[NFS-Ganesha-Devel] Re: Ganesha 2.5.4 - usage of device major, minor

15 Oct 2018


      Go ahead and submit it to Gerrithub, then we can review and discuss it there.

Frank
...
-----Original Message-----
From: Krishna Harathi [mailto:krishna.harathi@storagecraft.com]
Sent: Monday, October 15, 2018 3:14 PM
To: Frank Filz <ffilzlnx@mindspring.com>; 'Jeff Layton' <jlayton@redhat.com>;
'Sriram Patil' <sriramp@vmware.com>
Cc: devel@lists.nfs-ganesha.org
Subject: Re: [NFS-Ganesha-Devel] Re: Ganesha 2.5.4 - usage of device major,
minor
A patch that worked for us is attached. If this is along the lines that is
acceptable, I will submit a merge request.
Regards.
Krishna Harathi
On 10/15/18, 11:39 AM, "Krishna Harathi" <krishna.harathi@storagecraft.com>
wrote:
Thanks for all the input. BTW we do use (and configure) our own FS-derived
FSID major/minor that does not depend on device major and minor numbers.
Since we would like to use SIGHUP so as to not disrupt clients after
configuration changes, we will attempt to fix this along the lines Franks
suggested and submit a patch.
Regards.
    Krishna Harathi
On 10/11/18, 8:00 AM, "Frank Filz" <ffilzlnx@mindspring.com> wrote:
> From: Jeff Layton [mailto:jlayton@redhat.com]
        >
        > I'd suggest that the fundamental problem here is the use of device
major/minor
        > in filehandles. Device major+minor (at least on Linux and probably BSD
too) is
        > often not stable across reboots, when devices are added and removed.
Getting
        > ESTALEs because your server rebooted is pretty sucky.
        >
        > It is for good reason that we moved away from doing that in Linux' knfsd
years
        > ago. It does still use that in legacy cases, when there is no filesystem UUID
        > available. Most installations these days use filesystem UUID-based
filehandles,
        > which are stable no matter what device they show up on.
Ganesha does default to using UUID if available. The problem is that the
way getmntent works on Linux, sometimes a filesystem may show up several
times (I don't seem to currently have any of those, but I have seen it in the past).
We use the device ID to distinguish duplicate entries for the same filesystem.
The problem is that if a filesystem is unmounted and a different filesystem is
mounted, we have no way of knowing that. We do rescan filesystems when
adding exports (so you can dynamically mount a new filesystem and then export
it).
My suggestion is to check for filesystems that have gone away also
somewhere...
> I'd counsel against trying to track mounts and unmounts automagically
too. I
        > think you'll find it very difficult to do that in a way that isn't subject to
races.
        >
        > -- Jeff
        >
        > On Thu, 2018-10-11 at 04:28 +0000, Sriram Patil wrote:
        > > I have also encountered same issue where the underlying file system is
        > unmounted but ganesha still holds it details and the device major, minor
reuse
        > later causes problems.
        > >
        > > I can try and look into this and figure out a way to refresh the file
systems list
        > for ganesha. But, another problem in this is if the file system was exported
by
        > ganesha, should the export also be removed or should we wait for an
explicit
        > RemoveExport. Any way, since the file system is unmounted, the clients
will start
        > getting ESTALEs and may be even worse errors.
For FSALs that use actual filesystems (FSAL_VFS. FSAL_XFS, FSAL_GPFS), we
have a handle for the root open of the export that will generally prevent the
filesystem from being unmounted before being unexported (a force unmount
may work). We don't want to automatically unexport because if the sysadmin
really has taken a filesystem offline without unexporting, they will probably be
mounting it back again. Of course in the meantime, we throw ESTALE and clients
fall apart...
Frank
> >
        > > Thanks,
        > > Sriram
        > > On Oct 10, 2018, 11:04 PM +0530, Frank Filz <ffilzlnx@mindspring.com>,
        > wrote:
        > > > > - On the issue itself, I forgot to mention that we used SIGHUP to
        > > > > reload. As you suggested, will work on a patch to cleanup device
        > > > > major/minor to reuse if possible, although I understand delete is not
        > completely supported via SIGHUP.
        > > > > But I do see some action to remove even with SIGHUP.
