sysdeps/unix/sysv/linux/select.c

   1 /* Linux select implementation.
   2    Copyright (C) 2017-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library.  If not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <sys/time.h>
  20 #include <sys/types.h>
  21 #include <sys/select.h>
  22 #include <errno.h>
  23 #include <sysdep-cancel.h>
  24
  25 /* Check the first NFDS descriptors each in READFDS (if not NULL) for read
  26    readiness, in WRITEFDS (if not NULL) for write readiness, and in EXCEPTFDS
  27    (if not NULL) for exceptional conditions.  If TIMEOUT is not NULL, time out
  28    after waiting the interval specified therein.  Returns the number of ready
  29    descriptors, or -1 for errors.  */
  30
  31 #ifdef __NR__newselect
  32 # undef __NR_select
  33 # define __NR_select __NR__newselect
  34 #endif
  35
  36 int
  37 __select (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
  38           struct timeval *timeout)
  39 {
  40 #ifdef __NR_select
  41   return SYSCALL_CANCEL (select, nfds, readfds, writefds, exceptfds,
  42                          timeout);
  43 #else
  44   int result;
  45   struct timespec ts, *tsp = NULL;
  46
  47   if (timeout)
  48     {
  49       TIMEVAL_TO_TIMESPEC (timeout, &ts);
  50       tsp = &ts;
  51     }
  52
  53   result = SYSCALL_CANCEL (pselect6, nfds, readfds, writefds, exceptfds, tsp,
  54                            NULL);
  55
  56   if (timeout)
  57     {
  58       /* Linux by default will update the timeout after a pselect6 syscall
  59          (though the pselect() glibc call suppresses this behavior).
  60          Since select() on Linux has the same behavior as the pselect6
  61          syscall, we update the timeout here.  */
  62       TIMESPEC_TO_TIMEVAL (timeout, &ts);
  63     }
  64
  65   return result;
  66 #endif
  67 }
  68 libc_hidden_def (__select)
  69
  70 weak_alias (__select, select)
  71 weak_alias (__select, __libc_select)