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0001 config ARCH
0002         string
0003         option env="ARCH"
0006         string
0007         option env="KERNELVERSION"
0009 config DEFCONFIG_LIST
0010         string
0011         depends on !UML
0012         option defconfig_list
0013         default "/lib/modules/$UNAME_RELEASE/.config"
0014         default "/etc/kernel-config"
0015         default "/boot/config-$UNAME_RELEASE"
0016         default "$ARCH_DEFCONFIG"
0017         default "arch/$ARCH/defconfig"
0019 config CONSTRUCTORS
0020         bool
0021         depends on !UML
0023 config IRQ_WORK
0024         bool
0027         bool
0030         bool
0031         help
0032           Select this to move thread_info off the stack into task_struct.  To
0033           make this work, an arch will need to remove all thread_info fields
0034           except flags and fix any runtime bugs.
0036           One subtle change that will be needed is to use try_get_task_stack()
0037           and put_task_stack() in save_thread_stack_tsk() and get_wchan().
0039 menu "General setup"
0041 config BROKEN
0042         bool
0044 config BROKEN_ON_SMP
0045         bool
0046         depends on BROKEN || !SMP
0047         default y
0049 config INIT_ENV_ARG_LIMIT
0050         int
0051         default 32 if !UML
0052         default 128 if UML
0053         help
0054           Maximum of each of the number of arguments and environment
0055           variables passed to init from the kernel command line.
0058 config CROSS_COMPILE
0059         string "Cross-compiler tool prefix"
0060         help
0061           Same as running 'make CROSS_COMPILE=prefix-' but stored for
0062           default make runs in this kernel build directory.  You don't
0063           need to set this unless you want the configured kernel build
0064           directory to select the cross-compiler automatically.
0066 config COMPILE_TEST
0067         bool "Compile also drivers which will not load"
0068         depends on !UML
0069         default n
0070         help
0071           Some drivers can be compiled on a different platform than they are
0072           intended to be run on. Despite they cannot be loaded there (or even
0073           when they load they cannot be used due to missing HW support),
0074           developers still, opposing to distributors, might want to build such
0075           drivers to compile-test them.
0077           If you are a developer and want to build everything available, say Y
0078           here. If you are a user/distributor, say N here to exclude useless
0079           drivers to be distributed.
0081 config LOCALVERSION
0082         string "Local version - append to kernel release"
0083         help
0084           Append an extra string to the end of your kernel version.
0085           This will show up when you type uname, for example.
0086           The string you set here will be appended after the contents of
0087           any files with a filename matching localversion* in your
0088           object and source tree, in that order.  Your total string can
0089           be a maximum of 64 characters.
0092         bool "Automatically append version information to the version string"
0093         default y
0094         depends on !COMPILE_TEST
0095         help
0096           This will try to automatically determine if the current tree is a
0097           release tree by looking for git tags that belong to the current
0098           top of tree revision.
0100           A string of the format -gxxxxxxxx will be added to the localversion
0101           if a git-based tree is found.  The string generated by this will be
0102           appended after any matching localversion* files, and after the value
0103           set in CONFIG_LOCALVERSION.
0105           (The actual string used here is the first eight characters produced
0106           by running the command:
0108             $ git rev-parse --verify HEAD
0110           which is done within the script "scripts/setlocalversion".)
0112 config HAVE_KERNEL_GZIP
0113         bool
0115 config HAVE_KERNEL_BZIP2
0116         bool
0118 config HAVE_KERNEL_LZMA
0119         bool
0121 config HAVE_KERNEL_XZ
0122         bool
0124 config HAVE_KERNEL_LZO
0125         bool
0127 config HAVE_KERNEL_LZ4
0128         bool
0130 choice
0131         prompt "Kernel compression mode"
0132         default KERNEL_GZIP
0134         help
0135           The linux kernel is a kind of self-extracting executable.
0136           Several compression algorithms are available, which differ
0137           in efficiency, compression and decompression speed.
0138           Compression speed is only relevant when building a kernel.
0139           Decompression speed is relevant at each boot.
0141           If you have any problems with bzip2 or lzma compressed
0142           kernels, mail me (Alain Knaff) <>. (An older
0143           version of this functionality (bzip2 only), for 2.4, was
0144           supplied by Christian Ludwig)
0146           High compression options are mostly useful for users, who
0147           are low on disk space (embedded systems), but for whom ram
0148           size matters less.
0150           If in doubt, select 'gzip'
0152 config KERNEL_GZIP
0153         bool "Gzip"
0154         depends on HAVE_KERNEL_GZIP
0155         help
0156           The old and tried gzip compression. It provides a good balance
0157           between compression ratio and decompression speed.
0159 config KERNEL_BZIP2
0160         bool "Bzip2"
0161         depends on HAVE_KERNEL_BZIP2
0162         help
0163           Its compression ratio and speed is intermediate.
0164           Decompression speed is slowest among the choices.  The kernel
0165           size is about 10% smaller with bzip2, in comparison to gzip.
0166           Bzip2 uses a large amount of memory. For modern kernels you
0167           will need at least 8MB RAM or more for booting.
0169 config KERNEL_LZMA
0170         bool "LZMA"
0171         depends on HAVE_KERNEL_LZMA
0172         help
0173           This compression algorithm's ratio is best.  Decompression speed
0174           is between gzip and bzip2.  Compression is slowest.
0175           The kernel size is about 33% smaller with LZMA in comparison to gzip.
0177 config KERNEL_XZ
0178         bool "XZ"
0179         depends on HAVE_KERNEL_XZ
0180         help
0181           XZ uses the LZMA2 algorithm and instruction set specific
0182           BCJ filters which can improve compression ratio of executable
0183           code. The size of the kernel is about 30% smaller with XZ in
0184           comparison to gzip. On architectures for which there is a BCJ
0185           filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
0186           will create a few percent smaller kernel than plain LZMA.
0188           The speed is about the same as with LZMA: The decompression
0189           speed of XZ is better than that of bzip2 but worse than gzip
0190           and LZO. Compression is slow.
0192 config KERNEL_LZO
0193         bool "LZO"
0194         depends on HAVE_KERNEL_LZO
0195         help
0196           Its compression ratio is the poorest among the choices. The kernel
0197           size is about 10% bigger than gzip; however its speed
0198           (both compression and decompression) is the fastest.
0200 config KERNEL_LZ4
0201         bool "LZ4"
0202         depends on HAVE_KERNEL_LZ4
0203         help
0204           LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
0205           A preliminary version of LZ4 de/compression tool is available at
0206           <>.
0208           Its compression ratio is worse than LZO. The size of the kernel
0209           is about 8% bigger than LZO. But the decompression speed is
0210           faster than LZO.
0212 endchoice
0215         string "Default hostname"
0216         default "(none)"
0217         help
0218           This option determines the default system hostname before userspace
0219           calls sethostname(2). The kernel traditionally uses "(none)" here,
0220           but you may wish to use a different default here to make a minimal
0221           system more usable with less configuration.
0223 config SWAP
0224         bool "Support for paging of anonymous memory (swap)"
0225         depends on MMU && BLOCK
0226         default y
0227         help
0228           This option allows you to choose whether you want to have support
0229           for so called swap devices or swap files in your kernel that are
0230           used to provide more virtual memory than the actual RAM present
0231           in your computer.  If unsure say Y.
0233 config SYSVIPC
0234         bool "System V IPC"
0235         ---help---
0236           Inter Process Communication is a suite of library functions and
0237           system calls which let processes (running programs) synchronize and
0238           exchange information. It is generally considered to be a good thing,
0239           and some programs won't run unless you say Y here. In particular, if
0240           you want to run the DOS emulator dosemu under Linux (read the
0241           DOSEMU-HOWTO, available from <>),
0242           you'll need to say Y here.
0244           You can find documentation about IPC with "info ipc" and also in
0245           section 6.4 of the Linux Programmer's Guide, available from
0246           <>.
0248 config SYSVIPC_SYSCTL
0249         bool
0250         depends on SYSVIPC
0251         depends on SYSCTL
0252         default y
0254 config POSIX_MQUEUE
0255         bool "POSIX Message Queues"
0256         depends on NET
0257         ---help---
0258           POSIX variant of message queues is a part of IPC. In POSIX message
0259           queues every message has a priority which decides about succession
0260           of receiving it by a process. If you want to compile and run
0261           programs written e.g. for Solaris with use of its POSIX message
0262           queues (functions mq_*) say Y here.
0264           POSIX message queues are visible as a filesystem called 'mqueue'
0265           and can be mounted somewhere if you want to do filesystem
0266           operations on message queues.
0268           If unsure, say Y.
0271         bool
0272         depends on POSIX_MQUEUE
0273         depends on SYSCTL
0274         default y
0277         bool "Enable process_vm_readv/writev syscalls"
0278         depends on MMU
0279         default y
0280         help
0281           Enabling this option adds the system calls process_vm_readv and
0282           process_vm_writev which allow a process with the correct privileges
0283           to directly read from or write to another process' address space.
