[lxc-devel] [PATCH 1/1] lxc-user-nic: compute first available nic name in container

[Serge Hallyn]

Rather than always using eth0.  Otherwise unpriv containers cannot have
multiple lxc.network.type = veth's without manually setting
lxc.network.name =.

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/lxc_user_nic.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/src/lxc/lxc_user_nic.c b/src/lxc/lxc_user_nic.c
index 1105b3d..75e4851 100644
--- a/src/lxc/lxc_user_nic.c
+++ b/src/lxc/lxc_user_nic.c
@@ -470,7 +470,7 @@ again:
 	goto again;
 }
 
-static int rename_in_ns(int pid, char *oldname, char *newname)
+static int rename_in_ns(int pid, char *oldname, char **newnamep)
 {
 	char nspath[MAXPATHLEN];
 	int fd = -1, ofd = -1, ret;
@@ -495,8 +495,29 @@ static int rename_in_ns(int pid, char *oldname, char *newname)
 		goto out_err;
 	}
 	close(fd); fd = -1;
-	if ((ret = lxc_netdev_rename_by_name(oldname, newname)) < 0) {
-		fprintf(stderr, "Error %d renaming netdev %s to %s in container\n", ret, oldname, newname);
+
+	if (!*newnamep) {
+		int i = 0;
+		char nicname[10];
+		while (i < 100) {
+			ret = snprintf(nicname, 10, "eth%d", i);
+			if (ret < 0 || ret >= 10)
+				return -1;
+			if (if_nametoindex(nicname) == 0)
+				break;
+			i++;
+		}
+		if (i == 100) {
+			fprintf(stderr, "too many nics in container\n");
+			return -1;
+		}
+		*newnamep = strdup(nicname);
+		if (!*newnamep)
+			return -1;
+	}
+
+	if ((ret = lxc_netdev_rename_by_name(oldname, *newnamep)) < 0) {
+		fprintf(stderr, "Error %d renaming netdev %s to %s in container\n", ret, oldname, *newnamep);
 		goto out_err;
 	}
 	if (setns(ofd, 0) < 0) {
@@ -579,7 +600,7 @@ int main(int argc, char *argv[])
 	if (argc >= 5)
 		vethname = argv[4];
 	else
-		vethname = "eth0";
+		vethname = NULL;
 
 	errno = 0;
 	pid = (int) strtol(argv[1], NULL, 10);
@@ -614,7 +635,7 @@ int main(int argc, char *argv[])
 	}
 
 	// Now rename the link
-	if (rename_in_ns(pid, cnic, vethname) < 0) {
+	if (rename_in_ns(pid, cnic, &vethname) < 0) {
 		fprintf(stderr, "Failed to rename the link\n");
 		exit(1);
 	}
-- 
1.9.1