linux/init/Kconfig
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   1config ARCH
   2        string
   3        option env="ARCH"
   4
   5config KERNELVERSION
   6        string
   7        option env="KERNELVERSION"
   8
   9config DEFCONFIG_LIST
  10        string
  11        depends on !UML
  12        option defconfig_list
  13        default "/lib/modules/$UNAME_RELEASE/.config"
  14        default "/etc/kernel-config"
  15        default "/boot/config-$UNAME_RELEASE"
  16        default "$ARCH_DEFCONFIG"
  17        default "arch/$ARCH/defconfig"
  18
  19config CONSTRUCTORS
  20        bool
  21        depends on !UML
  22
  23config IRQ_WORK
  24        bool
  25
  26config BUILDTIME_EXTABLE_SORT
  27        bool
  28
  29menu "General setup"
  30
  31config BROKEN
  32        bool
  33
  34config BROKEN_ON_SMP
  35        bool
  36        depends on BROKEN || !SMP
  37        default y
  38
  39config INIT_ENV_ARG_LIMIT
  40        int
  41        default 32 if !UML
  42        default 128 if UML
  43        help
  44          Maximum of each of the number of arguments and environment
  45          variables passed to init from the kernel command line.
  46
  47
  48config CROSS_COMPILE
  49        string "Cross-compiler tool prefix"
  50        help
  51          Same as running 'make CROSS_COMPILE=prefix-' but stored for
  52          default make runs in this kernel build directory.  You don't
  53          need to set this unless you want the configured kernel build
  54          directory to select the cross-compiler automatically.
  55
  56config COMPILE_TEST
  57        bool "Compile also drivers which will not load"
  58        default n
  59        help
  60          Some drivers can be compiled on a different platform than they are
  61          intended to be run on. Despite they cannot be loaded there (or even
  62          when they load they cannot be used due to missing HW support),
  63          developers still, opposing to distributors, might want to build such
  64          drivers to compile-test them.
  65
  66          If you are a developer and want to build everything available, say Y
  67          here. If you are a user/distributor, say N here to exclude useless
  68          drivers to be distributed.
  69
  70config LOCALVERSION
  71        string "Local version - append to kernel release"
  72        help
  73          Append an extra string to the end of your kernel version.
  74          This will show up when you type uname, for example.
  75          The string you set here will be appended after the contents of
  76          any files with a filename matching localversion* in your
  77          object and source tree, in that order.  Your total string can
  78          be a maximum of 64 characters.
  79
  80config LOCALVERSION_AUTO
  81        bool "Automatically append version information to the version string"
  82        default y
  83        help
  84          This will try to automatically determine if the current tree is a
  85          release tree by looking for git tags that belong to the current
  86          top of tree revision.
  87
  88          A string of the format -gxxxxxxxx will be added to the localversion
  89          if a git-based tree is found.  The string generated by this will be
  90          appended after any matching localversion* files, and after the value
  91          set in CONFIG_LOCALVERSION.
  92
  93          (The actual string used here is the first eight characters produced
  94          by running the command:
  95
  96            $ git rev-parse --verify HEAD
  97
  98          which is done within the script "scripts/setlocalversion".)
  99
 100config HAVE_KERNEL_GZIP
 101        bool
 102
 103config HAVE_KERNEL_BZIP2
 104        bool
 105
 106config HAVE_KERNEL_LZMA
 107        bool
 108
 109config HAVE_KERNEL_XZ
 110        bool
 111
 112config HAVE_KERNEL_LZO
 113        bool
 114
 115config HAVE_KERNEL_LZ4
 116        bool
 117
 118choice
 119        prompt "Kernel compression mode"
 120        default KERNEL_GZIP
 121        depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
 122        help
 123          The linux kernel is a kind of self-extracting executable.
 124          Several compression algorithms are available, which differ
 125          in efficiency, compression and decompression speed.
 126          Compression speed is only relevant when building a kernel.
 127          Decompression speed is relevant at each boot.
 128
 129          If you have any problems with bzip2 or lzma compressed
 130          kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
 131          version of this functionality (bzip2 only), for 2.4, was
 132          supplied by Christian Ludwig)
 133
 134          High compression options are mostly useful for users, who
 135          are low on disk space (embedded systems), but for whom ram
 136          size matters less.
 137
 138          If in doubt, select 'gzip'
 139
 140config KERNEL_GZIP
 141        bool "Gzip"
 142        depends on HAVE_KERNEL_GZIP
 143        help
 144          The old and tried gzip compression. It provides a good balance
 145          between compression ratio and decompression speed.
 146
 147config KERNEL_BZIP2
 148        bool "Bzip2"
 149        depends on HAVE_KERNEL_BZIP2
 150        help
 151          Its compression ratio and speed is intermediate.
 152          Decompression speed is slowest among the choices.  The kernel
 153          size is about 10% smaller with bzip2, in comparison to gzip.
 154          Bzip2 uses a large amount of memory. For modern kernels you
 155          will need at least 8MB RAM or more for booting.
 156
 157config KERNEL_LZMA
 158        bool "LZMA"
 159        depends on HAVE_KERNEL_LZMA
 160        help
 161          This compression algorithm's ratio is best.  Decompression speed
 162          is between gzip and bzip2.  Compression is slowest.
 163          The kernel size is about 33% smaller with LZMA in comparison to gzip.
 164
 165config KERNEL_XZ
 166        bool "XZ"
 167        depends on HAVE_KERNEL_XZ
 168        help
 169          XZ uses the LZMA2 algorithm and instruction set specific
 170          BCJ filters which can improve compression ratio of executable
 171          code. The size of the kernel is about 30% smaller with XZ in
 172          comparison to gzip. On architectures for which there is a BCJ
 173          filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
 174          will create a few percent smaller kernel than plain LZMA.
 175
 176          The speed is about the same as with LZMA: The decompression
 177          speed of XZ is better than that of bzip2 but worse than gzip
 178          and LZO. Compression is slow.
 179
 180config KERNEL_LZO
 181        bool "LZO"
 182        depends on HAVE_KERNEL_LZO
 183        help
 184          Its compression ratio is the poorest among the choices. The kernel
 185          size is about 10% bigger than gzip; however its speed
 186          (both compression and decompression) is the fastest.
 187
 188config KERNEL_LZ4
 189        bool "LZ4"
 190        depends on HAVE_KERNEL_LZ4
 191        help
 192          LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
 193          A preliminary version of LZ4 de/compression tool is available at
 194          <https://code.google.com/p/lz4/>.
 195
 196          Its compression ratio is worse than LZO. The size of the kernel
 197          is about 8% bigger than LZO. But the decompression speed is
 198          faster than LZO.
 199
 200endchoice
 201
 202config DEFAULT_HOSTNAME
 203        string "Default hostname"
 204        default "(none)"
 205        help
 206          This option determines the default system hostname before userspace
 207          calls sethostname(2). The kernel traditionally uses "(none)" here,
 208          but you may wish to use a different default here to make a minimal
 209          system more usable with less configuration.
 210
 211config SWAP
 212        bool "Support for paging of anonymous memory (swap)"
 213        depends on MMU && BLOCK
 214        default y
 215        help
 216          This option allows you to choose whether you want to have support
 217          for so called swap devices or swap files in your kernel that are
 218          used to provide more virtual memory than the actual RAM present
 219          in your computer.  If unsure say Y.
 220
 221config SYSVIPC
 222        bool "System V IPC"
 223        ---help---
 224          Inter Process Communication is a suite of library functions and
 225          system calls which let processes (running programs) synchronize and
 226          exchange information. It is generally considered to be a good thing,
 227          and some programs won't run unless you say Y here. In particular, if
 228          you want to run the DOS emulator dosemu under Linux (read the
 229          DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
 230          you'll need to say Y here.
 231
 232          You can find documentation about IPC with "info ipc" and also in
 233          section 6.4 of the Linux Programmer's Guide, available from
 234          <http://www.tldp.org/guides.html>.
 235
 236config SYSVIPC_SYSCTL
 237        bool
 238        depends on SYSVIPC
 239        depends on SYSCTL
 240        default y
 241
 242config POSIX_MQUEUE
 243        bool "POSIX Message Queues"
 244        depends on NET
 245        ---help---
 246          POSIX variant of message queues is a part of IPC. In POSIX message
 247          queues every message has a priority which decides about succession
 248          of receiving it by a process. If you want to compile and run
 249          programs written e.g. for Solaris with use of its POSIX message
 250          queues (functions mq_*) say Y here.
