set lxc.rootfs.backend on container creation

Since specifying lxc.rootfs.backend can lead to performance improvements we
always set it during container creation.

This also fixes a bug. do_bdev_create() tried to be smart and retrieve the lower
directory when bdev->type == overlayfs or aufs thereby cutting the path.
However, this operation is done in ovl_mount() and aufs_mount() and both
functions need the full src path for this. The bug didn't show before because
when creating a overlayfs container with e.g.:

	lxc-create -n c -t busybox -B overlayfs

still left bdev->type set to dir and so the code for retrieving the lower dir in
do_bdev_create() was skipped. But by setting lxc.rootfs.backend on container
creation we force bdev->type to be set to e.g. overlayfs and the code gets
executed thereby exposing the bug.

Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>

diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
index 5c6d499339264ecb1212931cc818c2506f765e93..29cbd330c3d748dc4c82d0c9a81188b5974ce09a 100644 (file)
--- a/src/lxc/lxccontainer.c
+++ b/src/lxc/lxccontainer.c
@@ -1037,6 +1037,7 @@ static struct bdev *do_bdev_create(struct lxc_container *c, const char *type,
        }
 
        do_lxcapi_set_config_item(c, "lxc.rootfs", bdev->src);
+       do_lxcapi_set_config_item(c, "lxc.rootfs.backend", bdev->type);
 
        /* if we are not root, chown the rootfs dir to root in the
         * target uidmap */
@@ -1076,7 +1077,7 @@ static bool create_run_template(struct lxc_container *c, char *tpath, bool need_
        }
 
        if (pid == 0) { // child
-               char *patharg, *namearg, *rootfsarg, *src;
+               char *patharg, *namearg, *rootfsarg;
                struct bdev *bdev = NULL;
                int i;
                int ret, len, nargs = 0;
@@ -1087,18 +1088,7 @@ static bool create_run_template(struct lxc_container *c, char *tpath, bool need_
                        exit(1);
                }
 
-               src = c->lxc_conf->rootfs.path;
-               /*
-                * for an overlay create, what the user wants is the template to fill
-                * in what will become the readonly lower layer.  So don't mount for
-                * the template
-                */
-               if (strncmp(src, "overlayfs:", 10) == 0)
-                       src = ovl_getlower(src+10);
-               if (strncmp(src, "aufs:", 5) == 0)
-                       src = ovl_getlower(src+5);
-
-               bdev = bdev_init(c->lxc_conf, src, c->lxc_conf->rootfs.mount, NULL);
+               bdev = bdev_init(c->lxc_conf, c->lxc_conf->rootfs.path, c->lxc_conf->rootfs.mount, NULL);
                if (!bdev) {
                        ERROR("Error opening rootfs");
                        exit(1);