www.gnu.org/software/acct/>.
448
449config TASKSTATS
450 bool "Export task/process statistics through netlink"
451 depends on NET
452 depends on MULTIUSER
453 default n
454 help
455 Export selected statistics for tasks/processes through the
456 generic netlink interface. Unlike BSD process accounting, the
457 statistics are available during the lifetime of tasks/processes as
458 responses to commands. Like BSD accounting, they are sent to user
459 space on task exit.
460
461 Say N if unsure.
462
463config TASK_DELAY_ACCT
464 bool "Enable per-task delay accounting"
465 depends on TASKSTATS
466 select SCHED_INFO
467 help
468 Collect information on time spent by a task waiting for system
469 resources like cpu, synchronous block I/O completion and swapping
470 in pages. Such statistics can help in setting a task's priorities
471 relative to other tasks for cpu, io, rss limits etc.
472
473 Say N if unsure.
474
475config TASK_XACCT
476 bool "Enable extended accounting over taskstats"
477 depends on TASKSTATS
478 help
479 Collect extended task accounting data and send the data
480 to userland for processing over the taskstats interface.
481
482 Say N if unsure.
483
484config TASK_IO_ACCOUNTING
485 bool "Enable per-task storage I/O accounting"
486 depends on TASK_XACCT
487 help
488 Collect information on the number of bytes of storage I/O which this
489 task has caused.
490
491 Say N if unsure.
492
493config PSI
494 bool "Pressure stall information tracking"
495 help
496 Collect metrics that indicate how overcommitted the CPU, memory,
497 and IO capacity are in the system.
498
499 If you say Y here, the kernel will create /proc/pressure/ with the
500 pressure statistics files cpu, memory, and io. These will indicate
501 the share of walltime in which some or all tasks in the system are
502 delayed due to contention of the respective resource.
503
504 In kernels with cgroup support, cgroups (cgroup2 only) will
505 have cpu.pressure, memory.pressure, and io.pressure files,
506 which aggregate pressure stalls for the grouped tasks only.
507
508 For more details see Documentation/accounting/psi.txt.
509
510 Say N if unsure.
511
512config PSI_DEFAULT_DISABLED
513 bool "Require boot parameter to enable pressure stall information tracking"
514 default n
515 depends on PSI
516 help
517 If set, pressure stall information tracking will be disabled
518 per default but can be enabled through passing psi=1 on the
519 kernel commandline during boot.
520
521endmenu
522
523config CPU_ISOLATION
524 bool "CPU isolation"
525 depends on SMP || COMPILE_TEST
526 default y
527 help
528 Make sure that CPUs running critical tasks are not disturbed by
529 any source of "noise" such as unbound workqueues, timers, kthreads...
530 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
531 the "isolcpus=" boot parameter.
532
533 Say Y if unsure.
534
535source "kernel/rcu/Kconfig"
536
537config BUILD_BIN2C
538 bool
539 default n
540
541config IKCONFIG
542 tristate "Kernel .config support"
543 select BUILD_BIN2C
544 ---help---
545 This option enables the complete Linux kernel ".config" file
546 contents to be saved in the kernel. It provides documentation
547 of which kernel options are used in a running kernel or in an
548 on-disk kernel. This information can be extracted from the kernel
549 image file with the script scripts/extract-ikconfig and used as
550 input to rebuild the current kernel or to build another kernel.
551 It can also be extracted from a running kernel by reading
552 /proc/config.gz if enabled (below).
553
554config IKCONFIG_PROC
555 bool "Enable access to .config through /proc/config.gz"
556 depends on IKCONFIG && PROC_FS
557 ---help---
558 This option enables access to the kernel configuration file
559 through /proc/config.gz.
560
561config LOG_BUF_SHIFT
562 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
563 range 12 25
564 default 17
565 depends on PRINTK
566 help
567 Select the minimal kernel log buffer size as a power of 2.
568 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
569 parameter, see below. Any higher size also might be forced
570 by "log_buf_len" boot parameter.
571
572 Examples:
573 17 => 128 KB
574 16 => 64 KB
575 15 => 32 KB
576 14 => 16 KB
577 13 => 8 KB
578 12 => 4 KB
579
580config LOG_CPU_MAX_BUF_SHIFT
581 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
582 depends on SMP
583 range 0 21
584 default 12 if !BASE_SMALL
585 default 0 if BASE_SMALL
586 depends on PRINTK
587 help
588 This option allows to increase the default ring buffer size
589 according to the number of CPUs. The value defines the contribution
590 of each CPU as a power of 2. The used space is typically only few
591 lines however it might be much more when problems are reported,
592 e.g. backtraces.
593
594 The increased size means that a new buffer has to be allocated and
595 the original static one is unused. It makes sense only on systems
596 with more CPUs. Therefore this value is used only when the sum of
597 contributions is greater than the half of the default kernel ring
598 buffer as defined by LOG_BUF_SHIFT. The default values are set
599 so that more than 64 CPUs are needed to trigger the allocation.
600
601 Also this option is ignored when "log_buf_len" kernel parameter is
602 used as it forces an exact (power of two) size of the ring buffer.
603
604 The number of possible CPUs is used for this computation ignoring
605 hotplugging making the computation optimal for the worst case
606 scenario while allowing a simple algorithm to be used from bootup.
607
608 Examples shift values and their meaning:
609 17 => 128 KB for each CPU
610 16 => 64 KB for each CPU
611 15 => 32 KB for each CPU
612 14 => 16 KB for each CPU
613 13 => 8 KB for each CPU
614 12 => 4 KB for each CPU
615
616config PRINTK_SAFE_LOG_BUF_SHIFT
617 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
618 range 10 21
619 default 13
620 depends on PRINTK
621 help
622 Select the size of an alternate printk per-CPU buffer where messages
623 printed from usafe contexts are temporary stored. One example would
624 be NMI messages, another one - printk recursion. The messages are
625 copied to the main log buffer in a safe context to avoid a deadlock.
626 The value defines the size as a power of 2.
627
628 Those messages are rare and limited. The largest one is when
629 a backtrace is printed. It usually fits into 4KB. Select
630 8KB if you want to be on the safe side.