 251
 252          POSIX message queues are visible as a filesystem called 'mqueue'
 253          and can be mounted somewhere if you want to do filesystem
 254          operations on message queues.
 255
 256          If unsure, say Y.
 257
 258config POSIX_MQUEUE_SYSCTL
 259        bool
 260        depends on POSIX_MQUEUE
 261        depends on SYSCTL
 262        default y
 263
 264config FHANDLE
 265        bool "open by fhandle syscalls"
 266        select EXPORTFS
 267        help
 268          If you say Y here, a user level program will be able to map
 269          file names to handle and then later use the handle for
 270          different file system operations. This is useful in implementing
 271          userspace file servers, which now track files using handles instead
 272          of names. The handle would remain the same even if file names
 273          get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
 274          syscalls.
 275
 276config AUDIT
 277        bool "Auditing support"
 278        depends on NET
 279        help
 280          Enable auditing infrastructure that can be used with another
 281          kernel subsystem, such as SELinux (which requires this for
 282          logging of avc messages output).  Does not do system-call
 283          auditing without CONFIG_AUDITSYSCALL.
 284
 285config AUDITSYSCALL
 286        bool "Enable system-call auditing support"
 287        depends on AUDIT && (X86 || PPC || S390 || IA64 || UML || SPARC64 || SUPERH || (ARM && AEABI && !OABI_COMPAT))
 288        default y if SECURITY_SELINUX
 289        help
 290          Enable low-overhead system-call auditing infrastructure that
 291          can be used independently or with another kernel subsystem,
 292          such as SELinux.
 293
 294config AUDIT_WATCH
 295        def_bool y
 296        depends on AUDITSYSCALL
 297        select FSNOTIFY
 298
 299config AUDIT_TREE
 300        def_bool y
 301        depends on AUDITSYSCALL
 302        select FSNOTIFY
 303
 304config AUDIT_LOGINUID_IMMUTABLE
 305        bool "Make audit loginuid immutable"
 306        depends on AUDIT
 307        help
 308          The config option toggles if a task setting its loginuid requires
 309          CAP_SYS_AUDITCONTROL or if that task should require no special permissions
 310          but should instead only allow setting its loginuid if it was never
 311          previously set.  On systems which use systemd or a similar central
 312          process to restart login services this should be set to true.  On older
 313          systems in which an admin would typically have to directly stop and
 314          start processes this should be set to false.  Setting this to true allows
 315          one to drop potentially dangerous capabilites from the login tasks,
 316          but may not be backwards compatible with older init systems.
 317
 318source "kernel/irq/Kconfig"
 319source "kernel/time/Kconfig"
 320
 321menu "CPU/Task time and stats accounting"
 322
 323config VIRT_CPU_ACCOUNTING
 324        bool
 325
 326choice
 327        prompt "Cputime accounting"
 328        default TICK_CPU_ACCOUNTING if !PPC64
 329        default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
 330
 331# Kind of a stub config for the pure tick based cputime accounting
 332config TICK_CPU_ACCOUNTING
 333        bool "Simple tick based cputime accounting"
 334        depends on !S390 && !NO_HZ_FULL
 335        help
 336          This is the basic tick based cputime accounting that maintains
 337          statistics about user, system and idle time spent on per jiffies
 338          granularity.
 339
 340          If unsure, say Y.
 341
 342config VIRT_CPU_ACCOUNTING_NATIVE
 343        bool "Deterministic task and CPU time accounting"
 344        depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
 345        select VIRT_CPU_ACCOUNTING
 346        help
 347          Select this option to enable more accurate task and CPU time
 348          accounting.  This is done by reading a CPU counter on each
 349          kernel entry and exit and on transitions within the kernel
 350          between system, softirq and hardirq state, so there is a
 351          small performance impact.  In the case of s390 or IBM POWER > 5,
 352          this also enables accounting of stolen time on logically-partitioned
 353          systems.
 354
 355config VIRT_CPU_ACCOUNTING_GEN
 356        bool "Full dynticks CPU time accounting"
 357        depends on HAVE_CONTEXT_TRACKING && 64BIT
 358        select VIRT_CPU_ACCOUNTING
 359        select CONTEXT_TRACKING
 360        help
 361          Select this option to enable task and CPU time accounting on full
 362          dynticks systems. This accounting is implemented by watching every
 363          kernel-user boundaries using the context tracking subsystem.
 364          The accounting is thus performed at the expense of some significant
 365          overhead.
 366
 367          For now this is only useful if you are working on the full
 368          dynticks subsystem development.
 369
 370          If unsure, say N.
 371
 372config IRQ_TIME_ACCOUNTING
 373        bool "Fine granularity task level IRQ time accounting"
 374        depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
 375        help
 376          Select this option to enable fine granularity task irq time
 377          accounting. This is done by reading a timestamp on each
 378          transitions between softirq and hardirq state, so there can be a
 379          small performance impact.
 380
 381          If in doubt, say N here.
 382
 383endchoice
 384
 385config BSD_PROCESS_ACCT
 386        bool "BSD Process Accounting"
 387        help
 388          If you say Y here, a user level program will be able to instruct the
 389          kernel (via a special system call) to write process accounting
 390          information to a file: whenever a process exits, information about
 391          that process will be appended to the file by the kernel.  The
 392          information includes things such as creation time, owning user,
 393          command name, memory usage, controlling terminal etc. (the complete
 394          list is in the struct acct in <file:include/linux/acct.h>).  It is
 395          up to the user level program to do useful things with this
 396          information.  This is generally a good idea, so say Y.
 397
 398config BSD_PROCESS_ACCT_V3
 399        bool "BSD Process Accounting version 3 file format"
 400        depends on BSD_PROCESS_ACCT
 401        default n
 402        help
 403          If you say Y here, the process accounting information is written
 404          in a new file format that also logs the process IDs of each
 405          process and it's parent. Note that this file format is incompatible
 406          with previous v0/v1/v2 file formats, so you will need updated tools
 407          for processing it. A preliminary version of these tools is available
 408          at <http://www.gnu.org/software/acct/>.
 409
 410config TASKSTATS
 411        bool "Export task/process statistics through netlink"
 412        depends on NET
 413        default n
 414        help
 415          Export selected statistics for tasks/processes through the
 416          generic netlink interface. Unlike BSD process accounting, the
 417          statistics are available during the lifetime of tasks/processes as
 418          responses to commands. Like BSD accounting, they are sent to user
 419          space on task exit.
 420
 421          Say N if unsure.
 422
 423config TASK_DELAY_ACCT
 424        bool "Enable per-task delay accounting"
 425        depends on TASKSTATS
 426        help
 427          Collect information on time spent by a task waiting for system
 428          resources like cpu, synchronous block I/O completion and swapping
 429          in pages. Such statistics can help in setting a task's priorities
 430          relative to other tasks for cpu, io, rss limits etc.
 431
 432          Say N if unsure.
 433
 434config TASK_XACCT
 435        bool "Enable extended accounting over taskstats"
 436        depends on TASKSTATS
 437        help
 438          Collect extended task accounting data and send the data
 439          to userland for processing over the taskstats interface.
 440
 441          Say N if unsure.
 442
 443config TASK_IO_ACCOUNTING
 444        bool "Enable per-task storage I/O accounting"
 445        depends on TASK_XACCT
 446        help
 447          Collect information on the number of bytes of storage I/O which this
 448          task has caused.
 449
 450          Say N if unsure.
 451
 452endmenu # "CPU/Task time and stats accounting"
 453
 454menu "RCU Subsystem"
 455
 456choice
 457        prompt "RCU Implementation"
 458        default TREE_RCU
 459
 460config TREE_RCU
 461        bool "Tree-based hierarchical RCU"
 462        depends on !PREEMPT && SMP
 463        select IRQ_WORK
 464        help
 465          This option selects the RCU implementation that is
 466          designed for very large SMP system with hundreds or
 467          thousands of CPUs.  It also scales down nicely to
 468          smaller systems.
 469
 470config TREE_PREEMPT_RCU
 471        bool "Preemptible tree-based hierarchical RCU"
 472        depends on PREEMPT
 473        select IRQ_WORK
 474        help
 475          This option selects the RCU implementation that is
 476          designed for very large SMP systems with hundreds or
 477          thousands of CPUs, but for which real-time response
 478          is also required.  It also scales down nicely to
 479          smaller systems.
