[PATCH 2/3] util: Extend sock_probe_mem() to sock_probe_features()

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

sock_probe_mem() currently checks whether we're able to allocate large
socket buffers.  Extend it to also check whether the SO_BINDTODEVICE
socket option is available.  Rename to sock_probe_features() to reflect the
new functionality.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 passt.c |  2 +-
 passt.h |  1 +
 util.c  | 19 +++++++++++++++++--
 util.h  |  2 +-
 4 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/passt.c b/passt.c
index 4964427d..0b84ac6c 100644
--- a/passt.c
+++ b/passt.c
@@ -381,7 +381,7 @@ int main(int argc, char **argv)
 	if (setrlimit(RLIMIT_NOFILE, &limit))
 		die_perror("Failed to set current limit for open files");
 
-	sock_probe_mem(&c);
+	sock_probe_features(&c);
 
 	conf(&c, argc, argv);
 	trace_init(c.trace);
diff --git a/passt.h b/passt.h
index 15801b44..e7c1710a 100644
--- a/passt.h
+++ b/passt.h
@@ -281,6 +281,7 @@ struct ctx {
 
 	int low_wmem;
 	int low_rmem;
+	int no_bindtodevice;
 
 	struct vu_dev *vdev;
 
diff --git a/util.c b/util.c
index 347f34f5..bad38129 100644
--- a/util.c
+++ b/util.c
@@ -233,12 +233,13 @@ int sock_unix(char *sock_path)
 }
 
 /**
- * sock_probe_mem() - Check if setting high SO_SNDBUF and SO_RCVBUF is allowed
+ * sock_probe_features() - Probe for socket features we might use
  * @c:		Execution context
  */
-void sock_probe_mem(struct ctx *c)
+void sock_probe_features(struct ctx *c)
 {
 	int v = INT_MAX / 2, s;
+	const char lo[] = "lo";
 	socklen_t sl;
 
 	s = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP);
@@ -247,6 +248,7 @@ void sock_probe_mem(struct ctx *c)
 		return;
 	}
 
+	/* Check if setting high SO_SNDBUF and SO_RCVBUF is allowed */
 	sl = sizeof(v);
 	if (setsockopt(s, SOL_SOCKET, SO_SNDBUF, &v, sizeof(v))	||
 	    getsockopt(s, SOL_SOCKET, SO_SNDBUF, &v, &sl) ||
@@ -259,6 +261,19 @@ void sock_probe_mem(struct ctx *c)
 	    (size_t)v < RCVBUF_BIG)
 		c->low_rmem = 1;
 
+	/* Check if SO_BINDTODEVICE is available
+	 *
+	 * Supported since kernel version 5.7, commit c427bfec18f2 ("net: core:
+	 * enable SO_BINDTODEVICE for non-root users").  Some distro kernels may
+	 * have backports, of course.  Record whether we can use it so that we
+	 * can give more useful diagnostics.
+	 */
+	if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE, lo, sizeof(lo)-1)) {
+		if (errno != EPERM)
+			warn_perror("Unexpected error probing SO_BINDTODEVICE");
+		c->no_bindtodevice = 1;
+	}
+
 	close(s);
 }
 
diff --git a/util.h b/util.h
index a0b2ada6..200b6408 100644
--- a/util.h
+++ b/util.h
@@ -211,7 +211,7 @@ int sock_l4_sa(const struct ctx *c, enum epoll_type type,
 	       const void *sa, socklen_t sl,
 	       const char *ifname, bool v6only);
 int sock_unix(char *sock_path);
-void sock_probe_mem(struct ctx *c);
+void sock_probe_features(struct ctx *c);
 long timespec_diff_ms(const struct timespec *a, const struct timespec *b);
 int64_t timespec_diff_us(const struct timespec *a, const struct timespec *b);
 void bitmap_set(uint8_t *map, unsigned bit);
-- 
2.51.1