631
632 Examples:
633 17 => 128 KB for each CPU
634 16 => 64 KB for each CPU
635 15 => 32 KB for each CPU
636 14 => 16 KB for each CPU
637 13 => 8 KB for each CPU
638 12 => 4 KB for each CPU
639
640
641
642
643config HAVE_UNSTABLE_SCHED_CLOCK
644 bool
645
646config GENERIC_SCHED_CLOCK
647 bool
648
649
650
651
652
653config ARCH_SUPPORTS_NUMA_BALANCING
654 bool
655
656
657
658
659
660
661
662
663config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
664 bool
665
666
667
668
669config ARCH_SUPPORTS_INT128
670 bool
671
672
673
674
675config ARCH_WANT_NUMA_VARIABLE_LOCALITY
676 bool
677
678config NUMA_BALANCING
679 bool "Memory placement aware NUMA scheduler"
680 depends on ARCH_SUPPORTS_NUMA_BALANCING
681 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
682 depends on SMP && NUMA && MIGRATION
683 help
684 This option adds support for automatic NUMA aware memory/task placement.
685 The mechanism is quite primitive and is based on migrating memory when
686 it has references to the node the task is running on.
687
688 This system will be inactive on UMA systems.
689
690config NUMA_BALANCING_DEFAULT_ENABLED
691 bool "Automatically enable NUMA aware memory/task placement"
692 default y
693 depends on NUMA_BALANCING
694 help
695 If set, automatic NUMA balancing will be enabled if running on a NUMA
696 machine.
697
698menuconfig CGROUPS
699 bool "Control Group support"
700 select KERNFS
701 help
702 This option adds support for grouping sets of processes together, for
703 use with process control subsystems such as Cpusets, CFS, memory
704 controls or device isolation.
705 See
706 - Documentation/scheduler/sched-design-CFS.txt (CFS)
707 - Documentation/cgroup-v1/ (features for grouping, isolation
708 and resource control)
709
710 Say N if unsure.
711
712if CGROUPS
713
714config PAGE_COUNTER
715 bool
716
717config MEMCG
718 bool "Memory controller"
719 select PAGE_COUNTER
720 select EVENTFD
721 help
722 Provides control over the memory footprint of tasks in a cgroup.
723
724config MEMCG_SWAP
725 bool "Swap controller"
726 depends on MEMCG && SWAP
727 help
728 Provides control over the swap space consumed by tasks in a cgroup.
729
730config MEMCG_SWAP_ENABLED
731 bool "Swap controller enabled by default"
732 depends on MEMCG_SWAP
733 default y
734 help
735 Memory Resource Controller Swap Extension comes with its price in
736 a bigger memory consumption. General purpose distribution kernels
737 which want to enable the feature but keep it disabled by default
738 and let the user enable it by swapaccount=1 boot command line
739 parameter should have this option unselected.
740 For those who want to have the feature enabled by default should
741 select this option (if, for some reason, they need to disable it
742 then swapaccount=0 does the trick).
743
744config MEMCG_KMEM
745 bool
746 depends on MEMCG && !SLOB
747 default y
748
749config BLK_CGROUP
750 bool "IO controller"
751 depends on BLOCK
752 default n
753 ---help---
754 Generic block IO controller cgroup interface. This is the common
755 cgroup interface which should be used by various IO controlling
756 policies.
757
758 Currently, CFQ IO scheduler uses it to recognize task groups and
759 control disk bandwidth allocation (proportional time slice allocation)
760 to such task groups. It is also used by bio throttling logic in
761 block layer to implement upper limit in IO rates on a device.
762
763 This option only enables generic Block IO controller infrastructure.
764 One needs to also enable actual IO controlling logic/policy. For
765 enabling proportional weight division of disk bandwidth in CFQ, set
766 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
767 CONFIG_BLK_DEV_THROTTLING=y.
768
769 See Documentation/cgroup-v1/blkio-controller.txt for more information.
770
771config DEBUG_BLK_CGROUP
772 bool "IO controller debugging"
773 depends on BLK_CGROUP
774 default n
775 ---help---
776 Enable some debugging help. Currently it exports additional stat
777 files in a cgroup which can be useful for debugging.
778
779config CGROUP_WRITEBACK
780 bool
781 depends on MEMCG && BLK_CGROUP
782 default y
783
784menuconfig CGROUP_SCHED
785 bool "CPU controller"
786 default n
787 help
788 This feature lets CPU scheduler recognize task groups and control CPU
789 bandwidth allocation to such task groups. It uses cgroups to group
790 tasks.
791
792if CGROUP_SCHED
793config FAIR_GROUP_SCHED
794 bool "Group scheduling for SCHED_OTHER"
795 depends on CGROUP_SCHED
796 default CGROUP_SCHED
797
798config CFS_BANDWIDTH
799 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
800 depends on FAIR_GROUP_SCHED
801 default n
802 help
803 This option allows users to define CPU bandwidth rates (limits) for
804 tasks running within the fair group scheduler. Groups with no limit
805 set are considered to be unconstrained and will run with no
806 restriction.
807 See Documentation/scheduler/sched-bwc.txt for more information.
808
809config RT_GROUP_SCHED
810 bool "Group scheduling for SCHED_RR/FIFO"
811 depends on CGROUP_SCHED
812 default n
813 help
814 This feature lets you explicitly allocate real CPU bandwidth
815 to task groups. If enabled, it will also make it impossible to
816 schedule realtime tasks for non-root users until you allocate
817 realtime bandwidth for them.
818 See Documentation/scheduler/sched-rt-group.txt for more information.
819
820endif
821
822config CGROUP_PIDS
823 bool "PIDs controller"
824 help
825 Provides enforcement of process number limits in the scope of a
826 cgroup. Any attempt to fork more processes than is allowed in the
827 cgroup will fail. PIDs are fundamentally a global resource because it
828 is fairly trivial to reach PID exhaustion before you reach even a
829 conservative kmemcg limit. As a result, it is possible to grind a
830 system to halt without being limited by other cgroup policies. The
831 PIDs controller is designed to stop this from happening.
832
833 It should be noted that organisational operations (such as attaching
834 to a cgroup hierarchy will *not* be blocked by the PIDs controller),
835 since the PIDs limit only affects a process's ability to fork, not to
836 attach to a cgroup.
837
838config CGROUP_RDMA
839 bool "RDMA controller"
840 help
841 Provides enforcement of RDMA resources defined by IB stack.
842 It is fairly easy for consumers to exhaust RDMA resources, which
843 can result into resource unavailability to other consumers.
844 RDMA controller is designed to stop this from happening.
845 Attaching processes with active RDMA resources to the cgroup
846 hierarchy is allowed even if can cross the hierarchy's limit.
847
848config CGROUP_FREEZER
849 bool "Freezer controller"
850 help
851 Provides a way to freeze and unfreeze all tasks in a
852 cgroup.
853
854 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
855 controller includes important in-kernel memory consumers per default.
