7 option env="KERNELVERSION"
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"
28 depends on HAVE_IRQ_WORK
33 bool "Prompt for development and/or incomplete code/drivers"
35 Some of the various things that Linux supports (such as network
36 drivers, file systems, network protocols, etc.) can be in a state
37 of development where the functionality, stability, or the level of
38 testing is not yet high enough for general use. This is usually
39 known as the "alpha-test" phase among developers. If a feature is
40 currently in alpha-test, then the developers usually discourage
41 uninformed widespread use of this feature by the general public to
42 avoid "Why doesn't this work?" type mail messages. However, active
43 testing and use of these systems is welcomed. Just be aware that it
44 may not meet the normal level of reliability or it may fail to work
45 in some special cases. Detailed bug reports from people familiar
46 with the kernel internals are usually welcomed by the developers
47 (before submitting bug reports, please read the documents
48 <file:README>, <file:MAINTAINERS>, <file:REPORTING-BUGS>,
49 <file:Documentation/BUG-HUNTING>, and
50 <file:Documentation/oops-tracing.txt> in the kernel source).
52 This option will also make obsoleted drivers available. These are
53 drivers that have been replaced by something else, and/or are
54 scheduled to be removed in a future kernel release.
56 Unless you intend to help test and develop a feature or driver that
57 falls into this category, or you have a situation that requires
58 using these features, you should probably say N here, which will
59 cause the configurator to present you with fewer choices. If
60 you say Y here, you will be offered the choice of using features or
61 drivers that are currently considered to be in the alpha-test phase.
68 depends on BROKEN || !SMP
71 config INIT_ENV_ARG_LIMIT
76 Maximum of each of the number of arguments and environment
77 variables passed to init from the kernel command line.
81 string "Cross-compiler tool prefix"
83 Same as running 'make CROSS_COMPILE=prefix-' but stored for
84 default make runs in this kernel build directory. You don't
85 need to set this unless you want the configured kernel build
86 directory to select the cross-compiler automatically.
89 string "Local version - append to kernel release"
91 Append an extra string to the end of your kernel version.
92 This will show up when you type uname, for example.
93 The string you set here will be appended after the contents of
94 any files with a filename matching localversion* in your
95 object and source tree, in that order. Your total string can
96 be a maximum of 64 characters.
98 config LOCALVERSION_AUTO
99 bool "Automatically append version information to the version string"
102 This will try to automatically determine if the current tree is a
103 release tree by looking for git tags that belong to the current
104 top of tree revision.
106 A string of the format -gxxxxxxxx will be added to the localversion
107 if a git-based tree is found. The string generated by this will be
108 appended after any matching localversion* files, and after the value
109 set in CONFIG_LOCALVERSION.
111 (The actual string used here is the first eight characters produced
112 by running the command:
114 $ git rev-parse --verify HEAD
116 which is done within the script "scripts/setlocalversion".)
118 config HAVE_KERNEL_GZIP
121 config HAVE_KERNEL_BZIP2
124 config HAVE_KERNEL_LZMA
127 config HAVE_KERNEL_XZ
130 config HAVE_KERNEL_LZO
134 prompt "Kernel compression mode"
136 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO
138 The linux kernel is a kind of self-extracting executable.
139 Several compression algorithms are available, which differ
140 in efficiency, compression and decompression speed.
141 Compression speed is only relevant when building a kernel.
142 Decompression speed is relevant at each boot.
144 If you have any problems with bzip2 or lzma compressed
145 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
146 version of this functionality (bzip2 only), for 2.4, was
147 supplied by Christian Ludwig)
149 High compression options are mostly useful for users, who
150 are low on disk space (embedded systems), but for whom ram
153 If in doubt, select 'gzip'
157 depends on HAVE_KERNEL_GZIP
159 The old and tried gzip compression. It provides a good balance
160 between compression ratio and decompression speed.
164 depends on HAVE_KERNEL_BZIP2
166 Its compression ratio and speed is intermediate.
167 Decompression speed is slowest among the three. The kernel
168 size is about 10% smaller with bzip2, in comparison to gzip.
169 Bzip2 uses a large amount of memory. For modern kernels you
170 will need at least 8MB RAM or more for booting.
174 depends on HAVE_KERNEL_LZMA
176 The most recent compression algorithm.
177 Its ratio is best, decompression speed is between the other
178 two. Compression is slowest. The kernel size is about 33%
179 smaller with LZMA in comparison to gzip.
183 depends on HAVE_KERNEL_XZ
185 XZ uses the LZMA2 algorithm and instruction set specific
186 BCJ filters which can improve compression ratio of executable
187 code. The size of the kernel is about 30% smaller with XZ in
188 comparison to gzip. On architectures for which there is a BCJ
189 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
190 will create a few percent smaller kernel than plain LZMA.
192 The speed is about the same as with LZMA: The decompression
193 speed of XZ is better than that of bzip2 but worse than gzip
194 and LZO. Compression is slow.
