linux-kernel - Re: [PATCH] ceph: check set quota operation support before syncing setxattr.

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Message-ID: <20191204103629.GA22244@hermes.olymp>
Date:   Wed, 4 Dec 2019 10:36:29 +0000
From:   Luis Henriques <lhenriques@...e.com>
To:     Yanhu Cao <gmayyyha@...il.com>
Cc:     jlayton@...nel.org, sage@...hat.com, idryomov@...il.com,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ceph: check set quota operation support before syncing
 setxattr.

On Wed, Dec 04, 2019 at 11:10:05AM +0800, Yanhu Cao wrote:
> Environment
> -----------
> ceph version: 12.2.*
> kernel version: 4.19+
> 
> setfattr quota operation actually sends op to MDS, and settings
> effective. but kclient outputs 'Operation not supported'. This may confuse
> users' understandings.

What exactly do you mean by "settings effective"?  There have been
changes in the way CephFS quotas work in mimic and, if you're using a
Luminous cluster (12.2.*) the kernel client effectively does *not*
support quotas -- you'll be able to exceed the quotas you've tried to
set because the client won't be checking the limits.  Thus, -EOPNOTSUPP
seems appropriate for this scenario.

I guess that the confusing part is that the xattr is actually set in
that case, but the kernel client won't be able to use it to validate
quotas in the filesystem tree because realms won't be created.

Cheers,
--
Luís
> 
> If the kernel version and ceph version are not compatible, should check
> quota operations are supported first, then do sync_setxattr.
> 
> reference: https://docs.ceph.com/docs/master/cephfs/quota/
> 
> Signed-off-by: Yanhu Cao <gmayyyha@...il.com>
> ---
>  fs/ceph/xattr.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
> index cb18ee637cb7..189aace75186 100644
> --- a/fs/ceph/xattr.c
> +++ b/fs/ceph/xattr.c
> @@ -1132,8 +1132,8 @@ int __ceph_setxattr(struct inode *inode, const char *name,
>  				    "during filling trace\n", inode);
>  		err = -EBUSY;
>  	} else {
> -		err = ceph_sync_setxattr(inode, name, value, size, flags);
> -		if (err >= 0 && check_realm) {
> +		err = 0;
> +		if (check_realm) {
>  			/* check if snaprealm was created for quota inode */
>  			spin_lock(&ci->i_ceph_lock);
>  			if ((ci->i_max_files || ci->i_max_bytes) &&
> @@ -1142,6 +1142,8 @@ int __ceph_setxattr(struct inode *inode, const char *name,
>  				err = -EOPNOTSUPP;
>  			spin_unlock(&ci->i_ceph_lock);
>  		}
> +		if (err == 0)
> +			err = ceph_sync_setxattr(inode, name, value, size, flags);
>  	}
>  out:
>  	ceph_free_cap_flush(prealloc_cf);
> -- 
> 2.21.0 (Apple Git-122.2)
>