src/poll.c

   1 /* dnsmasq is Copyright (c) 2000-2015 Simon Kelley
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; version 2 dated June, 1991, or
   6    (at your option) version 3 dated 29 June, 2007.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  15 */
  16
  17 #include "dnsmasq.h"
  18
  19 /* Wrapper for poll(). Allocates and extends array of struct pollfds,
  20    keeps them in fd order so that we can set and test conditions on
  21    fd using a simple but efficient binary chop. */
  22
  23 /* poll_reset()
  24    poll_listen(fd, event)
  25    .
  26    .
  27    poll_listen(fd, event);
  28
  29    hits = do_poll(timeout);
  30
  31    if (poll_check(fd, event)
  32     .
  33     .
  34
  35    if (poll_check(fd, event)
  36     .
  37     .
  38
  39     event is OR of POLLIN, POLLOUT, POLLERR, etc
  40 */
  41
  42 static struct pollfd *pollfds = NULL;
  43 static nfds_t nfds, arrsize = 0;
  44
  45 /* Binary search. Returns either the pollfd with fd, or
  46    if the fd doesn't match, or return equals nfds, the entry
  47    to the left of which a new record should be inserted. */
  48 static nfds_t fd_search(int fd)
  49 {
  50   nfds_t left, right, mid;
  51
  52   if ((right = nfds) == 0)
  53     return 0;
  54
  55   left = 0;
  56
  57   while (1)
  58     {
  59       if (right == left + 1)
  60         return (pollfds[left].fd >= fd) ? left : right;
  61
  62       mid = (left + right)/2;
  63
  64       if (pollfds[mid].fd > fd)
  65         right = mid;
  66       else
  67         left = mid;
  68     }
  69 }
  70
  71 void poll_reset(void)
  72 {
  73   nfds = 0;
  74 }
  75
  76 int do_poll(int timeout)
  77 {
  78   return poll(pollfds, nfds, timeout);
  79 }
  80
  81 int poll_check(int fd, short event)
  82 {
  83   nfds_t i = fd_search(fd);
  84
  85   if (i < nfds && pollfds[i].fd == fd)
  86     return pollfds[i].revents & event;
  87
  88   return 0;
  89 }
  90
  91 void poll_listen(int fd, short event)
  92 {
  93    nfds_t i = fd_search(fd);
  94
  95    if (i < nfds && pollfds[i].fd == fd)
  96      pollfds[i].events |= event;
  97    else
  98      {
  99        if (arrsize != nfds)
 100          memmove(&pollfds[i+1], &pollfds[i], (nfds - i) * sizeof(struct pollfd));
 101        else
 102          {
 103            /* Array too small, extend. */
 104            struct pollfd *new;
 105            arrsize += 64;
 106
 107            if (!(new = whine_malloc(arrsize * sizeof(struct pollfd))))
 108              return;
 109
 110            if (pollfds)
 111              {
 112                memcpy(new, pollfds, i * sizeof(struct pollfd));
 113                memcpy(&new[i+1], &pollfds[i], (nfds - i) * sizeof(struct pollfd));
 114                free(pollfds);
 115              }
 116
 117            pollfds = new;
 118          }
 119
 120        pollfds[i].fd = fd;
 121        pollfds[i].events = event;
 122        nfds++;
 123      }
 124 }