856
857 If you're using cgroup2, say N.
858
859config CGROUP_HUGETLB
860 bool "HugeTLB controller"
861 depends on HUGETLB_PAGE
862 select PAGE_COUNTER
863 default n
864 help
865 Provides a cgroup controller for HugeTLB pages.
866 When you enable this, you can put a per cgroup limit on HugeTLB usage.
867 The limit is enforced during page fault. Since HugeTLB doesn't
868 support page reclaim, enforcing the limit at page fault time implies
869 that, the application will get SIGBUS signal if it tries to access
870 HugeTLB pages beyond its limit. This requires the application to know
871 beforehand how much HugeTLB pages it would require for its use. The
872 control group is tracked in the third page lru pointer. This means
873 that we cannot use the controller with huge page less than 3 pages.
874
875config CPUSETS
876 bool "Cpuset controller"
877 depends on SMP
878 help
879 This option will let you create and manage CPUSETs which
880 allow dynamically partitioning a system into sets of CPUs and
881 Memory Nodes and assigning tasks to run only within those sets.
882 This is primarily useful on large SMP or NUMA systems.
883
884 Say N if unsure.
885
886config PROC_PID_CPUSET
887 bool "Include legacy /proc/<pid>/cpuset file"
888 depends on CPUSETS
889 default y
890
891config CGROUP_DEVICE
892 bool "Device controller"
893 help
894 Provides a cgroup controller implementing whitelists for
895 devices which a process in the cgroup can mknod or open.
896
897config CGROUP_CPUACCT
898 bool "Simple CPU accounting controller"
899 help
900 Provides a simple controller for monitoring the
901 total CPU consumed by the tasks in a cgroup.
902
903config CGROUP_PERF
904 bool "Perf controller"
905 depends on PERF_EVENTS
906 help
907 This option extends the perf per-cpu mode to restrict monitoring
908 to threads which belong to the cgroup specified and run on the
909 designated cpu.
910
911 Say N if unsure.
912
913config CGROUP_BPF
914 bool "Support for eBPF programs attached to cgroups"
915 depends on BPF_SYSCALL
916 select SOCK_CGROUP_DATA
917 help
918 Allow attaching eBPF programs to a cgroup using the bpf(2)
919 syscall command BPF_PROG_ATTACH.
920
921 In which context these programs are accessed depends on the type
922 of attachment. For instance, programs that are attached using
923 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
924 inet sockets.
925
926config CGROUP_DEBUG
927 bool "Debug controller"
928 default n
929 depends on DEBUG_KERNEL
930 help
931 This option enables a simple controller that exports
932 debugging information about the cgroups framework. This
933 controller is for control cgroup debugging only. Its
934 interfaces are not stable.
935
936 Say N.
937
938config SOCK_CGROUP_DATA
939 bool
940 default n
941
942endif
943
944menuconfig NAMESPACES
945 bool "Namespaces support" if EXPERT
946 depends on MULTIUSER
947 default !EXPERT
948 help
949 Provides the way to make tasks work with different objects using
950 the same id. For example same IPC id may refer to different objects
951 or same user id or pid may refer to different tasks when used in
952 different namespaces.
953
954if NAMESPACES
955
956config UTS_NS
957 bool "UTS namespace"
958 default y
959 help
960 In this namespace tasks see different info provided with the
961 uname() system call
962
963config IPC_NS
964 bool "IPC namespace"
965 depends on (SYSVIPC || POSIX_MQUEUE)
966 default y
967 help
968 In this namespace tasks work with IPC ids which correspond to
969 different IPC objects in different namespaces.
970
971config USER_NS
972 bool "User namespace"
973 default n
974 help
975 This allows containers, i.e. vservers, to use user namespaces
976 to provide different user info for different servers.
977
978 When user namespaces are enabled in the kernel it is
979 recommended that the MEMCG option also be enabled and that
980 user-space use the memory control groups to limit the amount
981 of memory a memory unprivileged users can use.
982
983 If unsure, say N.
984
985config PID_NS
986 bool "PID Namespaces"
987 default y
988 help
989 Support process id namespaces. This allows having multiple
990 processes with the same pid as long as they are in different
991 pid namespaces. This is a building block of containers.
992
993config NET_NS
994 bool "Network namespace"
995 depends on NET
996 default y
997 help
998 Allow user space to create what appear to be multiple instances
999 of the network stack.
1000
1001endif
1002
1003config CHECKPOINT_RESTORE
1004 bool "Checkpoint/restore support"
1005 select PROC_CHILDREN
1006 default n
1007 help
1008 Enables additional kernel features in a sake of checkpoint/restore.
1009 In particular it adds auxiliary prctl codes to setup process text,
1010 data and heap segment sizes, and a few additional /proc filesystem
1011 entries.
1012
1013 If unsure, say N here.
1014
1015config SCHED_AUTOGROUP
1016 bool "Automatic process group scheduling"
1017 select CGROUPS
1018 select CGROUP_SCHED
1019 select FAIR_GROUP_SCHED
1020 help
1021 This option optimizes the scheduler for common desktop workloads by
1022 automatically creating and populating task groups. This separation
1023 of workloads isolates aggressive CPU burners (like build jobs) from
1024 desktop applications. Task group autogeneration is currently based
1025 upon task session.
1026
1027config SYSFS_DEPRECATED
1028 bool "Enable deprecated sysfs features to support old userspace tools"
1029 depends on SYSFS
1030 default n
1031 help
1032 This option adds code that switches the layout of the "block" class
1033 devices, to not show up in /sys/class/block/, but only in
1034 /sys/block/.
1035
1036 This switch is only active when the sysfs.deprecated=1 boot option is
1037 passed or the SYSFS_DEPRECATED_V2 option is set.
1038
1039 This option allows new kernels to run on old distributions and tools,
1040 which might get confused by /sys/class/block/. Since 2007/2008 all
1041 major distributions and tools handle this just fine.
1042
1043 Recent distributions and userspace tools after 2009/2010 depend on
1044 the existence of /sys/class/block/, and will not work with this
1045 option enabled.
1046
1047 Only if you are using a new kernel on an old distribution, you might
1048 need to say Y here.
1049
1050config SYSFS_DEPRECATED_V2
1051 bool "Enable deprecated sysfs features by default"
1052 default n
1053 depends on SYSFS
1054 depends on SYSFS_DEPRECATED
1055 help
1056 Enable deprecated sysfs by default.
1057
1058 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1059 option.
1060
1061 Only if you are using a new kernel on an old distribution, you might
1062 need to say Y here. Even then, odds are you would not need it
1063 enabled, you can always pass the boot option if absolutely necessary.
1064
1065config RELAY
1066 bool "Kernel->user space relay support (formerly relayfs)"
1067 select IRQ_WORK
1068 help
1069 This option enables support for relay interface support in
1070 certain file systems (such as debugfs).
