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        help
 474          This option selects the RCU implementation that is
 475          designed for very large SMP systems with hundreds or
 476          thousands of CPUs, but for which real-time response
 477          is also required.  It also scales down nicely to
 478          smaller systems.
 479
 480          Select this option if you are unsure.
 481
 482config TINY_RCU
 483        bool "UP-only small-memory-footprint RCU"
 484        depends on !PREEMPT && !SMP
 485        help
 486          This option selects the RCU implementation that is
 487          designed for UP systems from which real-time response
 488          is not required.  This option greatly reduces the
 489          memory footprint of RCU.
 490
 491endchoice
 492
 493config PREEMPT_RCU
 494        def_bool TREE_PREEMPT_RCU
 495        help
 496          This option enables preemptible-RCU code that is common between
 497          the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
 498
 499config RCU_STALL_COMMON
 500        def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
 501        help
 502          This option enables RCU CPU stall code that is common between
 503          the TINY and TREE variants of RCU.  The purpose is to allow
 504          the tiny variants to disable RCU CPU stall warnings, while
 505          making these warnings mandatory for the tree variants.
 506
 507config CONTEXT_TRACKING
 508       bool
 509
 510config RCU_USER_QS
 511        bool "Consider userspace as in RCU extended quiescent state"
 512        depends on HAVE_CONTEXT_TRACKING && SMP
 513        select CONTEXT_TRACKING
 514        help
 515          This option sets hooks on kernel / userspace boundaries and
 516          puts RCU in extended quiescent state when the CPU runs in
 517          userspace. It means that when a CPU runs in userspace, it is
 518          excluded from the global RCU state machine and thus doesn't
 519          try to keep the timer tick on for RCU.
 520
 521          Unless you want to hack and help the development of the full
 522          dynticks mode, you shouldn't enable this option.  It also
 523          adds unnecessary overhead.
 524
 525          If unsure say N
 526
 527config CONTEXT_TRACKING_FORCE
 528        bool "Force context tracking"
 529        depends on CONTEXT_TRACKING
 530        default CONTEXT_TRACKING
 531        help
 532          Probe on user/kernel boundaries by default in order to
 533          test the features that rely on it such as userspace RCU extended
 534          quiescent states.
 535          This test is there for debugging until we have a real user like the
 536          full dynticks mode.
 537
 538config RCU_FANOUT
 539        int "Tree-based hierarchical RCU fanout value"
 540        range 2 64 if 64BIT
 541        range 2 32 if !64BIT
 542        depends on TREE_RCU || TREE_PREEMPT_RCU
 543        default 64 if 64BIT
 544        default 32 if !64BIT
 545        help
 546          This option controls the fanout of hierarchical implementations
 547          of RCU, allowing RCU to work efficiently on machines with
 548          large numbers of CPUs.  This value must be at least the fourth
 549          root of NR_CPUS, which allows NR_CPUS to be insanely large.
 550          The default value of RCU_FANOUT should be used for production
 551          systems, but if you are stress-testing the RCU implementation
 552          itself, small RCU_FANOUT values allow you to test large-system
 553          code paths on small(er) systems.
 554
 555          Select a specific number if testing RCU itself.
 556          Take the default if unsure.
 557
 558config RCU_FANOUT_LEAF
 559        int "Tree-based hierarchical RCU leaf-level fanout value"
 560        range 2 RCU_FANOUT if 64BIT
 561        range 2 RCU_FANOUT if !64BIT
 562        depends on TREE_RCU || TREE_PREEMPT_RCU
 563        default 16
 564        help
 565          This option controls the leaf-level fanout of hierarchical
 566          implementations of RCU, and allows trading off cache misses
 567          against lock contention.  Systems that synchronize their
 568          scheduling-clock interrupts for energy-efficiency reasons will
 569          want the default because the smaller leaf-level fanout keeps
 570          lock contention levels acceptably low.  Very large systems
 571          (hundreds or thousands of CPUs) will instead want to set this
 572          value to the maximum value possible in order to reduce the
 573          number of cache misses incurred during RCU's grace-period
 574          initialization.  These systems tend to run CPU-bound, and thus
 575          are not helped by synchronized interrupts, and thus tend to
 576          skew them, which reduces lock contention enough that large
 577          leaf-level fanouts work well.
 578
 579          Select a specific number if testing RCU itself.
 580
 581          Select the maximum permissible value for large systems.
 582
 583          Take the default if unsure.
 584
 585config RCU_FANOUT_EXACT
 586        bool "Disable tree-based hierarchical RCU auto-balancing"
 587        depends on TREE_RCU || TREE_PREEMPT_RCU
 588        default n
 589        help
 590          This option forces use of the exact RCU_FANOUT value specified,
 591          regardless of imbalances in the hierarchy.  This is useful for
 592          testing RCU itself, and might one day be useful on systems with
 593          strong NUMA behavior.
 594
 595          Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
 596
 597          Say N if unsure.
 598
 599config RCU_FAST_NO_HZ
 600        bool "Accelerate last non-dyntick-idle CPU's grace periods"
 601        depends on NO_HZ_COMMON && SMP
 602        default n
 603        help
 604          This option permits CPUs to enter dynticks-idle state even if
 605          they have RCU callbacks queued, and prevents RCU from waking
 606          these CPUs up more than roughly once every four jiffies (by
 607          default, you can adjust this using the rcutree.rcu_idle_gp_delay
 608          parameter), thus improving energy efficiency.  On the other
 609          hand, this option increases the duration of RCU grace periods,
 610          for example, slowing down synchronize_rcu().
 611
 612          Say Y if energy efficiency is critically important, and you
 613                don't care about increased grace-period durations.
 614
 615          Say N if you are unsure.
 616
 617config TREE_RCU_TRACE
 618        def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
 619        select DEBUG_FS
 620        help
 621          This option provides tracing for the TREE_RCU and
 622          TREE_PREEMPT_RCU implementations, permitting Makefile to
 623          trivially select kernel/rcutree_trace.c.
 624
 625config RCU_BOOST
 626        bool "Enable RCU priority boosting"
 627        depends on RT_MUTEXES && PREEMPT_RCU
 628        default n
 629        help
 630          This option boosts the priority of preempted RCU readers that
 631          block the current preemptible RCU grace period for too long.
 632          This option also prevents heavy loads from blocking RCU
 633          callback invocation for all flavors of RCU.
