[PATCH 0/2] Clean up reset of tap connections

[PATCH 0/2] Clean up reset of tap connections

[David Gibson]

I ran into some mildly confusing stuff in the tap reset path while
working on the epoll rework.  Here's a couple of fixes for it.

David Gibson (2):
  tap: Clean up tap reset path
  tap: More sensible behaviour for error on listening qemu socket

 tap.c | 57 ++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 32 insertions(+), 25 deletions(-)

-- 
2.41.0

[PATCH 1/2] tap: Clean up tap reset path

[David Gibson]

In tap_handler() if we get an error on the tap device or socket, we use
tap_sock_init() to re-initialise it.  However, what we actually need for
this reset case has remarkably little in common with the case where we're
initialising for the first time:
    * Re-initialising the packet pools is unnecessary
    * The case of a passed in fd (--fd) isn't relevant
    * We don't even call this for pasta mode
    * We will never re-call tap_sock_unix_init() because we never clear
      fd_tap_listen

In fact the only thing we do in tap_sock_init() relevant to the reset case
is to remove the fd from the epoll and close it... which isn't used in the
first initialisation case.

So make a new tap_sock_reset() function just for this case, and simplify
tap_sock_init() slightly as being used only for the first time case.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tap.c | 52 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 29 insertions(+), 23 deletions(-)

diff --git a/tap.c b/tap.c
index a6a73d3..3a43263 100644
--- a/tap.c
+++ b/tap.c
@@ -1233,19 +1233,14 @@ void tap_sock_init(struct ctx *c)
 		tap6_l4[i].p = PACKET_INIT(pool_l4, TAP_SEQS, pkt_buf, sz);
 	}
 
-	if (c->fd_tap != -1) {
-		if (c->one_off) {	/* Passed as --fd */
-			struct epoll_event ev = { 0 };
-
-			ev.data.fd = c->fd_tap;
-			ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
-			epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
-			return;
-		}
+	if (c->fd_tap != -1) { /* Passed as --fd */
+		struct epoll_event ev = { 0 };
+		ASSERT(c->one_off);
 
-		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_tap, NULL);
-		close(c->fd_tap);
-		c->fd_tap = -1;
+		ev.data.fd = c->fd_tap;
+		ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
+		epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
+		return;
 	}
 
 	if (c->mode == MODE_PASST) {
@@ -1256,6 +1251,26 @@ void tap_sock_init(struct ctx *c)
 	}
 }
 
+/**
+ * tap_sock_reset() - Handle closing or failure of connect AF_UNIX socket
+ * @c:		Execution context
+ */
+static void tap_sock_reset(struct ctx *c)
+{
+	if (c->one_off) {
+		info("Client closed connection, exiting");
+		exit(EXIT_SUCCESS);
+	}
+
+	if (c->mode == MODE_PASTA)
+		die("Error on tap device, exiting");
+
+	/* Close the connected socket, wait for a new connection */
+	epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_tap, NULL);
+	close(c->fd_tap);
+	c->fd_tap = -1;
+}
+
 /**
  * tap_handler() - Packet handler for AF_UNIX or tuntap file descriptor
  * @c:		Execution context
@@ -1273,15 +1288,6 @@ void tap_handler(struct ctx *c, int fd, uint32_t events,
 
 	if ((c->mode == MODE_PASST && tap_handler_passt(c, now)) ||
 	    (c->mode == MODE_PASTA && tap_handler_pasta(c, now)) ||
-	    (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR))) {
-		if (c->one_off) {
-			info("Client closed connection, exiting");
-			exit(EXIT_SUCCESS);
-		}
-
-		if (c->mode == MODE_PASTA)
-			die("Error on tap device, exiting");
-
-		tap_sock_init(c);
-	}
+	    (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR)))
+		tap_sock_reset(c);
 }
-- 
@@ -1233,19 +1233,14 @@ void tap_sock_init(struct ctx *c)
 		tap6_l4[i].p = PACKET_INIT(pool_l4, TAP_SEQS, pkt_buf, sz);
 	}
 
-	if (c->fd_tap != -1) {
-		if (c->one_off) {	/* Passed as --fd */
-			struct epoll_event ev = { 0 };
-
-			ev.data.fd = c->fd_tap;
-			ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
-			epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
-			return;
-		}
+	if (c->fd_tap != -1) { /* Passed as --fd */
+		struct epoll_event ev = { 0 };
+		ASSERT(c->one_off);
 
-		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_tap, NULL);
-		close(c->fd_tap);
-		c->fd_tap = -1;
+		ev.data.fd = c->fd_tap;
+		ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
+		epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
+		return;
 	}
 
 	if (c->mode == MODE_PASST) {
@@ -1256,6 +1251,26 @@ void tap_sock_init(struct ctx *c)
 	}
 }
 
+/**
+ * tap_sock_reset() - Handle closing or failure of connect AF_UNIX socket
+ * @c:		Execution context
+ */
+static void tap_sock_reset(struct ctx *c)
+{
+	if (c->one_off) {
+		info("Client closed connection, exiting");
+		exit(EXIT_SUCCESS);
+	}
+
+	if (c->mode == MODE_PASTA)
+		die("Error on tap device, exiting");
+
+	/* Close the connected socket, wait for a new connection */
+	epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_tap, NULL);
+	close(c->fd_tap);
+	c->fd_tap = -1;
+}
+
 /**
  * tap_handler() - Packet handler for AF_UNIX or tuntap file descriptor
  * @c:		Execution context
@@ -1273,15 +1288,6 @@ void tap_handler(struct ctx *c, int fd, uint32_t events,
 
 	if ((c->mode == MODE_PASST && tap_handler_passt(c, now)) ||
 	    (c->mode == MODE_PASTA && tap_handler_pasta(c, now)) ||
-	    (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR))) {
-		if (c->one_off) {
-			info("Client closed connection, exiting");
-			exit(EXIT_SUCCESS);
-		}
-
-		if (c->mode == MODE_PASTA)
-			die("Error on tap device, exiting");
-
-		tap_sock_init(c);
-	}
+	    (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR)))
+		tap_sock_reset(c);
 }
-- 
2.41.0

[PATCH 2/2] tap: More sensible behaviour for error on listening qemu socket

[David Gibson]

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 an error event
on c->fd_tap_listen instead, we'll fall through to the "tap reset" path.

However, this won't do anything useful for an error on the listening
socket, it will just close the already connected socket.  If we wanted to
handle errors on this socket, we'd need to do something different than for
an error on the connected socket.

So, change the logic to explicitly do nothing for any !EPOLLIN events on
the listening socket.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tap.c b/tap.c
index 3a43263..a8e5ce6 100644
--- a/tap.c
+++ b/tap.c
@@ -1281,8 +1281,9 @@ 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) {
+		if (events == EPOLLIN)
+			tap_sock_unix_new(c);
 		return;
 	}
 
-- 
@@ -1281,8 +1281,9 @@ 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) {
+		if (events == EPOLLIN)
+			tap_sock_unix_new(c);
 		return;
 	}
 
-- 
2.41.0