Check for symlinks before attempting create.

Check for symlinks before attempting create.

When attempting to create the compulsory symlinks in /dev,
check for the existence of the link using stat first before
blindly attempting to create the link.

This works around an apparent quirk in the kernel VFS on read-only
file systems where the returned error code might be EEXIST or EROFS
depending on previous access to the /dev directory and its entries.

Reported-by: William Dauchy <william@gandi.net>
Signed-off-by: Michael H. Warfield <mhw@WittsEnd.com>
Tested-by: William Dauchy <william@gandi.net>

src/lxc/conf.c

@@ -828,17 +828,32 @@ static int setup_dev_symlinks(const struct lxc_rootfs *rootfs)
 {
 	char path[MAXPATHLEN];
 	int ret,i;
+	struct stat s;
 
 
 	for (i = 0; i < sizeof(dev_symlinks) / sizeof(dev_symlinks[0]); i++) {
 		const struct dev_symlinks *d = &dev_symlinks[i];
 		ret = snprintf(path, sizeof(path), "%s/dev/%s", rootfs->mount, d->name);
 		if (ret < 0 || ret >= MAXPATHLEN)
 			return -1;
+
+		/*
+		 * Stat the path first.  If we don't get an error
+		 * accept it as is and don't try to create it
+		 */
+		if (!stat(path, &s)) {
+			continue;
+		}
+
 		ret = symlink(d->oldpath, path);
+
 		if (ret && errno != EEXIST) {
-			SYSERROR("Error creating %s", path);
-			return -1;
+			if ( errno == EROFS ) {
+				WARN("Warning: Read Only file system while creating %s", path);
+			} else {
+				SYSERROR("Error creating %s", path);
+				return -1;
+			}
 		}
 	}
 	return 0;