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