Re: [PATCH] ceph: add a new vxattr to return auth mds for an inode

[Luis Henriques <lhenriques@suse.de>]

On Tue, Jul 27, 2021 at 07:35:09AM -0400, Jeff Layton wrote:
> Add a new vxattr that shows what MDS is authoritative for an inode (if
> we happen to have auth caps). If we don't have an auth cap for the inode
> then just return -1.
> 
> URL: https://tracker.ceph.com/issues/1276
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/ceph/xattr.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
> index 1242db8d3444..70664a19b8dc 100644
> --- a/fs/ceph/xattr.c
> +++ b/fs/ceph/xattr.c
> @@ -340,6 +340,15 @@ static ssize_t ceph_vxattrcb_caps(struct ceph_inode_info *ci, char *val,
>  			      ceph_cap_string(issued), issued);
>  }
>  
> +static ssize_t ceph_vxattrcb_auth_mds(struct ceph_inode_info *ci,
> +				       char *val, size_t size)
> +{
> +	/* return -1 if we don't have auth caps (and thus can't tell) */
> +	if (!ci->i_auth_cap)
> +		return ceph_fmt_xattr(val, size, "-1");

I don't really have an opinion on this as I don't have a usecase for this
xattr (other than debug, of course).  But I just checked a similar function
ceph_vxattrcb_layout_pool_namespace() and, if there's no value for ns for an
inode, it just returns 0.

Anyway, just my 5c, as I'm OK with returning a '-1' string too.

Cheers,
--
Luís

> +	return ceph_fmt_xattr(val, size, "%d", ci->i_auth_cap->session->s_mds);
> +}
> +
>  #define CEPH_XATTR_NAME(_type, _name)	XATTR_CEPH_PREFIX #_type "." #_name
>  #define CEPH_XATTR_NAME2(_type, _name, _name2)	\
>  	XATTR_CEPH_PREFIX #_type "." #_name "." #_name2
> @@ -473,6 +482,13 @@ static struct ceph_vxattr ceph_common_vxattrs[] = {
>  		.exists_cb = NULL,
>  		.flags = VXATTR_FLAG_READONLY,
>  	},
> +	{
> +		.name = "ceph.auth_mds",
> +		.name_size = sizeof("ceph.auth_mds"),
> +		.getxattr_cb = ceph_vxattrcb_auth_mds,
> +		.exists_cb = NULL,
> +		.flags = VXATTR_FLAG_READONLY,
> +	},
>  	{ .name = NULL, 0 }	/* Required table terminator */
>  };
>  
> -- 
> 2.31.1
>