 634
 635          Say Y here if you are working with real-time apps or heavy loads
 636          Say N here if you are unsure.
 637
 638config RCU_BOOST_PRIO
 639        int "Real-time priority to boost RCU readers to"
 640        range 1 99
 641        depends on RCU_BOOST
 642        default 1
 643        help
 644          This option specifies the real-time priority to which long-term
 645          preempted RCU readers are to be boosted.  If you are working
 646          with a real-time application that has one or more CPU-bound
 647          threads running at a real-time priority level, you should set
 648          RCU_BOOST_PRIO to a priority higher then the highest-priority
 649          real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
 650          of 1 is appropriate in the common case, which is real-time
 651          applications that do not have any CPU-bound threads.
 652
 653          Some real-time applications might not have a single real-time
 654          thread that saturates a given CPU, but instead might have
 655          multiple real-time threads that, taken together, fully utilize
 656          that CPU.  In this case, you should set RCU_BOOST_PRIO to
 657          a priority higher than the lowest-priority thread that is
 658          conspiring to prevent the CPU from running any non-real-time
 659          tasks.  For example, if one thread at priority 10 and another
 660          thread at priority 5 are between themselves fully consuming
 661          the CPU time on a given CPU, then RCU_BOOST_PRIO should be
 662          set to priority 6 or higher.
 663
 664          Specify the real-time priority, or take the default if unsure.
 665
 666config RCU_BOOST_DELAY
 667        int "Milliseconds to delay boosting after RCU grace-period start"
 668        range 0 3000
 669        depends on RCU_BOOST
 670        default 500
 671        help
 672          This option specifies the time to wait after the beginning of
 673          a given grace period before priority-boosting preempted RCU
 674          readers blocking that grace period.  Note that any RCU reader
 675          blocking an expedited RCU grace period is boosted immediately.
 676
 677          Accept the default if unsure.
 678
 679config RCU_NOCB_CPU
 680        bool "Offload RCU callback processing from boot-selected CPUs"
 681        depends on TREE_RCU || TREE_PREEMPT_RCU
 682        default n
 683        help
 684          Use this option to reduce OS jitter for aggressive HPC or
 685          real-time workloads.  It can also be used to offload RCU
 686          callback invocation to energy-efficient CPUs in battery-powered
 687          asymmetric multiprocessors.
 688
 689          This option offloads callback invocation from the set of
 690          CPUs specified at boot time by the rcu_nocbs parameter.
 691          For each such CPU, a kthread ("rcuox/N") will be created to
 692          invoke callbacks, where the "N" is the CPU being offloaded,
 693          and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
 694          "s" for RCU-sched.  Nothing prevents this kthread from running
 695          on the specified CPUs, but (1) the kthreads may be preempted
 696          between each callback, and (2) affinity or cgroups can be used
 697          to force the kthreads to run on whatever set of CPUs is desired.
 698
 699          Say Y here if you want to help to debug reduced OS jitter.
 700          Say N here if you are unsure.
 701
 702choice
 703        prompt "Build-forced no-CBs CPUs"
 704        default RCU_NOCB_CPU_NONE
 705        help
 706          This option allows no-CBs CPUs (whose RCU callbacks are invoked
 707          from kthreads rather than from softirq context) to be specified
 708          at build time.  Additional no-CBs CPUs may be specified by
 709          the rcu_nocbs= boot parameter.
 710
 711config RCU_NOCB_CPU_NONE
 712        bool "No build_forced no-CBs CPUs"
 713        depends on RCU_NOCB_CPU && !NO_HZ_FULL
 714        help
 715          This option does not force any of the CPUs to be no-CBs CPUs.
 716          Only CPUs designated by the rcu_nocbs= boot parameter will be
 717          no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
 718          kthreads whose names begin with "rcuo".  All other CPUs will
 719          invoke their own RCU callbacks in softirq context.
 720
 721          Select this option if you want to choose no-CBs CPUs at
 722          boot time, for example, to allow testing of different no-CBs
 723          configurations without having to rebuild the kernel each time.
 724
 725config RCU_NOCB_CPU_ZERO
 726        bool "CPU 0 is a build_forced no-CBs CPU"
 727        depends on RCU_NOCB_CPU && !NO_HZ_FULL
 728        help
 729          This option forces CPU 0 to be a no-CBs CPU, so that its RCU
 730          callbacks are invoked by a per-CPU kthread whose name begins
 731          with "rcuo".  Additional CPUs may be designated as no-CBs
 732          CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
 733          All other CPUs will invoke their own RCU callbacks in softirq
 734          context.
 735
 736          Select this if CPU 0 needs to be a no-CBs CPU for real-time
 737          or energy-efficiency reasons, but the real reason it exists
 738          is to ensure that randconfig testing covers mixed systems.
 739
 740config RCU_NOCB_CPU_ALL
 741        bool "All CPUs are build_forced no-CBs CPUs"
 742        depends on RCU_NOCB_CPU
 743        help
 744          This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
 745          boot parameter will be ignored.  All CPUs' RCU callbacks will
 746          be executed in the context of per-CPU rcuo kthreads created for
 747          this purpose.  Assuming that the kthreads whose names start with
 748          "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
 749          on the remaining CPUs, but might decrease memory locality during
 750          RCU-callback invocation, thus potentially degrading throughput.
 751
 752          Select this if all CPUs need to be no-CBs CPUs for real-time
 753          or energy-efficiency reasons.
 754
 755endchoice
 756
 757endmenu # "RCU Subsystem"
 758
 759config IKCONFIG
 760        tristate "Kernel .config support"
 761        ---help---
 762          This option enables the complete Linux kernel ".config" file
 763          contents to be saved in the kernel. It provides documentation
 764          of which kernel options are used in a running kernel or in an
 765          on-disk kernel.  This information can be extracted from the kernel
 766          image file with the script scripts/extract-ikconfig and used as
 767          input to rebuild the current kernel or to build another kernel.
 768          It can also be extracted from a running kernel by reading
 769          /proc/config.gz if enabled (below).
 770
 771config IKCONFIG_PROC
 772        bool "Enable access to .config through /proc/config.gz"
 773        depends on IKCONFIG && PROC_FS
 774        ---help---
 775          This option enables access to the kernel configuration file
 776          through /proc/config.gz.