 480
 481          Select this option if you are unsure.
 482
 483config TINY_RCU
 484        bool "UP-only small-memory-footprint RCU"
 485        depends on !PREEMPT && !SMP
 486        help
 487          This option selects the RCU implementation that is
 488          designed for UP systems from which real-time response
 489          is not required.  This option greatly reduces the
 490          memory footprint of RCU.
 491
 492endchoice
 493
 494config PREEMPT_RCU
 495        def_bool TREE_PREEMPT_RCU
 496        help
 497          This option enables preemptible-RCU code that is common between
 498          the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
 499
 500config RCU_STALL_COMMON
 501        def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
 502        help
 503          This option enables RCU CPU stall code that is common between
 504          the TINY and TREE variants of RCU.  The purpose is to allow
 505          the tiny variants to disable RCU CPU stall warnings, while
 506          making these warnings mandatory for the tree variants.
 507
 508config CONTEXT_TRACKING
 509       bool
 510
 511config RCU_USER_QS
 512        bool "Consider userspace as in RCU extended quiescent state"
 513        depends on HAVE_CONTEXT_TRACKING && SMP
 514        select CONTEXT_TRACKING
 515        help
 516          This option sets hooks on kernel / userspace boundaries and
 517          puts RCU in extended quiescent state when the CPU runs in
 518          userspace. It means that when a CPU runs in userspace, it is
 519          excluded from the global RCU state machine and thus doesn't
 520          try to keep the timer tick on for RCU.
 521
 522          Unless you want to hack and help the development of the full
 523          dynticks mode, you shouldn't enable this option.  It also
 524          adds unnecessary overhead.
 525
 526          If unsure say N
 527
 528config CONTEXT_TRACKING_FORCE
 529        bool "Force context tracking"
 530        depends on CONTEXT_TRACKING
 531        default y if !NO_HZ_FULL
 532        help
 533          The major pre-requirement for full dynticks to work is to
 534          support the context tracking subsystem. But there are also
 535          other dependencies to provide in order to make the full
 536          dynticks working.
 537
 538          This option stands for testing when an arch implements the
 539          context tracking backend but doesn't yet fullfill all the
 540          requirements to make the full dynticks feature working.
 541          Without the full dynticks, there is no way to test the support
 542          for context tracking and the subsystems that rely on it: RCU
 543          userspace extended quiescent state and tickless cputime
 544          accounting. This option copes with the absence of the full
 545          dynticks subsystem by forcing the context tracking on all
 546          CPUs in the system.
 547
 548          Say Y only if you're working on the developpement of an
 549          architecture backend for the context tracking.
 550
 551          Say N otherwise, this option brings an overhead that you
 552          don't want in production.
 553
 554
 555config RCU_FANOUT
 556        int "Tree-based hierarchical RCU fanout value"
 557        range 2 64 if 64BIT
 558        range 2 32 if !64BIT
 559        depends on TREE_RCU || TREE_PREEMPT_RCU
 560        default 64 if 64BIT
 561        default 32 if !64BIT
 562        help
 563          This option controls the fanout of hierarchical implementations
 564          of RCU, allowing RCU to work efficiently on machines with
 565          large numbers of CPUs.  This value must be at least the fourth
 566          root of NR_CPUS, which allows NR_CPUS to be insanely large.
 567          The default value of RCU_FANOUT should be used for production
 568          systems, but if you are stress-testing the RCU implementation
 569          itself, small RCU_FANOUT values allow you to test large-system
 570          code paths on small(er) systems.
 571
 572          Select a specific number if testing RCU itself.
 573          Take the default if unsure.
 574
 575config RCU_FANOUT_LEAF
 576        int "Tree-based hierarchical RCU leaf-level fanout value"
 577        range 2 RCU_FANOUT if 64BIT
 578        range 2 RCU_FANOUT if !64BIT
 579        depends on TREE_RCU || TREE_PREEMPT_RCU
 580        default 16
 581        help
 582          This option controls the leaf-level fanout of hierarchical
 583          implementations of RCU, and allows trading off cache misses
 584          against lock contention.  Systems that synchronize their
 585          scheduling-clock interrupts for energy-efficiency reasons will
 586          want the default because the smaller leaf-level fanout keeps
 587          lock contention levels acceptably low.  Very large systems
 588          (hundreds or thousands of CPUs) will instead want to set this
 589          value to the maximum value possible in order to reduce the
 590          number of cache misses incurred during RCU's grace-period
 591          initialization.  These systems tend to run CPU-bound, and thus
 592          are not helped by synchronized interrupts, and thus tend to
 593          skew them, which reduces lock contention enough that large
 594          leaf-level fanouts work well.
 595
 596          Select a specific number if testing RCU itself.
 597
 598          Select the maximum permissible value for large systems.
 599
 600          Take the default if unsure.
 601
 602config RCU_FANOUT_EXACT
 603        bool "Disable tree-based hierarchical RCU auto-balancing"
 604        depends on TREE_RCU || TREE_PREEMPT_RCU
 605        default n
 606        help
 607          This option forces use of the exact RCU_FANOUT value specified,
 608          regardless of imbalances in the hierarchy.  This is useful for
 609          testing RCU itself, and might one day be useful on systems with
 610          strong NUMA behavior.
 611
 612          Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
 613
 614          Say N if unsure.
 615
 616config RCU_FAST_NO_HZ
 617        bool "Accelerate last non-dyntick-idle CPU's grace periods"
 618        depends on NO_HZ_COMMON && SMP
 619        default n
 620        help
 621          This option permits CPUs to enter dynticks-idle state even if
 622          they have RCU callbacks queued, and prevents RCU from waking
 623          these CPUs up more than roughly once every four jiffies (by
 624          default, you can adjust this using the rcutree.rcu_idle_gp_delay
 625          parameter), thus improving energy efficiency.  On the other
 626          hand, this option increases the duration of RCU grace periods,
 627          for example, slowing down synchronize_rcu().
 628
 629          Say Y if energy efficiency is critically important, and you
 630                don't care about increased grace-period durations.
 631
 632          Say N if you are unsure.
 633
 634config TREE_RCU_TRACE
 635        def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
 636        select DEBUG_FS
 637        help
 638          This option provides tracing for the TREE_RCU and
 639          TREE_PREEMPT_RCU implementations, permitting Makefile to
 640          trivially select kernel/rcutree_trace.c.
 641
 642config RCU_BOOST
 643        bool "Enable RCU priority boosting"
 644        depends on RT_MUTEXES && PREEMPT_RCU
 645        default n
 646        help
 647          This option boosts the priority of preempted RCU readers that
 648          block the current preemptible RCU grace period for too long.
 649          This option also prevents heavy loads from blocking RCU
 650          callback invocation for all flavors of RCU.
 651
 652          Say Y here if you are working with real-time apps or heavy loads
 653          Say N here if you are unsure.
 654
 655config RCU_BOOST_PRIO
 656        int "Real-time priority to boost RCU readers to"
 657        range 1 99
 658        depends on RCU_BOOST
 659        default 1
 660        help
 661          This option specifies the real-time priority to which long-term
 662          preempted RCU readers are to be boosted.  If you are working
 663          with a real-time application that has one or more CPU-bound
 664          threads running at a real-time priority level, you should set
 665          RCU_BOOST_PRIO to a priority higher then the highest-priority
 666          real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
 667          of 1 is appropriate in the common case, which is real-time
 668          applications that do not have any CPU-bound threads.
 669
 670          Some real-time applications might not have a single real-time
 671          thread that saturates a given CPU, but instead might have
 672          multiple real-time threads that, taken together, fully utilize
 673          that CPU.  In this case, you should set RCU_BOOST_PRIO to
 674          a priority higher than the lowest-priority thread that is
 675          conspiring to prevent the CPU from running any non-real-time
 676          tasks.  For example, if one thread at priority 10 and another
 677          thread at priority 5 are between themselves fully consuming
 678          the CPU time on a given CPU, then RCU_BOOST_PRIO should be
 679          set to priority 6 or higher.
 680
 681          Specify the real-time priority, or take the default if unsure.
 682
 683config RCU_BOOST_DELAY
 684        int "Milliseconds to delay boosting after RCU grace-period start"
 685        range 0 3000
 686        depends on RCU_BOOST
 687        default 500
 688        help
 689          This option specifies the time to wait after the beginning of
 690          a given grace period before priority-boosting preempted RCU
 691          readers blocking that grace period.  Note that any RCU reader
 692          blocking an expedited RCU grace period is boosted immediately.