198 depends on HAVE_KERNEL_LZO
200 Its compression ratio is the poorest among the 4. The kernel
201 size is about 10% bigger than gzip; however its speed
202 (both compression and decompression) is the fastest.
206 config DEFAULT_HOSTNAME
207 string "Default hostname"
210 This option determines the default system hostname before userspace
211 calls sethostname(2). The kernel traditionally uses "(none)" here,
212 but you may wish to use a different default here to make a minimal
213 system more usable with less configuration.
216 bool "Support for paging of anonymous memory (swap)"
217 depends on MMU && BLOCK
220 This option allows you to choose whether you want to have support
221 for so called swap devices or swap files in your kernel that are
222 used to provide more virtual memory than the actual RAM present
223 in your computer. If unsure say Y.
228 Inter Process Communication is a suite of library functions and
229 system calls which let processes (running programs) synchronize and
230 exchange information. It is generally considered to be a good thing,
231 and some programs won't run unless you say Y here. In particular, if
232 you want to run the DOS emulator dosemu under Linux (read the
233 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
234 you'll need to say Y here.
236 You can find documentation about IPC with "info ipc" and also in
237 section 6.4 of the Linux Programmer's Guide, available from
238 <http://www.tldp.org/guides.html>.
240 config SYSVIPC_SYSCTL
247 bool "POSIX Message Queues"
248 depends on NET && EXPERIMENTAL
250 POSIX variant of message queues is a part of IPC. In POSIX message
251 queues every message has a priority which decides about succession
252 of receiving it by a process. If you want to compile and run
253 programs written e.g. for Solaris with use of its POSIX message
254 queues (functions mq_*) say Y here.
256 POSIX message queues are visible as a filesystem called 'mqueue'
257 and can be mounted somewhere if you want to do filesystem
258 operations on message queues.
262 config POSIX_MQUEUE_SYSCTL
264 depends on POSIX_MQUEUE
268 config BSD_PROCESS_ACCT
269 bool "BSD Process Accounting"
271 If you say Y here, a user level program will be able to instruct the
272 kernel (via a special system call) to write process accounting
273 information to a file: whenever a process exits, information about
274 that process will be appended to the file by the kernel. The
275 information includes things such as creation time, owning user,
276 command name, memory usage, controlling terminal etc. (the complete
277 list is in the struct acct in <file:include/linux/acct.h>). It is
278 up to the user level program to do useful things with this
279 information. This is generally a good idea, so say Y.
281 config BSD_PROCESS_ACCT_V3
282 bool "BSD Process Accounting version 3 file format"
283 depends on BSD_PROCESS_ACCT
286 If you say Y here, the process accounting information is written
287 in a new file format that also logs the process IDs of each
288 process and it's parent. Note that this file format is incompatible
289 with previous v0/v1/v2 file formats, so you will need updated tools
290 for processing it. A preliminary version of these tools is available
291 at <http://www.gnu.org/software/acct/>.
294 bool "open by fhandle syscalls"
297 If you say Y here, a user level program will be able to map
298 file names to handle and then later use the handle for
299 different file system operations. This is useful in implementing
300 userspace file servers, which now track files using handles instead
301 of names. The handle would remain the same even if file names
302 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
306 bool "Export task/process statistics through netlink (EXPERIMENTAL)"
310 Export selected statistics for tasks/processes through the
311 generic netlink interface. Unlike BSD process accounting, the
312 statistics are available during the lifetime of tasks/processes as
313 responses to commands. Like BSD accounting, they are sent to user
318 config TASK_DELAY_ACCT
319 bool "Enable per-task delay accounting (EXPERIMENTAL)"
322 Collect information on time spent by a task waiting for system
323 resources like cpu, synchronous block I/O completion and swapping
324 in pages. Such statistics can help in setting a task's priorities
325 relative to other tasks for cpu, io, rss limits etc.
330 bool "Enable extended accounting over taskstats (EXPERIMENTAL)"
333 Collect extended task accounting data and send the data
334 to userland for processing over the taskstats interface.
338 config TASK_IO_ACCOUNTING
339 bool "Enable per-task storage I/O accounting (EXPERIMENTAL)"
340 depends on TASK_XACCT
342 Collect information on the number of bytes of storage I/O which this
348 bool "Auditing support"
351 Enable auditing infrastructure that can be used with another
352 kernel subsystem, such as SELinux (which requires this for
353 logging of avc messages output). Does not do system-call
354 auditing without CONFIG_AUDITSYSCALL.