0284           See the man page for more details.
0286 config FHANDLE
0287         bool "open by fhandle syscalls" if EXPERT
0288         select EXPORTFS
0289         default y
0290         help
0291           If you say Y here, a user level program will be able to map
0292           file names to handle and then later use the handle for
0293           different file system operations. This is useful in implementing
0294           userspace file servers, which now track files using handles instead
0295           of names. The handle would remain the same even if file names
0296           get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
0297           syscalls.
0299 config USELIB
0300         bool "uselib syscall"
0301         def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
0302         help
0303           This option enables the uselib syscall, a system call used in the
0304           dynamic linker from libc5 and earlier.  glibc does not use this
0305           system call.  If you intend to run programs built on libc5 or
0306           earlier, you may need to enable this syscall.  Current systems
0307           running glibc can safely disable this.
0309 config AUDIT
0310         bool "Auditing support"
0311         depends on NET
0312         help
0313           Enable auditing infrastructure that can be used with another
0314           kernel subsystem, such as SELinux (which requires this for
0315           logging of avc messages output).  System call auditing is included
0316           on architectures which support it.
0319         bool
0321 config AUDITSYSCALL
0322         def_bool y
0323         depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
0325 config AUDIT_WATCH
0326         def_bool y
0327         depends on AUDITSYSCALL
0328         select FSNOTIFY
0330 config AUDIT_TREE
0331         def_bool y
0332         depends on AUDITSYSCALL
0333         select FSNOTIFY
0335 source "kernel/irq/Kconfig"
0336 source "kernel/time/Kconfig"
0338 menu "CPU/Task time and stats accounting"
0341         bool
0343 choice
0344         prompt "Cputime accounting"
0345         default TICK_CPU_ACCOUNTING if !PPC64
0346         default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
0348 # Kind of a stub config for the pure tick based cputime accounting
0350         bool "Simple tick based cputime accounting"
0351         depends on !S390 && !NO_HZ_FULL
0352         help
0353           This is the basic tick based cputime accounting that maintains
0354           statistics about user, system and idle time spent on per jiffies
0355           granularity.
0357           If unsure, say Y.
0360         bool "Deterministic task and CPU time accounting"
0361         depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
0362         select VIRT_CPU_ACCOUNTING
0363         help
0364           Select this option to enable more accurate task and CPU time
0365           accounting.  This is done by reading a CPU counter on each
0366           kernel entry and exit and on transitions within the kernel
0367           between system, softirq and hardirq state, so there is a
0368           small performance impact.  In the case of s390 or IBM POWER > 5,
0369           this also enables accounting of stolen time on logically-partitioned
0370           systems.
0373         bool "Full dynticks CPU time accounting"
0374         depends on HAVE_CONTEXT_TRACKING
0375         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
0376         select VIRT_CPU_ACCOUNTING
0377         select CONTEXT_TRACKING
0378         help
0379           Select this option to enable task and CPU time accounting on full
0380           dynticks systems. This accounting is implemented by watching every
0381           kernel-user boundaries using the context tracking subsystem.
0382           The accounting is thus performed at the expense of some significant
0383           overhead.
0385           For now this is only useful if you are working on the full
0386           dynticks subsystem development.
0388           If unsure, say N.
0390 endchoice
0393         bool "Fine granularity task level IRQ time accounting"
0395         help
0396           Select this option to enable fine granularity task irq time
0397           accounting. This is done by reading a timestamp on each
0398           transitions between softirq and hardirq state, so there can be a
0399           small performance impact.
0401           If in doubt, say N here.
0403 config BSD_PROCESS_ACCT
0404         bool "BSD Process Accounting"
0405         depends on MULTIUSER
0406         help
0407           If you say Y here, a user level program will be able to instruct the
0408           kernel (via a special system call) to write process accounting
0409           information to a file: whenever a process exits, information about
0410           that process will be appended to the file by the kernel.  The
0411           information includes things such as creation time, owning user,
0412           command name, memory usage, controlling terminal etc. (the complete
0413           list is in the struct acct in <file:include/linux/acct.h>).  It is
0414           up to the user level program to do useful things with this
0415           information.  This is generally a good idea, so say Y.
0417 config BSD_PROCESS_ACCT_V3
0418         bool "BSD Process Accounting version 3 file format"
0419         depends on BSD_PROCESS_ACCT
0420         default n
0421         help
0422           If you say Y here, the process accounting information is written
0423           in a new file format that also logs the process IDs of each
0424           process and it's parent. Note that this file format is incompatible
0425           with previous v0/v1/v2 file formats, so you will need updated tools
0426           for processing it. A preliminary version of these tools is available
0427           at <>.
0429 config TASKSTATS
0430         bool "Export task/process statistics through netlink"
0431         depends on NET
0432         depends on MULTIUSER
0433         default n
0434         help
0435           Export selected statistics for tasks/processes through the
0436           generic netlink interface. Unlike BSD process accounting, the
0437           statistics are available during the lifetime of tasks/processes as
0438           responses to commands. Like BSD accounting, they are sent to user
0439           space on task exit.
0441           Say N if unsure.
0443 config TASK_DELAY_ACCT
0444         bool "Enable per-task delay accounting"
0445         depends on TASKSTATS
0446         select SCHED_INFO
0447         help
0448           Collect information on time spent by a task waiting for system
0449           resources like cpu, synchronous block I/O completion and swapping
0450           in pages. Such statistics can help in setting a task's priorities
0451           relative to other tasks for cpu, io, rss limits etc.
0453           Say N if unsure.
0455 config TASK_XACCT
0456         bool "Enable extended accounting over taskstats"
0457         depends on TASKSTATS
0458         help
0459           Collect extended task accounting data and send the data
0460           to userland for processing over the taskstats interface.
0462           Say N if unsure.
0465         bool "Enable per-task storage I/O accounting"
0466         depends on TASK_XACCT
0467         help
0468           Collect information on the number of bytes of storage I/O which this
0469           task has caused.
0471           Say N if unsure.
0473 endmenu # "CPU/Task time and stats accounting"
0475 menu "RCU Subsystem"
0477 config TREE_RCU
0478         bool
0479         default y if !PREEMPT && SMP
0480         help
0481           This option selects the RCU implementation that is
0482           designed for very large SMP system with hundreds or
0483           thousands of CPUs.  It also scales down nicely to
0484           smaller systems.
0486 config PREEMPT_RCU
0487         bool
0488         default y if PREEMPT
0489         help
0490           This option selects the RCU implementation that is
0491           designed for very large SMP systems with hundreds or
0492           thousands of CPUs, but for which real-time response
0493           is also required.  It also scales down nicely to
0494           smaller systems.
0496           Select this option if you are unsure.
0498 config TINY_RCU
0499         bool
0500         default y if !PREEMPT && !SMP
0501         help
0502           This option selects the RCU implementation that is
0503           designed for UP systems from which real-time response
0504           is not required.  This option greatly reduces the
0505           memory footprint of RCU.
0507 config RCU_EXPERT
0508         bool "Make expert-level adjustments to RCU configuration"
0509         default n
0510         help
0511           This option needs to be enabled if you wish to make
0512           expert-level adjustments to RCU configuration.  By default,
0513           no such adjustments can be made, which has the often-beneficial
0514           side-effect of preventing "make oldconfig" from asking you all
0515           sorts of detailed questions about how you would like numerous
0516           obscure RCU options to be set up.
0518           Say Y if you need to make expert-level adjustments to RCU.
0520           Say N if you are unsure.
0522 config SRCU
0523         bool
0524         help
0525           This option selects the sleepable version of RCU. This version
0526           permits arbitrary sleeping or blocking within RCU read-side critical
0527           sections.
0529 config TASKS_RCU
0530         bool
0531         default n
0532         depends on !UML
0533         select SRCU
0534         help
0535           This option enables a task-based RCU implementation that uses
0536           only voluntary context switch (not preemption!), idle, and
0537           user-mode execution as quiescent states.
0539 config RCU_STALL_COMMON
0540         def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
0541         help
0542           This option enables RCU CPU stall code that is common between
0543           the TINY and TREE variants of RCU.  The purpose is to allow
0544           the tiny variants to disable RCU CPU stall warnings, while
0545           making these warnings mandatory for the tree variants.
0548        bool
0551         bool "Force context tracking"
0552         depends on CONTEXT_TRACKING
0553         default y if !NO_HZ_FULL
0554         help
0555           The major pre-requirement for full dynticks to work is to
0556           support the context tracking subsystem. But there are also
0557           other dependencies to provide in order to make the full
0558           dynticks working.
0560           This option stands for testing when an arch implements the
0561           context tracking backend but doesn't yet fullfill all the
0562           requirements to make the full dynticks feature working.