 693
 694          Accept the default if unsure.
 695
 696config RCU_NOCB_CPU
 697        bool "Offload RCU callback processing from boot-selected CPUs"
 698        depends on TREE_RCU || TREE_PREEMPT_RCU
 699        default n
 700        help
 701          Use this option to reduce OS jitter for aggressive HPC or
 702          real-time workloads.  It can also be used to offload RCU
 703          callback invocation to energy-efficient CPUs in battery-powered
 704          asymmetric multiprocessors.
 705
 706          This option offloads callback invocation from the set of
 707          CPUs specified at boot time by the rcu_nocbs parameter.
 708          For each such CPU, a kthread ("rcuox/N") will be created to
 709          invoke callbacks, where the "N" is the CPU being offloaded,
 710          and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
 711          "s" for RCU-sched.  Nothing prevents this kthread from running
 712          on the specified CPUs, but (1) the kthreads may be preempted
 713          between each callback, and (2) affinity or cgroups can be used
 714          to force the kthreads to run on whatever set of CPUs is desired.
 715
 716          Say Y here if you want to help to debug reduced OS jitter.
 717          Say N here if you are unsure.
 718
 719choice
 720        prompt "Build-forced no-CBs CPUs"
 721        default RCU_NOCB_CPU_NONE
 722        help
 723          This option allows no-CBs CPUs (whose RCU callbacks are invoked
 724          from kthreads rather than from softirq context) to be specified
 725          at build time.  Additional no-CBs CPUs may be specified by
 726          the rcu_nocbs= boot parameter.
 727
 728config RCU_NOCB_CPU_NONE
 729        bool "No build_forced no-CBs CPUs"
 730        depends on RCU_NOCB_CPU && !NO_HZ_FULL
 731        help
 732          This option does not force any of the CPUs to be no-CBs CPUs.
 733          Only CPUs designated by the rcu_nocbs= boot parameter will be
 734          no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
 735          kthreads whose names begin with "rcuo".  All other CPUs will
 736          invoke their own RCU callbacks in softirq context.
 737
 738          Select this option if you want to choose no-CBs CPUs at
 739          boot time, for example, to allow testing of different no-CBs
 740          configurations without having to rebuild the kernel each time.
 741
 742config RCU_NOCB_CPU_ZERO
 743        bool "CPU 0 is a build_forced no-CBs CPU"
 744        depends on RCU_NOCB_CPU && !NO_HZ_FULL
 745        help
 746          This option forces CPU 0 to be a no-CBs CPU, so that its RCU
 747          callbacks are invoked by a per-CPU kthread whose name begins
 748          with "rcuo".  Additional CPUs may be designated as no-CBs
 749          CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
 750          All other CPUs will invoke their own RCU callbacks in softirq
 751          context.
 752
 753          Select this if CPU 0 needs to be a no-CBs CPU for real-time
 754          or energy-efficiency reasons, but the real reason it exists
 755          is to ensure that randconfig testing covers mixed systems.
 756
 757config RCU_NOCB_CPU_ALL
 758        bool "All CPUs are build_forced no-CBs CPUs"
 759        depends on RCU_NOCB_CPU
 760        help
 761          This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
 762          boot parameter will be ignored.  All CPUs' RCU callbacks will
 763          be executed in the context of per-CPU rcuo kthreads created for
 764          this purpose.  Assuming that the kthreads whose names start with
 765          "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
 766          on the remaining CPUs, but might decrease memory locality during
 767          RCU-callback invocation, thus potentially degrading throughput.
 768
 769          Select this if all CPUs need to be no-CBs CPUs for real-time
 770          or energy-efficiency reasons.
 771
 772endchoice
 773
 774endmenu # "RCU Subsystem"
 775
 776config IKCONFIG
 777        tristate "Kernel .config support"
 778        ---help---
 779          This option enables the complete Linux kernel ".config" file
 780          contents to be saved in the kernel. It provides documentation
 781          of which kernel options are used in a running kernel or in an
 782          on-disk kernel.  This information can be extracted from the kernel
 783          image file with the script scripts/extract-ikconfig and used as
 784          input to rebuild the current kernel or to build another kernel.
 785          It can also be extracted from a running kernel by reading
 786          /proc/config.gz if enabled (below).
 787
 788config IKCONFIG_PROC
 789        bool "Enable access to .config through /proc/config.gz"
 790        depends on IKCONFIG && PROC_FS
 791        ---help---
 792          This option enables access to the kernel configuration file
 793          through /proc/config.gz.
 794
 795config LOG_BUF_SHIFT
 796        int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
 797        range 12 21
 798        default 17
 799        help
 800          Select kernel log buffer size as a power of 2.
 801          Examples:
 802                     17 => 128 KB
 803                     16 => 64 KB
 804                     15 => 32 KB
 805                     14 => 16 KB
 806                     13 =>  8 KB
 807                     12 =>  4 KB
 808
 809#
 810# Architectures with an unreliable sched_clock() should select this:
 811#
 812config HAVE_UNSTABLE_SCHED_CLOCK
 813        bool
 814
 815config GENERIC_SCHED_CLOCK
 816        bool
 817
 818#
 819# For architectures that want to enable the support for NUMA-affine scheduler
 820# balancing logic:
 821#
 822config ARCH_SUPPORTS_NUMA_BALANCING
 823        bool
 824
 825# For architectures that (ab)use NUMA to represent different memory regions
 826# all cpu-local but of different latencies, such as SuperH.
 827#
 828config ARCH_WANT_NUMA_VARIABLE_LOCALITY
 829        bool
 830
 831#
 832# For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
 833config ARCH_WANTS_PROT_NUMA_PROT_NONE
 834        bool
 835
 836config ARCH_USES_NUMA_PROT_NONE
 837        bool
 838        default y
 839        depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
 840        depends on NUMA_BALANCING
 841
 842config NUMA_BALANCING_DEFAULT_ENABLED
 843        bool "Automatically enable NUMA aware memory/task placement"
 844        default y
 845        depends on NUMA_BALANCING
 846        help
 847          If set, autonumic NUMA balancing will be enabled if running on a NUMA
 848          machine.
 849
 850config NUMA_BALANCING
 851        bool "Memory placement aware NUMA scheduler"
 852        depends on ARCH_SUPPORTS_NUMA_BALANCING
 853        depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
 854        depends on SMP && NUMA && MIGRATION
 855        help
 856          This option adds support for automatic NUMA aware memory/task placement.
 857          The mechanism is quite primitive and is based on migrating memory when
 858          it is references to the node the task is running on.
 859
 860          This system will be inactive on UMA systems.
 861
 862menuconfig CGROUPS
 863        boolean "Control Group support"
 864        depends on EVENTFD
 865        help
 866          This option adds support for grouping sets of processes together, for
 867          use with process control subsystems such as Cpusets, CFS, memory
 868          controls or device isolation.
 869          See
 870                - Documentation/scheduler/sched-design-CFS.txt  (CFS)
 871                - Documentation/cgroups/ (features for grouping, isolation
 872                                          and resource control)
 873
 874          Say N if unsure.
 875
 876if CGROUPS
 877
 878config CGROUP_DEBUG
 879        bool "Example debug cgroup subsystem"
 880        default n
 881        help
 882          This option enables a simple cgroup subsystem that
 883          exports useful debugging information about the cgroups
 884          framework.
 885
 886          Say N if unsure.
 887
 888config CGROUP_FREEZER
 889        bool "Freezer cgroup subsystem"
 890        help
 891          Provides a way to freeze and unfreeze all tasks in a
 892          cgroup.
 893
 894config CGROUP_DEVICE
 895        bool "Device controller for cgroups"
 896        help
 897          Provides a cgroup implementing whitelists for devices which
 898          a process in the cgroup can mknod or open.
 899
 900config CPUSETS
 901        bool "Cpuset support"
 902        help
 903          This option will let you create and manage CPUSETs which
 904          allow dynamically partitioning a system into sets of CPUs and
 905          Memory Nodes and assigning tasks to run only within those sets.
 906          This is primarily useful on large SMP or NUMA systems.
 907
 908          Say N if unsure.
 909
 910config PROC_PID_CPUSET
 911        bool "Include legacy /proc/<pid>/cpuset file"
 912        depends on CPUSETS
 913        default y
 914
 915config CGROUP_CPUACCT
 916        bool "Simple CPU accounting cgroup subsystem"
 917        help
 918          Provides a simple Resource Controller for monitoring the
 919          total CPU consumed by the tasks in a cgroup.
