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From: Dave Chinner <>
Subject: [PATCH 0/3] xfs: clean up buffer cache disk addressing
Date: Tue, 10 Aug 2021 15:28:48 +1000	[thread overview]
Message-ID: <> (raw)

Over time, we've moved from using bp->b_bn as the physical disk
address for a buffer to using the address of the first buffer map
attached to the buffer. This can be seen by the implementation of
XFS_BUF_ADDR() macro:

#define XFS_BUF_ADDR(bp) ((bp)->b_maps[0].bm_bn)

The bp->b_bn value is now used as the buffer cache index for the
buffer, and it is always set to XFS_BUF_DADDR_NULL for uncached
buffers. Hence code that uses bp->b_bn for the physical address of
the buffer will not do the right thing when passed an uncached

This series of patches addresses this problem. It adds a helper
function xfs_buf_daddr() to extract the physical address of the
buffer from it, and replaces all the open coded bp->b_bn accesses
and the XFS_BUF_ADDR() users to use it. It then renames b_bn to
b_index and converts all the internal cache lookup code to use
b_index rather than b_bn.

The result is that all code now uses xfs_buf_daddr() where physical
addresses are required, and the cache index variable isn't named in
a manner that engenders external use of access. The changes end up
being relatively small, and the impact on userspace outside libxfs
is even smaller (only a couple of dozen references to b_bn or

Version 1
- based on 5.14-rc4 + for-next + "xfs: rework feature flags"

             reply	other threads:[~2021-08-10  5:28 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-10  5:28 Dave Chinner [this message]
2021-08-10  5:28 ` [PATCH 1/3] xfs: introduce xfs_buf_daddr() Dave Chinner
2021-08-11  0:40   ` Darrick J. Wong
2021-08-12  8:10   ` Christoph Hellwig
2021-08-12  8:16     ` Christoph Hellwig
2021-08-10  5:28 ` [PATCH 2/3] xfs: convert bp->b_bn references to xfs_buf_daddr() Dave Chinner
2021-08-11  0:44   ` Darrick J. Wong
2021-08-12  8:20   ` Christoph Hellwig
2021-08-10  5:28 ` [PATCH 3/3] xfs: rename buffer cache index variable b_bn Dave Chinner
2021-08-11  0:46   ` Darrick J. Wong
2021-08-17 23:48     ` Dave Chinner
2021-08-17 23:56       ` Darrick J. Wong
2021-08-18  0:07         ` Dave Chinner
2021-08-12  8:23   ` Christoph Hellwig

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