0563           Without the full dynticks, there is no way to test the support
0564           for context tracking and the subsystems that rely on it: RCU
0565           userspace extended quiescent state and tickless cputime
0566           accounting. This option copes with the absence of the full
0567           dynticks subsystem by forcing the context tracking on all
0568           CPUs in the system.
0570           Say Y only if you're working on the development of an
0571           architecture backend for the context tracking.
0573           Say N otherwise, this option brings an overhead that you
0574           don't want in production.
0577 config RCU_FANOUT
0578         int "Tree-based hierarchical RCU fanout value"
0579         range 2 64 if 64BIT
0580         range 2 32 if !64BIT
0581         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
0582         default 64 if 64BIT
0583         default 32 if !64BIT
0584         help
0585           This option controls the fanout of hierarchical implementations
0586           of RCU, allowing RCU to work efficiently on machines with
0587           large numbers of CPUs.  This value must be at least the fourth
0588           root of NR_CPUS, which allows NR_CPUS to be insanely large.
0589           The default value of RCU_FANOUT should be used for production
0590           systems, but if you are stress-testing the RCU implementation
0591           itself, small RCU_FANOUT values allow you to test large-system
0592           code paths on small(er) systems.
0594           Select a specific number if testing RCU itself.
0595           Take the default if unsure.
0597 config RCU_FANOUT_LEAF
0598         int "Tree-based hierarchical RCU leaf-level fanout value"
0599         range 2 64 if 64BIT
0600         range 2 32 if !64BIT
0601         depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
0602         default 16
0603         help
0604           This option controls the leaf-level fanout of hierarchical
0605           implementations of RCU, and allows trading off cache misses
0606           against lock contention.  Systems that synchronize their
0607           scheduling-clock interrupts for energy-efficiency reasons will
0608           want the default because the smaller leaf-level fanout keeps
0609           lock contention levels acceptably low.  Very large systems
0610           (hundreds or thousands of CPUs) will instead want to set this
0611           value to the maximum value possible in order to reduce the
0612           number of cache misses incurred during RCU's grace-period
0613           initialization.  These systems tend to run CPU-bound, and thus
0614           are not helped by synchronized interrupts, and thus tend to
0615           skew them, which reduces lock contention enough that large
0616           leaf-level fanouts work well.
0618           Select a specific number if testing RCU itself.
0620           Select the maximum permissible value for large systems.
0622           Take the default if unsure.
0624 config RCU_FAST_NO_HZ
0625         bool "Accelerate last non-dyntick-idle CPU's grace periods"
0626         depends on NO_HZ_COMMON && SMP && RCU_EXPERT
0627         default n
0628         help
0629           This option permits CPUs to enter dynticks-idle state even if
0630           they have RCU callbacks queued, and prevents RCU from waking
0631           these CPUs up more than roughly once every four jiffies (by
0632           default, you can adjust this using the rcutree.rcu_idle_gp_delay
0633           parameter), thus improving energy efficiency.  On the other
0634           hand, this option increases the duration of RCU grace periods,
0635           for example, slowing down synchronize_rcu().
0637           Say Y if energy efficiency is critically important, and you
0638                 don't care about increased grace-period durations.
0640           Say N if you are unsure.
0642 config TREE_RCU_TRACE
0643         def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
0644         select DEBUG_FS
0645         help
0646           This option provides tracing for the TREE_RCU and
0647           PREEMPT_RCU implementations, permitting Makefile to
0648           trivially select kernel/rcutree_trace.c.
0650 config RCU_BOOST
0651         bool "Enable RCU priority boosting"
0652         depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
0653         default n
0654         help
0655           This option boosts the priority of preempted RCU readers that
0656           block the current preemptible RCU grace period for too long.
0657           This option also prevents heavy loads from blocking RCU
0658           callback invocation for all flavors of RCU.
0660           Say Y here if you are working with real-time apps or heavy loads
0661           Say N here if you are unsure.
0663 config RCU_KTHREAD_PRIO
0664         int "Real-time priority to use for RCU worker threads"
0665         range 1 99 if RCU_BOOST
0666         range 0 99 if !RCU_BOOST
0667         default 1 if RCU_BOOST
0668         default 0 if !RCU_BOOST
0669         depends on RCU_EXPERT
0670         help
0671           This option specifies the SCHED_FIFO priority value that will be
0672           assigned to the rcuc/n and rcub/n threads and is also the value
0673           used for RCU_BOOST (if enabled). If you are working with a
0674           real-time application that has one or more CPU-bound threads
0675           running at a real-time priority level, you should set
0676           RCU_KTHREAD_PRIO to a priority higher than the highest-priority
0677           real-time CPU-bound application thread.  The default RCU_KTHREAD_PRIO
0678           value of 1 is appropriate in the common case, which is real-time
0679           applications that do not have any CPU-bound threads.
0681           Some real-time applications might not have a single real-time
0682           thread that saturates a given CPU, but instead might have
0683           multiple real-time threads that, taken together, fully utilize
0684           that CPU.  In this case, you should set RCU_KTHREAD_PRIO to
0685           a priority higher than the lowest-priority thread that is
0686           conspiring to prevent the CPU from running any non-real-time
0687           tasks.  For example, if one thread at priority 10 and another
0688           thread at priority 5 are between themselves fully consuming
0689           the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
0690           set to priority 6 or higher.
0692           Specify the real-time priority, or take the default if unsure.
0694 config RCU_BOOST_DELAY
0695         int "Milliseconds to delay boosting after RCU grace-period start"
0696         range 0 3000
0697         depends on RCU_BOOST
0698         default 500
0699         help
0700           This option specifies the time to wait after the beginning of
0701           a given grace period before priority-boosting preempted RCU
0702           readers blocking that grace period.  Note that any RCU reader
0703           blocking an expedited RCU grace period is boosted immediately.
0705           Accept the default if unsure.
0707 config RCU_NOCB_CPU
0708         bool "Offload RCU callback processing from boot-selected CPUs"
0709         depends on TREE_RCU || PREEMPT_RCU
0710         depends on RCU_EXPERT || NO_HZ_FULL
0711         default n
0712         help
0713           Use this option to reduce OS jitter for aggressive HPC or
0714           real-time workloads.  It can also be used to offload RCU
0715           callback invocation to energy-efficient CPUs in battery-powered
0716           asymmetric multiprocessors.
0718           This option offloads callback invocation from the set of
0719           CPUs specified at boot time by the rcu_nocbs parameter.
0720           For each such CPU, a kthread ("rcuox/N") will be created to
0721           invoke callbacks, where the "N" is the CPU being offloaded,
0722           and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
0723           "s" for RCU-sched.  Nothing prevents this kthread from running
0724           on the specified CPUs, but (1) the kthreads may be preempted
0725           between each callback, and (2) affinity or cgroups can be used
0726           to force the kthreads to run on whatever set of CPUs is desired.
0728           Say Y here if you want to help to debug reduced OS jitter.
0729           Say N here if you are unsure.
0731 choice
0732         prompt "Build-forced no-CBs CPUs"
0733         default RCU_NOCB_CPU_NONE
0734         depends on RCU_NOCB_CPU
0735         help
0736           This option allows no-CBs CPUs (whose RCU callbacks are invoked
0737           from kthreads rather than from softirq context) to be specified
0738           at build time.  Additional no-CBs CPUs may be specified by
0739           the rcu_nocbs= boot parameter.
0741 config RCU_NOCB_CPU_NONE
0742         bool "No build_forced no-CBs CPUs"
0743         help
0744           This option does not force any of the CPUs to be no-CBs CPUs.
0745           Only CPUs designated by the rcu_nocbs= boot parameter will be
0746           no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
0747           kthreads whose names begin with "rcuo".  All other CPUs will
0748           invoke their own RCU callbacks in softirq context.
0750           Select this option if you want to choose no-CBs CPUs at
0751           boot time, for example, to allow testing of different no-CBs
0752           configurations without having to rebuild the kernel each time.
0754 config RCU_NOCB_CPU_ZERO
0755         bool "CPU 0 is a build_forced no-CBs CPU"
0756         help
0757           This option forces CPU 0 to be a no-CBs CPU, so that its RCU
0758           callbacks are invoked by a per-CPU kthread whose name begins
0759           with "rcuo".  Additional CPUs may be designated as no-CBs
0760           CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
0761           All other CPUs will invoke their own RCU callbacks in softirq
0762           context.
0764           Select this if CPU 0 needs to be a no-CBs CPU for real-time
0765           or energy-efficiency reasons, but the real reason it exists
0766           is to ensure that randconfig testing covers mixed systems.
0768 config RCU_NOCB_CPU_ALL
0769         bool "All CPUs are build_forced no-CBs CPUs"
0770         help
0771           This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
0772           boot parameter will be ignored.  All CPUs' RCU callbacks will
0773           be executed in the context of per-CPU rcuo kthreads created for
0774           this purpose.  Assuming that the kthreads whose names start with
0775           "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
0776           on the remaining CPUs, but might decrease memory locality during
0777           RCU-callback invocation, thus potentially degrading throughput.
0779           Select this if all CPUs need to be no-CBs CPUs for real-time
0780           or energy-efficiency reasons.