 920
 921config RESOURCE_COUNTERS
 922        bool "Resource counters"
 923        help
 924          This option enables controller independent resource accounting
 925          infrastructure that works with cgroups.
 926
 927config MEMCG
 928        bool "Memory Resource Controller for Control Groups"
 929        depends on RESOURCE_COUNTERS
 930        select MM_OWNER
 931        help
 932          Provides a memory resource controller that manages both anonymous
 933          memory and page cache. (See Documentation/cgroups/memory.txt)
 934
 935          Note that setting this option increases fixed memory overhead
 936          associated with each page of memory in the system. By this,
 937          8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
 938          usage tracking struct at boot. Total amount of this is printed out
 939          at boot.
 940
 941          Only enable when you're ok with these trade offs and really
 942          sure you need the memory resource controller. Even when you enable
 943          this, you can set "cgroup_disable=memory" at your boot option to
 944          disable memory resource controller and you can avoid overheads.
 945          (and lose benefits of memory resource controller)
 946
 947          This config option also selects MM_OWNER config option, which
 948          could in turn add some fork/exit overhead.
 949
 950config MEMCG_SWAP
 951        bool "Memory Resource Controller Swap Extension"
 952        depends on MEMCG && SWAP
 953        help
 954          Add swap management feature to memory resource controller. When you
 955          enable this, you can limit mem+swap usage per cgroup. In other words,
 956          when you disable this, memory resource controller has no cares to
 957          usage of swap...a process can exhaust all of the swap. This extension
 958          is useful when you want to avoid exhaustion swap but this itself
 959          adds more overheads and consumes memory for remembering information.
 960          Especially if you use 32bit system or small memory system, please
 961          be careful about enabling this. When memory resource controller
 962          is disabled by boot option, this will be automatically disabled and
 963          there will be no overhead from this. Even when you set this config=y,
 964          if boot option "swapaccount=0" is set, swap will not be accounted.
 965          Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
 966          size is 4096bytes, 512k per 1Gbytes of swap.
 967config MEMCG_SWAP_ENABLED
 968        bool "Memory Resource Controller Swap Extension enabled by default"
 969        depends on MEMCG_SWAP
 970        default y
 971        help
 972          Memory Resource Controller Swap Extension comes with its price in
 973          a bigger memory consumption. General purpose distribution kernels
 974          which want to enable the feature but keep it disabled by default
 975          and let the user enable it by swapaccount=1 boot command line
 976          parameter should have this option unselected.
 977          For those who want to have the feature enabled by default should
 978          select this option (if, for some reason, they need to disable it
 979          then swapaccount=0 does the trick).
 980config MEMCG_KMEM
 981        bool "Memory Resource Controller Kernel Memory accounting"
 982        depends on MEMCG
 983        depends on SLUB || SLAB
 984        help
 985          The Kernel Memory extension for Memory Resource Controller can limit
 986          the amount of memory used by kernel objects in the system. Those are
 987          fundamentally different from the entities handled by the standard
 988          Memory Controller, which are page-based, and can be swapped. Users of
 989          the kmem extension can use it to guarantee that no group of processes
 990          will ever exhaust kernel resources alone.
 991
 992config CGROUP_HUGETLB
 993        bool "HugeTLB Resource Controller for Control Groups"
 994        depends on RESOURCE_COUNTERS && HUGETLB_PAGE
 995        default n
 996        help
 997          Provides a cgroup Resource Controller for HugeTLB pages.
 998          When you enable this, you can put a per cgroup limit on HugeTLB usage.
 999          The limit is enforced during page fault. Since HugeTLB doesn't
1000          support page reclaim, enforcing the limit at page fault time implies
1001          that, the application will get SIGBUS signal if it tries to access
1002          HugeTLB pages beyond its limit. This requires the application to know
1003          beforehand how much HugeTLB pages it would require for its use. The
1004          control group is tracked in the third page lru pointer. This means
1005          that we cannot use the controller with huge page less than 3 pages.
1006
1007config CGROUP_PERF
1008        bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
1009        depends on PERF_EVENTS && CGROUPS
1010        help
1011          This option extends the per-cpu mode to restrict monitoring to
1012          threads which belong to the cgroup specified and run on the
1013          designated cpu.
1014
1015          Say N if unsure.
1016
1017menuconfig CGROUP_SCHED
1018        bool "Group CPU scheduler"
1019        default n
1020        help
1021          This feature lets CPU scheduler recognize task groups and control CPU
1022          bandwidth allocation to such task groups. It uses cgroups to group
1023          tasks.
1024
1025if CGROUP_SCHED
1026config FAIR_GROUP_SCHED
1027        bool "Group scheduling for SCHED_OTHER"
1028        depends on CGROUP_SCHED
1029        default CGROUP_SCHED
1030
1031config CFS_BANDWIDTH
1032        bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1033        depends on FAIR_GROUP_SCHED
1034        default n
1035        help
1036          This option allows users to define CPU bandwidth rates (limits) for
1037          tasks running within the fair group scheduler.  Groups with no limit
1038          set are considered to be unconstrained and will run with no
1039          restriction.
1040          See tip/Documentation/scheduler/sched-bwc.txt for more information.
1041
1042config RT_GROUP_SCHED
1043        bool "Group scheduling for SCHED_RR/FIFO"
1044        depends on CGROUP_SCHED
1045        default n
1046        help
1047          This feature lets you explicitly allocate real CPU bandwidth
1048          to task groups. If enabled, it will also make it impossible to
1049          schedule realtime tasks for non-root users until you allocate
1050          realtime bandwidth for them.
1051          See Documentation/scheduler/sched-rt-group.txt for more information.
1052
1053endif #CGROUP_SCHED
1054
1055config BLK_CGROUP
1056        bool "Block IO controller"
1057        depends on BLOCK
1058        default n
1059        ---help---
1060        Generic block IO controller cgroup interface. This is the common
1061        cgroup interface which should be used by various IO controlling
1062        policies.
1063
1064        Currently, CFQ IO scheduler uses it to recognize task groups and
1065        control disk bandwidth allocation (proportional time slice allocation)
1066        to such task groups. It is also used by bio throttling logic in
1067        block layer to implement upper limit in IO rates on a device.
1068
1069        This option only enables generic Block IO controller infrastructure.
1070        One needs to also enable actual IO controlling logic/policy. For
1071        enabling proportional weight division of disk bandwidth in CFQ, set
1072        CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1073        CONFIG_BLK_DEV_THROTTLING=y.
1074
1075        See Documentation/cgroups/blkio-controller.txt for more information.
1076
1077config DEBUG_BLK_CGROUP
1078        bool "Enable Block IO controller debugging"
1079        depends on BLK_CGROUP
1080        default n
1081        ---help---
1082        Enable some debugging help. Currently it exports additional stat
1083        files in a cgroup which can be useful for debugging.
1084
1085endif # CGROUPS
1086
1087config CHECKPOINT_RESTORE
1088        bool "Checkpoint/restore support" if EXPERT
1089        default n
1090        help
1091          Enables additional kernel features in a sake of checkpoint/restore.
1092          In particular it adds auxiliary prctl codes to setup process text,
1093          data and heap segment sizes, and a few additional /proc filesystem
1094          entries.
1095
1096          If unsure, say N here.
1097
1098menuconfig NAMESPACES
1099        bool "Namespaces support" if EXPERT
1100        default !EXPERT
1101        help
1102          Provides the way to make tasks work with different objects using
1103          the same id. For example same IPC id may refer to different objects
1104          or same user id or pid may refer to different tasks when used in
1105          different namespaces.
1106
1107if NAMESPACES
1108
1109config UTS_NS
1110        bool "UTS namespace"
1111        default y
1112        help
1113          In this namespace tasks see different info provided with the
1114          uname() system call
1115
1116config IPC_NS
1117        bool "IPC namespace"
1118        depends on (SYSVIPC || POSIX_MQUEUE)
1119        default y
1120        help
1121          In this namespace tasks work with IPC ids which correspond to
1122          different IPC objects in different namespaces.