357 bool "Enable system-call auditing support"
358 depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH)
359 default y if SECURITY_SELINUX
361 Enable low-overhead system-call auditing infrastructure that
362 can be used independently or with another kernel subsystem,
367 depends on AUDITSYSCALL
372 depends on AUDITSYSCALL
375 config AUDIT_LOGINUID_IMMUTABLE
376 bool "Make audit loginuid immutable"
379 The config option toggles if a task setting it's loginuid requires
380 CAP_SYS_AUDITCONTROL or if that task should require no special permissions
381 but should instead only allow setting its loginuid if it was never
382 previously set. On systems which use systemd or a similar central
383 process to restart login services this should be set to true. On older
384 systems in which an admin would typically have to directly stop and
385 start processes this should be set to false. Setting this to true allows
386 one to drop potentially dangerous capabilites from the login tasks,
387 but may not be backwards compatible with older init systems.
389 source "kernel/irq/Kconfig"
394 prompt "RCU Implementation"
398 bool "Tree-based hierarchical RCU"
399 depends on !PREEMPT && SMP
401 This option selects the RCU implementation that is
402 designed for very large SMP system with hundreds or
403 thousands of CPUs. It also scales down nicely to
406 config TREE_PREEMPT_RCU
407 bool "Preemptible tree-based hierarchical RCU"
408 depends on PREEMPT && SMP
410 This option selects the RCU implementation that is
411 designed for very large SMP systems with hundreds or
412 thousands of CPUs, but for which real-time response
413 is also required. It also scales down nicely to
417 bool "UP-only small-memory-footprint RCU"
418 depends on !PREEMPT && !SMP
420 This option selects the RCU implementation that is
421 designed for UP systems from which real-time response
422 is not required. This option greatly reduces the
423 memory footprint of RCU.
425 config TINY_PREEMPT_RCU
426 bool "Preemptible UP-only small-memory-footprint RCU"
427 depends on PREEMPT && !SMP
429 This option selects the RCU implementation that is designed
430 for real-time UP systems. This option greatly reduces the
431 memory footprint of RCU.
436 def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
438 This option enables preemptible-RCU code that is common between
439 the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
442 bool "Enable tracing for RCU"
444 This option provides tracing in RCU which presents stats
445 in debugfs for debugging RCU implementation.
447 Say Y here if you want to enable RCU tracing
448 Say N if you are unsure.
451 int "Tree-based hierarchical RCU fanout value"
454 depends on TREE_RCU || TREE_PREEMPT_RCU
458 This option controls the fanout of hierarchical implementations
459 of RCU, allowing RCU to work efficiently on machines with
460 large numbers of CPUs. This value must be at least the fourth
461 root of NR_CPUS, which allows NR_CPUS to be insanely large.
462 The default value of RCU_FANOUT should be used for production
463 systems, but if you are stress-testing the RCU implementation
464 itself, small RCU_FANOUT values allow you to test large-system
465 code paths on small(er) systems.
467 Select a specific number if testing RCU itself.
468 Take the default if unsure.
470 config RCU_FANOUT_EXACT
471 bool "Disable tree-based hierarchical RCU auto-balancing"
472 depends on TREE_RCU || TREE_PREEMPT_RCU
475 This option forces use of the exact RCU_FANOUT value specified,
476 regardless of imbalances in the hierarchy. This is useful for
477 testing RCU itself, and might one day be useful on systems with
478 strong NUMA behavior.
480 Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
484 config RCU_FAST_NO_HZ
485 bool "Accelerate last non-dyntick-idle CPU's grace periods"
486 depends on NO_HZ && SMP
489 This option causes RCU to attempt to accelerate grace periods
490 in order to allow CPUs to enter dynticks-idle state more
491 quickly. On the other hand, this option increases the overhead
492 of the dynticks-idle checking, particularly on systems with
493 large numbers of CPUs.
495 Say Y if energy efficiency is critically important, particularly
496 if you have relatively few CPUs.
498 Say N if you are unsure.
500 config TREE_RCU_TRACE
501 def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
504 This option provides tracing for the TREE_RCU and
505 TREE_PREEMPT_RCU implementations, permitting Makefile to
506 trivially select kernel/rcutree_trace.c.
509 bool "Enable RCU priority boosting"
510 depends on RT_MUTEXES && PREEMPT_RCU
513 This option boosts the priority of preempted RCU readers that
514 block the current preemptible RCU grace period for too long.
515 This option also prevents heavy loads from blocking RCU
516 callback invocation for all flavors of RCU.
518 Say Y here if you are working with real-time apps or heavy loads
519 Say N here if you are unsure.
521 config RCU_BOOST_PRIO
522 int "Real-time priority to boost RCU readers to"
527 This option specifies the real-time priority to which preempted
528 RCU readers are to be boosted. If you are working with CPU-bound
529 real-time applications, you should specify a priority higher then
530 the highest-priority CPU-bound application.
532 Specify the real-time priority, or take the default if unsure.
534 config RCU_BOOST_DELAY
535 int "Milliseconds to delay boosting after RCU grace-period start"
540 This option specifies the time to wait after the beginning of
541 a given grace period before priority-boosting preempted RCU
542 readers blocking that grace period. Note that any RCU reader
543 blocking an expedited RCU grace period is boosted immediately.
