[lxc-devel] [PATCH] overlay and aufs clone_paths: be more robust

[Serge Hallyn]

Currently when we clone a container, bdev_copy passes NULL as dst argument
of bdev_init, then sees bdev->dest (as a result) is NULL, and sets
bdev->dest to $lxcpath/$name/rootfs.  so $ops->clone_paths() can
assume that "/rootfs" is at the end of the path.  The overlayfs and
aufs clonepaths do assume that and index to endofstring-6 and append
delta0.  Let's be more robust by actually finding the last / in
the path.

Then, instead of always setting oldbdev->dest to $lxcpath/$name/rootfs,
set it to oldbdev->src.  Else dir_clonepaths fails when mounting src
onto dest bc dest does not exist.  We could also fix that by creating
bdev->dest if needed, but that addes an empty directory to the old
container.

This fixes 'lxc-clone -o x1 -n x2' if x1 has lxc.rootfs = /var/lib/lxc/x1/x
and makes the overlayfs and aufs paths less fragile should something else
change.

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/bdev.c | 68 ++++++++++++++++++++++++++--------------------------------
 1 file changed, 30 insertions(+), 38 deletions(-)

diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
index 4fc10f2..8a819ab 100644
--- a/src/lxc/bdev.c
+++ b/src/lxc/bdev.c
@@ -2265,20 +2265,24 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 		WARN("Failed to update ownership of %s", new->dest);
 
 	if (strcmp(orig->type, "dir") == 0) {
-		char *delta;
-		int ret, len;
+		char *delta, *lastslash;
+		int ret, len, lastslashidx;
 
 		// if we have /var/lib/lxc/c2/rootfs, then delta will be
 		//            /var/lib/lxc/c2/delta0
-		delta = strdup(new->dest);
-		if (!delta) {
-			return -1;
-		}
-		if (strlen(delta) < 6) {
-			free(delta);
+		lastslash = strrchr(new->dest, '/');
+		if (!lastslash)
 			return -22;
-		}
-		strcpy(&delta[strlen(delta)-6], "delta0");
+		if (strlen(lastslash) < 7)
+			return -22;
+		lastslash++;
+		lastslashidx = lastslash - new->dest;
+
+		delta = malloc(lastslashidx + 7);
+		if (!delta)
+			return -1;
+		strncpy(delta, new->dest, lastslashidx+1);
+		strcpy(delta+lastslashidx, "delta0");
 		if ((ret = mkdir(delta, 0755)) < 0) {
 			SYSERROR("error: mkdir %s", delta);
 			free(delta);
@@ -2319,7 +2323,7 @@ static int overlayfs_clonepaths(struct bdev *orig, struct bdev *new, const char
 			free(osrc);
 			return -ENOMEM;
 		}
-		if ((ret = mkdir(ndelta, 0755)) < 0) {
+		if ((ret = mkdir(ndelta, 0755)) < 0 && errno != EEXIST) {
 			SYSERROR("error: mkdir %s", ndelta);
 			free(osrc);
 			free(ndelta);
@@ -2560,20 +2564,24 @@ static int aufs_clonepaths(struct bdev *orig, struct bdev *new, const char *oldn
 		return -1;
 
 	if (strcmp(orig->type, "dir") == 0) {
-		char *delta;
-		int ret, len;
+		char *delta, *lastslash;
+		int ret, len, lastslashidx;
 
 		// if we have /var/lib/lxc/c2/rootfs, then delta will be
 		//            /var/lib/lxc/c2/delta0
-		delta = strdup(new->dest);
-		if (!delta) {
-			return -1;
-		}
-		if (strlen(delta) < 6) {
-			free(delta);
+		lastslash = strrchr(new->dest, '/');
+		if (!lastslash)
 			return -22;
-		}
-		strcpy(&delta[strlen(delta)-6], "delta0");
+		if (strlen(lastslash) < 7)
+			return -22;
+		lastslash++;
+		lastslashidx = lastslash - new->dest;
+
+		delta = malloc(lastslashidx + 7);
+		if (!delta)
+			return -1;
+		strncpy(delta, new->dest, lastslashidx+1);
+		strcpy(delta+lastslashidx, "delta0");
 		if ((ret = mkdir(delta, 0755)) < 0) {
 			SYSERROR("error: mkdir %s", delta);
 			free(delta);
@@ -3248,28 +3256,12 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
 		return NULL;
 	}
 
-	orig = bdev_init(c0->lxc_conf, src, NULL, NULL);
+	orig = bdev_init(c0->lxc_conf, src, src, NULL);
 	if (!orig) {
 		ERROR("failed to detect blockdev type for %s", src);
 		return NULL;
 	}
 
-	if (!orig->dest) {
-		int ret;
-		orig->dest = malloc(MAXPATHLEN);
-		if (!orig->dest) {
-			ERROR("out of memory");
-			bdev_put(orig);
-			return NULL;
-		}
-		ret = snprintf(orig->dest, MAXPATHLEN, "%s/%s/rootfs", oldpath, oldname);
-		if (ret < 0 || ret >= MAXPATHLEN) {
-			ERROR("rootfs path too long");
-			bdev_put(orig);
-			return NULL;
-		}
-	}
-
 	/*
 	 * special case for snapshot - if caller requested maybe_snapshot and
 	 * keepbdevtype and backing store is directory, then proceed with a copy
-- 
2.1.0