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Re: [PATCH 5/9] repair: detect CRC errors in AG headers

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 5/9] repair: detect CRC errors in AG headers
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 22 Apr 2014 09:35:12 +1000
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140421071106.GF20384@xxxxxxxxxxxxx>
References: <1397550301-31883-1-git-send-email-david@xxxxxxxxxxxxx> <1397550301-31883-6-git-send-email-david@xxxxxxxxxxxxx> <20140421071106.GF20384@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Apr 21, 2014 at 12:11:06AM -0700, Christoph Hellwig wrote:
> On Tue, Apr 15, 2014 at 06:24:57PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > repair doesn't currently detect verifier errors in AG header
> > blocks - apart from the primary superblock they are not detected.
> > They are, fortunately, corrected in the important cases (AGF, AGI
> > and AGFL) because these structures are rebuilt in phase 5, but if
> > you run xfs_repair in checking mode it won't report them as bad.
> Shouldn't we apply the same scheme as for directories here, that is if
> it fails with a verifier error re-read without the verifier and then
> still do the full check as well?

The directory code is the special case - it uses xfs_trans_read_buf*
interfaces, which return either a good buffer with no error or an
error with no buffer. Hence for the directory code, we have to
re-read the buffer without the verifier to grab the unchecked buffer
from the cache when the verifier detects an error.

> Btw, it might make sense to have special read_buf variants in libxfs
> that always return a valid buffer even if the verifier fails, just
> telling us about it without having to re-read.

That's exactly what they do now - you get the xfs_buf, the data in
bp->b_addr and the verifier error in bp->b_error all in one call.


Dave Chinner

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