1123
1124config USER_NS
1125        bool "User namespace"
1126        select UIDGID_STRICT_TYPE_CHECKS
1127
1128        default n
1129        help
1130          This allows containers, i.e. vservers, to use user namespaces
1131          to provide different user info for different servers.
1132
1133          When user namespaces are enabled in the kernel it is
1134          recommended that the MEMCG and MEMCG_KMEM options also be
1135          enabled and that user-space use the memory control groups to
1136          limit the amount of memory a memory unprivileged users can
1137          use.
1138
1139          If unsure, say N.
1140
1141config PID_NS
1142        bool "PID Namespaces"
1143        default y
1144        help
1145          Support process id namespaces.  This allows having multiple
1146          processes with the same pid as long as they are in different
1147          pid namespaces.  This is a building block of containers.
1148
1149config NET_NS
1150        bool "Network namespace"
1151        depends on NET
1152        default y
1153        help
1154          Allow user space to create what appear to be multiple instances
1155          of the network stack.
1156
1157endif # NAMESPACES
1158
1159config UIDGID_STRICT_TYPE_CHECKS
1160        bool "Require conversions between uid/gids and their internal representation"
1161        default n
1162        help
1163         While the nececessary conversions are being added to all subsystems this option allows
1164         the code to continue to build for unconverted subsystems.
1165
1166         Say Y here if you want the strict type checking enabled
1167
1168config SCHED_AUTOGROUP
1169        bool "Automatic process group scheduling"
1170        select EVENTFD
1171        select CGROUPS
1172        select CGROUP_SCHED
1173        select FAIR_GROUP_SCHED
1174        help
1175          This option optimizes the scheduler for common desktop workloads by
1176          automatically creating and populating task groups.  This separation
1177          of workloads isolates aggressive CPU burners (like build jobs) from
1178          desktop applications.  Task group autogeneration is currently based
1179          upon task session.
1180
1181config MM_OWNER
1182        bool
1183
1184config SYSFS_DEPRECATED
1185        bool "Enable deprecated sysfs features to support old userspace tools"
1186        depends on SYSFS
1187        default n
1188        help
1189          This option adds code that switches the layout of the "block" class
1190          devices, to not show up in /sys/class/block/, but only in
1191          /sys/block/.
1192
1193          This switch is only active when the sysfs.deprecated=1 boot option is
1194          passed or the SYSFS_DEPRECATED_V2 option is set.
1195
1196          This option allows new kernels to run on old distributions and tools,
1197          which might get confused by /sys/class/block/. Since 2007/2008 all
1198          major distributions and tools handle this just fine.
1199
1200          Recent distributions and userspace tools after 2009/2010 depend on
1201          the existence of /sys/class/block/, and will not work with this
1202          option enabled.
1203
1204          Only if you are using a new kernel on an old distribution, you might
1205          need to say Y here.
1206
1207config SYSFS_DEPRECATED_V2
1208        bool "Enable deprecated sysfs features by default"
1209        default n
1210        depends on SYSFS
1211        depends on SYSFS_DEPRECATED
1212        help
1213          Enable deprecated sysfs by default.
1214
1215          See the CONFIG_SYSFS_DEPRECATED option for more details about this
1216          option.
1217
1218          Only if you are using a new kernel on an old distribution, you might
1219          need to say Y here. Even then, odds are you would not need it
1220          enabled, you can always pass the boot option if absolutely necessary.
1221
1222config RELAY
1223        bool "Kernel->user space relay support (formerly relayfs)"
1224        help
1225          This option enables support for relay interface support in
1226          certain file systems (such as debugfs).
1227          It is designed to provide an efficient mechanism for tools and
1228          facilities to relay large amounts of data from kernel space to
1229          user space.
1230
1231          If unsure, say N.
1232
1233config BLK_DEV_INITRD
1234        bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1235        depends on BROKEN || !FRV
1236        help
1237          The initial RAM filesystem is a ramfs which is loaded by the
1238          boot loader (loadlin or lilo) and that is mounted as root
1239          before the normal boot procedure. It is typically used to
1240          load modules needed to mount the "real" root file system,
1241          etc. See <file:Documentation/initrd.txt> for details.
1242
1243          If RAM disk support (BLK_DEV_RAM) is also included, this
1244          also enables initial RAM disk (initrd) support and adds
1245          15 Kbytes (more on some other architectures) to the kernel size.
1246
1247          If unsure say Y.
1248
1249if BLK_DEV_INITRD
1250
1251source "usr/Kconfig"
1252
1253endif
1254
1255config CC_OPTIMIZE_FOR_SIZE
1256        bool "Optimize for size"
1257        help
1258          Enabling this option will pass "-Os" instead of "-O2" to gcc
1259          resulting in a smaller kernel.
1260
1261          If unsure, say N.
1262
1263config SYSCTL
1264        bool
1265
1266config ANON_INODES
1267        bool
1268
1269config HAVE_UID16
1270        bool
1271
1272config SYSCTL_EXCEPTION_TRACE
1273        bool
1274        help
1275          Enable support for /proc/sys/debug/exception-trace.
1276
1277config SYSCTL_ARCH_UNALIGN_NO_WARN
1278        bool
1279        help
1280          Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1281          Allows arch to define/use @no_unaligned_warning to possibly warn
1282          about unaligned access emulation going on under the hood.
1283
1284config SYSCTL_ARCH_UNALIGN_ALLOW
1285        bool
1286        help
1287          Enable support for /proc/sys/kernel/unaligned-trap
1288          Allows arches to define/use @unaligned_enabled to runtime toggle
1289          the unaligned access emulation.
1290          see arch/parisc/kernel/unaligned.c for reference
1291
1292config HAVE_PCSPKR_PLATFORM
1293        bool
1294
1295menuconfig EXPERT
1296        bool "Configure standard kernel features (expert users)"
1297        # Unhide debug options, to make the on-by-default options visible
1298        select DEBUG_KERNEL
1299        help
1300          This option allows certain base kernel options and settings
1301          to be disabled or tweaked. This is for specialized
1302          environments which can tolerate a "non-standard" kernel.
1303          Only use this if you really know what you are doing.
1304
1305config UID16
1306        bool "Enable 16-bit UID system calls" if EXPERT
1307        depends on HAVE_UID16
1308        default y
1309        help
1310          This enables the legacy 16-bit UID syscall wrappers.
1311
1312config SYSCTL_SYSCALL
1313        bool "Sysctl syscall support" if EXPERT
1314        depends on PROC_SYSCTL
1315        default n
1316        select SYSCTL
1317        ---help---
1318          sys_sysctl uses binary paths that have been found challenging
1319          to properly maintain and use.  The interface in /proc/sys
1320          using paths with ascii names is now the primary path to this
1321          information.
1322
1323          Almost nothing using the binary sysctl interface so if you are
1324          trying to save some space it is probably safe to disable this,
1325          making your kernel marginally smaller.
1326
1327          If unsure say N here.
1328
1329config KALLSYMS
1330         bool "Load all symbols for debugging/ksymoops" if EXPERT
1331         default y
1332         help
1333           Say Y here to let the kernel print out symbolic crash information and
1334           symbolic stack backtraces. This increases the size of the kernel
1335           somewhat, as all symbols have to be loaded into the kernel image.
1336
1337config KALLSYMS_ALL
1338        bool "Include all symbols in kallsyms"
1339        depends on DEBUG_KERNEL && KALLSYMS
1340        help
1341           Normally kallsyms only contains the symbols of functions for nicer
1342           OOPS messages and backtraces (i.e., symbols from the text and inittext
1343           sections). This is sufficient for most cases. And only in very rare
1344           cases (e.g., when a debugger is used) all symbols are required (e.g.,
1345           names of variables from the data sections, etc).
1346
1347           This option makes sure that all symbols are loaded into the kernel
1348           image (i.e., symbols from all sections) in cost of increased kernel
1349           size (depending on the kernel configuration, it may be 300KiB or
1350           something like this).
1351
1352           Say N unless you really need all symbols.
1353
1354config PRINTK
1355        default y
1356        bool "Enable support for printk" if EXPERT
1357        select IRQ_WORK
1358        help
1359          This option enables normal printk support. Removing it
1360          eliminates most of the message strings from the kernel image
1361          and makes the kernel more or less silent. As this makes it
1362          very difficult to diagnose system problems, saying N here is
1363          strongly discouraged.
