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Re: [PATCH] xfsdump: Revert dump version bump for 32bit projid fix

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfsdump: Revert dump version bump for 32bit projid fix
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 23 Oct 2012 09:31:39 +1100
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <5085AB70.2060904@xxxxxxxxxx>
References: <5085AB70.2060904@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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@xxxxxxxxxxxxx

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