[PATCH 2/3] conf, tap, repair: Uniformly use non-blocking accept() on Unix sockets

[David Gibson <david@gibson.dropbear.id.au>]

sock_unix(), which creates a listening Unix socket, doesn't set the
SOCK_NONBLOCK flag, meaning that accept() will block if called with no
pending connections.  Generally, this doesn't matter because we only
accept() once we've received an epoll event indicating there's a pending
connection request.

Control connections (pesto) are an exception, because the way we queue
connections requires that we call accept() when we close one connection to
see if there's another one waiting.  We rely on an EAGAIN here to know that
there's nothing waiting.  To handle these we have an explicit fcntl() to
enable NONBLOCK on the control listening socket.

However, always using non-blocking accept() for Unix sockets would make
things a bit more uniform, and should be a bit less fragile in the case
that we ever somehow got a spurious connection event.  So, alter
sock_unix() to always use the SOCK_NONBLOCK flag.  Remove the control
socket's special case fcntl(), and adjust the error handling on each
Unix socket accept() for the new behaviour.  As a bonus the last adds
reporting for accept() errors on tap socket connections.

we will need non-blocking accept() for the upcoming control/configuration
socket.  Always add SOCK_NONBLOCK, which is more robust and in keeping with
the normal non-blocking style of passt.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 conf.c   | 4 +---
 repair.c | 4 ++--
 tap.c    | 5 +++++
 util.c   | 2 +-
 4 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/conf.c b/conf.c
index 029b9c7c..dec43fca 100644
--- a/conf.c
+++ b/conf.c
@@ -1091,8 +1091,6 @@ static void conf_open_files(struct ctx *c)
 			die_perror("Couldn't open control socket %s",
 				   c->control_path);
 		}
-		if (fcntl(c->fd_control_listen, F_SETFL, O_NONBLOCK))
-			die_perror("Couldn't set O_NONBLOCK on control socket");
 	} else {
 		c->fd_control_listen = -1;
 	}
@@ -2087,7 +2085,7 @@ retry:
 	fd = accept4(c->fd_control_listen, NULL, NULL, SOCK_CLOEXEC);
 	if (fd < 0) {
 		if (errno != EAGAIN)
-			warn_perror("accept4() on configuration listening socket");
+			warn_perror("Error accept()ing configuration socket");
 		return;
 	}
 
diff --git a/repair.c b/repair.c
index 3e0e3e0a..42c4ae97 100644
--- a/repair.c
+++ b/repair.c
@@ -101,8 +101,8 @@ int repair_listen_handler(struct ctx *c, uint32_t events)
 
 	if ((c->fd_repair = accept4(c->fd_repair_listen, NULL, NULL,
 				    SOCK_CLOEXEC)) < 0) {
-		rc = errno;
-		debug_perror("accept4() on TCP_REPAIR helper listening socket");
+		if ((rc = errno) != EAGAIN)
+			warn_perror("Error accept()ing repair helper");
 		return rc;
 	}
 
diff --git a/tap.c b/tap.c
index e7cac9df..fda2da9b 100644
--- a/tap.c
+++ b/tap.c
@@ -1491,6 +1491,11 @@ void tap_listen_handler(struct ctx *c, uint32_t events)
 	}
 
 	c->fd_tap = accept4(c->fd_tap_listen, NULL, NULL, SOCK_CLOEXEC);
+	if (c->fd_tap < 0) {
+		if (errno != EAGAIN)
+			warn_perror("Error accepting tap client");
+		return;
+	}
 
 	if (!getsockopt(c->fd_tap, SOL_SOCKET, SO_PEERCRED, &ucred, &len))
 		info("accepted connection from PID %i", ucred.pid);
diff --git a/util.c b/util.c
index 73c9d51d..204391c7 100644
--- a/util.c
+++ b/util.c
@@ -238,7 +238,7 @@ int sock_l4_dualstack_any(const struct ctx *c, enum epoll_type type,
  */
 int sock_unix(char *sock_path)
 {
-	int fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
+	int fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
 	struct sockaddr_un addr = {
 		.sun_family = AF_UNIX,
 	};
-- 
2.54.0