From: Chris Mason <chris.mason@oracle.com>
To: Sage Weil <sage@newdream.net>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: snapshot creation
Date: Tue, 12 Jan 2010 15:25:50 -0500 [thread overview]
Message-ID: <20100112202550.GF14979@think> (raw)
In-Reply-To: <Pine.LNX.4.64.1001121116250.2394@cobra.newdream.net>
On Tue, Jan 12, 2010 at 11:24:39AM -0800, Sage Weil wrote:
> Hi Chris,
>
> What is the motivation behind the two phases of snapshot creation
> (create_pending_snapshot, finish_pending_snapshot)? Is it just to avoid
> putting a reference to the snap subvol inside the snapped version of the
> subvol (forming a loop)?
>
> If that's the case, I think the problem can be solved in other ways (by
> not following the subvol link if it loops to self, or by also delaying the
> root creation to avoid leaking an unreferenced root). And the rest of the
> time (when the link is outside the linked-to subvol) committing the root
> and it's reference in one commit.
>
> Unless I'm missing something else?
Part of the problem is that we want to make sure we have a consistent
view of a given root. So if we tell snapshot abc to point to a specific
root block, the reference that gets taken and all the cow rules get
complex in a hurry.
I'm guessing that you want to do snapshot creation without forcing a
commit?
-chris
next prev parent reply other threads:[~2010-01-12 20:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-12 19:24 snapshot creation Sage Weil
2010-01-12 20:25 ` Chris Mason [this message]
2010-01-12 20:47 ` Sage Weil
2010-01-13 14:44 ` Chris Mason
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