0782 endchoice
0785         bool
0786         default n
0787         help
0788           This option enables expedited grace periods at boot time,
0789           as if rcu_expedite_gp() had been invoked early in boot.
0790           The corresponding rcu_unexpedite_gp() is invoked from
0791           rcu_end_inkernel_boot(), which is intended to be invoked
0792           at the end of the kernel-only boot sequence, just before
0793           init is exec'ed.
0795           Accept the default if unsure.
0797 endmenu # "RCU Subsystem"
0799 config BUILD_BIN2C
0800         bool
0801         default n
0803 config IKCONFIG
0804         tristate "Kernel .config support"
0805         select BUILD_BIN2C
0806         ---help---
0807           This option enables the complete Linux kernel ".config" file
0808           contents to be saved in the kernel. It provides documentation
0809           of which kernel options are used in a running kernel or in an
0810           on-disk kernel.  This information can be extracted from the kernel
0811           image file with the script scripts/extract-ikconfig and used as
0812           input to rebuild the current kernel or to build another kernel.
0813           It can also be extracted from a running kernel by reading
0814           /proc/config.gz if enabled (below).
0816 config IKCONFIG_PROC
0817         bool "Enable access to .config through /proc/config.gz"
0818         depends on IKCONFIG && PROC_FS
0819         ---help---
0820           This option enables access to the kernel configuration file
0821           through /proc/config.gz.
0823 config LOG_BUF_SHIFT
0824         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
0825         range 12 25
0826         default 17
0827         depends on PRINTK
0828         help
0829           Select the minimal kernel log buffer size as a power of 2.
0830           The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
0831           parameter, see below. Any higher size also might be forced
0832           by "log_buf_len" boot parameter.
0834           Examples:
0835                      17 => 128 KB
0836                      16 => 64 KB
0837                      15 => 32 KB
0838                      14 => 16 KB
0839                      13 =>  8 KB
0840                      12 =>  4 KB
0843         int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
0844         depends on SMP
0845         range 0 21
0846         default 12 if !BASE_SMALL
0847         default 0 if BASE_SMALL
0848         depends on PRINTK
0849         help
0850           This option allows to increase the default ring buffer size
0851           according to the number of CPUs. The value defines the contribution
0852           of each CPU as a power of 2. The used space is typically only few
0853           lines however it might be much more when problems are reported,
0854           e.g. backtraces.
0856           The increased size means that a new buffer has to be allocated and
0857           the original static one is unused. It makes sense only on systems
0858           with more CPUs. Therefore this value is used only when the sum of
0859           contributions is greater than the half of the default kernel ring
0860           buffer as defined by LOG_BUF_SHIFT. The default values are set
0861           so that more than 64 CPUs are needed to trigger the allocation.
0863           Also this option is ignored when "log_buf_len" kernel parameter is
0864           used as it forces an exact (power of two) size of the ring buffer.
0866           The number of possible CPUs is used for this computation ignoring
0867           hotplugging making the computation optimal for the worst case
0868           scenario while allowing a simple algorithm to be used from bootup.
0870           Examples shift values and their meaning:
0871                      17 => 128 KB for each CPU
0872                      16 =>  64 KB for each CPU
0873                      15 =>  32 KB for each CPU
0874                      14 =>  16 KB for each CPU
0875                      13 =>   8 KB for each CPU
0876                      12 =>   4 KB for each CPU
0878 config NMI_LOG_BUF_SHIFT
0879         int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
0880         range 10 21
0881         default 13
0882         depends on PRINTK_NMI
0883         help
0884           Select the size of a per-CPU buffer where NMI messages are temporary
0885           stored. They are copied to the main log buffer in a safe context
0886           to avoid a deadlock. The value defines the size as a power of 2.
0888           NMI messages are rare and limited. The largest one is when
0889           a backtrace is printed. It usually fits into 4KB. Select
0890           8KB if you want to be on the safe side.
0892           Examples:
0893                      17 => 128 KB for each CPU
0894                      16 =>  64 KB for each CPU
0895                      15 =>  32 KB for each CPU
0896                      14 =>  16 KB for each CPU
0897                      13 =>   8 KB for each CPU
0898                      12 =>   4 KB for each CPU
0900 #
0901 # Architectures with an unreliable sched_clock() should select this:
0902 #
0904         bool
0907         bool
0909 #
0910 # For architectures that want to enable the support for NUMA-affine scheduler
0911 # balancing logic:
0912 #
0914         bool
0916 #
0917 # For architectures that prefer to flush all TLBs after a number of pages
0918 # are unmapped instead of sending one IPI per page to flush. The architecture
0919 # must provide guarantees on what happens if a clean TLB cache entry is
0920 # written after the unmap. Details are in mm/rmap.c near the check for
0921 # should_defer_flush. The architecture should also consider if the full flush
0922 # and the refill costs are offset by the savings of sending fewer IPIs.
0924         bool
0926 #
0927 # For architectures that know their GCC __int128 support is sound
0928 #
0929 config ARCH_SUPPORTS_INT128
0930         bool
0932 # For architectures that (ab)use NUMA to represent different memory regions
0933 # all cpu-local but of different latencies, such as SuperH.
0934 #
0936         bool
0938 config NUMA_BALANCING
0939         bool "Memory placement aware NUMA scheduler"
0940         depends on ARCH_SUPPORTS_NUMA_BALANCING
0941         depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
0942         depends on SMP && NUMA && MIGRATION
0943         help
0944           This option adds support for automatic NUMA aware memory/task placement.
0945           The mechanism is quite primitive and is based on migrating memory when
0946           it has references to the node the task is running on.
0948           This system will be inactive on UMA systems.
0951         bool "Automatically enable NUMA aware memory/task placement"
0952         default y
0953         depends on NUMA_BALANCING
0954         help
0955           If set, automatic NUMA balancing will be enabled if running on a NUMA
0956           machine.
0958 menuconfig CGROUPS
0959         bool "Control Group support"
0960         select KERNFS
0961         help
0962           This option adds support for grouping sets of processes together, for
0963           use with process control subsystems such as Cpusets, CFS, memory
0964           controls or device isolation.
0965           See
0966                 - Documentation/scheduler/sched-design-CFS.txt  (CFS)
0967                 - Documentation/cgroup-v1/ (features for grouping, isolation
0968                                           and resource control)
0970           Say N if unsure.
0972 if CGROUPS
0974 config PAGE_COUNTER
0975        bool
0977 config MEMCG
0978         bool "Memory controller"
0979         select PAGE_COUNTER
0980         select EVENTFD
0981         help
0982           Provides control over the memory footprint of tasks in a cgroup.
0984 config MEMCG_SWAP
0985         bool "Swap controller"
0986         depends on MEMCG && SWAP
0987         help
0988           Provides control over the swap space consumed by tasks in a cgroup.
0991         bool "Swap controller enabled by default"
0992         depends on MEMCG_SWAP
0993         default y
0994         help
0995           Memory Resource Controller Swap Extension comes with its price in
0996           a bigger memory consumption. General purpose distribution kernels
0997           which want to enable the feature but keep it disabled by default
0998           and let the user enable it by swapaccount=1 boot command line
0999           parameter should have this option unselected.
1000           For those who want to have the feature enabled by default should
1001           select this option (if, for some reason, they need to disable it
1002           then swapaccount=0 does the trick).
1004 config BLK_CGROUP
1005         bool "IO controller"
1006         depends on BLOCK
1007         default n
1008         ---help---
1009         Generic block IO controller cgroup interface. This is the common
1010         cgroup interface which should be used by various IO controlling
1011         policies.
1013         Currently, CFQ IO scheduler uses it to recognize task groups and
1014         control disk bandwidth allocation (proportional time slice allocation)
1015         to such task groups. It is also used by bio throttling logic in
1016         block layer to implement upper limit in IO rates on a device.
1018         This option only enables generic Block IO controller infrastructure.
1019         One needs to also enable actual IO controlling logic/policy. For
1020         enabling proportional weight division of disk bandwidth in CFQ, set
1021         CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1024         See Documentation/cgroup-v1/blkio-controller.txt for more information.
1026 config DEBUG_BLK_CGROUP
1027         bool "IO controller debugging"
1028         depends on BLK_CGROUP
1029         default n
1030         ---help---
1031         Enable some debugging help. Currently it exports additional stat
1032         files in a cgroup which can be useful for debugging.
1035         bool
1036         depends on MEMCG && BLK_CGROUP
1037         default y
1039 menuconfig CGROUP_SCHED
1040         bool "CPU controller"
1041         default n
1042         help
1043           This feature lets CPU scheduler recognize task groups and control CPU
1044           bandwidth allocation to such task groups. It uses cgroups to group
1045           tasks.
