+ /*
+ * On most BPF platforms, either you can do a "select()" or
+ * "poll()" on a BPF file descriptor and it works correctly,
+ * or you can do it and it will return "readable" if the
+ * hold buffer is full but not if the timeout expires *and*
+ * a non-blocking read will, if the hold buffer is empty
+ * but the store buffer isn't empty, rotate the buffers
+ * and return what packets are available.
+ *
+ * In the latter case, the fact that a non-blocking read
+ * will give you the available packets means you can work
+ * around the failure of "select()" and "poll()" to wake up
+ * and return "readable" when the timeout expires by using
+ * the timeout as the "select()" or "poll()" timeout, putting
+ * the BPF descriptor into non-blocking mode, and read from
+ * it regardless of whether "select()" reports it as readable
+ * or not.
+ *
+ * However, in FreeBSD 4.3 and 4.4, "select()" and "poll()"
+ * won't wake up and return "readable" if the timer expires
+ * and non-blocking reads return EWOULDBLOCK if the hold
+ * buffer is empty, even if the store buffer is non-empty.
+ *
+ * This means the workaround in question won't work.
+ *
+ * Therefore, on FreeBSD 4.3 and 4.4, we set "p->selectable_fd"
+ * to -1, which means "sorry, you can't use 'select()' or 'poll()'
+ * here". On all other BPF platforms, we set it to the FD for
+ * the BPF device; in NetBSD, OpenBSD, and Darwin, a non-blocking
+ * read will, if the hold buffer is empty and the store buffer
+ * isn't empty, rotate the buffers and return what packets are
+ * there (and in sufficiently recent versions of OpenBSD
+ * "select()" and "poll()" should work correctly).
+ *
+ * XXX - what about AIX?
+ */
+ if (uname(&osinfo) == 0) {
+ /*
+ * We can check what OS this is.
+ */
+ if (strcmp(osinfo.sysname, "FreeBSD") == 0 &&
+ (strcmp(osinfo.release, "4.3") == 0 ||
+ strcmp(osinfo.release, "4.4") == 0))
+ p->selectable_fd = -1;
+ else
+ p->selectable_fd = p->fd;
+ } else {
+ /*
+ * We can't find out what OS this is, so assume we can
+ * do a "select()" or "poll()".
+ */
+ p->selectable_fd = p->fd;
+ }
+
projects / libpcap / commitdiff
