linux-kernel - Re: [PATCH] fs/ceph/super: add mount options "snapdir{mode,uid,gid}"

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Message-ID: <CAKPOu+8qd+qybZWOMoaAYzOtTWXEQ=y5q1jJZjOVxE8pwX7CkQ@mail.gmail.com>
Date:   Tue, 25 Oct 2022 11:57:59 +0200
From:   Max Kellermann <max.kellermann@...os.com>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Jeff Layton <jlayton@...nel.org>, idryomov@...il.com,
        ceph-devel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/ceph/super: add mount options "snapdir{mode,uid,gid}"

On Tue, Oct 25, 2022 at 11:10 AM Xiubo Li <xiubli@...hat.com> wrote:
> $ sudo ./bin/mount.ceph privileged@.../ /mnt/privileged/mountpoint
>
> $ sudo ./bin/mount.ceph global@.../ /mnt/global/mountpoint

So you have two different mount points where different client
permissions are used. There are various problems with that
architecture:

- it complicates administration, because now every mount has to be done twice
- it complicates applications accessing ceph (and their
configuration), because there are now 2 mount points
- it increases resource usage for having twice as many ceph connections
- it interferes with fscache, doubling fscache's local disk usage,
reducing fscache's efficiency
- ownership of the snapdir is still the same as the parent directory,
and I can't have non-superuser processes to manage snapshots; all
processes mananging snapshots need to have write permission on the
parent directory
- this is still all-or-nothing; I can't forbid users to list (+r) or
access (+x) snapshots

All those problems don't exist with my patch.