 777
 778config LOG_BUF_SHIFT
 779        int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
 780        range 12 21
 781        default 17
 782        help
 783          Select kernel log buffer size as a power of 2.
 784          Examples:
 785                     17 => 128 KB
 786                     16 => 64 KB
 787                     15 => 32 KB
 788                     14 => 16 KB
 789                     13 =>  8 KB
 790                     12 =>  4 KB
 791
 792#
 793# Architectures with an unreliable sched_clock() should select this:
 794#
 795config HAVE_UNSTABLE_SCHED_CLOCK
 796        bool
 797
 798config GENERIC_SCHED_CLOCK
 799        bool
 800
 801#
 802# For architectures that want to enable the support for NUMA-affine scheduler
 803# balancing logic:
 804#
 805config ARCH_SUPPORTS_NUMA_BALANCING
 806        bool
 807
 808# For architectures that (ab)use NUMA to represent different memory regions
 809# all cpu-local but of different latencies, such as SuperH.
 810#
 811config ARCH_WANT_NUMA_VARIABLE_LOCALITY
 812        bool
 813
 814#
 815# For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
 816config ARCH_WANTS_PROT_NUMA_PROT_NONE
 817        bool
 818
 819config ARCH_USES_NUMA_PROT_NONE
 820        bool
 821        default y
 822        depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
 823        depends on NUMA_BALANCING
 824
 825config NUMA_BALANCING_DEFAULT_ENABLED
 826        bool "Automatically enable NUMA aware memory/task placement"
 827        default y
 828        depends on NUMA_BALANCING
 829        help
 830          If set, autonumic NUMA balancing will be enabled if running on a NUMA
 831          machine.
 832
 833config NUMA_BALANCING
 834        bool "Memory placement aware NUMA scheduler"
 835        depends on ARCH_SUPPORTS_NUMA_BALANCING
 836        depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
 837        depends on SMP && NUMA && MIGRATION
 838        help
 839          This option adds support for automatic NUMA aware memory/task placement.
 840          The mechanism is quite primitive and is based on migrating memory when
 841          it is references to the node the task is running on.
 842
 843          This system will be inactive on UMA systems.
 844
 845menuconfig CGROUPS
 846        boolean "Control Group support"
 847        depends on EVENTFD
 848        help
 849          This option adds support for grouping sets of processes together, for
 850          use with process control subsystems such as Cpusets, CFS, memory
 851          controls or device isolation.
 852          See
 853                - Documentation/scheduler/sched-design-CFS.txt  (CFS)
 854                - Documentation/cgroups/ (features for grouping, isolation
 855                                          and resource control)
 856
 857          Say N if unsure.
 858
 859if CGROUPS
 860
 861config CGROUP_DEBUG
 862        bool "Example debug cgroup subsystem"
 863        default n
 864        help
 865          This option enables a simple cgroup subsystem that
 866          exports useful debugging information about the cgroups
 867          framework.
 868
 869          Say N if unsure.
 870
 871config CGROUP_FREEZER
 872        bool "Freezer cgroup subsystem"
 873        help
 874          Provides a way to freeze and unfreeze all tasks in a
 875          cgroup.
 876
 877config CGROUP_DEVICE
 878        bool "Device controller for cgroups"
 879        help
 880          Provides a cgroup implementing whitelists for devices which
 881          a process in the cgroup can mknod or open.
 882
 883config CPUSETS
 884        bool "Cpuset support"
 885        help
 886          This option will let you create and manage CPUSETs which
 887          allow dynamically partitioning a system into sets of CPUs and
 888          Memory Nodes and assigning tasks to run only within those sets.
 889          This is primarily useful on large SMP or NUMA systems.
 890
 891          Say N if unsure.
 892
 893config PROC_PID_CPUSET
 894        bool "Include legacy /proc/<pid>/cpuset file"
 895        depends on CPUSETS
 896        default y
 897
 898config CGROUP_CPUACCT
 899        bool "Simple CPU accounting cgroup subsystem"
 900        help
 901          Provides a simple Resource Controller for monitoring the
 902          total CPU consumed by the tasks in a cgroup.
 903
 904config RESOURCE_COUNTERS
 905        bool "Resource counters"
 906        help
 907          This option enables controller independent resource accounting
 908          infrastructure that works with cgroups.
 909
 910config MEMCG
 911        bool "Memory Resource Controller for Control Groups"
 912        depends on RESOURCE_COUNTERS
 913        select MM_OWNER
 914        help
 915          Provides a memory resource controller that manages both anonymous
 916          memory and page cache. (See Documentation/cgroups/memory.txt)
 917
 918          Note that setting this option increases fixed memory overhead
 919          associated with each page of memory in the system. By this,
 920          8(16)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
 921          usage tracking struct at boot. Total amount of this is printed out
 922          at boot.
 923
 924          Only enable when you're ok with these trade offs and really
 925          sure you need the memory resource controller. Even when you enable
 926          this, you can set "cgroup_disable=memory" at your boot option to
 927          disable memory resource controller and you can avoid overheads.
 928          (and lose benefits of memory resource controller)
 929
 930          This config option also selects MM_OWNER config option, which
 931          could in turn add some fork/exit overhead.
 932
 933config MEMCG_SWAP
 934        bool "Memory Resource Controller Swap Extension"
 935        depends on MEMCG && SWAP
 936        help
 937          Add swap management feature to memory resource controller. When you
 938          enable this, you can limit mem+swap usage per cgroup. In other words,
 939          when you disable this, memory resource controller has no cares to
 940          usage of swap...a process can exhaust all of the swap. This extension
 941          is useful when you want to avoid exhaustion swap but this itself
 942          adds more overheads and consumes memory for remembering information.
 943          Especially if you use 32bit system or small memory system, please
 944          be careful about enabling this. When memory resource controller
 945          is disabled by boot option, this will be automatically disabled and
 946          there will be no overhead from this. Even when you set this config=y,
 947          if boot option "swapaccount=0" is set, swap will not be accounted.
 948          Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
 949          size is 4096bytes, 512k per 1Gbytes of swap.
 950config MEMCG_SWAP_ENABLED
 951        bool "Memory Resource Controller Swap Extension enabled by default"
 952        depends on MEMCG_SWAP
 953        default y
 954        help
 955          Memory Resource Controller Swap Extension comes with its price in
 956          a bigger memory consumption. General purpose distribution kernels
 957          which want to enable the feature but keep it disabled by default
 958          and let the user enable it by swapaccount=1 boot command line
 959          parameter should have this option unselected.
