use btrfs snapshot feature to restore snapshots

fixes #131

changes since v1;
* uses btrfs snapshot feature only if src and dest are on same fs

Signed-off-by: S.Çağlar Onur <caglar@10ur.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
index 627c09aacbd35482b1049e736ea8efaf2cf31369..31d1a49e06ce1737d681e01fd8c1675e08f42d1f 100644 (file)
--- a/src/lxc/bdev.c
+++ b/src/lxc/bdev.c
@@ -1336,6 +1336,57 @@ static int btrfs_subvolume_create(const char *path)
        return ret;
 }
 
+#define BTRFS_FSID_SIZE 16
+struct btrfs_ioctl_fs_info_args {
+       unsigned long long max_id;
+       unsigned long long num_devices;
+       char fsid[BTRFS_FSID_SIZE];
+       unsigned long long reserved[124];
+};
+
+#define BTRFS_IOC_FS_INFO _IOR(BTRFS_IOCTL_MAGIC, 31, \
+               struct btrfs_ioctl_fs_info_args)
+
+static int btrfs_same_fs(const char *orig, const char *new) {
+       int fd_orig = -1, fd_new = -1, ret = -1;
+       struct btrfs_ioctl_fs_info_args orig_args, new_args;
+
+       fd_orig = open(orig, O_RDONLY);
+       if (fd_orig < 0) {
+               SYSERROR("Error opening original rootfs %s", orig);
+               goto out;
+       }
+       ret = ioctl(fd_orig, BTRFS_IOC_FS_INFO, &orig_args);
+       if (ret < 0) {
+               SYSERROR("BTRFS_IOC_FS_INFO %s", orig);
+               goto out;
+       }
+
+       fd_new = open(new, O_RDONLY);
+       if (fd_new < 0) {
+               SYSERROR("Error opening new container dir %s", new);
+               err = -1;
+               goto out;
+       }
+       ret = ioctl(fd_new, BTRFS_IOC_FS_INFO, &new_args);
+       if (ret < 0) {
+               SYSERROR("BTRFS_IOC_FS_INFO %s", new);
+               goto out;
+       }
+
+       if (strncmp(orig_args.fsid, new_args.fsid, BTRFS_FSID_SIZE) != 0) {
+               ret = -1;
+               goto out;
+       }
+       ret = 0;
+out:
+       if (fd_new != -1)
+               close(fd_new);
+       if (fd_orig != -1)
+               close(fd_orig);
+       return ret;
+}
+
 static int btrfs_snapshot(const char *orig, const char *new)
 {
        int fd = -1, fddst = -1, ret = -1;
@@ -2587,9 +2638,7 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
        if (new->ops->clone_paths(orig, new, oldname, cname, oldpath, lxcpath,
                                snap, newsize, c0->lxc_conf) < 0) {
                ERROR("failed getting pathnames for cloned storage: %s", src);
-               bdev_put(orig);
-               bdev_put(new);
-               return NULL;
+               goto err;
        }
 
        if (am_unpriv() && chown_mapped_root(new->src, c0->lxc_conf) < 0)
@@ -2598,12 +2647,33 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
        if (snap)
                return new;
 
+       /*
+        * https://github.com/lxc/lxc/issues/131
+        * Use btrfs snapshot feature instead of rsync to restore if both orig and new are btrfs
+        */
+       if (bdevtype &&
+                       strcmp(orig->type, "btrfs") == 0 && strcmp(new->type, "btrfs") == 0 &&
+                       btrfs_same_fs(orig->dest, new->dest) == 0) {
+               if (btrfs_destroy(new) < 0) {
+                       ERROR("Error destroying %s subvolume", new->dest);
+                       goto err;
+               }
+               if (mkdir_p(new->dest, 0755) < 0) {
+                       ERROR("Error creating %s directory", new->dest);
+                       goto err;
+               }
+               if (btrfs_snapshot(orig->dest, new->dest) < 0) {
+                       ERROR("Error restoring %s to %s", orig->dest, new->dest);
+                       goto err;
+               }
+               bdev_put(orig);
+               return new;
+       }
+
        pid = fork();
        if (pid < 0) {
                SYSERROR("fork");
-               bdev_put(orig);
-               bdev_put(new);
-               return NULL;
+               goto err;
        }
 
        if (pid > 0) {
@@ -2624,6 +2694,11 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
                ret = rsync_rootfs(&data);
 
        exit(ret == 0 ? 0 : 1);
+
+err:
+       bdev_put(orig);
+       bdev_put(new);
+       return NULL;
 }
 
 static struct bdev * do_bdev_create(const char *dest, const char *type,