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From:   Neal Gompa <ngompa13@gmail.com>
Date:   Wed, 28 Jul 2021 08:26:12 -0400
Message-ID: <CAEg-Je8Pqbw0tTw6NWkAcD=+zGStOJR0J-409mXuZ1vmb6dZsA@mail.gmail.com>
Subject: Re: [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly
To:     NeilBrown <neilb@suse.de>
Cc:     Wang Yugui <wangyugui@e16-tech.com>,
        Christoph Hellwig <hch@infradead.org>,
        Josef Bacik <josef@toxicpanda.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
        David Sterba <dsterba@suse.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nfs@vger.kernel.org,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
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On Wed, Jul 28, 2021 at 3:02 AM NeilBrown <neilb@suse.de> wrote:
>
> On Wed, 28 Jul 2021, Wang Yugui wrote:
> > Hi,
> >
> > This patchset works well in 5.14-rc3.
>
> Thanks for testing.
>
> >
> > 1, fixed dummy inode(255, BTRFS_FIRST_FREE_OBJECTID - 1 )  is changed t=
o
> > dynamic dummy inode(18446744073709551358, or 18446744073709551359, ...)
>
> The BTRFS_FIRST_FREE_OBJECTID-1 was a just a hack, I never wanted it to
> be permanent.
> The new number is ULONG_MAX - subvol_id (where subvol_id starts at 257 I
> think).
> This is a bit less of a hack.  It is an easily available number that is
> fairly unique.
>
> >
> > 2, btrfs subvol mount info is shown in /proc/mounts, even if nfsd/nfs i=
s
> > not used.
> > /dev/sdc                btrfs   94G  3.5M   93G   1% /mnt/test
> > /dev/sdc                btrfs   94G  3.5M   93G   1% /mnt/test/sub1
> > /dev/sdc                btrfs   94G  3.5M   93G   1% /mnt/test/sub2
> >
> > This is a visiual feature change for btrfs user.
>
> Hopefully it is an improvement.  But it is certainly a change that needs
> to be carefully considered.

I think this is behavior people generally expect, but I wonder what
the consequences of this would be with huge numbers of subvolumes. If
there are hundreds or thousands of them (which is quite possible on
SUSE systems, for example, with its auto-snapshotting regime), this
would be a mess, wouldn't it?

Or can we add a way to mark these things to not show up there or is
there some kind of behavioral change we can make to snapper or other
tools to make them not show up here?


--=20
=E7=9C=9F=E5=AE=9F=E3=81=AF=E3=81=84=E3=81=A4=E3=82=82=E4=B8=80=E3=81=A4=EF=
=BC=81/ Always, there's only one truth!