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To:     cattelan@thebarn.com
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Subject: Re: page_buf breakage... 
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Date:   Wed, 12 Jul 2000 16:35:04 +1000
From:   Daniel Moore <dxm@clouds.melbourne.sgi.com>
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Russell Cattelan writes:
 => Daniel Moore wrote:
 => > Is pb_count_desired meant to be supported or is it an IRIX hang
 => > over that needs to be removed?
 => 
 => Hmm... well we need to write out the correct number of bytes.
 => Let me look at this and see if we should change xfs or pagebuf...

XFS_BUF_SET_COUNT is the only writer of pb_count_desired in XFS.
xlog_bwrite is the only user of XFS_BUF_SET_COUNT in XFS.
xlog_bwrite is local to xfs_log_recover.c
 
 => Where in pagebuf is it ignoring the count field?

I think all the time - there seems to be an assumption that
pb_count_desired == pb->pb_buffer_length or perhaps that it's
a rounded up version of pb_buffer_length (not sure).

The log recovery code seems to be the only code that allocates
a buffer of size X and then requests (through pb_count_desired)
that only Y bytes get written (where Y<X).

Pagebuf writing the whole lot is ok most of the time until you
try to mount when the log head is close to the end of the log,
then the big write goes outside the log and clobbers stuff.

-----------------------------------------------------
 Daniel Moore                  dxm@sgi.com
 R&D Software Engineer         Phone: +61-3-98348209
 SGI Performance Tools Group   Fax:   +61-3-98132378
-----------------------------------------------------