1048 config FAIR_GROUP_SCHED
1049         bool "Group scheduling for SCHED_OTHER"
1050         depends on CGROUP_SCHED
1051         default CGROUP_SCHED
1053 config CFS_BANDWIDTH
1054         bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1055         depends on FAIR_GROUP_SCHED
1056         default n
1057         help
1058           This option allows users to define CPU bandwidth rates (limits) for
1059           tasks running within the fair group scheduler.  Groups with no limit
1060           set are considered to be unconstrained and will run with no
1061           restriction.
1062           See tip/Documentation/scheduler/sched-bwc.txt for more information.
1064 config RT_GROUP_SCHED
1065         bool "Group scheduling for SCHED_RR/FIFO"
1066         depends on CGROUP_SCHED
1067         default n
1068         help
1069           This feature lets you explicitly allocate real CPU bandwidth
1070           to task groups. If enabled, it will also make it impossible to
1071           schedule realtime tasks for non-root users until you allocate
1072           realtime bandwidth for them.
1073           See Documentation/scheduler/sched-rt-group.txt for more information.
1075 endif #CGROUP_SCHED
1077 config CGROUP_PIDS
1078         bool "PIDs controller"
1079         help
1080           Provides enforcement of process number limits in the scope of a
1081           cgroup. Any attempt to fork more processes than is allowed in the
1082           cgroup will fail. PIDs are fundamentally a global resource because it
1083           is fairly trivial to reach PID exhaustion before you reach even a
1084           conservative kmemcg limit. As a result, it is possible to grind a
1085           system to halt without being limited by other cgroup policies. The
1086           PIDs controller is designed to stop this from happening.
1088           It should be noted that organisational operations (such as attaching
1089           to a cgroup hierarchy will *not* be blocked by the PIDs controller),
1090           since the PIDs limit only affects a process's ability to fork, not to
1091           attach to a cgroup.
1093 config CGROUP_FREEZER
1094         bool "Freezer controller"
1095         help
1096           Provides a way to freeze and unfreeze all tasks in a
1097           cgroup.
1099           This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1100           controller includes important in-kernel memory consumers per default.
1102           If you're using cgroup2, say N.
1104 config CGROUP_HUGETLB
1105         bool "HugeTLB controller"
1106         depends on HUGETLB_PAGE
1107         select PAGE_COUNTER
1108         default n
1109         help
1110           Provides a cgroup controller for HugeTLB pages.
1111           When you enable this, you can put a per cgroup limit on HugeTLB usage.
1112           The limit is enforced during page fault. Since HugeTLB doesn't
1113           support page reclaim, enforcing the limit at page fault time implies
1114           that, the application will get SIGBUS signal if it tries to access
1115           HugeTLB pages beyond its limit. This requires the application to know
1116           beforehand how much HugeTLB pages it would require for its use. The
1117           control group is tracked in the third page lru pointer. This means
1118           that we cannot use the controller with huge page less than 3 pages.
1120 config CPUSETS
1121         bool "Cpuset controller"
1122         help
1123           This option will let you create and manage CPUSETs which
1124           allow dynamically partitioning a system into sets of CPUs and
1125           Memory Nodes and assigning tasks to run only within those sets.
1126           This is primarily useful on large SMP or NUMA systems.
1128           Say N if unsure.
1130 config PROC_PID_CPUSET
1131         bool "Include legacy /proc/<pid>/cpuset file"
1132         depends on CPUSETS
1133         default y
1135 config CGROUP_DEVICE
1136         bool "Device controller"
1137         help
1138           Provides a cgroup controller implementing whitelists for
1139           devices which a process in the cgroup can mknod or open.
1141 config CGROUP_CPUACCT
1142         bool "Simple CPU accounting controller"
1143         help
1144           Provides a simple controller for monitoring the
1145           total CPU consumed by the tasks in a cgroup.
1147 config CGROUP_PERF
1148         bool "Perf controller"
1149         depends on PERF_EVENTS
1150         help
1151           This option extends the perf per-cpu mode to restrict monitoring
1152           to threads which belong to the cgroup specified and run on the
1153           designated cpu.
1155           Say N if unsure.
1157 config CGROUP_BPF
1158         bool "Support for eBPF programs attached to cgroups"
1159         depends on BPF_SYSCALL
1160         select SOCK_CGROUP_DATA
1161         help
1162           Allow attaching eBPF programs to a cgroup using the bpf(2)
1163           syscall command BPF_PROG_ATTACH.
1165           In which context these programs are accessed depends on the type
1166           of attachment. For instance, programs that are attached using
1167           BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1168           inet sockets.
1170 config CGROUP_DEBUG
1171         bool "Example controller"
1172         default n
1173         help
1174           This option enables a simple controller that exports
1175           debugging information about the cgroups framework.
1177           Say N.
1179 config SOCK_CGROUP_DATA
1180         bool
1181         default n
1183 endif # CGROUPS
1186         bool "Checkpoint/restore support" if EXPERT
1187         select PROC_CHILDREN
1188         default n
1189         help
1190           Enables additional kernel features in a sake of checkpoint/restore.
1191           In particular it adds auxiliary prctl codes to setup process text,
1192           data and heap segment sizes, and a few additional /proc filesystem
1193           entries.
1195           If unsure, say N here.
1197 menuconfig NAMESPACES
1198         bool "Namespaces support" if EXPERT
1199         depends on MULTIUSER
1200         default !EXPERT
1201         help
1202           Provides the way to make tasks work with different objects using
1203           the same id. For example same IPC id may refer to different objects
1204           or same user id or pid may refer to different tasks when used in
1205           different namespaces.
1209 config UTS_NS
1210         bool "UTS namespace"
1211         default y
1212         help
1213           In this namespace tasks see different info provided with the
1214           uname() system call
1216 config IPC_NS
1217         bool "IPC namespace"
1218         depends on (SYSVIPC || POSIX_MQUEUE)
1219         default y
1220         help
1221           In this namespace tasks work with IPC ids which correspond to
1222           different IPC objects in different namespaces.
1224 config USER_NS
1225         bool "User namespace"
1226         default n
1227         help
1228           This allows containers, i.e. vservers, to use user namespaces
1229           to provide different user info for different servers.
1231           When user namespaces are enabled in the kernel it is
1232           recommended that the MEMCG option also be enabled and that
1233           user-space use the memory control groups to limit the amount
1234           of memory a memory unprivileged users can use.
1236           If unsure, say N.
1238 config PID_NS
1239         bool "PID Namespaces"
1240         default y
1241         help
1242           Support process id namespaces.  This allows having multiple
1243           processes with the same pid as long as they are in different
1244           pid namespaces.  This is a building block of containers.
1246 config NET_NS
1247         bool "Network namespace"
1248         depends on NET
1249         default y
1250         help
1251           Allow user space to create what appear to be multiple instances
1252           of the network stack.
1254 endif # NAMESPACES
1257         bool "Automatic process group scheduling"
1258         select CGROUPS
1259         select CGROUP_SCHED
1260         select FAIR_GROUP_SCHED
1261         help
1262           This option optimizes the scheduler for common desktop workloads by
1263           automatically creating and populating task groups.  This separation
1264           of workloads isolates aggressive CPU burners (like build jobs) from
1265           desktop applications.  Task group autogeneration is currently based
1266           upon task session.
1269         bool "Enable deprecated sysfs features to support old userspace tools"
1270         depends on SYSFS
1271         default n
1272         help
1273           This option adds code that switches the layout of the "block" class
1274           devices, to not show up in /sys/class/block/, but only in
1275           /sys/block/.
1277           This switch is only active when the sysfs.deprecated=1 boot option is
1278           passed or the SYSFS_DEPRECATED_V2 option is set.
1280           This option allows new kernels to run on old distributions and tools,
1281           which might get confused by /sys/class/block/. Since 2007/2008 all
1282           major distributions and tools handle this just fine.
1284           Recent distributions and userspace tools after 2009/2010 depend on
1285           the existence of /sys/class/block/, and will not work with this
1286           option enabled.
1288           Only if you are using a new kernel on an old distribution, you might
1289           need to say Y here.
1292         bool "Enable deprecated sysfs features by default"
1293         default n
1294         depends on SYSFS
1295         depends on SYSFS_DEPRECATED
1296         help
1297           Enable deprecated sysfs by default.
1299           See the CONFIG_SYSFS_DEPRECATED option for more details about this
1300           option.
1302           Only if you are using a new kernel on an old distribution, you might
1303           need to say Y here. Even then, odds are you would not need it
1304           enabled, you can always pass the boot option if absolutely necessary.
1306 config RELAY
1307         bool "Kernel->user space relay support (formerly relayfs)"
1308         select IRQ_WORK
1309         help
1310           This option enables support for relay interface support in
1311           certain file systems (such as debugfs).
1312           It is designed to provide an efficient mechanism for tools and
1313           facilities to relay large amounts of data from kernel space to
1314           user space.
