libc/bionic/sysconf.cpp

/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pthread.h>
#include <stdio.h>  // For FOPEN_MAX.
#include <sys/auxv.h>
#include <sys/param.h>
#include <sys/resource.h>
#include <sys/sysinfo.h>
#include <time.h>
#include <unistd.h>

#include "private/bionic_tls.h"

static long __sysconf_rlimit(int resource) {
  rlimit rl;
  getrlimit(resource, &rl);
  return rl.rlim_cur;
}

long sysconf(int name) {
  switch (name) {
    //
    // Things we actually have to calculate...
    //
    case _SC_ARG_MAX:
      // You might think that just returning a constant 128KiB (ARG_MAX) would
      // make sense, as this guy did:
      //
      //   https://lkml.org/lkml/2017/11/15/813...
      //
      //   I suspect a 128kB sysconf(_SC_ARG_MAX) is the sanest bet, simply
      //   because of that "conservative is better than aggressive".
      //
      //   Especially since _technically_ we're still limiting things to that
      //   128kB due to the single-string limit.
      //
      //                 Linus
      //
      // In practice that caused us trouble with toybox tests for xargs edge
      // cases. The tests assume that they can at least reach the kernel's
      // "minimum maximum" of 128KiB, but if we report 128KiB for _SC_ARG_MAX
      // and xargs starts subtracting the environment space and so on from that,
      // then xargs will think it's run out of space when given 128KiB of data,
      // which should always work. See this thread for more:
      //
      // http://lists.landley.net/pipermail/toybox-landley.net/2019-November/011229.html
      //
      // So let's resign ourselves to tracking what the kernel actually does.
      // Right now (2019, Linux 5.3) that amounts to:
      return MAX(MIN(__sysconf_rlimit(RLIMIT_STACK) / 4, 3 * _STK_LIM / 4), ARG_MAX);

    case _SC_AVPHYS_PAGES:      return get_avphys_pages();
    case _SC_CHILD_MAX:         return __sysconf_rlimit(RLIMIT_NPROC);
    case _SC_CLK_TCK:           return static_cast<long>(getauxval(AT_CLKTCK));
    case _SC_NPROCESSORS_CONF:  return get_nprocs_conf();
    case _SC_NPROCESSORS_ONLN:  return get_nprocs();
    case _SC_OPEN_MAX:          return __sysconf_rlimit(RLIMIT_NOFILE);

    case _SC_PAGESIZE:
    case _SC_PAGE_SIZE:
      // _SC_PAGESIZE and _SC_PAGE_SIZE are distinct, but return the same value.
      return getpagesize();

    case _SC_PHYS_PAGES:        return get_phys_pages();

    //
    // Constants...
    //
    case _SC_BC_BASE_MAX:       return _POSIX2_BC_BASE_MAX;   // Minimum requirement.
    case _SC_BC_DIM_MAX:        return _POSIX2_BC_DIM_MAX;    // Minimum requirement.
    case _SC_BC_SCALE_MAX:      return _POSIX2_BC_SCALE_MAX;  // Minimum requirement.
    case _SC_BC_STRING_MAX:     return _POSIX2_BC_STRING_MAX; // Minimum requirement.
    case _SC_COLL_WEIGHTS_MAX:  return _POSIX2_COLL_WEIGHTS_MAX;  // Minimum requirement.
    case _SC_EXPR_NEST_MAX:     return _POSIX2_EXPR_NEST_MAX;     // Minimum requirement.
    case _SC_LINE_MAX:          return _POSIX2_LINE_MAX;          // Minimum requirement.
    case _SC_NGROUPS_MAX:       return NGROUPS_MAX;
    case _SC_PASS_MAX:          return PASS_MAX;
    case _SC_2_C_BIND:          return _POSIX2_C_BIND;
    case _SC_2_C_DEV:           return _POSIX2_C_DEV;
    case _SC_2_CHAR_TERM:       return _POSIX2_CHAR_TERM;
    case _SC_2_FORT_DEV:        return -1;
    case _SC_2_FORT_RUN:        return -1;
    case _SC_2_LOCALEDEF:       return _POSIX2_LOCALEDEF;
    case _SC_2_SW_DEV:          return _POSIX2_SW_DEV;
    case _SC_2_UPE:             return _POSIX2_UPE;
    case _SC_2_VERSION:         return _POSIX2_VERSION;
    case _SC_JOB_CONTROL:       return _POSIX_JOB_CONTROL;
    case _SC_SAVED_IDS:         return _POSIX_SAVED_IDS;
    case _SC_VERSION:           return _POSIX_VERSION;
    case _SC_RE_DUP_MAX:        return _POSIX_RE_DUP_MAX;         // Minimum requirement.
    case _SC_STREAM_MAX:        return FOPEN_MAX;
    case _SC_TZNAME_MAX:        return _POSIX_TZNAME_MAX;         // Minimum requirement.
    case _SC_XOPEN_CRYPT:       return _XOPEN_CRYPT;
    case _SC_XOPEN_ENH_I18N:    return _XOPEN_ENH_I18N;
    case _SC_XOPEN_SHM:         return _XOPEN_SHM;
    case _SC_XOPEN_VERSION:     return _XOPEN_VERSION;
    case _SC_XOPEN_REALTIME:    return _XOPEN_REALTIME;
    case _SC_XOPEN_REALTIME_THREADS: return _XOPEN_REALTIME_THREADS;
    case _SC_XOPEN_LEGACY:      return _XOPEN_LEGACY;
    case _SC_ATEXIT_MAX:        return LONG_MAX;    // Unlimited.
    case _SC_IOV_MAX:           return IOV_MAX;