1071 It is designed to provide an efficient mechanism for tools and
1072 facilities to relay large amounts of data from kernel space to
1073 user space.
1074
1075 If unsure, say N.
1076
1077config BLK_DEV_INITRD
1078 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1079 help
1080 The initial RAM filesystem is a ramfs which is loaded by the
1081 boot loader (loadlin or lilo) and that is mounted as root
1082 before the normal boot procedure. It is typically used to
1083 load modules needed to mount the "real" root file system,
1084 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1085
1086 If RAM disk support (BLK_DEV_RAM) is also included, this
1087 also enables initial RAM disk (initrd) support and adds
1088 15 Kbytes (more on some other architectures) to the kernel size.
1089
1090 If unsure say Y.
1091
1092if BLK_DEV_INITRD
1093
1094source "usr/Kconfig"
1095
1096endif
1097
1098choice
1099 prompt "Compiler optimization level"
1100 default CC_OPTIMIZE_FOR_PERFORMANCE
1101
1102config CC_OPTIMIZE_FOR_PERFORMANCE
1103 bool "Optimize for performance"
1104 help
1105 This is the default optimization level for the kernel, building
1106 with the "-O2" compiler flag for best performance and most
1107 helpful compile-time warnings.
1108
1109config CC_OPTIMIZE_FOR_SIZE
1110 bool "Optimize for size"
1111 help
1112 Enabling this option will pass "-Os" instead of "-O2" to
1113 your compiler resulting in a smaller kernel.
1114
1115 If unsure, say N.
1116
1117endchoice
1118
1119config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1120 bool
1121 help
1122 This requires that the arch annotates or otherwise protects
1123 its external entry points from being discarded. Linker scripts
1124 must also merge .text.*, .data.*, and .bss.* correctly into
1125 output sections. Care must be taken not to pull in unrelated
1126 sections (e.g., '.text.init'). Typically '.' in section names
1127 is used to distinguish them from label names / C identifiers.
1128
1129config LD_DEAD_CODE_DATA_ELIMINATION
1130 bool "Dead code and data elimination (EXPERIMENTAL)"
1131 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1132 depends on EXPERT
1133 depends on $(cc-option,-ffunction-sections -fdata-sections)
1134 depends on $(ld-option,--gc-sections)
1135 help
1136 Enable this if you want to do dead code and data elimination with
1137 the linker by compiling with -ffunction-sections -fdata-sections,
1138 and linking with --gc-sections.
1139
1140 This can reduce on disk and in-memory size of the kernel
1141 code and static data, particularly for small configs and
1142 on small systems. This has the possibility of introducing
1143 silently broken kernel if the required annotations are not
1144 present. This option is not well tested yet, so use at your
1145 own risk.
1146
1147config SYSCTL
1148 bool
1149
1150config ANON_INODES
1151 bool
1152
1153config HAVE_UID16
1154 bool
1155
1156config SYSCTL_EXCEPTION_TRACE
1157 bool
1158 help
1159 Enable support for /proc/sys/debug/exception-trace.
1160
1161config SYSCTL_ARCH_UNALIGN_NO_WARN
1162 bool
1163 help
1164 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1165 Allows arch to define/use @no_unaligned_warning to possibly warn
1166 about unaligned access emulation going on under the hood.
1167
1168config SYSCTL_ARCH_UNALIGN_ALLOW
1169 bool
1170 help
1171 Enable support for /proc/sys/kernel/unaligned-trap
1172 Allows arches to define/use @unaligned_enabled to runtime toggle
1173 the unaligned access emulation.
1174 see arch/parisc/kernel/unaligned.c for reference
1175
1176config HAVE_PCSPKR_PLATFORM
1177 bool
1178
1179
1180config BPF
1181 bool
1182
1183menuconfig EXPERT
1184 bool "Configure standard kernel features (expert users)"
1185
1186 select DEBUG_KERNEL
1187 help
1188 This option allows certain base kernel options and settings
1189 to be disabled or tweaked. This is for specialized
1190 environments which can tolerate a "non-standard" kernel.
1191 Only use this if you really know what you are doing.
1192
1193config UID16
1194 bool "Enable 16-bit UID system calls" if EXPERT
1195 depends on HAVE_UID16 && MULTIUSER
1196 default y
1197 help
1198 This enables the legacy 16-bit UID syscall wrappers.
1199
1200config MULTIUSER
1201 bool "Multiple users, groups and capabilities support" if EXPERT
1202 default y
1203 help
1204 This option enables support for non-root users, groups and
1205 capabilities.
1206
1207 If you say N here, all processes will run with UID 0, GID 0, and all
1208 possible capabilities. Saying N here also compiles out support for
1209 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1210 setgid, and capset.
1211
1212 If unsure, say Y here.
1213
1214config SGETMASK_SYSCALL
1215 bool "sgetmask/ssetmask syscalls support" if EXPERT
1216 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1217 ---help---
1218 sys_sgetmask and sys_ssetmask are obsolete system calls
1219 no longer supported in libc but still enabled by default in some
1220 architectures.
1221
1222 If unsure, leave the default option here.
1223
1224config SYSFS_SYSCALL
1225 bool "Sysfs syscall support" if EXPERT
1226 default y
1227 ---help---
1228 sys_sysfs is an obsolete system call no longer supported in libc.
1229 Note that disabling this option is more secure but might break
1230 compatibility with some systems.
1231
1232 If unsure say Y here.
1233
1234config SYSCTL_SYSCALL
1235 bool "Sysctl syscall support" if EXPERT
1236 depends on PROC_SYSCTL
1237 default n
1238 select SYSCTL
1239 ---help---
1240 sys_sysctl uses binary paths that have been found challenging
1241 to properly maintain and use. The interface in /proc/sys
1242 using paths with ascii names is now the primary path to this
1243 information.
1244
1245 Almost nothing using the binary sysctl interface so if you are
1246 trying to save some space it is probably safe to disable this,
1247 making your kernel marginally smaller.
1248
1249 If unsure say N here.
1250
1251config FHANDLE
1252 bool "open by fhandle syscalls" if EXPERT
1253 select EXPORTFS
1254 default y
1255 help
1256 If you say Y here, a user level program will be able to map
1257 file names to handle and then later use the handle for
1258 different file system operations. This is useful in implementing
1259 userspace file servers, which now track files using handles instead
1260 of names. The handle would remain the same even if file names
1261 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1262 syscalls.
1263
1264config POSIX_TIMERS
1265 bool "Posix Clocks & timers" if EXPERT
1266 default y
1267 help
1268 This includes native support for POSIX timers to the kernel.
1269 Some embedded systems have no use for them and therefore they
1270 can be configured out to reduce the size of the kernel image.
