[lxc-devel] [PATCH] use btrfs snapshot feature to restore snapshots (fixes #131)

[Serge Hallyn]

Hi,

sounds like a good idea, but a question below.

Quoting S.Çağlar Onur (caglar at 10ur.org):
> Signed-off-by: S.Çağlar Onur <caglar at 10ur.org>
> ---
>  src/lxc/bdev.c | 34 ++++++++++++++++++++++++++++------
>  1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/src/lxc/bdev.c b/src/lxc/bdev.c
> index 627c09a..a7786c1 100644
> --- a/src/lxc/bdev.c
> +++ b/src/lxc/bdev.c
> @@ -2587,9 +2587,7 @@ 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 +2596,31 @@ 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) {

Is it possible to hit this case when a user does

lxc-clone -p /opt/btr1 -P /opt/btr2 -B btrfs -o p1 -n p2 ?

So they want to copy-clone a btrfs container to a new btrfs container
on a different btrfs filesystem ?

> +		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 +2641,11 @@ 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,
> -- 
> 1.8.3.2
> 
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