Use poll() instead of select() to remove limits on open file descriptors.

src/poll.c

@@ -0,0 +1,124 @@
+/* dnsmasq is Copyright (c) 2000-2015 Simon Kelley
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 dated June, 1991, or
+   (at your option) version 3 dated 29 June, 2007.
+ 
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+     
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "dnsmasq.h"
+
+/* Wrapper for poll(). Allocates and extends array of struct pollfds,
+   keeps them in fd order so that we can set and test conditions on
+   fd using a simple but efficient binary chop. */
+
+/* poll_reset()
+   poll_listen(fd, event)
+   .
+   .
+   poll_listen(fd, event);
+
+   hits = do_poll(timeout);
+
+   if (poll_check(fd, event)
+    .
+    .
+
+   if (poll_check(fd, event)
+    .
+    .
+
+    event is OR of POLLIN, POLLOUT, POLLERR, etc
+*/
+
+static struct pollfd *pollfds = NULL;
+static nfds_t nfds, arrsize = 0;
+
+/* Binary search. Returns either the pollfd with fd, or
+   if the fd doesn't match, or return equals nfds, the entry
+   to the left of which a new record should be inserted. */
+static nfds_t fd_search(int fd)
+{
+  nfds_t left, right, mid;
+  
+  if ((right = nfds) == 0)
+    return 0;
+  
+  left = 0;
+  
+  while (1)
+    {
+      if (right == left + 1)
+	return (pollfds[left].fd >= fd) ? left : right;
+      
+      mid = (left + right)/2;
+      
+      if (pollfds[mid].fd > fd)
+	right = mid;
+      else 
+	left = mid;
+    }
+}
+
+void poll_reset(void)
+{
+  nfds = 0;
+}
+
+int do_poll(int timeout)
+{
+  return poll(pollfds, nfds, timeout);
+}
+
+int poll_check(int fd, short event)
+{
+  nfds_t i = fd_search(fd);
+  
+  if (i < nfds && pollfds[i].fd == fd)
+    return pollfds[i].revents & event;
+
+  return 0;
+}
+
+void poll_listen(int fd, short event)
+{
+   nfds_t i = fd_search(fd);
+  
+   if (i < nfds && pollfds[i].fd == fd)
+     pollfds[i].events |= event;
+   else
+     {
+       if (arrsize != nfds)
+	 memmove(&pollfds[i+1], &pollfds[i], (nfds - i) * sizeof(struct pollfd));
+       else
+	 {
+	   /* Array too small, extend. */
+	   struct pollfd *new;
+	   arrsize += 64;
+	   
+	   if (!(new = whine_malloc(arrsize * sizeof(struct pollfd))))
+	     return;
+
+	   if (pollfds)
+	     {
+	       memcpy(new, pollfds, i * sizeof(struct pollfd));
+	       memcpy(&new[i+1], &pollfds[i], (nfds - i) * sizeof(struct pollfd));
+	       free(pollfds);
+	     }
+	   
+	   pollfds = new;
+	 }
+       
+       pollfds[i].fd = fd;
+       pollfds[i].events = event;
+       nfds++;
+     }
+}