    case _SC_XOPEN_UNIX:        return _XOPEN_UNIX;
    case _SC_AIO_LISTIO_MAX:    return _POSIX_AIO_LISTIO_MAX;     // Minimum requirement.
    case _SC_AIO_MAX:           return _POSIX_AIO_MAX;            // Minimum requirement.
    case _SC_AIO_PRIO_DELTA_MAX:return 0;                         // Minimum requirement.
    case _SC_DELAYTIMER_MAX:    return INT_MAX;
    case _SC_MQ_OPEN_MAX:       return _POSIX_MQ_OPEN_MAX;        // Minimum requirement.
    case _SC_MQ_PRIO_MAX:       return _POSIX_MQ_PRIO_MAX;        // Minimum requirement.
    case _SC_RTSIG_MAX:         return RTSIG_MAX;
    case _SC_SEM_NSEMS_MAX:     return _POSIX_SEM_NSEMS_MAX;      // Minimum requirement.
    case _SC_SEM_VALUE_MAX:     return SEM_VALUE_MAX;
    case _SC_SIGQUEUE_MAX:      return _POSIX_SIGQUEUE_MAX;       // Minimum requirement.
    case _SC_TIMER_MAX:         return _POSIX_TIMER_MAX;          // Minimum requirement.
    case _SC_ASYNCHRONOUS_IO:   return _POSIX_ASYNCHRONOUS_IO;
    case _SC_FSYNC:             return _POSIX_FSYNC;
    case _SC_MAPPED_FILES:      return _POSIX_MAPPED_FILES;
    case _SC_MEMLOCK:           return _POSIX_MEMLOCK;
    case _SC_MEMLOCK_RANGE:     return _POSIX_MEMLOCK_RANGE;
    case _SC_MEMORY_PROTECTION: return _POSIX_MEMORY_PROTECTION;
    case _SC_MESSAGE_PASSING:   return _POSIX_MESSAGE_PASSING;
    case _SC_PRIORITIZED_IO:    return _POSIX_PRIORITIZED_IO;
    case _SC_PRIORITY_SCHEDULING:  return _POSIX_PRIORITY_SCHEDULING;
    case _SC_REALTIME_SIGNALS:  return _POSIX_REALTIME_SIGNALS;
    case _SC_SEMAPHORES:        return _POSIX_SEMAPHORES;
    case _SC_SHARED_MEMORY_OBJECTS:  return _POSIX_SHARED_MEMORY_OBJECTS;
    case _SC_SYNCHRONIZED_IO:   return _POSIX_SYNCHRONIZED_IO;
    case _SC_TIMERS:            return _POSIX_TIMERS;
    case _SC_GETGR_R_SIZE_MAX:  return 1024;
    case _SC_GETPW_R_SIZE_MAX:  return 1024;
    case _SC_LOGIN_NAME_MAX:    return LOGIN_NAME_MAX;
    case _SC_THREAD_DESTRUCTOR_ITERATIONS: return PTHREAD_DESTRUCTOR_ITERATIONS;
    case _SC_THREAD_KEYS_MAX:   return PTHREAD_KEYS_MAX;
    case _SC_THREAD_STACK_MIN:    return PTHREAD_STACK_MIN;
    case _SC_THREAD_THREADS_MAX:  return -1; // No specific limit.
    case _SC_TTY_NAME_MAX:        return TTY_NAME_MAX;
    case _SC_THREADS:             return _POSIX_THREADS;
    case _SC_THREAD_ATTR_STACKADDR:   return _POSIX_THREAD_ATTR_STACKADDR;
    case _SC_THREAD_ATTR_STACKSIZE:   return _POSIX_THREAD_ATTR_STACKSIZE;
    case _SC_THREAD_PRIORITY_SCHEDULING:  return _POSIX_THREAD_PRIORITY_SCHEDULING;
    case _SC_THREAD_PRIO_INHERIT: return _POSIX_THREAD_PRIO_INHERIT;
    case _SC_THREAD_PRIO_PROTECT: return _POSIX_THREAD_PRIO_PROTECT;
    case _SC_THREAD_SAFE_FUNCTIONS:  return _POSIX_THREAD_SAFE_FUNCTIONS;
    case _SC_MONOTONIC_CLOCK:   return _POSIX_MONOTONIC_CLOCK;