1364
1365config BUG
1366        bool "BUG() support" if EXPERT
1367        default y
1368        help
1369          Disabling this option eliminates support for BUG and WARN, reducing
1370          the size of your kernel image and potentially quietly ignoring
1371          numerous fatal conditions. You should only consider disabling this
1372          option for embedded systems with no facilities for reporting errors.
1373          Just say Y.
1374
1375config ELF_CORE
1376        depends on COREDUMP
1377        default y
1378        bool "Enable ELF core dumps" if EXPERT
1379        help
1380          Enable support for generating core dumps. Disabling saves about 4k.
1381
1382
1383config PCSPKR_PLATFORM
1384        bool "Enable PC-Speaker support" if EXPERT
1385        depends on HAVE_PCSPKR_PLATFORM
1386        select I8253_LOCK
1387        default y
1388        help
1389          This option allows to disable the internal PC-Speaker
1390          support, saving some memory.
1391
1392config BASE_FULL
1393        default y
1394        bool "Enable full-sized data structures for core" if EXPERT
1395        help
1396          Disabling this option reduces the size of miscellaneous core
1397          kernel data structures. This saves memory on small machines,
1398          but may reduce performance.
1399
1400config FUTEX
1401        bool "Enable futex support" if EXPERT
1402        default y
1403        select RT_MUTEXES
1404        help
1405          Disabling this option will cause the kernel to be built without
1406          support for "fast userspace mutexes".  The resulting kernel may not
1407          run glibc-based applications correctly.
1408
1409config EPOLL
1410        bool "Enable eventpoll support" if EXPERT
1411        default y
1412        select ANON_INODES
1413        help
1414          Disabling this option will cause the kernel to be built without
1415          support for epoll family of system calls.
1416
1417config SIGNALFD
1418        bool "Enable signalfd() system call" if EXPERT
1419        select ANON_INODES
1420        default y
1421        help
1422          Enable the signalfd() system call that allows to receive signals
1423          on a file descriptor.
1424
1425          If unsure, say Y.
1426
1427config TIMERFD
1428        bool "Enable timerfd() system call" if EXPERT
1429        select ANON_INODES
1430        default y
1431        help
1432          Enable the timerfd() system call that allows to receive timer
1433          events on a file descriptor.
1434
1435          If unsure, say Y.
1436
1437config EVENTFD
1438        bool "Enable eventfd() system call" if EXPERT
1439        select ANON_INODES
1440        default y
1441        help
1442          Enable the eventfd() system call that allows to receive both
1443          kernel notification (ie. KAIO) or userspace notifications.
1444
1445          If unsure, say Y.
1446
1447config SHMEM
1448        bool "Use full shmem filesystem" if EXPERT
1449        default y
1450        depends on MMU
1451        help
1452          The shmem is an internal filesystem used to manage shared memory.
1453          It is backed by swap and manages resource limits. It is also exported
1454          to userspace as tmpfs if TMPFS is enabled. Disabling this
1455          option replaces shmem and tmpfs with the much simpler ramfs code,
1456          which may be appropriate on small systems without swap.
1457
1458config AIO
1459        bool "Enable AIO support" if EXPERT
1460        default y
1461        help
1462          This option enables POSIX asynchronous I/O which may by used
1463          by some high performance threaded applications. Disabling
1464          this option saves about 7k.
1465
1466config PCI_QUIRKS
1467        default y
1468        bool "Enable PCI quirk workarounds" if EXPERT
1469        depends on PCI
1470        help
1471          This enables workarounds for various PCI chipset
1472          bugs/quirks. Disable this only if your target machine is
1473          unaffected by PCI quirks.
1474
1475config EMBEDDED
1476        bool "Embedded system"
1477        select EXPERT
1478        help
1479          This option should be enabled if compiling the kernel for
1480          an embedded system so certain expert options are available
1481          for configuration.
1482
1483config HAVE_PERF_EVENTS
1484        bool
1485        help
1486          See tools/perf/design.txt for details.
1487
1488config PERF_USE_VMALLOC
1489        bool
1490        help
1491          See tools/perf/design.txt for details
1492
1493menu "Kernel Performance Events And Counters"
1494
1495config PERF_EVENTS
1496        bool "Kernel performance events and counters"
1497        default y if PROFILING
1498        depends on HAVE_PERF_EVENTS
1499        select ANON_INODES
1500        select IRQ_WORK
1501        help
1502          Enable kernel support for various performance events provided
1503          by software and hardware.
1504
1505          Software events are supported either built-in or via the
1506          use of generic tracepoints.
1507
1508          Most modern CPUs support performance events via performance
1509          counter registers. These registers count the number of certain
1510          types of hw events: such as instructions executed, cachemisses
1511          suffered, or branches mis-predicted - without slowing down the
1512          kernel or applications. These registers can also trigger interrupts
1513          when a threshold number of events have passed - and can thus be
1514          used to profile the code that runs on that CPU.
1515
1516          The Linux Performance Event subsystem provides an abstraction of
1517          these software and hardware event capabilities, available via a
1518          system call and used by the "perf" utility in tools/perf/. It
1519          provides per task and per CPU counters, and it provides event
1520          capabilities on top of those.
1521
1522          Say Y if unsure.
1523
1524config DEBUG_PERF_USE_VMALLOC
1525        default n
1526        bool "Debug: use vmalloc to back perf mmap() buffers"
1527        depends on PERF_EVENTS && DEBUG_KERNEL
1528        select PERF_USE_VMALLOC
1529        help
1530         Use vmalloc memory to back perf mmap() buffers.
1531
1532         Mostly useful for debugging the vmalloc code on platforms
1533         that don't require it.
1534
1535         Say N if unsure.
1536
1537endmenu
1538
1539config VM_EVENT_COUNTERS
1540        default y
1541        bool "Enable VM event counters for /proc/vmstat" if EXPERT
1542        help
1543          VM event counters are needed for event counts to be shown.
1544          This option allows the disabling of the VM event counters
1545          on EXPERT systems.  /proc/vmstat will only show page counts
1546          if VM event counters are disabled.
1547
1548config SLUB_DEBUG
1549        default y
1550        bool "Enable SLUB debugging support" if EXPERT
1551        depends on SLUB && SYSFS
1552        help
1553          SLUB has extensive debug support features. Disabling these can
1554          result in significant savings in code size. This also disables
1555          SLUB sysfs support. /sys/slab will not exist and there will be
1556          no support for cache validation etc.
1557
1558config COMPAT_BRK
1559        bool "Disable heap randomization"
1560        default y
1561        help
1562          Randomizing heap placement makes heap exploits harder, but it
1563          also breaks ancient binaries (including anything libc5 based).
1564          This option changes the bootup default to heap randomization
1565          disabled, and can be overridden at runtime by setting
1566          /proc/sys/kernel/randomize_va_space to 2.
1567
1568          On non-ancient distros (post-2000 ones) N is usually a safe choice.
1569
1570choice
1571        prompt "Choose SLAB allocator"
1572        default SLUB
1573        help
1574           This option allows to select a slab allocator.
1575
1576config SLAB
1577        bool "SLAB"
1578        help
1579          The regular slab allocator that is established and known to work
1580          well in all environments. It organizes cache hot objects in
1581          per cpu and per node queues.
1582
1583config SLUB
1584        bool "SLUB (Unqueued Allocator)"
1585        help
1586           SLUB is a slab allocator that minimizes cache line usage
1587           instead of managing queues of cached objects (SLAB approach).
1588           Per cpu caching is realized using slabs of objects instead
1589           of queues of objects. SLUB can use memory efficiently
1590           and has enhanced diagnostics. SLUB is the default choice for
1591           a slab allocator.
1592
1593config SLOB
1594        depends on EXPERT
1595        bool "SLOB (Simple Allocator)"
1596        help
1597           SLOB replaces the stock allocator with a drastically simpler
1598           allocator. SLOB is generally more space efficient but
1599           does not perform as well on large systems.
1600
1601endchoice
1602
1603config SLUB_CPU_PARTIAL
1604        default y
1605        depends on SLUB && SMP
1606        bool "SLUB per cpu partial cache"
1607        help
1608          Per cpu partial caches accellerate objects allocation and freeing
1609          that is local to a processor at the price of more indeterminism
1610          in the latency of the free. On overflow these caches will be cleared
1611          which requires the taking of locks that may cause latency spikes.
