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

[Luis Henriques <lhenriques@suse.com>]

On Thu, Dec 05, 2019 at 10:42:46AM +0800, Yanhu Cao wrote:
> On Wed, Dec 4, 2019 at 6:36 PM Luis Henriques <lhenriques@suse.com> wrote:
> >
> > 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.
> >
> Yes. we use kcephfs+nfs for CentOS6.*, it does not support ceph-fuse(12.2.*).
> The operating system of other applications is CentOS7.*, which uses
> ceph-fuse and can get quota settings set by kclient.

Ok, so if I understand correctly, you're setting quotas with the kernel
client but actually using ceph-fuse on CentOS7 (I'm assuming a Luminous
cluster).  This should work fine for the fuse-client, but please note
that the kernel client will not respect quotas.

Anyway, the ideal solution for this would be for the kernel to not set
the xattr if the cluster doesn't support the new quotas format
introduced in Mimic.  Unfortunately, the only way we have to find that
out is to set the xattr and see if we get a snap_realm. 

Cheers,
--
Luís

> 
> Thanks.
> BRs
> 
> > 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@gmail.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)
> > >