From: Dave Chinner <david@fromorbit.com>
To: Eric Sandeen <sandeen@redhat.com>
Cc: xfs-oss <xfs@oss.sgi.com>
Subject: Re: [PATCH] xfsdump: Revert dump version bump for 32bit projid fix
Date: Tue, 23 Oct 2012 09:31:39 +1100 [thread overview]
Message-ID: <20121022223139.GC4291@dastard> (raw)
In-Reply-To: <5085AB70.2060904@redhat.com>
On Mon, Oct 22, 2012 at 03:24:16PM -0500, Eric Sandeen wrote:
> commit 1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36 fixed xfsdump to
> properly save & restore the top 16 bits of a 32-bit projid, which
> otherwise was being dropped (and restored as 0) in older xfsdump.
>
> The original thought was to bump the dump version, so that we know
> whether the dump (may) have the top 16 bits filled in. In practice
> this would prevent older restores from restoring newer dumps, and
> losing the top 16 bits contained in these newer dumps.
>
> However, in hindsight this appears to be of limited value. I
> propose that the dump version change is unuseful/unwanted for a
> couple reasons:
>
> * There is no actual dump *format* change; the structure size
> is the same, and the top 16 bits were properly zeroed before; old
> restores will read these fixed dumps without problems and without
> restoring garbage. IOW, they will behave exactly as buggily as
> they did before. And worst case, if a dump containing the top 16
> bits is mangled by an old restore, this can be easily remedied by
> simply re-restoring with updated userspace.
>
> * We have no reliable method to know whether 32 bit project IDs are
> in use; the feature flag was not added to the GEOM call at the time
> of implementation. Therefore we cannot reliably bump to V4 only
> for projid32bit filesystems, and we cannot restrict V4 restores
> only to projid32bit filesystems. So the dump version is not
> useful for feature cross-checking purposes.
Seems reasonable. Definitely solves most of the nasty problems
you've been juggling caused by a version bump and 32bit projid
detection. Do we have an xfstest that verifies these assumptions are
valid?
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2012-10-22 22:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-22 20:24 [PATCH] xfsdump: Revert dump version bump for 32bit projid fix Eric Sandeen
2012-10-22 22:31 ` Dave Chinner [this message]
2012-10-23 0:05 ` Eric Sandeen
2012-10-23 19:51 ` Ben Myers
2012-10-26 20:31 ` Ben Myers
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