1271
1272 When this option is disabled, the following syscalls won't be
1273 available: timer_create, timer_gettime: timer_getoverrun,
1274 timer_settime, timer_delete, clock_adjtime, getitimer,
1275 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1276 clock_getres and clock_nanosleep syscalls will be limited to
1277 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1278
1279 If unsure say y.
1280
1281config PRINTK
1282 default y
1283 bool "Enable support for printk" if EXPERT
1284 select IRQ_WORK
1285 help
1286 This option enables normal printk support. Removing it
1287 eliminates most of the message strings from the kernel image
1288 and makes the kernel more or less silent. As this makes it
1289 very difficult to diagnose system problems, saying N here is
1290 strongly discouraged.
1291
1292config PRINTK_NMI
1293 def_bool y
1294 depends on PRINTK
1295 depends on HAVE_NMI
1296
1297config BUG
1298 bool "BUG() support" if EXPERT
1299 default y
1300 help
1301 Disabling this option eliminates support for BUG and WARN, reducing
1302 the size of your kernel image and potentially quietly ignoring
1303 numerous fatal conditions. You should only consider disabling this
1304 option for embedded systems with no facilities for reporting errors.
1305 Just say Y.
1306
1307config ELF_CORE
1308 depends on COREDUMP
1309 default y
1310 bool "Enable ELF core dumps" if EXPERT
1311 help
1312 Enable support for generating core dumps. Disabling saves about 4k.
1313
1314
1315config PCSPKR_PLATFORM
1316 bool "Enable PC-Speaker support" if EXPERT
1317 depends on HAVE_PCSPKR_PLATFORM
1318 select I8253_LOCK
1319 default y
1320 help
1321 This option allows to disable the internal PC-Speaker
1322 support, saving some memory.
1323
1324config BASE_FULL
1325 default y
1326 bool "Enable full-sized data structures for core" if EXPERT
1327 help
1328 Disabling this option reduces the size of miscellaneous core
1329 kernel data structures. This saves memory on small machines,
1330 but may reduce performance.
1331
1332config FUTEX
1333 bool "Enable futex support" if EXPERT
1334 default y
1335 imply RT_MUTEXES
1336 help
1337 Disabling this option will cause the kernel to be built without
1338 support for "fast userspace mutexes". The resulting kernel may not
1339 run glibc-based applications correctly.
1340
1341config FUTEX_PI
1342 bool
1343 depends on FUTEX && RT_MUTEXES
1344 default y
1345
1346config HAVE_FUTEX_CMPXCHG
1347 bool
1348 depends on FUTEX
1349 help
1350 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1351 is implemented and always working. This removes a couple of runtime
1352 checks.
1353
1354config EPOLL
1355 bool "Enable eventpoll support" if EXPERT
1356 default y
1357 select ANON_INODES
1358 help
1359 Disabling this option will cause the kernel to be built without
1360 support for epoll family of system calls.
1361
1362config SIGNALFD
1363 bool "Enable signalfd() system call" if EXPERT
1364 select ANON_INODES
1365 default y
1366 help
1367 Enable the signalfd() system call that allows to receive signals
1368 on a file descriptor.
1369
1370 If unsure, say Y.
1371
1372config TIMERFD
1373 bool "Enable timerfd() system call" if EXPERT
1374 select ANON_INODES
1375 default y
1376 help
1377 Enable the timerfd() system call that allows to receive timer
1378 events on a file descriptor.
1379
1380 If unsure, say Y.
1381
1382config EVENTFD
1383 bool "Enable eventfd() system call" if EXPERT
1384 select ANON_INODES
1385 default y
1386 help
1387 Enable the eventfd() system call that allows to receive both
1388 kernel notification (ie. KAIO) or userspace notifications.
1389
1390 If unsure, say Y.
1391
1392config SHMEM
1393 bool "Use full shmem filesystem" if EXPERT
1394 default y
1395 depends on MMU
1396 help
1397 The shmem is an internal filesystem used to manage shared memory.
1398 It is backed by swap and manages resource limits. It is also exported
1399 to userspace as tmpfs if TMPFS is enabled. Disabling this
1400 option replaces shmem and tmpfs with the much simpler ramfs code,
1401 which may be appropriate on small systems without swap.
1402
1403config AIO
1404 bool "Enable AIO support" if EXPERT
1405 default y
1406 help
1407 This option enables POSIX asynchronous I/O which may by used
1408 by some high performance threaded applications. Disabling
1409 this option saves about 7k.
1410
1411config ADVISE_SYSCALLS
1412 bool "Enable madvise/fadvise syscalls" if EXPERT
1413 default y
1414 help
1415 This option enables the madvise and fadvise syscalls, used by
1416 applications to advise the kernel about their future memory or file
1417 usage, improving performance. If building an embedded system where no
1418 applications use these syscalls, you can disable this option to save
1419 space.
1420
1421config MEMBARRIER
1422 bool "Enable membarrier() system call" if EXPERT
1423 default y
1424 help
1425 Enable the membarrier() system call that allows issuing memory
1426 barriers across all running threads, which can be used to distribute
1427 the cost of user-space memory barriers asymmetrically by transforming
1428 pairs of memory barriers into pairs consisting of membarrier() and a
1429 compiler barrier.
1430
1431 If unsure, say Y.
1432
1433config KALLSYMS
1434 bool "Load all symbols for debugging/ksymoops" if EXPERT
1435 default y
1436 help
1437 Say Y here to let the kernel print out symbolic crash information and
1438 symbolic stack backtraces. This increases the size of the kernel
1439 somewhat, as all symbols have to be loaded into the kernel image.
1440
1441config KALLSYMS_ALL
1442 bool "Include all symbols in kallsyms"
1443 depends on DEBUG_KERNEL && KALLSYMS
1444 help
1445 Normally kallsyms only contains the symbols of functions for nicer
1446 OOPS messages and backtraces (i.e., symbols from the text and inittext
1447 sections). This is sufficient for most cases. And only in very rare
1448 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1449 names of variables from the data sections, etc).
1450
1451 This option makes sure that all symbols are loaded into the kernel
1452 image (i.e., symbols from all sections) in cost of increased kernel
1453 size (depending on the kernel configuration, it may be 300KiB or
1454 something like this).
1455
1456 Say N unless you really need all symbols.
1457
1458config KALLSYMS_ABSOLUTE_PERCPU
1459 bool
1460 depends on KALLSYMS
1461 default X86_64 && SMP
1462
1463config KALLSYMS_BASE_RELATIVE
1464 bool
1465 depends on KALLSYMS
1466 default !IA64
1467 help
1468 Instead of emitting them as absolute values in the native word size,
1469 emit the symbol references in the kallsyms table as 32-bit entries,
1470 each containing a relative value in the range [base, base + U32_MAX]
1471 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1472 an absolute value in the range [0, S32_MAX] or a relative value in the
1473 range [base, base + S32_MAX], where base is the lowest relative symbol
1474 address encountered in the image.