 960          For those who want to have the feature enabled by default should
 961          select this option (if, for some reason, they need to disable it
 962          then swapaccount=0 does the trick).
 963config MEMCG_KMEM
 964        bool "Memory Resource Controller Kernel Memory accounting"
 965        depends on MEMCG
 966        depends on SLUB || SLAB
 967        help
 968          The Kernel Memory extension for Memory Resource Controller can limit
 969          the amount of memory used by kernel objects in the system. Those are
 970          fundamentally different from the entities handled by the standard
 971          Memory Controller, which are page-based, and can be swapped. Users of
 972          the kmem extension can use it to guarantee that no group of processes
 973          will ever exhaust kernel resources alone.
 974
 975config CGROUP_HUGETLB
 976        bool "HugeTLB Resource Controller for Control Groups"
 977        depends on RESOURCE_COUNTERS && HUGETLB_PAGE
 978        default n
 979        help
 980          Provides a cgroup Resource Controller for HugeTLB pages.
 981          When you enable this, you can put a per cgroup limit on HugeTLB usage.
 982          The limit is enforced during page fault. Since HugeTLB doesn't
 983          support page reclaim, enforcing the limit at page fault time implies
 984          that, the application will get SIGBUS signal if it tries to access
 985          HugeTLB pages beyond its limit. This requires the application to know
 986          beforehand how much HugeTLB pages it would require for its use. The
 987          control group is tracked in the third page lru pointer. This means
 988          that we cannot use the controller with huge page less than 3 pages.
 989
 990config CGROUP_PERF
 991        bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
 992        depends on PERF_EVENTS && CGROUPS
 993        help
 994          This option extends the per-cpu mode to restrict monitoring to
 995          threads which belong to the cgroup specified and run on the
 996          designated cpu.
 997
 998          Say N if unsure.
 999
1000menuconfig CGROUP_SCHED
1001        bool "Group CPU scheduler"
1002        default n
1003        help
1004          This feature lets CPU scheduler recognize task groups and control CPU
1005          bandwidth allocation to such task groups. It uses cgroups to group
1006          tasks.
1007
1008if CGROUP_SCHED
1009config FAIR_GROUP_SCHED
1010        bool "Group scheduling for SCHED_OTHER"
1011        depends on CGROUP_SCHED
1012        default CGROUP_SCHED
1013
1014config CFS_BANDWIDTH
1015        bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1016        depends on FAIR_GROUP_SCHED
1017        default n
1018        help
1019          This option allows users to define CPU bandwidth rates (limits) for
1020          tasks running within the fair group scheduler.  Groups with no limit
1021          set are considered to be unconstrained and will run with no
1022          restriction.
1023          See tip/Documentation/scheduler/sched-bwc.txt for more information.
1024
1025config RT_GROUP_SCHED
1026        bool "Group scheduling for SCHED_RR/FIFO"
1027        depends on CGROUP_SCHED
1028        default n
1029        help
1030          This feature lets you explicitly allocate real CPU bandwidth
1031          to task groups. If enabled, it will also make it impossible to
1032          schedule realtime tasks for non-root users until you allocate
1033          realtime bandwidth for them.
1034          See Documentation/scheduler/sched-rt-group.txt for more information.
1035
1036endif #CGROUP_SCHED
1037
1038config BLK_CGROUP
1039        bool "Block IO controller"
1040        depends on BLOCK
1041        default n
1042        ---help---
1043        Generic block IO controller cgroup interface. This is the common
1044        cgroup interface which should be used by various IO controlling
1045        policies.
1046
1047        Currently, CFQ IO scheduler uses it to recognize task groups and
1048        control disk bandwidth allocation (proportional time slice allocation)
1049        to such task groups. It is also used by bio throttling logic in
1050        block layer to implement upper limit in IO rates on a device.
1051
1052        This option only enables generic Block IO controller infrastructure.
1053        One needs to also enable actual IO controlling logic/policy. For
1054        enabling proportional weight division of disk bandwidth in CFQ, set
1055        CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
1056        CONFIG_BLK_DEV_THROTTLING=y.
1057
1058        See Documentation/cgroups/blkio-controller.txt for more information.
1059
1060config DEBUG_BLK_CGROUP
1061        bool "Enable Block IO controller debugging"
1062        depends on BLK_CGROUP
1063        default n
1064        ---help---
1065        Enable some debugging help. Currently it exports additional stat
1066        files in a cgroup which can be useful for debugging.
1067
1068endif # CGROUPS
1069
1070config CHECKPOINT_RESTORE
1071        bool "Checkpoint/restore support" if EXPERT
1072        default n
1073        help
1074          Enables additional kernel features in a sake of checkpoint/restore.
1075          In particular it adds auxiliary prctl codes to setup process text,
1076          data and heap segment sizes, and a few additional /proc filesystem
1077          entries.
1078
1079          If unsure, say N here.
1080
1081menuconfig NAMESPACES
1082        bool "Namespaces support" if EXPERT
1083        default !EXPERT
1084        help
1085          Provides the way to make tasks work with different objects using
1086          the same id. For example same IPC id may refer to different objects
1087          or same user id or pid may refer to different tasks when used in
1088          different namespaces.
1089
1090if NAMESPACES
1091
1092config UTS_NS
1093        bool "UTS namespace"
1094        default y
1095        help
1096          In this namespace tasks see different info provided with the
1097          uname() system call
1098
1099config IPC_NS
1100        bool "IPC namespace"
1101        depends on (SYSVIPC || POSIX_MQUEUE)
1102        default y
1103        help
1104          In this namespace tasks work with IPC ids which correspond to
1105          different IPC objects in different namespaces.
1106
1107config USER_NS
1108        bool "User namespace"
1109        depends on UIDGID_CONVERTED
1110        select UIDGID_STRICT_TYPE_CHECKS
1111
1112        default n
1113        help
1114          This allows containers, i.e. vservers, to use user namespaces
1115          to provide different user info for different servers.
1116
1117          When user namespaces are enabled in the kernel it is
1118          recommended that the MEMCG and MEMCG_KMEM options also be
1119          enabled and that user-space use the memory control groups to
1120          limit the amount of memory a memory unprivileged users can
1121          use.