545 Accept the default if unsure.
547 endmenu # "RCU Subsystem"
550 tristate "Kernel .config support"
552 This option enables the complete Linux kernel ".config" file
553 contents to be saved in the kernel. It provides documentation
554 of which kernel options are used in a running kernel or in an
555 on-disk kernel. This information can be extracted from the kernel
556 image file with the script scripts/extract-ikconfig and used as
557 input to rebuild the current kernel or to build another kernel.
558 It can also be extracted from a running kernel by reading
559 /proc/config.gz if enabled (below).
562 bool "Enable access to .config through /proc/config.gz"
563 depends on IKCONFIG && PROC_FS
565 This option enables access to the kernel configuration file
566 through /proc/config.gz.
569 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
573 Select kernel log buffer size as a power of 2.
583 # Architectures with an unreliable sched_clock() should select this:
585 config HAVE_UNSTABLE_SCHED_CLOCK
589 boolean "Control Group support"
592 This option adds support for grouping sets of processes together, for
593 use with process control subsystems such as Cpusets, CFS, memory
594 controls or device isolation.
596 - Documentation/scheduler/sched-design-CFS.txt (CFS)
597 - Documentation/cgroups/ (features for grouping, isolation
598 and resource control)
605 bool "Example debug cgroup subsystem"
608 This option enables a simple cgroup subsystem that
609 exports useful debugging information about the cgroups
614 config CGROUP_FREEZER
615 bool "Freezer cgroup subsystem"
617 Provides a way to freeze and unfreeze all tasks in a
621 bool "Device controller for cgroups"
623 Provides a cgroup implementing whitelists for devices which
624 a process in the cgroup can mknod or open.
627 bool "Cpuset support"
629 This option will let you create and manage CPUSETs which
630 allow dynamically partitioning a system into sets of CPUs and
631 Memory Nodes and assigning tasks to run only within those sets.
632 This is primarily useful on large SMP or NUMA systems.
636 config PROC_PID_CPUSET
637 bool "Include legacy /proc/<pid>/cpuset file"
641 config CGROUP_CPUACCT
642 bool "Simple CPU accounting cgroup subsystem"
644 Provides a simple Resource Controller for monitoring the
645 total CPU consumed by the tasks in a cgroup.
647 config RESOURCE_COUNTERS
648 bool "Resource counters"
650 This option enables controller independent resource accounting
651 infrastructure that works with cgroups.
653 config CGROUP_MEM_RES_CTLR
654 bool "Memory Resource Controller for Control Groups"
655 depends on RESOURCE_COUNTERS
658 Provides a memory resource controller that manages both anonymous
659 memory and page cache. (See Documentation/cgroups/memory.txt)
661 Note that setting this option increases fixed memory overhead
662 associated with each page of memory in the system. By this,
663 20(40)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
664 usage tracking struct at boot. Total amount of this is printed out
667 Only enable when you're ok with these trade offs and really
668 sure you need the memory resource controller. Even when you enable
669 this, you can set "cgroup_disable=memory" at your boot option to
670 disable memory resource controller and you can avoid overheads.
671 (and lose benefits of memory resource controller)
673 This config option also selects MM_OWNER config option, which
674 could in turn add some fork/exit overhead.
676 config CGROUP_MEM_RES_CTLR_SWAP
677 bool "Memory Resource Controller Swap Extension"
678 depends on CGROUP_MEM_RES_CTLR && SWAP
680 Add swap management feature to memory resource controller. When you
681 enable this, you can limit mem+swap usage per cgroup. In other words,
682 when you disable this, memory resource controller has no cares to
683 usage of swap...a process can exhaust all of the swap. This extension
684 is useful when you want to avoid exhaustion swap but this itself
685 adds more overheads and consumes memory for remembering information.
686 Especially if you use 32bit system or small memory system, please
687 be careful about enabling this. When memory resource controller
688 is disabled by boot option, this will be automatically disabled and
689 there will be no overhead from this. Even when you set this config=y,
690 if boot option "swapaccount=0" is set, swap will not be accounted.
691 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
692 size is 4096bytes, 512k per 1Gbytes of swap.
693 config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
694 bool "Memory Resource Controller Swap Extension enabled by default"
695 depends on CGROUP_MEM_RES_CTLR_SWAP
698 Memory Resource Controller Swap Extension comes with its price in
699 a bigger memory consumption. General purpose distribution kernels
700 which want to enable the feature but keep it disabled by default
701 and let the user enable it by swapaccount boot command line
702 parameter should have this option unselected.
703 For those who want to have the feature enabled by default should
704 select this option (if, for some reason, they need to disable it
705 then swapaccount=0 does the trick).