1475
1476 On 64-bit builds, this reduces the size of the address table by 50%,
1477 but more importantly, it results in entries whose values are build
1478 time constants, and no relocation pass is required at runtime to fix
1479 up the entries based on the runtime load address of the kernel.
1480
1481
1482
1483
1484config BPF_SYSCALL
1485 bool "Enable bpf() system call"
1486 select ANON_INODES
1487 select BPF
1488 select IRQ_WORK
1489 default n
1490 help
1491 Enable the bpf() system call that allows to manipulate eBPF
1492 programs and maps via file descriptors.
1493
1494config BPF_JIT_ALWAYS_ON
1495 bool "Permanently enable BPF JIT and remove BPF interpreter"
1496 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
1497 help
1498 Enables BPF JIT and removes BPF interpreter to avoid
1499 speculative execution of BPF instructions by the interpreter
1500
1501config USERFAULTFD
1502 bool "Enable userfaultfd() system call"
1503 select ANON_INODES
1504 depends on MMU
1505 help
1506 Enable the userfaultfd() system call that allows to intercept and
1507 handle page faults in userland.
1508
1509config ARCH_HAS_MEMBARRIER_CALLBACKS
1510 bool
1511
1512config ARCH_HAS_MEMBARRIER_SYNC_CORE
1513 bool
1514
1515config RSEQ
1516 bool "Enable rseq() system call" if EXPERT
1517 default y
1518 depends on HAVE_RSEQ
1519 select MEMBARRIER
1520 help
1521 Enable the restartable sequences system call. It provides a
1522 user-space cache for the current CPU number value, which
1523 speeds up getting the current CPU number from user-space,
1524 as well as an ABI to speed up user-space operations on
1525 per-CPU data.
1526
1527 If unsure, say Y.
1528
1529config DEBUG_RSEQ
1530 default n
1531 bool "Enabled debugging of rseq() system call" if EXPERT
1532 depends on RSEQ && DEBUG_KERNEL
1533 help
1534 Enable extra debugging checks for the rseq system call.
1535
1536 If unsure, say N.
1537
1538config EMBEDDED
1539 bool "Embedded system"
1540 option allnoconfig_y
1541 select EXPERT
1542 help
1543 This option should be enabled if compiling the kernel for
1544 an embedded system so certain expert options are available
1545 for configuration.
1546
1547config HAVE_PERF_EVENTS
1548 bool
1549 help
1550 See tools/perf/design.txt for details.
1551
1552config PERF_USE_VMALLOC
1553 bool
1554 help
1555 See tools/perf/design.txt for details
1556
1557config PC104
1558 bool "PC/104 support" if EXPERT
1559 help
1560 Expose PC/104 form factor device drivers and options available for
1561 selection and configuration. Enable this option if your target
1562 machine has a PC/104 bus.
1563
1564menu "Kernel Performance Events And Counters"
1565
1566config PERF_EVENTS
1567 bool "Kernel performance events and counters"
1568 default y if PROFILING
1569 depends on HAVE_PERF_EVENTS
1570 select ANON_INODES
1571 select IRQ_WORK
1572 select SRCU
1573 help
1574 Enable kernel support for various performance events provided
1575 by software and hardware.
1576
1577 Software events are supported either built-in or via the
1578 use of generic tracepoints.
1579
1580 Most modern CPUs support performance events via performance
1581 counter registers. These registers count the number of certain
1582 types of hw events: such as instructions executed, cachemisses
1583 suffered, or branches mis-predicted - without slowing down the
1584 kernel or applications. These registers can also trigger interrupts
1585 when a threshold number of events have passed - and can thus be
1586 used to profile the code that runs on that CPU.
1587
1588 The Linux Performance Event subsystem provides an abstraction of
1589 these software and hardware event capabilities, available via a
1590 system call and used by the "perf" utility in tools/perf/. It
1591 provides per task and per CPU counters, and it provides event
1592 capabilities on top of those.
1593
1594 Say Y if unsure.
1595
1596config DEBUG_PERF_USE_VMALLOC
1597 default n
1598 bool "Debug: use vmalloc to back perf mmap() buffers"
1599 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1600 select PERF_USE_VMALLOC
1601 help
1602 Use vmalloc memory to back perf mmap() buffers.
1603
1604 Mostly useful for debugging the vmalloc code on platforms
1605 that don't require it.
1606
1607 Say N if unsure.
1608
1609endmenu
1610
1611config VM_EVENT_COUNTERS
1612 default y
1613 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1614 help
1615 VM event counters are needed for event counts to be shown.
1616 This option allows the disabling of the VM event counters
1617 on EXPERT systems. /proc/vmstat will only show page counts
1618 if VM event counters are disabled.
1619
1620config SLUB_DEBUG
1621 default y
1622 bool "Enable SLUB debugging support" if EXPERT
1623 depends on SLUB && SYSFS
1624 help
1625 SLUB has extensive debug support features. Disabling these can
1626 result in significant savings in code size. This also disables
1627 SLUB sysfs support. /sys/slab will not exist and there will be
1628 no support for cache validation etc.
1629
1630config SLUB_MEMCG_SYSFS_ON
1631 default n
1632 bool "Enable memcg SLUB sysfs support by default" if EXPERT
1633 depends on SLUB && SYSFS && MEMCG
1634 help
1635 SLUB creates a directory under /sys/kernel/slab for each
1636 allocation cache to host info and debug files. If memory
1637 cgroup is enabled, each cache can have per memory cgroup
1638 caches. SLUB can create the same sysfs directories for these
1639 caches under /sys/kernel/slab/CACHE/cgroup but it can lead
1640 to a very high number of debug files being created. This is
1641 controlled by slub_memcg_sysfs boot parameter and this
1642 config option determines the parameter's default value.
1643
1644config COMPAT_BRK
1645 bool "Disable heap randomization"
1646 default y
1647 help
1648 Randomizing heap placement makes heap exploits harder, but it
1649 also breaks ancient binaries (including anything libc5 based).
1650 This option changes the bootup default to heap randomization
1651 disabled, and can be overridden at runtime by setting
1652 /proc/sys/kernel/randomize_va_space to 2.
1653
1654 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1655
1656choice
1657 prompt "Choose SLAB allocator"
1658 default SLUB
1659 help
1660 This option allows to select a slab allocator.
1661
1662config SLAB
1663 bool "SLAB"
1664 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1665 help
1666 The regular slab allocator that is established and known to work
1667 well in all environments. It organizes cache hot objects in
1668 per cpu and per node queues.
