Re: [PATCH 3/3] rbd: encapsulate code that gets snapshot info

[Josh Durgin <josh.durgin@inktank.com>]

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

On 09/07/2012 12:25 PM, Alex Elder wrote:
> Create a function that encapsulates looking up the name, size and
> features related to a given snapshot, which is indicated by its
> index in an rbd device's snapshot context array of snapshot ids.
>
> This interface will be used to hide differences between the format 1
> and format 2 images.
>
> At the moment this (looking up the name anyway) is slightly less
> efficient than what's done currently, but we may be able to optimize
> this a bit later on by cacheing the last lookup if it proves to be a
> problem.
>
> Signed-off-by: Alex Elder <elder@inktank.com>
> ---
>   drivers/block/rbd.c |   36 ++++++++++++++++++++++++++++++------
>   1 file changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index c62d3f4..e6b8fa6 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -2097,6 +2097,25 @@ err:
>   	return ERR_PTR(ret);
>   }
>
> +static char *rbd_dev_v1_snap_info(struct rbd_device *rbd_dev, u32 which,
> +		u64 *snap_size, u64 *snap_features)
> +{
> +	char *snap_name;
> +
> +	rbd_assert(which < rbd_dev->header.snapc->num_snaps);
> +
> +	*snap_size = rbd_dev->header.snap_sizes[which];
> +	*snap_features = 0;	/* No features for v1 */
> +
> +	/* Skip over names until we find the one we are looking for */
> +
> +	snap_name = rbd_dev->header.snap_names;
> +	while (which--)
> +		snap_name += strlen(snap_name) + 1;
> +
> +	return snap_name;
> +}
> +
>   /*
>    * Scan the rbd device's current snapshot list and compare it to the
>    * newly-received snapshot context.  Remove any existing snapshots
> @@ -2113,7 +2132,6 @@ static int rbd_dev_snaps_update(struct rbd_device
> *rbd_dev)
>   {
>   	struct ceph_snap_context *snapc = rbd_dev->header.snapc;
>   	const u32 snap_count = snapc->num_snaps;
> -	char *snap_name = rbd_dev->header.snap_names;
>   	struct list_head *head = &rbd_dev->snaps;
>   	struct list_head *links = head->next;
>   	u32 index = 0;
> @@ -2122,6 +2140,9 @@ static int rbd_dev_snaps_update(struct rbd_device
> *rbd_dev)
>   	while (index < snap_count || links != head) {
>   		u64 snap_id;
>   		struct rbd_snap *snap;
> +		char *snap_name;
> +		u64 snap_size = 0;
> +		u64 snap_features = 0;
>
>   		snap_id = index < snap_count ? snapc->snaps[index]
>   					     : CEPH_NOSNAP;
> @@ -2148,16 +2169,20 @@ static int rbd_dev_snaps_update(struct
> rbd_device *rbd_dev)
>   			continue;
>   		}
>
> +		snap_name = rbd_dev_v1_snap_info(rbd_dev, index,
> +						&snap_size, &snap_features);
> +		if (IS_ERR(snap_name))
> +			return PTR_ERR(snap_name);
> +
>   		dout("entry %u: snap_id = %llu\n", (unsigned int) snap_count,
>   			(unsigned long long) snap_id);
>   		if (!snap || (snap_id != CEPH_NOSNAP && snap->id < snap_id)) {
> -			struct rbd_image_header	*header = &rbd_dev->header;
>   			struct rbd_snap *new_snap;
>
>   			/* We haven't seen this snapshot before */
>
>   			new_snap = __rbd_add_snap_dev(rbd_dev, snap_name,
> -					snap_id, header->snap_sizes[index], 0);
> +					snap_id, snap_size, snap_features);
>   			if (IS_ERR(new_snap)) {
>   				int err = PTR_ERR(new_snap);
>
> @@ -2178,9 +2203,9 @@ static int rbd_dev_snaps_update(struct rbd_device
> *rbd_dev)
>
>   			dout("  already present\n");
>
> -			rbd_assert(snap->size ==
> -					rbd_dev->header.snap_sizes[index]);
> +			rbd_assert(snap->size == snap_size);
>   			rbd_assert(!strcmp(snap->name, snap_name));
> +			rbd_assert(snap->features == snap_features);
>
>   			/* Done with this list entry; advance */
>
> @@ -2190,7 +2215,6 @@ static int rbd_dev_snaps_update(struct rbd_device
> *rbd_dev)
>   		/* Advance to the next entry in the snapshot context */
>
>   		index++;
> -		snap_name += strlen(snap_name) + 1;
>   	}
>   	dout("%s: done\n", __func__);
>