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From: Jeff Layton <jlayton@redhat.com>
To: Venky Shankar <vshankar@redhat.com>, pdonnell@redhat.com
Cc: ceph-devel@vger.kernel.org
Subject: Re: [PATCH 0/2] ceph: add debugfs entries signifying new mount syntax support
Date: Thu, 19 Aug 2021 13:28:54 -0400	[thread overview]
Message-ID: <754ccb93528a7d19b5e943641d7e73aa3fe48fc1.camel@redhat.com> (raw)
In-Reply-To: <20210819060701.25486-1-vshankar@redhat.com>

On Thu, 2021-08-19 at 11:36 +0530, Venky Shankar wrote:
> [This is based on top of new mount syntax series]
> Patrick proposed the idea of having debugfs entries to signify if
> kernel supports the new (v2) mount syntax. The primary use of this
> information is to catch any bugs in the new syntax implementation.
> This would be done as follows::
> The userspace mount helper tries to mount using the new mount syntax
> and fallsback to using old syntax if the mount using new syntax fails.
> However, a bug in the new mount syntax implementation can silently
> result in the mount helper switching to old syntax.
> So, the debugfs entries can be relied upon by the mount helper to
> check if the kernel supports the new mount syntax. Cases when the
> mount using the new syntax fails, but the kernel does support the
> new mount syntax, the mount helper could probably log before switching
> to the old syntax (or fail the mount altogether when run in test mode).
> Debugfs entries are as follows::
>     /sys/kernel/debug/ceph/
>     ....
>     ....
>     /sys/kernel/debug/ceph/dev_support
>     /sys/kernel/debug/ceph/dev_support/v2
>     ....
>     ....

Hmm I'm not sure I like the idea of adding a directory _just_ to
indicate whether v2-style mounts are supported. I think we might want to
add something more generic here to indicate what sort of client-side
features the kernel supports.

That's useful for teuthology, and also potentially for support in
general. How about we rename this dir as:


...and then we can have a file in there for "v2_mount_device" or

> Note that there is no entry signifying v1 mount syntax. That's because
> the kernel still supports mounting with old syntax and older kernels do
> not have debug entries for the same.

I think we probably _should_ add a v1_mount_device file too. Eventually
we may want to drop support for v1 style mounts, once older releases
roll off the support matrix. If we drop the file at that time, then that
could be a handy way to indicate that the kernel no longer supports

> Venky Shankar (2):
>   ceph: add helpers to create/cleanup debugfs sub-directories under
>     "ceph" directory
>   ceph: add debugfs entries for v2 (new) mount syntax support
>  fs/ceph/debugfs.c            | 28 ++++++++++++++++++++++++++++
>  fs/ceph/super.c              |  3 +++
>  fs/ceph/super.h              |  2 ++
>  include/linux/ceph/debugfs.h |  3 +++
>  net/ceph/debugfs.c           | 27 +++++++++++++++++++++++++--
>  5 files changed, 61 insertions(+), 2 deletions(-)

Jeff Layton <jlayton@redhat.com>

      parent reply	other threads:[~2021-08-19 17:28 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19  6:06 [PATCH 0/2] ceph: add debugfs entries signifying new mount syntax support Venky Shankar
2021-08-19  6:07 ` [PATCH 1/2] ceph: add helpers to create/cleanup debugfs sub-directories under "ceph" directory Venky Shankar
2021-08-19 17:16   ` Jeff Layton
2021-08-23  4:55     ` Venky Shankar
2021-08-23 10:30       ` Jeff Layton
2021-08-19  6:07 ` [PATCH 2/2] ceph: add debugfs entries for v2 (new) mount syntax support Venky Shankar
2021-08-19 17:28 ` Jeff Layton [this message]

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