tap: Clean up behaviour for errors on listening Unix socket

We call tap_sock_unix_new() to handle a new connection to the qemu socket
if we get an EPOLLIN event on c->fd_tap_listen.  If we get any other event
on the fd, we'll fall through to the "tap reset" path.  But that won't do
anything relevant to the listening socket, it will just close the already
connected socket.  Furthermore, the only other event we're subscribed to
for the listening socket is EPOLLRDHUP, which doesn't apply to a non
connected socket.

Remove EPOLLRDHUP from the subscribed events.  We don't need to explicitly
add EPOLLERR, because errors are always reported.  There's no obvious case
that would cause an error on a listening socket anyway, and it's not
obvious how we'd recover, treat it as a fatal error if it ever does happen.

Finally, fold all this handling into the tap_sock_unix_new() function,
there's no real reason to split it between there and tap_handler().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/tap.c b/tap.c
index 279440b..fb7f543 100644
--- a/tap.c
+++ b/tap.c
@@ -1108,7 +1108,7 @@ static void tap_sock_unix_init(struct ctx *c)
 	listen(fd, 0);
 
 	ev.data.fd = c->fd_tap_listen = fd;
-	ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
+	ev.events = EPOLLIN | EPOLLET;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap_listen, &ev);
 
 	info("You can now start qemu (>= 7.2, with commit 13c6be96618c):");
@@ -1121,14 +1121,18 @@ static void tap_sock_unix_init(struct ctx *c)
 /**
  * tap_sock_unix_new() - Handle new connection on listening socket
  * @c:		Execution context
+ * @events:	epoll events
  */
-static void tap_sock_unix_new(struct ctx *c)
+static void tap_sock_unix_new(struct ctx *c, uint32_t events)
 {
 	struct epoll_event ev = { 0 };
 	int v = INT_MAX / 2;
 	struct ucred ucred;
 	socklen_t len;
 
+	if (events != EPOLLIN)
+		die("Error on listening Unix socket, exiting");
+
 	len = sizeof(ucred);
 
 	/* Another client is already connected: accept and close right away. */
@@ -1284,8 +1288,8 @@ static void tap_sock_reset(struct ctx *c)
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now)
 {
-	if (fd == c->fd_tap_listen && events == EPOLLIN) {
-		tap_sock_unix_new(c);
+	if (fd == c->fd_tap_listen) {
+		tap_sock_unix_new(c, events);
 		return;
 	}