    case _SC_2_PBS:             return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_2_PBS_ACCOUNTING:  return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_2_PBS_CHECKPOINT:  return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_2_PBS_LOCATE:      return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_2_PBS_MESSAGE:     return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_2_PBS_TRACK:       return -1;     // Obsolescent in POSIX.1-2008.
    case _SC_ADVISORY_INFO:     return _POSIX_ADVISORY_INFO;
    case _SC_BARRIERS:          return _POSIX_BARRIERS;
    case _SC_CLOCK_SELECTION:   return _POSIX_CLOCK_SELECTION;
    case _SC_CPUTIME:           return _POSIX_CPUTIME;

    case _SC_HOST_NAME_MAX:     return _POSIX_HOST_NAME_MAX;    // Minimum requirement.
    case _SC_IPV6:              return _POSIX_IPV6;
    case _SC_RAW_SOCKETS:       return _POSIX_RAW_SOCKETS;
    case _SC_READER_WRITER_LOCKS: return _POSIX_READER_WRITER_LOCKS;
    case _SC_REGEXP:            return _POSIX_REGEXP;
    case _SC_SHELL:             return _POSIX_SHELL;
    case _SC_SPAWN:             return _POSIX_SPAWN;
    case _SC_SPIN_LOCKS:        return _POSIX_SPIN_LOCKS;
    case _SC_SPORADIC_SERVER:   return _POSIX_SPORADIC_SERVER;
    case _SC_SS_REPL_MAX:       return -1;
    case _SC_SYMLOOP_MAX:       return _POSIX_SYMLOOP_MAX;      // Minimum requirement.
    case _SC_THREAD_CPUTIME:    return _POSIX_THREAD_CPUTIME;

    case _SC_THREAD_PROCESS_SHARED: return _POSIX_THREAD_PROCESS_SHARED;
    case _SC_THREAD_ROBUST_PRIO_INHERIT:  return _POSIX_THREAD_ROBUST_PRIO_INHERIT;
    case _SC_THREAD_ROBUST_PRIO_PROTECT:  return _POSIX_THREAD_ROBUST_PRIO_PROTECT;
    case _SC_THREAD_SPORADIC_SERVER:      return _POSIX_THREAD_SPORADIC_SERVER;
    case _SC_TIMEOUTS:          return _POSIX_TIMEOUTS;
    case _SC_TRACE:             return -1;             // Obsolescent in POSIX.1-2008.
    case _SC_TRACE_EVENT_FILTER:      return -1;       // Obsolescent in POSIX.1-2008.
    case _SC_TRACE_EVENT_NAME_MAX:    return -1;
    case _SC_TRACE_INHERIT:     return -1;             // Obsolescent in POSIX.1-2008.
    case _SC_TRACE_LOG:         return -1;             // Obsolescent in POSIX.1-2008.
    case _SC_TRACE_NAME_MAX:    return -1;
    case _SC_TRACE_SYS_MAX:     return -1;
    case _SC_TRACE_USER_EVENT_MAX:    return -1;
    case _SC_TYPED_MEMORY_OBJECTS:    return _POSIX_TYPED_MEMORY_OBJECTS;
    case _SC_V7_ILP32_OFF32:    return _POSIX_V7_ILP32_OFF32;
    case _SC_V7_ILP32_OFFBIG:   return _POSIX_V7_ILP32_OFFBIG;
    case _SC_V7_LP64_OFF64:     return _POSIX_V7_LP64_OFF64;
    case _SC_V7_LPBIG_OFFBIG:   return _POSIX_V7_LPBIG_OFFBIG;
    case _SC_XOPEN_STREAMS:     return -1;            // Obsolescent in POSIX.1-2008.
    case _SC_XOPEN_UUCP:        return -1;

    // We do not have actual implementations for cache queries.
    // It's valid to return 0 as the result is unknown.
    case _SC_LEVEL1_ICACHE_SIZE:      return 0;
    case _SC_LEVEL1_ICACHE_ASSOC:     return 0;
    case _SC_LEVEL1_ICACHE_LINESIZE:  return 0;
    case _SC_LEVEL1_DCACHE_SIZE:      return 0;
    case _SC_LEVEL1_DCACHE_ASSOC:     return 0;
    case _SC_LEVEL1_DCACHE_LINESIZE:  return 0;
    case _SC_LEVEL2_CACHE_SIZE:       return 0;
    case _SC_LEVEL2_CACHE_ASSOC:      return 0;
    case _SC_LEVEL2_CACHE_LINESIZE:   return 0;
    case _SC_LEVEL3_CACHE_SIZE:       return 0;
    case _SC_LEVEL3_CACHE_ASSOC:      return 0;
    case _SC_LEVEL3_CACHE_LINESIZE:   return 0;
    case _SC_LEVEL4_CACHE_SIZE:       return 0;
    case _SC_LEVEL4_CACHE_ASSOC:      return 0;
    case _SC_LEVEL4_CACHE_LINESIZE:   return 0;

    default:
      errno = EINVAL;
      return -1;
  }
}