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[PATCH 17/37] xfs: fix incorrect b_offset initialisation

To: xfs@xxxxxxxxxxx
Subject: [PATCH 17/37] xfs: fix incorrect b_offset initialisation
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 23 Apr 2012 15:58:47 +1000
In-reply-to: <1335160747-17254-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1335160747-17254-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

Because we no longer use the page cache for buffering, there is no
direct block number to page offset relationship anymore.
xfs_buf_get_pages is still setting up b_offset as if there was some
relationship, and that is leading to incorrectly setting up
*uncached* buffers that don't overwrite b_offset once they've had
pages allocated.

For cached buffers, the first block of the buffer is always at offset
zero into the allocated memory. This is true for sub-page sized
buffers, as well as for multiple-page buffers.

For uncached buffers, b_offset is only non-zero when we are
associating specific memory to the buffers, and that is set
correctly by the code setting up the buffer.

Hence remove the setting of b_offset in xfs_buf_get_pages, because
it is now always the wrong thing to do.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>
 fs/xfs/xfs_buf.c |    1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 86d9af7..ddfc58f 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -227,7 +227,6 @@ _xfs_buf_get_pages(
        /* Make sure that we have a page list */
        if (bp->b_pages == NULL) {
-               bp->b_offset = xfs_buf_poff(bp->b_file_offset);
                bp->b_page_count = page_count;
                if (page_count <= XB_PAGES) {
                        bp->b_pages = bp->b_page_array;

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