1669
1670config SLUB
1671 bool "SLUB (Unqueued Allocator)"
1672 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1673 help
1674 SLUB is a slab allocator that minimizes cache line usage
1675 instead of managing queues of cached objects (SLAB approach).
1676 Per cpu caching is realized using slabs of objects instead
1677 of queues of objects. SLUB can use memory efficiently
1678 and has enhanced diagnostics. SLUB is the default choice for
1679 a slab allocator.
1680
1681config SLOB
1682 depends on EXPERT
1683 bool "SLOB (Simple Allocator)"
1684 help
1685 SLOB replaces the stock allocator with a drastically simpler
1686 allocator. SLOB is generally more space efficient but
1687 does not perform as well on large systems.
1688
1689endchoice
1690
1691config SLAB_MERGE_DEFAULT
1692 bool "Allow slab caches to be merged"
1693 default y
1694 help
1695 For reduced kernel memory fragmentation, slab caches can be
1696 merged when they share the same size and other characteristics.
1697 This carries a risk of kernel heap overflows being able to
1698 overwrite objects from merged caches (and more easily control
1699 cache layout), which makes such heap attacks easier to exploit
1700 by attackers. By keeping caches unmerged, these kinds of exploits
1701 can usually only damage objects in the same cache. To disable
1702 merging at runtime, "slab_nomerge" can be passed on the kernel
1703 command line.
1704
1705config SLAB_FREELIST_RANDOM
1706 default n
1707 depends on SLAB || SLUB
1708 bool "SLAB freelist randomization"
1709 help
1710 Randomizes the freelist order used on creating new pages. This
1711 security feature reduces the predictability of the kernel slab
1712 allocator against heap overflows.
1713
1714config SLAB_FREELIST_HARDENED
1715 bool "Harden slab freelist metadata"
1716 depends on SLUB
1717 help
1718 Many kernel heap attacks try to target slab cache metadata and
1719 other infrastructure. This options makes minor performance
1720 sacrifies to harden the kernel slab allocator against common
1721 freelist exploit methods.
1722
1723config SLUB_CPU_PARTIAL
1724 default y
1725 depends on SLUB && SMP
1726 bool "SLUB per cpu partial cache"
1727 help
1728 Per cpu partial caches accellerate objects allocation and freeing
1729 that is local to a processor at the price of more indeterminism
1730 in the latency of the free. On overflow these caches will be cleared
1731 which requires the taking of locks that may cause latency spikes.
1732 Typically one would choose no for a realtime system.
1733
1734config MMAP_ALLOW_UNINITIALIZED
1735 bool "Allow mmapped anonymous memory to be uninitialized"
1736 depends on EXPERT && !MMU
1737 default n
1738 help
1739 Normally, and according to the Linux spec, anonymous memory obtained
1740 from mmap() has its contents cleared before it is passed to
1741 userspace. Enabling this config option allows you to request that
1742 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1743 providing a huge performance boost. If this option is not enabled,
1744 then the flag will be ignored.
1745
1746 This is taken advantage of by uClibc's malloc(), and also by
1747 ELF-FDPIC binfmt's brk and stack allocator.
1748
1749 Because of the obvious security issues, this option should only be
1750 enabled on embedded devices where you control what is run in
1751 userspace. Since that isn't generally a problem on no-MMU systems,
1752 it is normally safe to say Y here.
1753
1754 See Documentation/nommu-mmap.txt for more information.
1755
1756config SYSTEM_DATA_VERIFICATION
1757 def_bool n
1758 select SYSTEM_TRUSTED_KEYRING
1759 select KEYS
1760 select CRYPTO
1761 select CRYPTO_RSA
1762 select ASYMMETRIC_KEY_TYPE
1763 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1764 select ASN1
1765 select OID_REGISTRY
1766 select X509_CERTIFICATE_PARSER
1767 select PKCS7_MESSAGE_PARSER
1768 help
1769 Provide PKCS#7 message verification using the contents of the system
1770 trusted keyring to provide public keys. This then can be used for
1771 module verification, kexec image verification and firmware blob
1772 verification.
1773
1774config PROFILING
1775 bool "Profiling support"
1776 help
1777 Say Y here to enable the extended profiling support mechanisms used
1778 by profilers such as OProfile.
1779
1780
1781
1782
1783
1784config TRACEPOINTS
1785 bool
1786
1787endmenu
1788
1789source "arch/Kconfig"
1790
1791config RT_MUTEXES
1792 bool
1793
1794config BASE_SMALL
1795 int
1796 default 0 if BASE_FULL
1797 default 1 if !BASE_FULL
1798
1799menuconfig MODULES
1800 bool "Enable loadable module support"
1801 option modules
1802 help
1803 Kernel modules are small pieces of compiled code which can
1804 be inserted in the running kernel, rather than being
1805 permanently built into the kernel. You use the "modprobe"
1806 tool to add (and sometimes remove) them. If you say Y here,
1807 many parts of the kernel can be built as modules (by
1808 answering M instead of Y where indicated): this is most
1809 useful for infrequently used options which are not required
1810 for booting. For more information, see the man pages for
1811 modprobe, lsmod, modinfo, insmod and rmmod.
1812
1813 If you say Y here, you will need to run "make
1814 modules_install" to put the modules under /lib/modules/
1815 where modprobe can find them (you may need to be root to do
1816 this).
1817
1818 If unsure, say Y.
1819
1820if MODULES
1821
1822config MODULE_FORCE_LOAD
1823 bool "Forced module loading"
1824 default n
1825 help
1826 Allow loading of modules without version information (ie. modprobe
1827 --force). Forced module loading sets the 'F' (forced) taint flag and
1828 is usually a really bad idea.
1829
1830config MODULE_UNLOAD
1831 bool "Module unloading"
1832 help
1833 Without this option you will not be able to unload any
1834 modules (note that some modules may not be unloadable
1835 anyway), which makes your kernel smaller, faster
1836 and simpler. If unsure, say Y.
1837
1838config MODULE_FORCE_UNLOAD
1839 bool "Forced module unloading"
1840 depends on MODULE_UNLOAD
1841 help
1842 This option allows you to force a module to unload, even if the
1843 kernel believes it is unsafe: the kernel will remove the module
1844 without waiting for anyone to stop using it (using the -f option to
1845 rmmod). This is mainly for kernel developers and desperate users.
