Re: [PATCH 3/4] rbd: implement feature checks

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

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

On 10/09/2012 02:01 PM, Alex Elder wrote:
> Version 2 images have two sets of feature bit fields.  The first
> indicates features possibly used by the image.  The second indicates
> features that the client *must* support in order to use the image.
>
> When an image (or snapshot) is first examined, we need to make sure
> that the local implementation supports the image's required
> features.  If not, fail the probe for the image.
>
> Signed-off-by: Alex Elder <elder@inktank.com>
> ---
>   drivers/block/rbd.c |   16 +++++++++++++++-
>   1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 23f3beb..86ab032 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -70,6 +70,14 @@
>   #define RBD_IMAGE_ID_LEN_MAX    64
>   #define RBD_OBJ_PREFIX_LEN_MAX    64
>
> +/* Feature bits */
> +
> +#define RBD_FEATURE_LAYERING      1
> +
> +/* Features supported by this (client software) implementation. */
> +
> +#define RBD_FEATURES_ALL          (0)
> +
>   /*
>    * An RBD device name will be "rbd#", where the "rbd" comes from
>    * RBD_DRV_NAME above, and # is a unique integer identifier.
> @@ -2225,6 +2233,7 @@ static int _rbd_dev_v2_snap_features(struct
> rbd_device *rbd_dev, u64 snap_id,
>           __le64 features;
>           __le64 incompat;
>       } features_buf = { 0 };
> +    u64 incompat;
>       int ret;
>
>       ret = rbd_req_sync_exec(rbd_dev, rbd_dev->header_name,
> @@ -2235,6 +2244,11 @@ static int _rbd_dev_v2_snap_features(struct
> rbd_device *rbd_dev, u64 snap_id,
>       dout("%s: rbd_req_sync_exec returned %d\n", __func__, ret);
>       if (ret < 0)
>           return ret;
> +
> +    incompat = le64_to_cpu(features_buf.incompat);
> +    if (incompat & ~RBD_FEATURES_ALL)
> +        return -ENOTSUPP;
> +
>       *snap_features = le64_to_cpu(features_buf.features);
>
>       dout("  snap_id 0x%016llx features = 0x%016llx incompat =
> 0x%016llx\n",
> @@ -2976,7 +2990,7 @@ static int rbd_dev_v2_probe(struct rbd_device
> *rbd_dev)
>       if (ret < 0)
>           goto out_err;
>
> -    /* Get the features for the image */
> +    /* Get the and check features for the image */
>
>       ret = rbd_dev_v2_features(rbd_dev);
>       if (ret < 0)