1316           If unsure, say N.
1318 config BLK_DEV_INITRD
1319         bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1320         depends on BROKEN || !FRV
1321         help
1322           The initial RAM filesystem is a ramfs which is loaded by the
1323           boot loader (loadlin or lilo) and that is mounted as root
1324           before the normal boot procedure. It is typically used to
1325           load modules needed to mount the "real" root file system,
1326           etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1328           If RAM disk support (BLK_DEV_RAM) is also included, this
1329           also enables initial RAM disk (initrd) support and adds
1330           15 Kbytes (more on some other architectures) to the kernel size.
1332           If unsure say Y.
1336 source "usr/Kconfig"
1338 endif
1340 choice
1341         prompt "Compiler optimization level"
1345         bool "Optimize for performance"
1346         help
1347           This is the default optimization level for the kernel, building
1348           with the "-O2" compiler flag for best performance and most
1349           helpful compile-time warnings.
1352         bool "Optimize for size"
1353         help
1354           Enabling this option will pass "-Os" instead of "-O2" to
1355           your compiler resulting in a smaller kernel.
1357           If unsure, say N.
1359 endchoice
1361 config SYSCTL
1362         bool
1364 config ANON_INODES
1365         bool
1367 config HAVE_UID16
1368         bool
1371         bool
1372         help
1373           Enable support for /proc/sys/debug/exception-trace.
1376         bool
1377         help
1378           Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1379           Allows arch to define/use @no_unaligned_warning to possibly warn
1380           about unaligned access emulation going on under the hood.
1383         bool
1384         help
1385           Enable support for /proc/sys/kernel/unaligned-trap
1386           Allows arches to define/use @unaligned_enabled to runtime toggle
1387           the unaligned access emulation.
1388           see arch/parisc/kernel/unaligned.c for reference
1391         bool
1393 # interpreter that classic socket filters depend on
1394 config BPF
1395         bool
1397 menuconfig EXPERT
1398         bool "Configure standard kernel features (expert users)"
1399         # Unhide debug options, to make the on-by-default options visible
1400         select DEBUG_KERNEL
1401         help
1402           This option allows certain base kernel options and settings
1403           to be disabled or tweaked. This is for specialized
1404           environments which can tolerate a "non-standard" kernel.
1405           Only use this if you really know what you are doing.
1407 config UID16
1408         bool "Enable 16-bit UID system calls" if EXPERT
1409         depends on HAVE_UID16 && MULTIUSER
1410         default y
1411         help
1412           This enables the legacy 16-bit UID syscall wrappers.
1414 config MULTIUSER
1415         bool "Multiple users, groups and capabilities support" if EXPERT
1416         default y
1417         help
1418           This option enables support for non-root users, groups and
1419           capabilities.
1421           If you say N here, all processes will run with UID 0, GID 0, and all
1422           possible capabilities.  Saying N here also compiles out support for
1423           system calls related to UIDs, GIDs, and capabilities, such as setuid,
1424           setgid, and capset.
1426           If unsure, say Y here.
1429         bool "sgetmask/ssetmask syscalls support" if EXPERT
1430         def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
1431         ---help---
1432           sys_sgetmask and sys_ssetmask are obsolete system calls
1433           no longer supported in libc but still enabled by default in some
1434           architectures.
1436           If unsure, leave the default option here.
1438 config SYSFS_SYSCALL
1439         bool "Sysfs syscall support" if EXPERT
1440         default y
1441         ---help---
1442           sys_sysfs is an obsolete system call no longer supported in libc.
1443           Note that disabling this option is more secure but might break
1444           compatibility with some systems.
1446           If unsure say Y here.
1448 config SYSCTL_SYSCALL
1449         bool "Sysctl syscall support" if EXPERT
1450         depends on PROC_SYSCTL
1451         default n
1452         select SYSCTL
1453         ---help---
1454           sys_sysctl uses binary paths that have been found challenging
1455           to properly maintain and use.  The interface in /proc/sys
1456           using paths with ascii names is now the primary path to this
1457           information.
1459           Almost nothing using the binary sysctl interface so if you are
1460           trying to save some space it is probably safe to disable this,
1461           making your kernel marginally smaller.
1463           If unsure say N here.
1465 config POSIX_TIMERS
1466         bool "Posix Clocks & timers" if EXPERT
1467         default y
1468         help
1469           This includes native support for POSIX timers to the kernel.
1470           Some embedded systems have no use for them and therefore they
1471           can be configured out to reduce the size of the kernel image.
1473           When this option is disabled, the following syscalls won't be
1474           available: timer_create, timer_gettime: timer_getoverrun,
1475           timer_settime, timer_delete, clock_adjtime, getitimer,
1476           setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1477           clock_getres and clock_nanosleep syscalls will be limited to
1480           If unsure say y.
1482 config KALLSYMS
1483          bool "Load all symbols for debugging/ksymoops" if EXPERT
1484          default y
1485          help
1486            Say Y here to let the kernel print out symbolic crash information and
1487            symbolic stack backtraces. This increases the size of the kernel
1488            somewhat, as all symbols have to be loaded into the kernel image.
1490 config KALLSYMS_ALL
1491         bool "Include all symbols in kallsyms"
1492         depends on DEBUG_KERNEL && KALLSYMS
1493         help
1494            Normally kallsyms only contains the symbols of functions for nicer
1495            OOPS messages and backtraces (i.e., symbols from the text and inittext
1496            sections). This is sufficient for most cases. And only in very rare
1497            cases (e.g., when a debugger is used) all symbols are required (e.g.,
1498            names of variables from the data sections, etc).
1500            This option makes sure that all symbols are loaded into the kernel
1501            image (i.e., symbols from all sections) in cost of increased kernel
1502            size (depending on the kernel configuration, it may be 300KiB or
1503            something like this).
1505            Say N unless you really need all symbols.
1508         bool
1509         depends on KALLSYMS
1510         default X86_64 && SMP
1513         bool
1514         depends on KALLSYMS
1515         default !IA64 && !(TILE && 64BIT)
1516         help
1517           Instead of emitting them as absolute values in the native word size,
1518           emit the symbol references in the kallsyms table as 32-bit entries,
1519           each containing a relative value in the range [base, base + U32_MAX]
1520           or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1521           an absolute value in the range [0, S32_MAX] or a relative value in the
1522           range [base, base + S32_MAX], where base is the lowest relative symbol
1523           address encountered in the image.
1525           On 64-bit builds, this reduces the size of the address table by 50%,
1526           but more importantly, it results in entries whose values are build
1527           time constants, and no relocation pass is required at runtime to fix
1528           up the entries based on the runtime load address of the kernel.
1530 config PRINTK
1531         default y
1532         bool "Enable support for printk" if EXPERT
1533         select IRQ_WORK
1534         help
1535           This option enables normal printk support. Removing it
1536           eliminates most of the message strings from the kernel image
1537           and makes the kernel more or less silent. As this makes it
1538           very difficult to diagnose system problems, saying N here is
1539           strongly discouraged.
1541 config PRINTK_NMI
1542         def_bool y
1543         depends on PRINTK
1544         depends on HAVE_NMI
1546 config BUG
1547         bool "BUG() support" if EXPERT
1548         default y
1549         help
1550           Disabling this option eliminates support for BUG and WARN, reducing
1551           the size of your kernel image and potentially quietly ignoring
1552           numerous fatal conditions. You should only consider disabling this
1553           option for embedded systems with no facilities for reporting errors.
1554           Just say Y.
1556 config ELF_CORE
1557         depends on COREDUMP
1558         default y
1559         bool "Enable ELF core dumps" if EXPERT
1560         help
1561           Enable support for generating core dumps. Disabling saves about 4k.
1565         bool "Enable PC-Speaker support" if EXPERT
1566         depends on HAVE_PCSPKR_PLATFORM
1567         select I8253_LOCK
1568         default y
1569         help
1570           This option allows to disable the internal PC-Speaker
1571           support, saving some memory.
1573 config BASE_FULL
1574         default y
1575         bool "Enable full-sized data structures for core" if EXPERT
1576         help
1577           Disabling this option reduces the size of miscellaneous core
1578           kernel data structures. This saves memory on small machines,
1579           but may reduce performance.
1581 config FUTEX
1582         bool "Enable futex support" if EXPERT
1583         default y
1584         select RT_MUTEXES
1585         help
1586           Disabling this option will cause the kernel to be built without
1587           support for "fast userspace mutexes".  The resulting kernel may not
1588           run glibc-based applications correctly.
1591         bool
1592         depends on FUTEX
1593         help
1594           Architectures should select this if futex_atomic_cmpxchg_inatomic()
1595           is implemented and always working. This removes a couple of runtime
1596           checks.
1598 config EPOLL
1599         bool "Enable eventpoll support" if EXPERT
1600         default y
1601         select ANON_INODES
1602         help
1603           Disabling this option will cause the kernel to be built without
1604           support for epoll family of system calls.
