Default to read-only on snapshot creation and have a flag if snapshot should be writable (was: [PATCH 0/5] btrfs: Readonly snapshots)

[Mike Fedyk <mfedyk@mikefedyk.com>]

On Mon, Nov 29, 2010 at 12:02 AM, Li Zefan <lizf@cn.fujitsu.com> wrote:
> (Cc: Sage Weil <sage@newdream.net> for changes in async snapshots)
>
> This patchset adds readonly-snapshots support. You can create a
> readonly snapshot, and you can also set a snapshot readonly/writable
> on the fly.
>
> A few readonly checks are added in setattr, permission, remove_xattr
> and set_xattr callbacks, as well as in some ioctls.
>

Great work!

I have a suggestion on defaults when snapshots are created.  I think
they should default to being read-only and if they are meant to be
read-write a flag can be set at creation time (and changable at a
later time as well of course).

This way user/admin preconceptions of a snapshot being read-only can
be enforced by default, and the exception when you want a read-write
snapshot can be available with a switch at the cli level (and probably
a flag at the ioctl level).

It gives one more natural distinction between a snapshot and a
subvolume at the user conceptual level.

What do you think?