lib/util/select.c

   1 /*
   2    Unix SMB/Netbios implementation.
   3    Version 3.0
   4    Samba select/poll implementation
   5    Copyright (C) Andrew Tridgell 1992-1998
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21 #include "includes.h"
  22 #include "system/filesys.h"
  23 #include "system/select.h"
  24 #include "lib/util/select.h"
  25
  26 /* This is here because it allows us to avoid a nasty race in signal handling.
  27    We need to guarantee that when we get a signal we get out of a select immediately
  28    but doing that involves a race condition. We can avoid the race by getting the
  29    signal handler to write to a pipe that is in the select/poll list
  30
  31    This means all Samba signal handlers should call sys_select_signal().
  32 */
  33
  34 static pid_t initialised;
  35 static int select_pipe[2];
  36 static volatile unsigned pipe_written, pipe_read;
  37
  38 /*
  39  * sys_poll expects pollfd's to be a talloc'ed array.
  40  *
  41  * It expects the talloc_array_length(fds) >= num_fds+1 to give space
  42  * to the signal pipe.
  43  */
  44
  45 int sys_poll(struct pollfd *fds, int num_fds, int timeout)
  46 {
  47         int ret;
  48
  49         if (talloc_array_length(fds) < num_fds+1) {
  50                 errno = ENOSPC;
  51                 return -1;
  52         }
  53
  54         if (initialised != sys_getpid()) {
  55                 if (pipe(select_pipe) == -1)
  56                 {
  57                         int saved_errno = errno;
  58                         DEBUG(0, ("sys_poll: pipe failed (%s)\n",
  59                                 strerror(errno)));
  60                         errno = saved_errno;
  61                         return -1;
  62                 }
  63
  64                 /*
  65                  * These next two lines seem to fix a bug with the Linux
  66                  * 2.0.x kernel (and probably other UNIXes as well) where
  67                  * the one byte read below can block even though the
  68                  * select returned that there is data in the pipe and
  69                  * the pipe_written variable was incremented. Thanks to
  70                  * HP for finding this one. JRA.
  71                  */
  72
  73                 if(set_blocking(select_pipe[0],0)==-1)
  74                         smb_panic("select_pipe[0]: O_NONBLOCK failed");
  75                 if(set_blocking(select_pipe[1],0)==-1)
  76                         smb_panic("select_pipe[1]: O_NONBLOCK failed");
  77
  78                 initialised = sys_getpid();
  79         }
  80
  81         ZERO_STRUCT(fds[num_fds]);
  82         fds[num_fds].fd = select_pipe[0];
  83         fds[num_fds].events = POLLIN|POLLHUP;
  84
  85         errno = 0;
  86         ret = poll(fds, num_fds+1, timeout);
  87
  88         if ((ret >= 0) && (fds[num_fds].revents & (POLLIN|POLLHUP|POLLERR))) {
  89                 char c;
  90                 int saved_errno = errno;
  91
  92                 if (read(select_pipe[0], &c, 1) == 1) {
  93                         pipe_read += 1;
  94
  95                         /* Mark Weaver <mark-clist@npsl.co.uk> pointed out a critical
  96                            fix to ensure we don't lose signals. We must always
  97                            return -1 when the select pipe is set, otherwise if another
  98                            fd is also ready (so ret == 2) then we used to eat the
  99                            byte in the pipe and lose the signal. JRA.
 100                         */
 101                         ret = -1;
 102 #if 0
 103                         /* JRA - we can use this to debug the signal messaging... */
 104                         DEBUG(0,("select got %u signal\n", (unsigned int)c));
 105 #endif
 106                         errno = EINTR;
 107                 } else {
 108                         ret -= 1;
 109                         errno = saved_errno;
 110                 }
 111         }
 112
 113         return ret;
 114 }
 115
 116 int sys_poll_intr(struct pollfd *fds, int num_fds, int timeout)
 117 {
 118         int orig_timeout = timeout;
 119         struct timespec start;
 120         int ret;
 121
 122         clock_gettime_mono(&start);
 123
 124         while (true) {
 125                 struct timespec now;
 126                 int64_t elapsed;
 127
 128                 ret = poll(fds, num_fds, timeout);
 129                 if (ret != -1) {
 130                         break;
 131                 }
 132                 if (errno != EINTR) {
 133                         break;
 134                 }
 135                 clock_gettime_mono(&now);
 136                 elapsed = nsec_time_diff(&now, &start);
 137                 timeout = (orig_timeout - elapsed) / 1000000;
 138         };
 139         return ret;
 140 }