From fd926ed4eea319b94bd0e09e093b90846bcb169b Mon Sep 17 00:00:00 2001
From: Jan Moskyto Matejka <mq@ucw.cz>
Date: Tue, 15 Mar 2016 14:57:49 +0100
Subject: [PATCH] Poll: Prevent the improbable case of EAGAIN after POLLIN

---
 proto/bfd/io.c   |  4 ++--
 sysdep/unix/io.c | 11 ++++++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/proto/bfd/io.c b/proto/bfd/io.c
index fb150040..79ed9af7 100644
--- a/proto/bfd/io.c
+++ b/proto/bfd/io.c
@@ -576,7 +576,7 @@ sockets_close_fds(struct birdloop *loop)
   loop->close_scheduled = 0;
 }
 
-int sk_read(sock *s);
+int sk_read(sock *s, int revents);
 int sk_write(sock *s);
 
 static void
@@ -605,7 +605,7 @@ sockets_fire(struct birdloop *loop)
 
     if (pfd->revents & POLLIN)
       while (e && *psk && (*psk)->rx_hook)
-	e = sk_read(*psk);
+	e = sk_read(*psk, 0);
 
     e = 1;
     if (pfd->revents & POLLOUT)
diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index bc212de1..b769de58 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -1760,7 +1760,7 @@ sk_send_full(sock *s, unsigned len, struct iface *ifa,
  /* sk_read() and sk_write() are called from BFD's event loop */
 
 int
-sk_read(sock *s)
+sk_read(sock *s, int revents)
 {
   switch (s->type)
   {
@@ -1779,6 +1779,11 @@ sk_read(sock *s)
       {
 	if (errno != EINTR && errno != EAGAIN)
 	  s->err_hook(s, errno);
+	else if (errno == EAGAIN && !(revents & POLLIN))
+	{
+	  log(L_ERR "Got EAGAIN from read when revents=%x (without POLLIN)", revents);
+	  s->err_hook(s, 0);
+	}
       }
       else if (!c)
 	s->err_hook(s, 0);
@@ -2159,7 +2164,7 @@ io_loop(void)
 		  {
 		    steps--;
 		    io_log_event(s->rx_hook, s->data);
-		    e = sk_read(s);
+		    e = sk_read(s, pfd[s->index].revents);
 		    if (s != current_sock)
 		      goto next;
 		  }
@@ -2203,7 +2208,7 @@ io_loop(void)
 		{
 		  count++;
 		  io_log_event(s->rx_hook, s->data);
-		  sk_read(s);
+		  sk_read(s, pfd[s->index].revents);
 		  if (s != current_sock)
 		      goto next2;
 		}