1122
1123          If unsure, say N.
1124
1125config PID_NS
1126        bool "PID Namespaces"
1127        default y
1128        help
1129          Support process id namespaces.  This allows having multiple
1130          processes with the same pid as long as they are in different
1131          pid namespaces.  This is a building block of containers.
1132
1133config NET_NS
1134        bool "Network namespace"
1135        depends on NET
1136        default y
1137        help
1138          Allow user space to create what appear to be multiple instances
1139          of the network stack.
1140
1141endif # NAMESPACES
1142
1143config UIDGID_CONVERTED
1144        # True if all of the selected software conmponents are known
1145        # to have uid_t and gid_t converted to kuid_t and kgid_t
1146        # where appropriate and are otherwise safe to use with
1147        # the user namespace.
1148        bool
1149        default y
1150
1151        # Filesystems
1152        depends on XFS_FS = n
1153
1154config UIDGID_STRICT_TYPE_CHECKS
1155        bool "Require conversions between uid/gids and their internal representation"
1156        depends on UIDGID_CONVERTED
1157        default n
1158        help
1159         While the nececessary conversions are being added to all subsystems this option allows
1160         the code to continue to build for unconverted subsystems.
1161
1162         Say Y here if you want the strict type checking enabled
1163
1164config SCHED_AUTOGROUP
1165        bool "Automatic process group scheduling"
1166        select EVENTFD
1167        select CGROUPS
1168        select CGROUP_SCHED
1169        select FAIR_GROUP_SCHED
1170        help
1171          This option optimizes the scheduler for common desktop workloads by
1172          automatically creating and populating task groups.  This separation
1173          of workloads isolates aggressive CPU burners (like build jobs) from
1174          desktop applications.  Task group autogeneration is currently based
1175          upon task session.
1176
1177config MM_OWNER
1178        bool
1179
1180config SYSFS_DEPRECATED
1181        bool "Enable deprecated sysfs features to support old userspace tools"
1182        depends on SYSFS
1183        default n
1184        help
1185          This option adds code that switches the layout of the "block" class
1186          devices, to not show up in /sys/class/block/, but only in
1187          /sys/block/.
1188
1189          This switch is only active when the sysfs.deprecated=1 boot option is
1190          passed or the SYSFS_DEPRECATED_V2 option is set.
1191
1192          This option allows new kernels to run on old distributions and tools,
1193          which might get confused by /sys/class/block/. Since 2007/2008 all
1194          major distributions and tools handle this just fine.
1195
1196          Recent distributions and userspace tools after 2009/2010 depend on
1197          the existence of /sys/class/block/, and will not work with this
1198          option enabled.
1199
1200          Only if you are using a new kernel on an old distribution, you might
1201          need to say Y here.
1202
1203config SYSFS_DEPRECATED_V2
1204        bool "Enable deprecated sysfs features by default"
1205        default n
1206        depends on SYSFS
1207        depends on SYSFS_DEPRECATED
1208        help
1209          Enable deprecated sysfs by default.
1210
1211          See the CONFIG_SYSFS_DEPRECATED option for more details about this
1212          option.
1213
1214          Only if you are using a new kernel on an old distribution, you might
1215          need to say Y here. Even then, odds are you would not need it
1216          enabled, you can always pass the boot option if absolutely necessary.
1217
1218config RELAY
1219        bool "Kernel->user space relay support (formerly relayfs)"
1220        help
1221          This option enables support for relay interface support in
1222          certain file systems (such as debugfs).
1223          It is designed to provide an efficient mechanism for tools and
1224          facilities to relay large amounts of data from kernel space to
1225          user space.
1226
1227          If unsure, say N.
1228
1229config BLK_DEV_INITRD
1230        bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1231        depends on BROKEN || !FRV
1232        help
1233          The initial RAM filesystem is a ramfs which is loaded by the
1234          boot loader (loadlin or lilo) and that is mounted as root
1235          before the normal boot procedure. It is typically used to
1236          load modules needed to mount the "real" root file system,
1237          etc. See <file:Documentation/initrd.txt> for details.
1238
1239          If RAM disk support (BLK_DEV_RAM) is also included, this
1240          also enables initial RAM disk (initrd) support and adds
1241          15 Kbytes (more on some other architectures) to the kernel size.
1242
1243          If unsure say Y.
1244
1245if BLK_DEV_INITRD
1246
1247source "usr/Kconfig"
1248
1249endif
1250
1251config CC_OPTIMIZE_FOR_SIZE
1252        bool "Optimize for size"
1253        help
1254          Enabling this option will pass "-Os" instead of "-O2" to gcc
1255          resulting in a smaller kernel.
1256
1257          If unsure, say N.
1258
1259config SYSCTL
1260        bool
1261
1262config ANON_INODES
1263        bool
1264
1265config HAVE_UID16
1266        bool
1267
1268config SYSCTL_EXCEPTION_TRACE
1269        bool
1270        help
1271          Enable support for /proc/sys/debug/exception-trace.
1272
1273config SYSCTL_ARCH_UNALIGN_NO_WARN
1274        bool
1275        help
1276          Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1277          Allows arch to define/use @no_unaligned_warning to possibly warn
1278          about unaligned access emulation going on under the hood.
1279
1280config SYSCTL_ARCH_UNALIGN_ALLOW
1281        bool
1282        help
1283          Enable support for /proc/sys/kernel/unaligned-trap
1284          Allows arches to define/use @unaligned_enabled to runtime toggle
1285          the unaligned access emulation.
1286          see arch/parisc/kernel/unaligned.c for reference
1287
1288config HAVE_PCSPKR_PLATFORM
1289        bool
1290
1291menuconfig EXPERT
1292        bool "Configure standard kernel features (expert users)"
1293        # Unhide debug options, to make the on-by-default options visible
1294        select DEBUG_KERNEL
1295        help
1296          This option allows certain base kernel options and settings
1297          to be disabled or tweaked. This is for specialized
1298          environments which can tolerate a "non-standard" kernel.
1299          Only use this if you really know what you are doing.
1300
1301config UID16
1302        bool "Enable 16-bit UID system calls" if EXPERT
1303        depends on HAVE_UID16
1304        default y
1305        help
1306          This enables the legacy 16-bit UID syscall wrappers.
1307
1308config SYSCTL_SYSCALL
1309        bool "Sysctl syscall support" if EXPERT
1310        depends on PROC_SYSCTL
1311        default n
1312        select SYSCTL
1313        ---help---
1314          sys_sysctl uses binary paths that have been found challenging
1315          to properly maintain and use.  The interface in /proc/sys
1316          using paths with ascii names is now the primary path to this
1317          information.