706 config CGROUP_MEM_RES_CTLR_KMEM
707 bool "Memory Resource Controller Kernel Memory accounting (EXPERIMENTAL)"
708 depends on CGROUP_MEM_RES_CTLR && EXPERIMENTAL
711 The Kernel Memory extension for Memory Resource Controller can limit
712 the amount of memory used by kernel objects in the system. Those are
713 fundamentally different from the entities handled by the standard
714 Memory Controller, which are page-based, and can be swapped. Users of
715 the kmem extension can use it to guarantee that no group of processes
716 will ever exhaust kernel resources alone.
719 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
720 depends on PERF_EVENTS && CGROUPS
722 This option extends the per-cpu mode to restrict monitoring to
723 threads which belong to the cgroup specified and run on the
728 menuconfig CGROUP_SCHED
729 bool "Group CPU scheduler"
730 depends on EXPERIMENTAL
733 This feature lets CPU scheduler recognize task groups and control CPU
734 bandwidth allocation to such task groups. It uses cgroups to group
738 config FAIR_GROUP_SCHED
739 bool "Group scheduling for SCHED_OTHER"
740 depends on CGROUP_SCHED
744 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
745 depends on EXPERIMENTAL
746 depends on FAIR_GROUP_SCHED
749 This option allows users to define CPU bandwidth rates (limits) for
750 tasks running within the fair group scheduler. Groups with no limit
751 set are considered to be unconstrained and will run with no
753 See tip/Documentation/scheduler/sched-bwc.txt for more information.
755 config RT_GROUP_SCHED
756 bool "Group scheduling for SCHED_RR/FIFO"
757 depends on EXPERIMENTAL
758 depends on CGROUP_SCHED
761 This feature lets you explicitly allocate real CPU bandwidth
762 to task groups. If enabled, it will also make it impossible to
763 schedule realtime tasks for non-root users until you allocate
764 realtime bandwidth for them.
765 See Documentation/scheduler/sched-rt-group.txt for more information.
770 tristate "Block IO controller"
774 Generic block IO controller cgroup interface. This is the common
775 cgroup interface which should be used by various IO controlling
778 Currently, CFQ IO scheduler uses it to recognize task groups and
779 control disk bandwidth allocation (proportional time slice allocation)
780 to such task groups. It is also used by bio throttling logic in
781 block layer to implement upper limit in IO rates on a device.
783 This option only enables generic Block IO controller infrastructure.
784 One needs to also enable actual IO controlling logic/policy. For
785 enabling proportional weight division of disk bandwidth in CFQ, set
786 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
787 CONFIG_BLK_DEV_THROTTLING=y.
789 See Documentation/cgroups/blkio-controller.txt for more information.
791 config DEBUG_BLK_CGROUP
792 bool "Enable Block IO controller debugging"
793 depends on BLK_CGROUP
796 Enable some debugging help. Currently it exports additional stat
797 files in a cgroup which can be useful for debugging.
801 menuconfig NAMESPACES
802 bool "Namespaces support" if EXPERT
805 Provides the way to make tasks work with different objects using
806 the same id. For example same IPC id may refer to different objects
807 or same user id or pid may refer to different tasks when used in
808 different namespaces.
816 In this namespace tasks see different info provided with the
821 depends on (SYSVIPC || POSIX_MQUEUE)
824 In this namespace tasks work with IPC ids which correspond to
825 different IPC objects in different namespaces.
828 bool "User namespace (EXPERIMENTAL)"
829 depends on EXPERIMENTAL
832 This allows containers, i.e. vservers, to use user namespaces
833 to provide different user info for different servers.
837 bool "PID Namespaces"
840 Support process id namespaces. This allows having multiple
841 processes with the same pid as long as they are in different
842 pid namespaces. This is a building block of containers.
845 bool "Network namespace"
849 Allow user space to create what appear to be multiple instances
850 of the network stack.
854 config SCHED_AUTOGROUP
855 bool "Automatic process group scheduling"
859 select FAIR_GROUP_SCHED
861 This option optimizes the scheduler for common desktop workloads by
862 automatically creating and populating task groups. This separation
863 of workloads isolates aggressive CPU burners (like build jobs) from
864 desktop applications. Task group autogeneration is currently based
870 config SYSFS_DEPRECATED
871 bool "Enable deprecated sysfs features to support old userspace tools"
875 This option adds code that switches the layout of the "block" class
876 devices, to not show up in /sys/class/block/, but only in
879 This switch is only active when the sysfs.deprecated=1 boot option is
880 passed or the SYSFS_DEPRECATED_V2 option is set.
882 This option allows new kernels to run on old distributions and tools,
883 which might get confused by /sys/class/block/. Since 2007/2008 all
884 major distributions and tools handle this just fine.