1612          Typically one would choose no for a realtime system.
1613
1614config MMAP_ALLOW_UNINITIALIZED
1615        bool "Allow mmapped anonymous memory to be uninitialized"
1616        depends on EXPERT && !MMU
1617        default n
1618        help
1619          Normally, and according to the Linux spec, anonymous memory obtained
1620          from mmap() has it's contents cleared before it is passed to
1621          userspace.  Enabling this config option allows you to request that
1622          mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1623          providing a huge performance boost.  If this option is not enabled,
1624          then the flag will be ignored.
1625
1626          This is taken advantage of by uClibc's malloc(), and also by
1627          ELF-FDPIC binfmt's brk and stack allocator.
1628
1629          Because of the obvious security issues, this option should only be
1630          enabled on embedded devices where you control what is run in
1631          userspace.  Since that isn't generally a problem on no-MMU systems,
1632          it is normally safe to say Y here.
1633
1634          See Documentation/nommu-mmap.txt for more information.
1635
1636config PROFILING
1637        bool "Profiling support"
1638        help
1639          Say Y here to enable the extended profiling support mechanisms used
1640          by profilers such as OProfile.
1641
1642#
1643# Place an empty function call at each tracepoint site. Can be
1644# dynamically changed for a probe function.
1645#
1646config TRACEPOINTS
1647        bool
1648
1649source "arch/Kconfig"
1650
1651endmenu         # General setup
1652
1653config HAVE_GENERIC_DMA_COHERENT
1654        bool
1655        default n
1656
1657config SLABINFO
1658        bool
1659        depends on PROC_FS
1660        depends on SLAB || SLUB_DEBUG
1661        default y
1662
1663config RT_MUTEXES
1664        boolean
1665
1666config BASE_SMALL
1667        int
1668        default 0 if BASE_FULL
1669        default 1 if !BASE_FULL
1670
1671menuconfig MODULES
1672        bool "Enable loadable module support"
1673        option modules
1674        help
1675          Kernel modules are small pieces of compiled code which can
1676          be inserted in the running kernel, rather than being
1677          permanently built into the kernel.  You use the "modprobe"
1678          tool to add (and sometimes remove) them.  If you say Y here,
1679          many parts of the kernel can be built as modules (by
1680          answering M instead of Y where indicated): this is most
1681          useful for infrequently used options which are not required
1682          for booting.  For more information, see the man pages for
1683          modprobe, lsmod, modinfo, insmod and rmmod.
1684
1685          If you say Y here, you will need to run "make
1686          modules_install" to put the modules under /lib/modules/
1687          where modprobe can find them (you may need to be root to do
1688          this).
1689
1690          If unsure, say Y.
1691
1692if MODULES
1693
1694config MODULE_FORCE_LOAD
1695        bool "Forced module loading"
1696        default n
1697        help
1698          Allow loading of modules without version information (ie. modprobe
1699          --force).  Forced module loading sets the 'F' (forced) taint flag and
1700          is usually a really bad idea.
1701
1702config MODULE_UNLOAD
1703        bool "Module unloading"
1704        help
1705          Without this option you will not be able to unload any
1706          modules (note that some modules may not be unloadable
1707          anyway), which makes your kernel smaller, faster
1708          and simpler.  If unsure, say Y.
1709
1710config MODULE_FORCE_UNLOAD
1711        bool "Forced module unloading"
1712        depends on MODULE_UNLOAD
1713        help
1714          This option allows you to force a module to unload, even if the
1715          kernel believes it is unsafe: the kernel will remove the module
1716          without waiting for anyone to stop using it (using the -f option to
1717          rmmod).  This is mainly for kernel developers and desperate users.
1718          If unsure, say N.
1719
1720config MODVERSIONS
1721        bool "Module versioning support"
1722        help
1723          Usually, you have to use modules compiled with your kernel.
1724          Saying Y here makes it sometimes possible to use modules
1725          compiled for different kernels, by adding enough information
1726          to the modules to (hopefully) spot any changes which would
1727          make them incompatible with the kernel you are running.  If
1728          unsure, say N.
1729
1730config MODULE_SRCVERSION_ALL
1731        bool "Source checksum for all modules"
1732        help
1733          Modules which contain a MODULE_VERSION get an extra "srcversion"
1734          field inserted into their modinfo section, which contains a
1735          sum of the source files which made it.  This helps maintainers
1736          see exactly which source was used to build a module (since
1737          others sometimes change the module source without updating
1738          the version).  With this option, such a "srcversion" field
1739          will be created for all modules.  If unsure, say N.
1740
1741config MODULE_SIG
1742        bool "Module signature verification"
1743        depends on MODULES
1744        select KEYS
1745        select CRYPTO
1746        select ASYMMETRIC_KEY_TYPE
1747        select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1748        select PUBLIC_KEY_ALGO_RSA
1749        select ASN1
1750        select OID_REGISTRY
1751        select X509_CERTIFICATE_PARSER
1752        help
1753          Check modules for valid signatures upon load: the signature
1754          is simply appended to the module. For more information see
1755          Documentation/module-signing.txt.
1756
1757          !!!WARNING!!!  If you enable this option, you MUST make sure that the
1758          module DOES NOT get stripped after being signed.  This includes the
1759          debuginfo strip done by some packagers (such as rpmbuild) and
1760          inclusion into an initramfs that wants the module size reduced.
1761
1762config MODULE_SIG_FORCE
1763        bool "Require modules to be validly signed"
1764        depends on MODULE_SIG
1765        help
1766          Reject unsigned modules or signed modules for which we don't have a
1767          key.  Without this, such modules will simply taint the kernel.
1768
1769config MODULE_SIG_ALL
1770        bool "Automatically sign all modules"
1771        default y
1772        depends on MODULE_SIG
1773        help
1774          Sign all modules during make modules_install. Without this option,
1775          modules must be signed manually, using the scripts/sign-file tool.
1776
1777comment "Do not forget to sign required modules with scripts/sign-file"
1778        depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1779
1780choice
1781        prompt "Which hash algorithm should modules be signed with?"
1782        depends on MODULE_SIG
1783        help
1784          This determines which sort of hashing algorithm will be used during
1785          signature generation.  This algorithm _must_ be built into the kernel
1786          directly so that signature verification can take place.  It is not
1787          possible to load a signed module containing the algorithm to check
1788          the signature on that module.
1789
1790config MODULE_SIG_SHA1
1791        bool "Sign modules with SHA-1"
1792        select CRYPTO_SHA1
1793
1794config MODULE_SIG_SHA224
1795        bool "Sign modules with SHA-224"
1796        select CRYPTO_SHA256
1797
1798config MODULE_SIG_SHA256
1799        bool "Sign modules with SHA-256"
1800        select CRYPTO_SHA256
1801
1802config MODULE_SIG_SHA384
1803        bool "Sign modules with SHA-384"
1804        select CRYPTO_SHA512
1805
1806config MODULE_SIG_SHA512
1807        bool "Sign modules with SHA-512"
1808        select CRYPTO_SHA512
1809
1810endchoice
1811
1812config MODULE_SIG_HASH
1813        string
1814        depends on MODULE_SIG
1815        default "sha1" if MODULE_SIG_SHA1
1816        default "sha224" if MODULE_SIG_SHA224
1817        default "sha256" if MODULE_SIG_SHA256
1818        default "sha384" if MODULE_SIG_SHA384
1819        default "sha512" if MODULE_SIG_SHA512
1820
1821endif # MODULES
1822
1823config INIT_ALL_POSSIBLE
1824        bool
1825        help
1826          Back when each arch used to define their own cpu_online_mask and
1827          cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1828          with all 1s, and others with all 0s.  When they were centralised,
1829          it was better to provide this option than to break all the archs
1830          and have several arch maintainers pursuing me down dark alleys.
1831
1832config STOP_MACHINE
1833        bool
1834        default y
1835        depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1836        help
1837          Need stop_machine() primitive.
1838
1839source "block/Kconfig"
1840
1841config PREEMPT_NOTIFIERS
1842        bool
1843
1844config PADATA
1845        depends on SMP
1846        bool
1847
1848# Can be selected by architectures with broken toolchains
1849# that get confused by correct const<->read_only section
1850# mappings
1851config BROKEN_RODATA
1852        bool
1853
1854config ASN1
1855        tristate
1856        help
1857          Build a simple ASN.1 grammar compiler that produces a bytecode output
1858          that can be interpreted by the ASN.1 stream decoder and used to
1859          inform it as to what tags are to be expected in a stream and what
1860          functions to call on what tags.
1861
1862source "kernel/Kconfig.locks"
1863
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