1318
1319          Almost nothing using the binary sysctl interface so if you are
1320          trying to save some space it is probably safe to disable this,
1321          making your kernel marginally smaller.
1322
1323          If unsure say N here.
1324
1325config KALLSYMS
1326         bool "Load all symbols for debugging/ksymoops" if EXPERT
1327         default y
1328         help
1329           Say Y here to let the kernel print out symbolic crash information and
1330           symbolic stack backtraces. This increases the size of the kernel
1331           somewhat, as all symbols have to be loaded into the kernel image.
1332
1333config KALLSYMS_ALL
1334        bool "Include all symbols in kallsyms"
1335        depends on DEBUG_KERNEL && KALLSYMS
1336        help
1337           Normally kallsyms only contains the symbols of functions for nicer
1338           OOPS messages and backtraces (i.e., symbols from the text and inittext
1339           sections). This is sufficient for most cases. And only in very rare
1340           cases (e.g., when a debugger is used) all symbols are required (e.g.,
1341           names of variables from the data sections, etc).
1342
1343           This option makes sure that all symbols are loaded into the kernel
1344           image (i.e., symbols from all sections) in cost of increased kernel
1345           size (depending on the kernel configuration, it may be 300KiB or
1346           something like this).
1347
1348           Say N unless you really need all symbols.
1349
1350config PRINTK
1351        default y
1352        bool "Enable support for printk" if EXPERT
1353        select IRQ_WORK
1354        help
1355          This option enables normal printk support. Removing it
1356          eliminates most of the message strings from the kernel image
1357          and makes the kernel more or less silent. As this makes it
1358          very difficult to diagnose system problems, saying N here is
1359          strongly discouraged.
1360
1361config BUG
1362        bool "BUG() support" if EXPERT
1363        default y
1364        help
1365          Disabling this option eliminates support for BUG and WARN, reducing
1366          the size of your kernel image and potentially quietly ignoring
1367          numerous fatal conditions. You should only consider disabling this
1368          option for embedded systems with no facilities for reporting errors.
1369          Just say Y.
1370
1371config ELF_CORE
1372        depends on COREDUMP
1373        default y
1374        bool "Enable ELF core dumps" if EXPERT
1375        help
1376          Enable support for generating core dumps. Disabling saves about 4k.
1377
1378
1379config PCSPKR_PLATFORM
1380        bool "Enable PC-Speaker support" if EXPERT
1381        depends on HAVE_PCSPKR_PLATFORM
1382        select I8253_LOCK
1383        default y
1384        help
1385          This option allows to disable the internal PC-Speaker
1386          support, saving some memory.
1387
1388config BASE_FULL
1389        default y
1390        bool "Enable full-sized data structures for core" if EXPERT
1391        help
1392          Disabling this option reduces the size of miscellaneous core
1393          kernel data structures. This saves memory on small machines,
1394          but may reduce performance.
1395
1396config FUTEX
1397        bool "Enable futex support" if EXPERT
1398        default y
1399        select RT_MUTEXES
1400        help
1401          Disabling this option will cause the kernel to be built without
1402          support for "fast userspace mutexes".  The resulting kernel may not
1403          run glibc-based applications correctly.
1404
1405config EPOLL
1406        bool "Enable eventpoll support" if EXPERT
1407        default y
1408        select ANON_INODES
1409        help
1410          Disabling this option will cause the kernel to be built without
1411          support for epoll family of system calls.
1412
1413config SIGNALFD
1414        bool "Enable signalfd() system call" if EXPERT
1415        select ANON_INODES
1416        default y
1417        help
1418          Enable the signalfd() system call that allows to receive signals
1419          on a file descriptor.
1420
1421          If unsure, say Y.
1422
1423config TIMERFD
1424        bool "Enable timerfd() system call" if EXPERT
1425        select ANON_INODES
1426        default y
1427        help
1428          Enable the timerfd() system call that allows to receive timer
1429          events on a file descriptor.
1430
1431          If unsure, say Y.
1432
1433config EVENTFD
1434        bool "Enable eventfd() system call" if EXPERT
1435        select ANON_INODES
1436        default y
1437        help
1438          Enable the eventfd() system call that allows to receive both
1439          kernel notification (ie. KAIO) or userspace notifications.
1440
1441          If unsure, say Y.
1442
1443config SHMEM
1444        bool "Use full shmem filesystem" if EXPERT
1445        default y
1446        depends on MMU
1447        help
1448          The shmem is an internal filesystem used to manage shared memory.
1449          It is backed by swap and manages resource limits. It is also exported
1450          to userspace as tmpfs if TMPFS is enabled. Disabling this
1451          option replaces shmem and tmpfs with the much simpler ramfs code,
1452          which may be appropriate on small systems without swap.
1453
1454config AIO
1455        bool "Enable AIO support" if EXPERT
1456        default y
1457        help
1458          This option enables POSIX asynchronous I/O which may by used
1459          by some high performance threaded applications. Disabling
1460          this option saves about 7k.
1461
1462config PCI_QUIRKS
1463        default y
1464        bool "Enable PCI quirk workarounds" if EXPERT
1465        depends on PCI
1466        help
1467          This enables workarounds for various PCI chipset
1468          bugs/quirks. Disable this only if your target machine is
1469          unaffected by PCI quirks.
1470
1471config EMBEDDED
1472        bool "Embedded system"
1473        select EXPERT
1474        help
1475          This option should be enabled if compiling the kernel for
1476          an embedded system so certain expert options are available
1477          for configuration.
1478
1479config HAVE_PERF_EVENTS
1480        bool
1481        help
1482          See tools/perf/design.txt for details.
1483
1484config PERF_USE_VMALLOC
1485        bool
1486        help
1487          See tools/perf/design.txt for details
1488
1489menu "Kernel Performance Events And Counters"
1490
1491config PERF_EVENTS
1492        bool "Kernel performance events and counters"
1493        default y if PROFILING
1494        depends on HAVE_PERF_EVENTS
1495        select ANON_INODES
1496        select IRQ_WORK
1497        help
1498          Enable kernel support for various performance events provided
1499          by software and hardware.