886 Recent distributions and userspace tools after 2009/2010 depend on
887 the existence of /sys/class/block/, and will not work with this
890 Only if you are using a new kernel on an old distribution, you might
893 config SYSFS_DEPRECATED_V2
894 bool "Enable deprecated sysfs features by default"
897 depends on SYSFS_DEPRECATED
899 Enable deprecated sysfs by default.
901 See the CONFIG_SYSFS_DEPRECATED option for more details about this
904 Only if you are using a new kernel on an old distribution, you might
905 need to say Y here. Even then, odds are you would not need it
906 enabled, you can always pass the boot option if absolutely necessary.
909 bool "Kernel->user space relay support (formerly relayfs)"
911 This option enables support for relay interface support in
912 certain file systems (such as debugfs).
913 It is designed to provide an efficient mechanism for tools and
914 facilities to relay large amounts of data from kernel space to
919 config BLK_DEV_INITRD
920 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
921 depends on BROKEN || !FRV
923 The initial RAM filesystem is a ramfs which is loaded by the
924 boot loader (loadlin or lilo) and that is mounted as root
925 before the normal boot procedure. It is typically used to
926 load modules needed to mount the "real" root file system,
927 etc. See <file:Documentation/initrd.txt> for details.
929 If RAM disk support (BLK_DEV_RAM) is also included, this
930 also enables initial RAM disk (initrd) support and adds
931 15 Kbytes (more on some other architectures) to the kernel size.
941 config CC_OPTIMIZE_FOR_SIZE
942 bool "Optimize for size"
944 Enabling this option will pass "-Os" instead of "-O2" to gcc
945 resulting in a smaller kernel.
956 bool "Configure standard kernel features (expert users)"
957 # Unhide debug options, to make the on-by-default options visible
960 This option allows certain base kernel options and settings
961 to be disabled or tweaked. This is for specialized
962 environments which can tolerate a "non-standard" kernel.
963 Only use this if you really know what you are doing.
966 bool "Enable 16-bit UID system calls" if EXPERT
967 depends on ARM || BLACKFIN || CRIS || FRV || H8300 || X86_32 || M68K || (S390 && !64BIT) || SUPERH || SPARC32 || (SPARC64 && COMPAT) || UML || (X86_64 && IA32_EMULATION)
970 This enables the legacy 16-bit UID syscall wrappers.
972 config SYSCTL_SYSCALL
973 bool "Sysctl syscall support" if EXPERT
974 depends on PROC_SYSCTL
978 sys_sysctl uses binary paths that have been found challenging
979 to properly maintain and use. The interface in /proc/sys
980 using paths with ascii names is now the primary path to this
983 Almost nothing using the binary sysctl interface so if you are
984 trying to save some space it is probably safe to disable this,
985 making your kernel marginally smaller.
987 If unsure say N here.
990 bool "Load all symbols for debugging/ksymoops" if EXPERT
993 Say Y here to let the kernel print out symbolic crash information and
994 symbolic stack backtraces. This increases the size of the kernel
995 somewhat, as all symbols have to be loaded into the kernel image.
998 bool "Include all symbols in kallsyms"
999 depends on DEBUG_KERNEL && KALLSYMS
1001 Normally kallsyms only contains the symbols of functions for nicer
1002 OOPS messages and backtraces (i.e., symbols from the text and inittext
1003 sections). This is sufficient for most cases. And only in very rare
1004 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1005 names of variables from the data sections, etc).
1007 This option makes sure that all symbols are loaded into the kernel
1008 image (i.e., symbols from all sections) in cost of increased kernel
1009 size (depending on the kernel configuration, it may be 300KiB or
1010 something like this).
1012 Say N unless you really need all symbols.
1015 bool "Support for hot-pluggable devices" if EXPERT
1018 This option is provided for the case where no hotplug or uevent
1019 capabilities is wanted by the kernel. You should only consider
1020 disabling this option for embedded systems that do not use modules, a
1021 dynamic /dev tree, or dynamic device discovery. Just say Y.
1025 bool "Enable support for printk" if EXPERT
1027 This option enables normal printk support. Removing it
1028 eliminates most of the message strings from the kernel image
1029 and makes the kernel more or less silent. As this makes it
1030 very difficult to diagnose system problems, saying N here is
1031 strongly discouraged.
1034 bool "BUG() support" if EXPERT
1037 Disabling this option eliminates support for BUG and WARN, reducing
1038 the size of your kernel image and potentially quietly ignoring
1039 numerous fatal conditions. You should only consider disabling this
1040 option for embedded systems with no facilities for reporting errors.
1045 bool "Enable ELF core dumps" if EXPERT
1047 Enable support for generating core dumps. Disabling saves about 4k.
1050 config PCSPKR_PLATFORM
1051 bool "Enable PC-Speaker support" if EXPERT
1052 depends on HAVE_PCSPKR_PLATFORM
1056 This option allows to disable the internal PC-Speaker
1057 support, saving some memory.
1059 config HAVE_PCSPKR_PLATFORM
1064 bool "Enable full-sized data structures for core" if EXPERT
1066 Disabling this option reduces the size of miscellaneous core
1067 kernel data structures. This saves memory on small machines,
1068 but may reduce performance.