1606 config SIGNALFD
1607         bool "Enable signalfd() system call" if EXPERT
1608         select ANON_INODES
1609         default y
1610         help
1611           Enable the signalfd() system call that allows to receive signals
1612           on a file descriptor.
1614           If unsure, say Y.
1616 config TIMERFD
1617         bool "Enable timerfd() system call" if EXPERT
1618         select ANON_INODES
1619         default y
1620         help
1621           Enable the timerfd() system call that allows to receive timer
1622           events on a file descriptor.
1624           If unsure, say Y.
1626 config EVENTFD
1627         bool "Enable eventfd() system call" if EXPERT
1628         select ANON_INODES
1629         default y
1630         help
1631           Enable the eventfd() system call that allows to receive both
1632           kernel notification (ie. KAIO) or userspace notifications.
1634           If unsure, say Y.
1636 # syscall, maps, verifier
1637 config BPF_SYSCALL
1638         bool "Enable bpf() system call"
1639         select ANON_INODES
1640         select BPF
1641         default n
1642         help
1643           Enable the bpf() system call that allows to manipulate eBPF
1644           programs and maps via file descriptors.
1646 config SHMEM
1647         bool "Use full shmem filesystem" if EXPERT
1648         default y
1649         depends on MMU
1650         help
1651           The shmem is an internal filesystem used to manage shared memory.
1652           It is backed by swap and manages resource limits. It is also exported
1653           to userspace as tmpfs if TMPFS is enabled. Disabling this
1654           option replaces shmem and tmpfs with the much simpler ramfs code,
1655           which may be appropriate on small systems without swap.
1657 config AIO
1658         bool "Enable AIO support" if EXPERT
1659         default y
1660         help
1661           This option enables POSIX asynchronous I/O which may by used
1662           by some high performance threaded applications. Disabling
1663           this option saves about 7k.
1666         bool "Enable madvise/fadvise syscalls" if EXPERT
1667         default y
1668         help
1669           This option enables the madvise and fadvise syscalls, used by
1670           applications to advise the kernel about their future memory or file
1671           usage, improving performance. If building an embedded system where no
1672           applications use these syscalls, you can disable this option to save
1673           space.
1675 config USERFAULTFD
1676         bool "Enable userfaultfd() system call"
1677         select ANON_INODES
1678         depends on MMU
1679         help
1680           Enable the userfaultfd() system call that allows to intercept and
1681           handle page faults in userland.
1683 config PCI_QUIRKS
1684         default y
1685         bool "Enable PCI quirk workarounds" if EXPERT
1686         depends on PCI
1687         help
1688           This enables workarounds for various PCI chipset
1689           bugs/quirks. Disable this only if your target machine is
1690           unaffected by PCI quirks.
1692 config MEMBARRIER
1693         bool "Enable membarrier() system call" if EXPERT
1694         default y
1695         help
1696           Enable the membarrier() system call that allows issuing memory
1697           barriers across all running threads, which can be used to distribute
1698           the cost of user-space memory barriers asymmetrically by transforming
1699           pairs of memory barriers into pairs consisting of membarrier() and a
1700           compiler barrier.
1702           If unsure, say Y.
1704 config EMBEDDED
1705         bool "Embedded system"
1706         option allnoconfig_y
1707         select EXPERT
1708         help
1709           This option should be enabled if compiling the kernel for
1710           an embedded system so certain expert options are available
1711           for configuration.
1713 config HAVE_PERF_EVENTS
1714         bool
1715         help
1716           See tools/perf/design.txt for details.
1718 config PERF_USE_VMALLOC
1719         bool
1720         help
1721           See tools/perf/design.txt for details
1723 menu "Kernel Performance Events And Counters"
1725 config PERF_EVENTS
1726         bool "Kernel performance events and counters"
1727         default y if PROFILING
1728         depends on HAVE_PERF_EVENTS
1729         select ANON_INODES
1730         select IRQ_WORK
1731         select SRCU
1732         help
1733           Enable kernel support for various performance events provided
1734           by software and hardware.
1736           Software events are supported either built-in or via the
1737           use of generic tracepoints.
1739           Most modern CPUs support performance events via performance
1740           counter registers. These registers count the number of certain
1741           types of hw events: such as instructions executed, cachemisses
1742           suffered, or branches mis-predicted - without slowing down the
1743           kernel or applications. These registers can also trigger interrupts
1744           when a threshold number of events have passed - and can thus be
1745           used to profile the code that runs on that CPU.
1747           The Linux Performance Event subsystem provides an abstraction of
1748           these software and hardware event capabilities, available via a
1749           system call and used by the "perf" utility in tools/perf/. It
1750           provides per task and per CPU counters, and it provides event
1751           capabilities on top of those.
1753           Say Y if unsure.
1756         default n
1757         bool "Debug: use vmalloc to back perf mmap() buffers"
1758         depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1759         select PERF_USE_VMALLOC
1760         help
1761          Use vmalloc memory to back perf mmap() buffers.
1763          Mostly useful for debugging the vmalloc code on platforms
1764          that don't require it.
1766          Say N if unsure.
1768 endmenu
1771         default y
1772         bool "Enable VM event counters for /proc/vmstat" if EXPERT
1773         help
1774           VM event counters are needed for event counts to be shown.
1775           This option allows the disabling of the VM event counters
1776           on EXPERT systems.  /proc/vmstat will only show page counts
1777           if VM event counters are disabled.
1779 config SLUB_DEBUG
1780         default y
1781         bool "Enable SLUB debugging support" if EXPERT
1782         depends on SLUB && SYSFS
1783         help
1784           SLUB has extensive debug support features. Disabling these can
1785           result in significant savings in code size. This also disables
1786           SLUB sysfs support. /sys/slab will not exist and there will be
1787           no support for cache validation etc.
1789 config COMPAT_BRK
1790         bool "Disable heap randomization"
1791         default y
1792         help
1793           Randomizing heap placement makes heap exploits harder, but it
1794           also breaks ancient binaries (including anything libc5 based).
1795           This option changes the bootup default to heap randomization
1796           disabled, and can be overridden at runtime by setting
1797           /proc/sys/kernel/randomize_va_space to 2.
1799           On non-ancient distros (post-2000 ones) N is usually a safe choice.
1801 choice
1802         prompt "Choose SLAB allocator"
1803         default SLUB
1804         help
1805            This option allows to select a slab allocator.
1807 config SLAB
1808         bool "SLAB"
1810         help
1811           The regular slab allocator that is established and known to work
1812           well in all environments. It organizes cache hot objects in
1813           per cpu and per node queues.
1815 config SLUB
1816         bool "SLUB (Unqueued Allocator)"
1818         help
1819            SLUB is a slab allocator that minimizes cache line usage
1820            instead of managing queues of cached objects (SLAB approach).
1821            Per cpu caching is realized using slabs of objects instead
1822            of queues of objects. SLUB can use memory efficiently
1823            and has enhanced diagnostics. SLUB is the default choice for
1824            a slab allocator.
1826 config SLOB
1827         depends on EXPERT
1828         bool "SLOB (Simple Allocator)"
1829         help
1830            SLOB replaces the stock allocator with a drastically simpler
1831            allocator. SLOB is generally more space efficient but
1832            does not perform as well on large systems.
1834 endchoice
1837         default n
1838         depends on SLAB || SLUB
1839         bool "SLAB freelist randomization"
1840         help
1841           Randomizes the freelist order used on creating new pages. This
1842           security feature reduces the predictability of the kernel slab
1843           allocator against heap overflows.
1845 config SLUB_CPU_PARTIAL
1846         default y
1847         depends on SLUB && SMP
1848         bool "SLUB per cpu partial cache"
1849         help
1850           Per cpu partial caches accellerate objects allocation and freeing
1851           that is local to a processor at the price of more indeterminism
1852           in the latency of the free. On overflow these caches will be cleared
1853           which requires the taking of locks that may cause latency spikes.
1854           Typically one would choose no for a realtime system.
1857         bool "Allow mmapped anonymous memory to be uninitialized"
1858         depends on EXPERT && !MMU
1859         default n
1860         help
1861           Normally, and according to the Linux spec, anonymous memory obtained
1862           from mmap() has it's contents cleared before it is passed to
1863           userspace.  Enabling this config option allows you to request that
1864           mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1865           providing a huge performance boost.  If this option is not enabled,
1866           then the flag will be ignored.
1868           This is taken advantage of by uClibc's malloc(), and also by
1869           ELF-FDPIC binfmt's brk and stack allocator.
1871           Because of the obvious security issues, this option should only be
1872           enabled on embedded devices where you control what is run in
1873           userspace.  Since that isn't generally a problem on no-MMU systems,
1874           it is normally safe to say Y here.
