Re: [PATCH 4/9] rbd: get image features for a v2 image

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

On 09/07/2012 02:13 PM, Alex Elder wrote:
> The features values for an rbd format 2 image are fetched from the
> server using a "get_features" method.  The same method is used for
> getting the features for a snapshot, so structure this addition with
> a generic helper routine that can get this information for either.
>
> The server will provide two 64-bit feature masks, one representing
> the features used for this image (or snapshot) and one representing
> features which cannot be used by the client when working with the
> image (or snapshot).

This second mask is features that are required for the client to
access the image correctly. They are called incompatible because
the are the subset of features used for this image that are not
backwards compatible with clients that do not support them.

With the commit message fixed:

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

> For the time being, neither of these is really used so we keep
> things simple and just record the first feature vector.  Once we
> start using these feature masks, what we record and what we expose
> to the user will most likely change.
>
> Signed-off-by: Alex Elder <elder@inktank.com>
> ---
>   drivers/block/rbd.c |   40 ++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 40 insertions(+)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 36e848a..d48f025 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -2200,6 +2200,40 @@ out:
>   	return ret;
>   }
>
> +static int _rbd_dev_v2_snap_features(struct rbd_device *rbd_dev, u64
> snap_id,
> +		u64 *snap_features)
> +{
> +	__le64 snapid = cpu_to_le64(snap_id);
> +	struct {
> +		__le64 features;
> +		__le64 incompat;
> +	} features_buf = { 0 };
> +	int ret;
> +
> +	ret = rbd_req_sync_exec(rbd_dev, rbd_dev->header_name,
> +				"rbd", "get_features",
> +				(char *) &snapid, sizeof (snapid),
> +				(char *) &features_buf, sizeof (features_buf),
> +				CEPH_OSD_FLAG_READ, NULL);
> +	dout("%s: rbd_req_sync_exec returned %d\n", __func__, ret);
> +	if (ret < 0)
> +		return ret;
> +	*snap_features = le64_to_cpu(features_buf.features);
> +
> +	dout("  snap_id 0x%016llx features = 0x%016llx incompat = 0x%016llx\n",
> +		(unsigned long long) snap_id,
> +		(unsigned long long) *snap_features,
> +		(unsigned long long) le64_to_cpu(features_buf.incompat));
> +
> +	return 0;
> +}
> +
> +static int rbd_dev_v2_features(struct rbd_device *rbd_dev)
> +{
> +	return _rbd_dev_v2_snap_features(rbd_dev, CEPH_NOSNAP,
> +						&rbd_dev->header.features);
> +}
> +
>   /*
>    * Scan the rbd device's current snapshot list and compare it to the
>    * newly-received snapshot context.  Remove any existing snapshots
> @@ -2733,6 +2767,12 @@ static int rbd_dev_v2_probe(struct rbd_device
> *rbd_dev)
>   	ret = rbd_dev_v2_object_prefix(rbd_dev);
>   	if (ret < 0)
>   		goto out_err;
> +
> +	/* Get the features for the image */
> +
> +	ret = rbd_dev_v2_features(rbd_dev);
> +	if (ret < 0)
> +		goto out_err;
>   	rbd_dev->image_format = 2;
>
>   	dout("discovered version 2 image, header name is %s\n",
>