1071 bool "Enable futex support" if EXPERT
1075 Disabling this option will cause the kernel to be built without
1076 support for "fast userspace mutexes". The resulting kernel may not
1077 run glibc-based applications correctly.
1080 bool "Enable eventpoll support" if EXPERT
1084 Disabling this option will cause the kernel to be built without
1085 support for epoll family of system calls.
1088 bool "Enable signalfd() system call" if EXPERT
1092 Enable the signalfd() system call that allows to receive signals
1093 on a file descriptor.
1098 bool "Enable timerfd() system call" if EXPERT
1102 Enable the timerfd() system call that allows to receive timer
1103 events on a file descriptor.
1108 bool "Enable eventfd() system call" if EXPERT
1112 Enable the eventfd() system call that allows to receive both
1113 kernel notification (ie. KAIO) or userspace notifications.
1118 bool "Use full shmem filesystem" if EXPERT
1122 The shmem is an internal filesystem used to manage shared memory.
1123 It is backed by swap and manages resource limits. It is also exported
1124 to userspace as tmpfs if TMPFS is enabled. Disabling this
1125 option replaces shmem and tmpfs with the much simpler ramfs code,
1126 which may be appropriate on small systems without swap.
1129 bool "Enable AIO support" if EXPERT
1132 This option enables POSIX asynchronous I/O which may by used
1133 by some high performance threaded applications. Disabling
1134 this option saves about 7k.
1137 bool "Embedded system"
1140 This option should be enabled if compiling the kernel for
1141 an embedded system so certain expert options are available
1144 config HAVE_PERF_EVENTS
1147 See tools/perf/design.txt for details.
1149 config PERF_USE_VMALLOC
1152 See tools/perf/design.txt for details
1154 menu "Kernel Performance Events And Counters"
1157 bool "Kernel performance events and counters"
1158 default y if (PROFILING || PERF_COUNTERS)
1159 depends on HAVE_PERF_EVENTS
1163 Enable kernel support for various performance events provided
1164 by software and hardware.
1166 Software events are supported either built-in or via the
1167 use of generic tracepoints.
1169 Most modern CPUs support performance events via performance
1170 counter registers. These registers count the number of certain
1171 types of hw events: such as instructions executed, cachemisses
1172 suffered, or branches mis-predicted - without slowing down the
1173 kernel or applications. These registers can also trigger interrupts
1174 when a threshold number of events have passed - and can thus be
1175 used to profile the code that runs on that CPU.
1177 The Linux Performance Event subsystem provides an abstraction of
1178 these software and hardware event capabilities, available via a
1179 system call and used by the "perf" utility in tools/perf/. It
1180 provides per task and per CPU counters, and it provides event
1181 capabilities on top of those.
1185 config PERF_COUNTERS
1186 bool "Kernel performance counters (old config option)"
1187 depends on HAVE_PERF_EVENTS
1189 This config has been obsoleted by the PERF_EVENTS
1190 config option - please see that one for details.
1192 It has no effect on the kernel whether you enable
1193 it or not, it is a compatibility placeholder.
1197 config DEBUG_PERF_USE_VMALLOC
1199 bool "Debug: use vmalloc to back perf mmap() buffers"
1200 depends on PERF_EVENTS && DEBUG_KERNEL
1201 select PERF_USE_VMALLOC
1203 Use vmalloc memory to back perf mmap() buffers.
1205 Mostly useful for debugging the vmalloc code on platforms
1206 that don't require it.
1212 config VM_EVENT_COUNTERS
1214 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1216 VM event counters are needed for event counts to be shown.
1217 This option allows the disabling of the VM event counters
1218 on EXPERT systems. /proc/vmstat will only show page counts
1219 if VM event counters are disabled.
1223 bool "Enable PCI quirk workarounds" if EXPERT
1226 This enables workarounds for various PCI chipset
1227 bugs/quirks. Disable this only if your target machine is
1228 unaffected by PCI quirks.
1232 bool "Enable SLUB debugging support" if EXPERT
1233 depends on SLUB && SYSFS
1235 SLUB has extensive debug support features. Disabling these can
1236 result in significant savings in code size. This also disables
1237 SLUB sysfs support. /sys/slab will not exist and there will be
1238 no support for cache validation etc.
1241 bool "Disable heap randomization"
1244 Randomizing heap placement makes heap exploits harder, but it
1245 also breaks ancient binaries (including anything libc5 based).
1246 This option changes the bootup default to heap randomization
1247 disabled, and can be overridden at runtime by setting
1248 /proc/sys/kernel/randomize_va_space to 2.
1250 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1253 prompt "Choose SLAB allocator"
1256 This option allows to select a slab allocator.
1261 The regular slab allocator that is established and known to work
1262 well in all environments. It organizes cache hot objects in
1263 per cpu and per node queues.