1846 If unsure, say N.
1847
1848config MODVERSIONS
1849 bool "Module versioning support"
1850 help
1851 Usually, you have to use modules compiled with your kernel.
1852 Saying Y here makes it sometimes possible to use modules
1853 compiled for different kernels, by adding enough information
1854 to the modules to (hopefully) spot any changes which would
1855 make them incompatible with the kernel you are running. If
1856 unsure, say N.
1857
1858config MODULE_REL_CRCS
1859 bool
1860 depends on MODVERSIONS
1861
1862config MODULE_SRCVERSION_ALL
1863 bool "Source checksum for all modules"
1864 help
1865 Modules which contain a MODULE_VERSION get an extra "srcversion"
1866 field inserted into their modinfo section, which contains a
1867 sum of the source files which made it. This helps maintainers
1868 see exactly which source was used to build a module (since
1869 others sometimes change the module source without updating
1870 the version). With this option, such a "srcversion" field
1871 will be created for all modules. If unsure, say N.
1872
1873config MODULE_SIG
1874 bool "Module signature verification"
1875 depends on MODULES
1876 select SYSTEM_DATA_VERIFICATION
1877 help
1878 Check modules for valid signatures upon load: the signature
1879 is simply appended to the module. For more information see
1880 <file:Documentation/admin-guide/module-signing.rst>.
1881
1882 Note that this option adds the OpenSSL development packages as a
1883 kernel build dependency so that the signing tool can use its crypto
1884 library.
1885
1886 !!!WARNING!!! If you enable this option, you MUST make sure that the
1887 module DOES NOT get stripped after being signed. This includes the
1888 debuginfo strip done by some packagers (such as rpmbuild) and
1889 inclusion into an initramfs that wants the module size reduced.
1890
1891config MODULE_SIG_FORCE
1892 bool "Require modules to be validly signed"
1893 depends on MODULE_SIG
1894 help
1895 Reject unsigned modules or signed modules for which we don't have a
1896 key. Without this, such modules will simply taint the kernel.
1897
1898config MODULE_SIG_ALL
1899 bool "Automatically sign all modules"
1900 default y
1901 depends on MODULE_SIG
1902 help
1903 Sign all modules during make modules_install. Without this option,
1904 modules must be signed manually, using the scripts/sign-file tool.
1905
1906comment "Do not forget to sign required modules with scripts/sign-file"
1907 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1908
1909choice
1910 prompt "Which hash algorithm should modules be signed with?"
1911 depends on MODULE_SIG
1912 help
1913 This determines which sort of hashing algorithm will be used during
1914 signature generation. This algorithm _must_ be built into the kernel
1915 directly so that signature verification can take place. It is not
1916 possible to load a signed module containing the algorithm to check
1917 the signature on that module.
1918
1919config MODULE_SIG_SHA1
1920 bool "Sign modules with SHA-1"
1921 select CRYPTO_SHA1
1922
1923config MODULE_SIG_SHA224
1924 bool "Sign modules with SHA-224"
1925 select CRYPTO_SHA256
1926
1927config MODULE_SIG_SHA256
1928 bool "Sign modules with SHA-256"
1929 select CRYPTO_SHA256
1930
1931config MODULE_SIG_SHA384
1932 bool "Sign modules with SHA-384"
1933 select CRYPTO_SHA512
1934
1935config MODULE_SIG_SHA512
1936 bool "Sign modules with SHA-512"
1937 select CRYPTO_SHA512
1938
1939endchoice
1940
1941config MODULE_SIG_HASH
1942 string
1943 depends on MODULE_SIG
1944 default "sha1" if MODULE_SIG_SHA1
1945 default "sha224" if MODULE_SIG_SHA224
1946 default "sha256" if MODULE_SIG_SHA256
1947 default "sha384" if MODULE_SIG_SHA384
1948 default "sha512" if MODULE_SIG_SHA512
1949
1950config MODULE_COMPRESS
1951 bool "Compress modules on installation"
1952 depends on MODULES
1953 help
1954
1955 Compresses kernel modules when 'make modules_install' is run; gzip or
1956 xz depending on "Compression algorithm" below.
1957
1958 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
1959
1960 Out-of-tree kernel modules installed using Kbuild will also be
1961 compressed upon installation.
1962
1963 Note: for modules inside an initrd or initramfs, it's more efficient
1964 to compress the whole initrd or initramfs instead.
1965
1966 Note: This is fully compatible with signed modules.
1967
1968 If in doubt, say N.
1969
1970choice
1971 prompt "Compression algorithm"
1972 depends on MODULE_COMPRESS
1973 default MODULE_COMPRESS_GZIP
1974 help
1975 This determines which sort of compression will be used during
1976 'make modules_install'.
1977
1978 GZIP (default) and XZ are supported.
1979
1980config MODULE_COMPRESS_GZIP
1981 bool "GZIP"
1982
1983config MODULE_COMPRESS_XZ
1984 bool "XZ"
1985
1986endchoice
1987
1988config TRIM_UNUSED_KSYMS
1989 bool "Trim unused exported kernel symbols"
1990 depends on MODULES && !UNUSED_SYMBOLS
1991 help
1992 The kernel and some modules make many symbols available for
1993 other modules to use via EXPORT_SYMBOL() and variants. Depending
1994 on the set of modules being selected in your kernel configuration,
1995 many of those exported symbols might never be used.
1996
1997 This option allows for unused exported symbols to be dropped from
1998 the build. In turn, this provides the compiler more opportunities
1999 (especially when using LTO) for optimizing the code and reducing
2000 binary size. This might have some security advantages as well.
2001
2002 If unsure, or if you need to build out-of-tree modules, say N.
2003
2004endif
2005
2006config MODULES_TREE_LOOKUP
2007 def_bool y
2008 depends on PERF_EVENTS || TRACING
2009
2010config INIT_ALL_POSSIBLE
2011 bool
2012 help
2013 Back when each arch used to define their own cpu_online_mask and
2014 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2015 with all 1s, and others with all 0s. When they were centralised,
2016 it was better to provide this option than to break all the archs
2017 and have several arch maintainers pursuing me down dark alleys.
2018
2019source "block/Kconfig"
2020
2021config PREEMPT_NOTIFIERS
2022 bool
2023
2024config PADATA
2025 depends on SMP
2026 bool
2027
2028config ASN1
2029 tristate
2030 help
2031 Build a simple ASN.1 grammar compiler that produces a bytecode output
2032 that can be interpreted by the ASN.1 stream decoder and used to
2033 inform it as to what tags are to be expected in a stream and what
2034 functions to call on what tags.
2035
2036source "kernel/Kconfig.locks"
2037
2038config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2039 bool
2040
2041
2042
2043
2044
2045
2046
2047
2048config ARCH_HAS_SYSCALL_WRAPPER
2049 def_bool n
2050