1500
1501          Software events are supported either built-in or via the
1502          use of generic tracepoints.
1503
1504          Most modern CPUs support performance events via performance
1505          counter registers. These registers count the number of certain
1506          types of hw events: such as instructions executed, cachemisses
1507          suffered, or branches mis-predicted - without slowing down the
1508          kernel or applications. These registers can also trigger interrupts
1509          when a threshold number of events have passed - and can thus be
1510          used to profile the code that runs on that CPU.
1511
1512          The Linux Performance Event subsystem provides an abstraction of
1513          these software and hardware event capabilities, available via a
1514          system call and used by the "perf" utility in tools/perf/. It
1515          provides per task and per CPU counters, and it provides event
1516          capabilities on top of those.
1517
1518          Say Y if unsure.
1519
1520config DEBUG_PERF_USE_VMALLOC
1521        default n
1522        bool "Debug: use vmalloc to back perf mmap() buffers"
1523        depends on PERF_EVENTS && DEBUG_KERNEL
1524        select PERF_USE_VMALLOC
1525        help
1526         Use vmalloc memory to back perf mmap() buffers.
1527
1528         Mostly useful for debugging the vmalloc code on platforms
1529         that don't require it.
1530
1531         Say N if unsure.
1532
1533endmenu
1534
1535config VM_EVENT_COUNTERS
1536        default y
1537        bool "Enable VM event counters for /proc/vmstat" if EXPERT
1538        help
1539          VM event counters are needed for event counts to be shown.
1540          This option allows the disabling of the VM event counters
1541          on EXPERT systems.  /proc/vmstat will only show page counts
1542          if VM event counters are disabled.
1543
1544config SLUB_DEBUG
1545        default y
1546        bool "Enable SLUB debugging support" if EXPERT
1547        depends on SLUB && SYSFS
1548        help
1549          SLUB has extensive debug support features. Disabling these can
1550          result in significant savings in code size. This also disables
1551          SLUB sysfs support. /sys/slab will not exist and there will be
1552          no support for cache validation etc.
1553
1554config COMPAT_BRK
1555        bool "Disable heap randomization"
1556        default y
1557        help
1558          Randomizing heap placement makes heap exploits harder, but it
1559          also breaks ancient binaries (including anything libc5 based).
1560          This option changes the bootup default to heap randomization
1561          disabled, and can be overridden at runtime by setting
1562          /proc/sys/kernel/randomize_va_space to 2.
1563
1564          On non-ancient distros (post-2000 ones) N is usually a safe choice.
1565
1566choice
1567        prompt "Choose SLAB allocator"
1568        default SLUB
1569        help
1570           This option allows to select a slab allocator.
1571
1572config SLAB
1573        bool "SLAB"
1574        help
1575          The regular slab allocator that is established and known to work
1576          well in all environments. It organizes cache hot objects in
1577          per cpu and per node queues.
1578
1579config SLUB
1580        bool "SLUB (Unqueued Allocator)"
1581        help
1582           SLUB is a slab allocator that minimizes cache line usage
1583           instead of managing queues of cached objects (SLAB approach).
1584           Per cpu caching is realized using slabs of objects instead
1585           of queues of objects. SLUB can use memory efficiently
1586           and has enhanced diagnostics. SLUB is the default choice for
1587           a slab allocator.
1588
1589config SLOB
1590        depends on EXPERT
1591        bool "SLOB (Simple Allocator)"
1592        help
1593           SLOB replaces the stock allocator with a drastically simpler
1594           allocator. SLOB is generally more space efficient but
1595           does not perform as well on large systems.
1596
1597endchoice
1598
1599config SLUB_CPU_PARTIAL
1600        default y
1601        depends on SLUB
1602        bool "SLUB per cpu partial cache"
1603        help
1604          Per cpu partial caches accellerate objects allocation and freeing
1605          that is local to a processor at the price of more indeterminism
1606          in the latency of the free. On overflow these caches will be cleared
1607          which requires the taking of locks that may cause latency spikes.
1608          Typically one would choose no for a realtime system.
1609
1610config MMAP_ALLOW_UNINITIALIZED
1611        bool "Allow mmapped anonymous memory to be uninitialized"
1612        depends on EXPERT && !MMU
1613        default n
1614        help
1615          Normally, and according to the Linux spec, anonymous memory obtained
1616          from mmap() has it's contents cleared before it is passed to
1617          userspace.  Enabling this config option allows you to request that
1618          mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1619          providing a huge performance boost.  If this option is not enabled,
1620          then the flag will be ignored.
1621
1622          This is taken advantage of by uClibc's malloc(), and also by
1623          ELF-FDPIC binfmt's brk and stack allocator.
1624
1625          Because of the obvious security issues, this option should only be
1626          enabled on embedded devices where you control what is run in
1627          userspace.  Since that isn't generally a problem on no-MMU systems,
1628          it is normally safe to say Y here.
1629
1630          See Documentation/nommu-mmap.txt for more information.
1631
1632config PROFILING
1633        bool "Profiling support"
1634        help
1635          Say Y here to enable the extended profiling support mechanisms used
1636          by profilers such as OProfile.
1637
1638#
1639# Place an empty function call at each tracepoint site. Can be
1640# dynamically changed for a probe function.
1641#
1642config TRACEPOINTS
1643        bool
1644
1645source "arch/Kconfig"
1646
1647endmenu         # General setup
1648
1649config HAVE_GENERIC_DMA_COHERENT
1650        bool
1651        default n
1652
1653config SLABINFO
1654        bool
1655        depends on PROC_FS
1656        depends on SLAB || SLUB_DEBUG
1657        default y
1658
1659config RT_MUTEXES
1660        boolean
1661
1662config BASE_SMALL
1663        int
1664        default 0 if BASE_FULL
1665        default 1 if !BASE_FULL
1666
1667menuconfig MODULES
1668        bool "Enable loadable module support"
1669        help
1670          Kernel modules are small pieces of compiled code which can
1671          be inserted in the running kernel, rather than being
1672          permanently built into the kernel.  You use the "modprobe"
1673          tool to add (and sometimes remove) them.  If you say Y here,
1674          many parts of the kernel can be built as modules (by
1675          answering M instead of Y where indicated): this is most
1676          useful for infrequently used options which are not required
1677          for booting.  For more information, see the man pages for
1678          modprobe, lsmod, modinfo, insmod and rmmod.