1266 bool "SLUB (Unqueued Allocator)"
1268 SLUB is a slab allocator that minimizes cache line usage
1269 instead of managing queues of cached objects (SLAB approach).
1270 Per cpu caching is realized using slabs of objects instead
1271 of queues of objects. SLUB can use memory efficiently
1272 and has enhanced diagnostics. SLUB is the default choice for
1277 bool "SLOB (Simple Allocator)"
1279 SLOB replaces the stock allocator with a drastically simpler
1280 allocator. SLOB is generally more space efficient but
1281 does not perform as well on large systems.
1285 config MMAP_ALLOW_UNINITIALIZED
1286 bool "Allow mmapped anonymous memory to be uninitialized"
1287 depends on EXPERT && !MMU
1290 Normally, and according to the Linux spec, anonymous memory obtained
1291 from mmap() has it's contents cleared before it is passed to
1292 userspace. Enabling this config option allows you to request that
1293 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1294 providing a huge performance boost. If this option is not enabled,
1295 then the flag will be ignored.
1297 This is taken advantage of by uClibc's malloc(), and also by
1298 ELF-FDPIC binfmt's brk and stack allocator.
1300 Because of the obvious security issues, this option should only be
1301 enabled on embedded devices where you control what is run in
1302 userspace. Since that isn't generally a problem on no-MMU systems,
1303 it is normally safe to say Y here.
1305 See Documentation/nommu-mmap.txt for more information.
1308 bool "Profiling support"
1310 Say Y here to enable the extended profiling support mechanisms used
1311 by profilers such as OProfile.
1314 # Place an empty function call at each tracepoint site. Can be
1315 # dynamically changed for a probe function.
1320 source "arch/Kconfig"
1322 endmenu # General setup
1324 config HAVE_GENERIC_DMA_COHERENT
1331 depends on SLAB || SLUB_DEBUG
1339 default 0 if BASE_FULL
1340 default 1 if !BASE_FULL
1343 bool "Enable loadable module support"
1345 Kernel modules are small pieces of compiled code which can
1346 be inserted in the running kernel, rather than being
1347 permanently built into the kernel. You use the "modprobe"
1348 tool to add (and sometimes remove) them. If you say Y here,
1349 many parts of the kernel can be built as modules (by
1350 answering M instead of Y where indicated): this is most
1351 useful for infrequently used options which are not required
1352 for booting. For more information, see the man pages for
1353 modprobe, lsmod, modinfo, insmod and rmmod.
1355 If you say Y here, you will need to run "make
1356 modules_install" to put the modules under /lib/modules/
1357 where modprobe can find them (you may need to be root to do
1364 config MODULE_FORCE_LOAD
1365 bool "Forced module loading"
1368 Allow loading of modules without version information (ie. modprobe
1369 --force). Forced module loading sets the 'F' (forced) taint flag and
1370 is usually a really bad idea.
1372 config MODULE_UNLOAD
1373 bool "Module unloading"
1375 Without this option you will not be able to unload any
1376 modules (note that some modules may not be unloadable
1377 anyway), which makes your kernel smaller, faster
1378 and simpler. If unsure, say Y.
1380 config MODULE_FORCE_UNLOAD
1381 bool "Forced module unloading"
1382 depends on MODULE_UNLOAD && EXPERIMENTAL
1384 This option allows you to force a module to unload, even if the
1385 kernel believes it is unsafe: the kernel will remove the module
1386 without waiting for anyone to stop using it (using the -f option to
1387 rmmod). This is mainly for kernel developers and desperate users.
1391 bool "Module versioning support"
1393 Usually, you have to use modules compiled with your kernel.
1394 Saying Y here makes it sometimes possible to use modules
1395 compiled for different kernels, by adding enough information
1396 to the modules to (hopefully) spot any changes which would
1397 make them incompatible with the kernel you are running. If
1400 config MODULE_SRCVERSION_ALL
1401 bool "Source checksum for all modules"
1403 Modules which contain a MODULE_VERSION get an extra "srcversion"
1404 field inserted into their modinfo section, which contains a
1405 sum of the source files which made it. This helps maintainers
1406 see exactly which source was used to build a module (since
1407 others sometimes change the module source without updating
1408 the version). With this option, such a "srcversion" field
1409 will be created for all modules. If unsure, say N.
1413 config INIT_ALL_POSSIBLE
1416 Back when each arch used to define their own cpu_online_map and
1417 cpu_possible_map, some of them chose to initialize cpu_possible_map
1418 with all 1s, and others with all 0s. When they were centralised,
1419 it was better to provide this option than to break all the archs
1420 and have several arch maintainers pursuing me down dark alleys.
1425 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1427 Need stop_machine() primitive.
1429 source "block/Kconfig"
1431 config PREEMPT_NOTIFIERS
1438 source "kernel/Kconfig.locks"