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Re: [PATCH] xfsdump: fix metadata restore on split files

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfsdump: fix metadata restore on split files
From: Bill Kendall <wkendall@xxxxxxx>
Date: Mon, 31 Oct 2011 07:14:38 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20111028093716.GA23069@xxxxxxxxxxxxx>
References: <1319671483-27787-1-git-send-email-wkendall@xxxxxxx> <20111028093716.GA23069@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20110921 Thunderbird/3.1.15
On 10/28/2011 04:37 AM, Christoph Hellwig wrote:
On Wed, Oct 26, 2011 at 06:24:43PM -0500, Bill Kendall wrote:
xfsrestore does not apply certain metadata until all of the file's
data has been restored. This allows, for example, files with the
immutable flag set to be restored properly.

While testing multi-stream restores, I noticed that files split
across multiple streams did not have their metadata restored.
Looking into this further, it also applies to the single-stream
case where files are split across media files, such as when a
backup spans multiple tapes.

The fix is to check to see if a file is completely restored
whenever we hit the end of a media file. The current code
is broken because it relies on all media files being applied
during the same restore session.

This also moves the S_ISREG() check into restore_complete_reg()
rather than relying on callers to make the check.

Uhh, that's a nasty bug for people storing large files over multiple
tapes.  Any chance we could get an xfstests test case for this?

I mischaracterized the existing bug, files split across tapes
are okay. The bug occurs when:

- a file ends right at the end of a tape in a multi-tape dump, and
- the next tape is not loaded during the same restore session
  (i.e., the restore is interrupted and resumed later)

Can we somehow simulate multiple tapes using small files?

We can simulate multiple tapes on a single tape by asking for a
small media file size. I've got a couple of tests which do this
which I'll post later today.

I don't have a test for the exact scenario above. That would
require using 2 tapes (or 2 files on small loopback filesystems)
and knowing the exact number of bytes that will fit in the dump
file, then working backwards to find a file size that will end
at the right spot on media. Sounds like a very fragile test. It
would break if, for example, a file in the filesystem being
dumped was written as 2 extents instead of 1.

I'll repost this patch with correct commit message.


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