[PATCH] tap: Add informational messages for UNIX domain socket connections

[Stefano Brivio <sbrivio@redhat.com>]

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...namely, as connections are discarded or accepted. This was quite
useful to debug an issue with libvirtd failing to start qemu (because
passt refused the new connection) as a previous qemu instance was
still active.

Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
---
 tap.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tap.c b/tap.c
index 04ceade..23414db 100644
--- a/tap.c
+++ b/tap.c
@@ -856,12 +856,19 @@ static void tap_sock_unix_new(struct ctx *c)
 {
 	struct epoll_event ev = { 0 };
 	int v = INT_MAX / 2;
+	struct ucred ucred;
+	socklen_t len;
+
+	len = sizeof(ucred);
 
 	/* Another client is already connected: accept and close right away. */
 	if (c->fd_tap != -1) {
 		int discard = accept4(c->fd_tap_listen, NULL, NULL,
 				      SOCK_NONBLOCK);
 
+		if (!getsockopt(discard, SOL_SOCKET, SO_PEERCRED, &ucred, &len))
+			info("discardingq connection from PID %i", ucred.pid);
+
 		if (discard != -1)
 			close(discard);
 
@@ -870,6 +877,9 @@ static void tap_sock_unix_new(struct ctx *c)
 
 	c->fd_tap = accept4(c->fd_tap_listen, NULL, NULL, 0);
 
+	if (!getsockopt(c->fd_tap, SOL_SOCKET, SO_PEERCRED, &ucred, &len))
+		info("accepted connection from PID %i", ucred.pid);
+
 	if (!c->low_rmem &&
 	    setsockopt(c->fd_tap, SOL_SOCKET, SO_RCVBUF, &v, sizeof(v)))
 		trace("tap: failed to set SO_RCVBUF to %i", v);
-- 
@@ -856,12 +856,19 @@ static void tap_sock_unix_new(struct ctx *c)
 {
 	struct epoll_event ev = { 0 };
 	int v = INT_MAX / 2;
+	struct ucred ucred;
+	socklen_t len;
+
+	len = sizeof(ucred);
 
 	/* Another client is already connected: accept and close right away. */
 	if (c->fd_tap != -1) {
 		int discard = accept4(c->fd_tap_listen, NULL, NULL,
 				      SOCK_NONBLOCK);
 
+		if (!getsockopt(discard, SOL_SOCKET, SO_PEERCRED, &ucred, &len))
+			info("discardingq connection from PID %i", ucred.pid);
+
 		if (discard != -1)
 			close(discard);
 
@@ -870,6 +877,9 @@ static void tap_sock_unix_new(struct ctx *c)
 
 	c->fd_tap = accept4(c->fd_tap_listen, NULL, NULL, 0);
 
+	if (!getsockopt(c->fd_tap, SOL_SOCKET, SO_PEERCRED, &ucred, &len))
+		info("accepted connection from PID %i", ucred.pid);
+
 	if (!c->low_rmem &&
 	    setsockopt(c->fd_tap, SOL_SOCKET, SO_RCVBUF, &v, sizeof(v)))
 		trace("tap: failed to set SO_RCVBUF to %i", v);
-- 
2.35.1