lib: Correctly handle ppoll pfds.events == 0

The frrevent system is spitting out this message in bgpd:
20:40:15 mem1-roc-f2-b1-r5-t2-d4 bgpd[13166]: [XETTR-D5MR0][EC 100663316] Attempting to process an I/O event but for fd: 214(8) no thread to handle this!

This is because as each io event is processed, it is possible that a
.events is set to 0.  This can leave a situation where we ask
ppoll to handle anything that happens on a fd with a .events of 0,
in this situation ppoll can return POLLERR, which indicates that
something bad has happened on the fd.

Let's set the ppoll fds.fd value to -1 when there are no more
events to be processed.  ppoll specifically calls out that
it will just skip this particular one.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>

diff --git a/lib/event.c b/lib/event.c
index d925d0d5f0fc497b029deeca5853c6da969cd9e0..c573923f519155b7fcca388b8af7f58b9bca2705 100644 (file)
--- a/lib/event.c
+++ b/lib/event.c
@@ -979,7 +979,7 @@ void _event_add_read_write(const struct xref_eventsched *xref,
                 * if we already have a pollfd for our file descriptor, find and
                 * use it
                 */
-               for (nfds_t i = 0; i < m->handler.pfdcount; i++)
+               for (nfds_t i = 0; i < m->handler.pfdcount; i++) {
                        if (m->handler.pfds[i].fd == fd) {
                                queuepos = i;
 
@@ -993,6 +993,15 @@ void _event_add_read_write(const struct xref_eventsched *xref,
 #endif
                                break;
                        }
+                       /*
+                        * We are setting the fd = -1 for the
+                        * case when a read/write event is going
+                        * away.  if we find a -1 we can stuff it
+                        * into that spot, so note it
+                        */
+                       if (m->handler.pfds[i].fd == -1 && queuepos == m->handler.pfdcount)
+                               queuepos = i;
+               }
 
                /* make sure we have room for this fd + pipe poker fd */
                assert(queuepos + 1 < m->handler.pfdsize);
@@ -1269,6 +1278,14 @@ static void cancel_arg_helper(struct event_loop *master,
        for (i = 0; i < master->handler.pfdcount;) {
                pfd = master->handler.pfds + i;
 
+               /*
+                * Skip this spot, nothing here to see
+                */
+               if (pfd->fd == -1) {
+                       i++;
+                       continue;
+               }
+
                if (pfd->events & POLLIN)
                        t = master->read[pfd->fd];
                else
@@ -1590,6 +1607,12 @@ static int thread_process_io_helper(struct event_loop *m, struct event *thread,
         * we should.
         */
        m->handler.pfds[pos].events &= ~(state);
+       /*
+        * ppoll man page says that a fd of -1 causes the particular
+        * array item to be skipped.  So let's skip it
+        */
+       if (m->handler.pfds[pos].events == 0)
+               m->handler.pfds[pos].fd = -1;
 
        if (!thread) {
                if ((actual_state & (POLLHUP|POLLIN)) != POLLHUP)