        > > >
        > > > You have to use DBUS to unexport. I couldn’t come up with a way to
do
        > unexport with SIGHUP. Actually, I do have an idea, add a Unexport = true;
        > option. If that's set and the export is present, unexport, otherwise ignore
the
        > export - then you can leave exports in your config but have them not be
        > present....
        > > >
        > > > If an export is removed with unexport, that should release it's
filesystems,
        > and then a filesystem re-scan has the potential of removing filesystems no
        > longer present (but we have to be careful there, GPFS has some issues
with
        > filesystems going offline and then messing up exports).
        > > >
        > > > Frank
        > > >
        > > > > - On this list subscription - I did subscribe to the list as well as
registered
        > myself.
        > > > > But I had trouble posting to the list, I had to login directly and
        > > > > post. I also not received my own post yet, although I do and did get
other
        > posts.
        > > > >
        > > > > Regards.
        > > > > Krishna Harathi
        > > > >
        > > > >
        > > > > On 10/9/18, 4:19 PM, "Frank Filz" <ffilzlnx@mindspring.com> wrote:
        > > > >
        > > > > Ganesha's management of filesystems is probably not ideal. We can
        > > > > add new ones, but I don't think we implemented removing unused
ones.
        > > > >
        > > > > I would suggest looking at the filesystem management code to see
        > > > > if there's a good way to remove them.
        > > > >
        > > > > You would have to unmount the filesystem, trigger Ganesha to clean
        > > > > up and remove the filesystem, and then mount the new filesystem.
        > > > >
        > > > > The filesystem enumeration showed multiple entries using the same
        > > > > device major and minor (all really related to the same filesystem,
        > > > > but something about the way Linux handles volumes and such) which
        > > > > means Ganesha must pick a filesystem to use for a given device
        > > > > major and minor. If the device major and minor is reused and
        > > > > Ganesha hasn't cleaned out the old filesystem, it will detect the
        > > > > duplicate and just re-use the original filesystem (which of course no
longer
        > is mounted...).
        > > > >
        > > > > Frank
        > > > >
        > > > > > -----Original Message-----
        > > > > > From: krishna.harathi@storagecraft.com
        > > > > > [mailto:krishna.harathi@storagecraft.com]
        > > > > > Sent: Tuesday, October 9, 2018 3:30 PM
        > > > > > To: devel@lists.nfs-ganesha.org
        > > > > > Subject: [NFS-Ganesha-Devel] Ganesha 2.5.4 - usage of device
        > > > > > major, minor
        > > > > >
        > > > > > We are using Ganesha 2.5.4 VFS FSAL with FUSE based filesystem.
        > > > > >
        > > > > > During our testing of deleting existing exports and creating new
        > > > > > ones, found
        > > > >  that
        > > > > > if a device major and minor is reused, clients get ESTALE for
        > > > > > accessing a
        > > > >  newly
        > > > > > created export (nfs2 below).
        > > > > > This seems to cause the following log entry, and explains the
        > > > > > ESTALE
        > > > >  response.
        > > > > > 04/10/2018 T15:16:59.769027-0700 : nfs-ganesha-26627[sigmgr]
        > > > > > 1595 :claim_posix_filesystems :FSAL :INFO :Root fs for export
        > > > > > /exports/nfs1 is
        > > > > > /exports/nfs2
        > > > > >
        > > > > > We use our own Exportid and unique FSID configured for each
        > > > > > export in the configuration file.
        > > > > >
        > > > > > I would like to know more about the intent and purpose of the
        > > > > > usage of
        > > > >  device
        > > > > > major and minor of an export in this context.
        > > > > > Any help in fixing this reuse issue is also appreciated.
        > > > > >
        > > > > > Thanks.
        > > > > >
        > > > > >
        > > > > > Regards.
        > > > > > Krishna Harathi
        > > > > > _______________________________________________
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        > --
        > Jeff Layton <jlayton@redhat.com>
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