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SubjectRe: [PATCH] ceph: allow object copies across different filesystems in the same cluster
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On Fri, 2019-09-06 at 17:26 +0100, Luis Henriques wrote:
> "Jeff Layton" <jlayton@kernel.org> writes:
>
> > On Fri, 2019-09-06 at 14:57 +0100, Luis Henriques wrote:
> > > OSDs are able to perform object copies across different pools. Thus,
> > > there's no need to prevent copy_file_range from doing remote copies if the
> > > source and destination superblocks are different. Only return -EXDEV if
> > > they have different fsid (the cluster ID).
> > >
> > > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > > ---
> > > fs/ceph/file.c | 23 +++++++++++++++++++----
> > > 1 file changed, 19 insertions(+), 4 deletions(-)
> > >
> > > Hi!
> > >
> > > I've finally managed to run some tests using multiple filesystems, both
> > > within a single cluster and also using two different clusters. The
> > > behaviour of copy_file_range (with this patch, of course) was what I
> > > expected:
> > >
> > > - Object copies work fine across different filesystems within the same
> > > cluster (even with pools in different PGs);
> > > - -EXDEV is returned if the fsid is different
> > >
> > > (OT: I wonder why the cluster ID is named 'fsid'; historical reasons?
> > > Because this is actually what's in ceph.conf fsid in "[global]"
> > > section. Anyway...)
> > >
> > > So, what's missing right now is (I always mention this when I have the
> > > opportunity!) to merge https://github.com/ceph/ceph/pull/25374 :-)
> > > And add the corresponding support for the new flag to the kernel
> > > client, of course.
> > >
> > > Cheers,
> > > --
> > > Luis
> > >
> > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > > index 685a03cc4b77..88d116893c2b 100644
> > > --- a/fs/ceph/file.c
> > > +++ b/fs/ceph/file.c
> > > @@ -1904,6 +1904,7 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > > struct ceph_inode_info *src_ci = ceph_inode(src_inode);
> > > struct ceph_inode_info *dst_ci = ceph_inode(dst_inode);
> > > struct ceph_cap_flush *prealloc_cf;
> > > + struct ceph_fs_client *src_fsc = ceph_inode_to_client(src_inode);
> > > struct ceph_object_locator src_oloc, dst_oloc;
> > > struct ceph_object_id src_oid, dst_oid;
> > > loff_t endoff = 0, size;
> > > @@ -1915,8 +1916,22 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >
> > > if (src_inode == dst_inode)
> > > return -EINVAL;
> > > - if (src_inode->i_sb != dst_inode->i_sb)
> > > - return -EXDEV;
> > > + if (src_inode->i_sb != dst_inode->i_sb) {
> > > + struct ceph_fs_client *dst_fsc = ceph_inode_to_client(dst_inode);
> > > +
> > > + if (!src_fsc->client->have_fsid || !dst_fsc->client->have_fsid) {
> > > + dout("No fsid in a fs client\n");
> > > + return -EXDEV;
> > > + }
> >
> > In what situation is there no fsid? Old cluster version?
> >
> > If there is no fsid, can we take that to indicate that there is only a
> > single filesystem possible in the cluster and that we should attempt the
> > copy anyway?
>
> TBH I'm not sure if 'have_fsid' can ever be 'false' in this call. It is
> set to 'true' when handling the monmap, and it's never changed back to
> 'false'. Since I don't think copy_file_range will be invoked *before*
> we get the monmap, it should be safe to drop this check. Maybe it could
> be replaced it by a WARN_ON()?
>

Yeah. I think the have_fsid flag just allows us to avoid the pr_err msg
in ceph_check_fsid when the client is initially created. Maybe there is
some better way to achieve that?

In any case, I'd just drop that condition here.
--
Jeff Layton <jlayton@kernel.org>

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