[PATCH passt 3/5] Add --fd option

["Richard W.M. Jones" <rjones@redhat.com>]

This passes a fully connected stream socket to passt.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 conf.c  | 15 +++++++++++++++
 passt.1 | 10 ++++++++++
 passt.c |  2 +-
 passt.h |  2 ++
 tap.c   | 22 +++++++++++++++++++++-
 5 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/conf.c b/conf.c
index 1adcf83..5e08bd6 100644
--- a/conf.c
+++ b/conf.c
@@ -1089,6 +1089,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"log-file",	required_argument,	NULL,		'l' },
 		{"help",	no_argument,		NULL,		'h' },
 		{"socket",	required_argument,	NULL,		's' },
+		{"fd",		required_argument,	NULL,		'F' },
 		{"ns-ifname",	required_argument,	NULL,		'I' },
 		{"pcap",	required_argument,	NULL,		'p' },
 		{"pid",		required_argument,	NULL,		'P' },
@@ -1366,6 +1367,15 @@ void conf(struct ctx *c, int argc, char **argv)
 				usage(argv[0]);
 			}
 			break;
+		case 'F':
+			if (c->sock_fd >= 0) {
+				err("Multiple --fd options given");
+				usage(argv[0]);
+			}
+
+			errno = 0;
+			c->sock_fd = strtol(optarg, NULL, 0);
+			break;
 		case 'I':
 			if (*c->pasta_ifn) {
 				err("Multiple --ns-ifname options given");
@@ -1600,6 +1610,11 @@ void conf(struct ctx *c, int argc, char **argv)
 		usage(argv[0]);
 	}
 
+	if (*c->sock_path && c->sock_fd >= 0) {
+		err("Options --socket and --fd are mutually exclusive");
+		usage(argv[0]);
+	}
+
 	ret = conf_ugid(runas, &uid, &gid);
 	if (ret)
 		usage(argv[0]);
diff --git a/passt.1 b/passt.1
index e34a3e0..66d5eb6 100644
--- a/passt.1
+++ b/passt.1
@@ -297,6 +297,16 @@ Path for UNIX domain socket used by \fBqemu\fR(1) or \fBqrap\fR(1) to connect to
 Default is to probe a free socket, not accepting connections, starting from
 \fI/tmp/passt_1.socket\fR to \fI/tmp/passt_64.socket\fR.
 
+.TP
+.BR \-F ", " \-\-fd " " \fIFD
+Pass a pre-opened, connected socket to
+\fBpasst\fR.
+Usually the socket is opened in the parent process and
+\fBpasst\fR
+inherits it when run as a child.  This allows the parent process to
+open sockets using another address family or requiring special
+privileges.
+
 .TP
 .BR \-1 ", " \-\-one-off
 Quit after handling a single client connection, that is, once the client closes
diff --git a/passt.c b/passt.c
index 7d323c2..ef4643e 100644
--- a/passt.c
+++ b/passt.c
@@ -187,7 +187,7 @@ int main(int argc, char **argv)
 
 	isolate_initial();
 
-	c.pasta_netns_fd = c.fd_tap = c.fd_tap_listen = -1;
+	c.pasta_netns_fd = c.fd_tap = c.fd_tap_listen = c.sock_fd = -1;
 
 	sigemptyset(&sa.sa_mask);
 	sa.sa_flags = 0;
diff --git a/passt.h b/passt.h
index e93eea8..32fc4ae 100644
--- a/passt.h
+++ b/passt.h
@@ -149,6 +149,7 @@ struct ip6_ctx {
  * @stderr:		Force logging to stderr
  * @nofile:		Maximum number of open files (ulimit -n)
  * @sock_path:		Path for UNIX domain socket
+ * @sock_fd:		Connected UNIX domain socket
  * @pcap:		Path for packet capture file
  * @pid_file:		Path to PID file, empty string if not configured
  * @pasta_netns_fd:	File descriptor for network namespace in pasta mode
@@ -198,6 +199,7 @@ struct ctx {
 	int stderr;
 	int nofile;
 	char sock_path[UNIX_PATH_MAX];
+	int sock_fd;
 	char pcap[PATH_MAX];
 	char pid_file[PATH_MAX];
 	int one_off;
diff --git a/tap.c b/tap.c
index abeff25..418a788 100644
--- a/tap.c
+++ b/tap.c
@@ -1063,6 +1063,24 @@ static void tap_sock_tun_init(struct ctx *c)
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
 }
 
+/**
+ * tap_sock_fd_init() - Set up a connected socket (c->sock_fd)
+ * @c:		Execution context
+ */
+void tap_sock_fd_init(struct ctx *c)
+{
+	struct epoll_event ev = { 0 };
+
+	c->fd_tap = c->sock_fd;
+	c->sock_fd = -1;
+
+	info("Setting up fd %d as tap socket", c->fd_tap);
+
+	ev.data.fd = c->fd_tap;
+	ev.events = EPOLLIN | EPOLLRDHUP;
+	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
+}
+
 /**
  * tap_sock_init() - Create and set up AF_UNIX socket or tuntap file descriptor
  * @c:		Execution context
@@ -1087,7 +1105,9 @@ void tap_sock_init(struct ctx *c)
 	}
 
 	if (c->mode == MODE_PASST) {
-		if (c->fd_tap_listen == -1)
+		if (c->sock_fd >= 0)
+			tap_sock_fd_init(c);
+		else if (c->fd_tap_listen == -1)
 			tap_sock_unix_init(c);
 	} else {
 		tap_sock_tun_init(c);
-- 
@@ -1063,6 +1063,24 @@ static void tap_sock_tun_init(struct ctx *c)
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
 }
 
+/**
+ * tap_sock_fd_init() - Set up a connected socket (c->sock_fd)
+ * @c:		Execution context
+ */
+void tap_sock_fd_init(struct ctx *c)
+{
+	struct epoll_event ev = { 0 };
+
+	c->fd_tap = c->sock_fd;
+	c->sock_fd = -1;
+
+	info("Setting up fd %d as tap socket", c->fd_tap);
+
+	ev.data.fd = c->fd_tap;
+	ev.events = EPOLLIN | EPOLLRDHUP;
+	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
+}
+
 /**
  * tap_sock_init() - Create and set up AF_UNIX socket or tuntap file descriptor
  * @c:		Execution context
@@ -1087,7 +1105,9 @@ void tap_sock_init(struct ctx *c)
 	}
 
 	if (c->mode == MODE_PASST) {
-		if (c->fd_tap_listen == -1)
+		if (c->sock_fd >= 0)
+			tap_sock_fd_init(c);
+		else if (c->fd_tap_listen == -1)
 			tap_sock_unix_init(c);
 	} else {
 		tap_sock_tun_init(c);
-- 
2.37.0.rc2