1876           See Documentation/nommu-mmap.txt for more information.
1879         def_bool n
1880         select SYSTEM_TRUSTED_KEYRING
1881         select KEYS
1882         select CRYPTO
1883         select CRYPTO_RSA
1884         select ASYMMETRIC_KEY_TYPE
1886         select ASN1
1887         select OID_REGISTRY
1888         select X509_CERTIFICATE_PARSER
1889         select PKCS7_MESSAGE_PARSER
1890         help
1891           Provide PKCS#7 message verification using the contents of the system
1892           trusted keyring to provide public keys.  This then can be used for
1893           module verification, kexec image verification and firmware blob
1894           verification.
1896 config PROFILING
1897         bool "Profiling support"
1898         help
1899           Say Y here to enable the extended profiling support mechanisms used
1900           by profilers such as OProfile.
1902 #
1903 # Place an empty function call at each tracepoint site. Can be
1904 # dynamically changed for a probe function.
1905 #
1906 config TRACEPOINTS
1907         bool
1909 source "arch/Kconfig"
1911 endmenu         # General setup
1914         bool
1915         default n
1917 config SLABINFO
1918         bool
1919         depends on PROC_FS
1920         depends on SLAB || SLUB_DEBUG
1921         default y
1923 config RT_MUTEXES
1924         bool
1926 config BASE_SMALL
1927         int
1928         default 0 if BASE_FULL
1929         default 1 if !BASE_FULL
1931 menuconfig MODULES
1932         bool "Enable loadable module support"
1933         option modules
1934         help
1935           Kernel modules are small pieces of compiled code which can
1936           be inserted in the running kernel, rather than being
1937           permanently built into the kernel.  You use the "modprobe"
1938           tool to add (and sometimes remove) them.  If you say Y here,
1939           many parts of the kernel can be built as modules (by
1940           answering M instead of Y where indicated): this is most
1941           useful for infrequently used options which are not required
1942           for booting.  For more information, see the man pages for
1943           modprobe, lsmod, modinfo, insmod and rmmod.
1945           If you say Y here, you will need to run "make
1946           modules_install" to put the modules under /lib/modules/
1947           where modprobe can find them (you may need to be root to do
1948           this).
1950           If unsure, say Y.
1952 if MODULES
1955         bool "Forced module loading"
1956         default n
1957         help
1958           Allow loading of modules without version information (ie. modprobe
1959           --force).  Forced module loading sets the 'F' (forced) taint flag and
1960           is usually a really bad idea.
1962 config MODULE_UNLOAD
1963         bool "Module unloading"
1964         help
1965           Without this option you will not be able to unload any
1966           modules (note that some modules may not be unloadable
1967           anyway), which makes your kernel smaller, faster
1968           and simpler.  If unsure, say Y.
1971         bool "Forced module unloading"
1972         depends on MODULE_UNLOAD
1973         help
1974           This option allows you to force a module to unload, even if the
1975           kernel believes it is unsafe: the kernel will remove the module
1976           without waiting for anyone to stop using it (using the -f option to
1977           rmmod).  This is mainly for kernel developers and desperate users.
1978           If unsure, say N.
1980 config MODVERSIONS
1981         bool "Module versioning support"
1982         help
1983           Usually, you have to use modules compiled with your kernel.
1984           Saying Y here makes it sometimes possible to use modules
1985           compiled for different kernels, by adding enough information
1986           to the modules to (hopefully) spot any changes which would
1987           make them incompatible with the kernel you are running.  If
1988           unsure, say N.
1990 config MODULE_REL_CRCS
1991         bool
1992         depends on MODVERSIONS
1995         bool "Source checksum for all modules"
1996         help
1997           Modules which contain a MODULE_VERSION get an extra "srcversion"
1998           field inserted into their modinfo section, which contains a
1999           sum of the source files which made it.  This helps maintainers
2000           see exactly which source was used to build a module (since
2001           others sometimes change the module source without updating
2002           the version).  With this option, such a "srcversion" field
2003           will be created for all modules.  If unsure, say N.
2005 config MODULE_SIG
2006         bool "Module signature verification"
2007         depends on MODULES
2008         select SYSTEM_DATA_VERIFICATION
2009         help
2010           Check modules for valid signatures upon load: the signature
2011           is simply appended to the module. For more information see
2012           Documentation/module-signing.txt.
2014           Note that this option adds the OpenSSL development packages as a
2015           kernel build dependency so that the signing tool can use its crypto
2016           library.
2018           !!!WARNING!!!  If you enable this option, you MUST make sure that the
2019           module DOES NOT get stripped after being signed.  This includes the
2020           debuginfo strip done by some packagers (such as rpmbuild) and
2021           inclusion into an initramfs that wants the module size reduced.
2023 config MODULE_SIG_FORCE
2024         bool "Require modules to be validly signed"
2025         depends on MODULE_SIG
2026         help
2027           Reject unsigned modules or signed modules for which we don't have a
2028           key.  Without this, such modules will simply taint the kernel.
2030 config MODULE_SIG_ALL
2031         bool "Automatically sign all modules"
2032         default y
2033         depends on MODULE_SIG
2034         help
2035           Sign all modules during make modules_install. Without this option,
2036           modules must be signed manually, using the scripts/sign-file tool.
2038 comment "Do not forget to sign required modules with scripts/sign-file"
2039         depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2041 choice
2042         prompt "Which hash algorithm should modules be signed with?"
2043         depends on MODULE_SIG
2044         help
2045           This determines which sort of hashing algorithm will be used during
2046           signature generation.  This algorithm _must_ be built into the kernel
2047           directly so that signature verification can take place.  It is not
2048           possible to load a signed module containing the algorithm to check
2049           the signature on that module.
2051 config MODULE_SIG_SHA1
2052         bool "Sign modules with SHA-1"
2053         select CRYPTO_SHA1
2055 config MODULE_SIG_SHA224
2056         bool "Sign modules with SHA-224"
2057         select CRYPTO_SHA256
2059 config MODULE_SIG_SHA256
2060         bool "Sign modules with SHA-256"
2061         select CRYPTO_SHA256
2063 config MODULE_SIG_SHA384
2064         bool "Sign modules with SHA-384"
2065         select CRYPTO_SHA512
2067 config MODULE_SIG_SHA512
2068         bool "Sign modules with SHA-512"
2069         select CRYPTO_SHA512
2071 endchoice
2073 config MODULE_SIG_HASH
2074         string
2075         depends on MODULE_SIG
2076         default "sha1" if MODULE_SIG_SHA1
2077         default "sha224" if MODULE_SIG_SHA224
2078         default "sha256" if MODULE_SIG_SHA256
2079         default "sha384" if MODULE_SIG_SHA384
2080         default "sha512" if MODULE_SIG_SHA512
2083         bool "Compress modules on installation"
2084         depends on MODULES
2085         help
2087           Compresses kernel modules when 'make modules_install' is run; gzip or
2088           xz depending on "Compression algorithm" below.
2090           module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2092           Out-of-tree kernel modules installed using Kbuild will also be
2093           compressed upon installation.
2095           Note: for modules inside an initrd or initramfs, it's more efficient
2096           to compress the whole initrd or initramfs instead.
2098           Note: This is fully compatible with signed modules.
2100           If in doubt, say N.
2102 choice
2103         prompt "Compression algorithm"
2104         depends on MODULE_COMPRESS
2105         default MODULE_COMPRESS_GZIP
2106         help
2107           This determines which sort of compression will be used during
2108           'make modules_install'.
2110           GZIP (default) and XZ are supported.
2113         bool "GZIP"
2116         bool "XZ"
2118 endchoice
2121         bool "Trim unused exported kernel symbols"
2122         depends on MODULES && !UNUSED_SYMBOLS
2123         help
2124           The kernel and some modules make many symbols available for
2125           other modules to use via EXPORT_SYMBOL() and variants. Depending
2126           on the set of modules being selected in your kernel configuration,
2127           many of those exported symbols might never be used.
2129           This option allows for unused exported symbols to be dropped from
2130           the build. In turn, this provides the compiler more opportunities
2131           (especially when using LTO) for optimizing the code and reducing
2132           binary size.  This might have some security advantages as well.
2134           If unsure, or if you need to build out-of-tree modules, say N.
2136 endif # MODULES
2139         def_bool y
2140         depends on PERF_EVENTS || TRACING
2143         bool
2144         help
2145           Back when each arch used to define their own cpu_online_mask and
2146           cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2147           with all 1s, and others with all 0s.  When they were centralised,
2148           it was better to provide this option than to break all the archs
2149           and have several arch maintainers pursuing me down dark alleys.
2151 source "block/Kconfig"
2154         bool
2156 config PADATA
2157         depends on SMP
2158         bool
2160 config ASN1
2161         tristate
2162         help
2163           Build a simple ASN.1 grammar compiler that produces a bytecode output
2164           that can be interpreted by the ASN.1 stream decoder and used to
2165           inform it as to what tags are to be expected in a stream and what
2166           functions to call on what tags.
2168 source "kernel/Kconfig.locks"