1679
1680          If you say Y here, you will need to run "make
1681          modules_install" to put the modules under /lib/modules/
1682          where modprobe can find them (you may need to be root to do
1683          this).
1684
1685          If unsure, say Y.
1686
1687if MODULES
1688
1689config MODULE_FORCE_LOAD
1690        bool "Forced module loading"
1691        default n
1692        help
1693          Allow loading of modules without version information (ie. modprobe
1694          --force).  Forced module loading sets the 'F' (forced) taint flag and
1695          is usually a really bad idea.
1696
1697config MODULE_UNLOAD
1698        bool "Module unloading"
1699        help
1700          Without this option you will not be able to unload any
1701          modules (note that some modules may not be unloadable
1702          anyway), which makes your kernel smaller, faster
1703          and simpler.  If unsure, say Y.
1704
1705config MODULE_FORCE_UNLOAD
1706        bool "Forced module unloading"
1707        depends on MODULE_UNLOAD
1708        help
1709          This option allows you to force a module to unload, even if the
1710          kernel believes it is unsafe: the kernel will remove the module
1711          without waiting for anyone to stop using it (using the -f option to
1712          rmmod).  This is mainly for kernel developers and desperate users.
1713          If unsure, say N.
1714
1715config MODVERSIONS
1716        bool "Module versioning support"
1717        help
1718          Usually, you have to use modules compiled with your kernel.
1719          Saying Y here makes it sometimes possible to use modules
1720          compiled for different kernels, by adding enough information
1721          to the modules to (hopefully) spot any changes which would
1722          make them incompatible with the kernel you are running.  If
1723          unsure, say N.
1724
1725config MODULE_SRCVERSION_ALL
1726        bool "Source checksum for all modules"
1727        help
1728          Modules which contain a MODULE_VERSION get an extra "srcversion"
1729          field inserted into their modinfo section, which contains a
1730          sum of the source files which made it.  This helps maintainers
1731          see exactly which source was used to build a module (since
1732          others sometimes change the module source without updating
1733          the version).  With this option, such a "srcversion" field
1734          will be created for all modules.  If unsure, say N.
1735
1736config MODULE_SIG
1737        bool "Module signature verification"
1738        depends on MODULES
1739        select KEYS
1740        select CRYPTO
1741        select ASYMMETRIC_KEY_TYPE
1742        select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1743        select PUBLIC_KEY_ALGO_RSA
1744        select ASN1
1745        select OID_REGISTRY
1746        select X509_CERTIFICATE_PARSER
1747        help
1748          Check modules for valid signatures upon load: the signature
1749          is simply appended to the module. For more information see
1750          Documentation/module-signing.txt.
1751
1752          !!!WARNING!!!  If you enable this option, you MUST make sure that the
1753          module DOES NOT get stripped after being signed.  This includes the
1754          debuginfo strip done by some packagers (such as rpmbuild) and
1755          inclusion into an initramfs that wants the module size reduced.
1756
1757config MODULE_SIG_FORCE
1758        bool "Require modules to be validly signed"
1759        depends on MODULE_SIG
1760        help
1761          Reject unsigned modules or signed modules for which we don't have a
1762          key.  Without this, such modules will simply taint the kernel.
1763
1764config MODULE_SIG_ALL
1765        bool "Automatically sign all modules"
1766        default y
1767        depends on MODULE_SIG
1768        help
1769          Sign all modules during make modules_install. Without this option,
1770          modules must be signed manually, using the scripts/sign-file tool.
1771
1772comment "Do not forget to sign required modules with scripts/sign-file"
1773        depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
1774
1775choice
1776        prompt "Which hash algorithm should modules be signed with?"
1777        depends on MODULE_SIG
1778        help
1779          This determines which sort of hashing algorithm will be used during
1780          signature generation.  This algorithm _must_ be built into the kernel
1781          directly so that signature verification can take place.  It is not
1782          possible to load a signed module containing the algorithm to check
1783          the signature on that module.
1784
1785config MODULE_SIG_SHA1
1786        bool "Sign modules with SHA-1"
1787        select CRYPTO_SHA1
1788
1789config MODULE_SIG_SHA224
1790        bool "Sign modules with SHA-224"
1791        select CRYPTO_SHA256
1792
1793config MODULE_SIG_SHA256
1794        bool "Sign modules with SHA-256"
1795        select CRYPTO_SHA256
1796
1797config MODULE_SIG_SHA384
1798        bool "Sign modules with SHA-384"
1799        select CRYPTO_SHA512
1800
1801config MODULE_SIG_SHA512
1802        bool "Sign modules with SHA-512"
1803        select CRYPTO_SHA512
1804
1805endchoice
1806
1807config MODULE_SIG_HASH
1808        string
1809        depends on MODULE_SIG
1810        default "sha1" if MODULE_SIG_SHA1
1811        default "sha224" if MODULE_SIG_SHA224
1812        default "sha256" if MODULE_SIG_SHA256
1813        default "sha384" if MODULE_SIG_SHA384
1814        default "sha512" if MODULE_SIG_SHA512
1815
1816endif # MODULES
1817
1818config INIT_ALL_POSSIBLE
1819        bool
1820        help
1821          Back when each arch used to define their own cpu_online_mask and
1822          cpu_possible_mask, some of them chose to initialize cpu_possible_mask
1823          with all 1s, and others with all 0s.  When they were centralised,
1824          it was better to provide this option than to break all the archs
1825          and have several arch maintainers pursuing me down dark alleys.
1826
1827config STOP_MACHINE
1828        bool
1829        default y
1830        depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
1831        help
1832          Need stop_machine() primitive.
1833
1834source "block/Kconfig"
1835
1836config PREEMPT_NOTIFIERS
1837        bool
1838
1839config PADATA
1840        depends on SMP
1841        bool
1842
1843# Can be selected by architectures with broken toolchains
1844# that get confused by correct const<->read_only section
1845# mappings
1846config BROKEN_RODATA
1847        bool
1848
1849config ASN1
1850        tristate
1851        help
1852          Build a simple ASN.1 grammar compiler that produces a bytecode output
1853          that can be interpreted by the ASN.1 stream decoder and used to
1854          inform it as to what tags are to be expected in a stream and what
1855          functions to call on what tags.
1856
1857source "kernel/Kconfig.locks"
1858
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