On Fri, Nov 10, 2017 at 7:24 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Fri, 2017-11-10 at 10:31 +0800, Yan, Zheng wrote:
>> On Fri, Nov 10, 2017 at 12:03 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>> > From: Jeff Layton <jlayton@xxxxxxxxxx>
>> >
>> > FSAL_CEPH just does a ceph_ll_get_inode when asked to create a
>> > filehandle today, which only does a query of the local Ceph client
>> > cache. This means, it can only find Inodes that were previously found
>> > via name lookup.
>> >
>> > When ganesha is restarted, we have a blank-slate Client, and the Inode
>> > will not be in cache. That ends up with the NFS client getting back an
>> > ESTALE.
>> >
>> > We must be able to find Inodes that may not be in the cache. When
>> > ceph_ll_get_inode can't find an Inode, try a lookup vs. the MDS for it.
>> >
>> > The only problem is that we currently have no way to look up a snapped
>> > inode from scratch. I think we'll probably need to add that ability to
>> > libcephfs, but for now the best we can do is just bail out with an
>> > ESTALE in that case.
>> >
>> > While we're in there, remove the comment about ceph_ll_connectable_m.
>> > There is no such function in libcephfs and never has been. The ds
>> > code does seem to refer to such a call, but it's not clear to me
>> > what it's supposed to do.
>> >
>> > Change-Id: I2d0e362ef8f28ba78575b60f3fb2890096d98fc6
>> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
>> > ---
>> >
>> > I sent this up through git-review to ganesha's gerrit, but I'd
>> > like some cephfs folks to have a look too. This patch is basically
>> > a workaround for the FSAL_CEPH code for now.
>> >
>> > Do we need to worry about inodes that are not CEPH_NOSNAP? It
>> > seems like we might need for libcephfs to grow an interface that
>> > can look up snapped inodes as well?
>> >
>> > Either that, or teach ceph_ll_get_inode how to look up inodes
>> > that are not in its cache. Would that be a better fix here?
>> >
>> > src/FSAL/FSAL_CEPH/export.c | 19 +++++++++++++++----
>> > 1 file changed, 15 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/src/FSAL/FSAL_CEPH/export.c b/src/FSAL/FSAL_CEPH/export.c
>> > index 3de25fdfaf41..a31e3bb3ebef 100644
>> > --- a/src/FSAL/FSAL_CEPH/export.c
>> > +++ b/src/FSAL/FSAL_CEPH/export.c
>> > @@ -234,12 +234,23 @@ static fsal_status_t create_handle(struct fsal_export *export_pub,
>> > return status;
>> > }
>> >
>> > + /* Check our local cache first */
>> > i = ceph_ll_get_inode(export->cmount, *vi);
>> > - if (!i)
>> > - return ceph2fsal_error(-ESTALE);
>> > + if (!i) {
>> > + /*
>> > + * Try the slow way, may not be in cache now.
>> > + *
>> > + * Currently, there is no interface for looking up a snapped
>> > + * inode, so we just bail here in that case.
>> > + */
>> > + if (vi->snapid.val != CEPH_NOSNAP)
>> > + return ceph2fsal_error(-ESTALE);
>> > +
>> > + rc = ceph_ll_lookup_inode(export->cmount, vi->ino, &i);
>> > + if (rc)
>> > + return ceph2fsal_error(rc);
>> > + }
>> >
>> > - /* The ceph_ll_connectable_m should have populated libceph's
>> > - cache with all this anyway */
>> > rc = fsal_ceph_ll_getattr(export->cmount, i, &stx,
>> > attrs_out ? CEPH_STATX_ATTR_MASK : CEPH_STATX_HANDLE_MASK,
>> > op_ctx->creds);
>> > --
>> > 2.13.6
>> >
>>
>> Looks good to me,
>>
>> Tested-by: "Yan, Zheng" <zyan@xxxxxxxxxx>
>>
>
> Thanks. I still wonder whether this is a sufficient fix.
>
> ceph_ll_lookup_inode does not take the snapid into account. Do we need a
> version of ceph_ll_lookup_inode that can find snapshotted inodes after
> ganesha has restarted?
>
lookup snapped inode by number hasn't been implemented in mds. not
sure if we can extend backtrace to support snapped inode.
Regards
Yan, Zheng
> It does seem like we could allow a nfs client do work in a snapshotted
> directory, and then have ganesha restart. That client may be very
> confused when the server comes back and all of the existing filehandles
> go stale.
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
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