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author | Alex Elder <aelder@sgi.com> | 2010-04-13 05:22:40 (GMT) |
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committer | Alex Elder <aelder@sgi.com> | 2010-05-19 14:58:12 (GMT) |
commit | 8511998baaf541710f457315958cef0d0a7864a1 (patch) | |
tree | b7ac320a8e0d7b150bb1a72055f1e08d9a7aef39 /fs/xfs | |
parent | 6881a229f66f74e4e0a73504389695213987955b (diff) | |
download | linux-fsl-qoriq-8511998baaf541710f457315958cef0d0a7864a1.tar.xz |
xfs: simplify XLOG_SECTOR_ROUND*()
XLOG_SECTOR_ROUNDUP_BBCOUNT() is defined in "fs/xfs/xfs_log_recover.c"
in an overly-complicated way. It is basically roundup(), but that
is not at all clear from its definition. (Actually, there is
another macro round_up() that applies for power-of-two-based masks
which I'll be using here.)
The operands in XLOG_SECTOR_ROUNDUP_BBCOUNT() are basically the
block number (bbs) and the log sector basic block mask
(log->l_sectbb_mask). I'll call them B and M for this discussion.
The macro computes is value this way:
M && (B & M) ? (B + M + 1) & ~M : B
Put another way, we can break it into 3 cases:
1) ! M -> B # 0 mask, no effect
2) ! (B & M) -> B # sector aligned
3) M && (B & M) -> (B + M + 1) & ~M # round up otherwise
The round_up() macro is cleverly defined using a value, v, and a
power-of-2, p, and the result is the nearest multiple of p greater
than or equal to v. Its value is computed something like this:
((v - 1) | (p - 1)) + 1
Let's consider using this in the context of the 3 cases above.
When p = 2^0 = 1, the result boils down to ((v - 1) | 0) + 1, so it
just translates any value v to itself. That handles case (1) above.
When p = 2^n, n > 0, we know that (p - 1) will be a mask with all n
bits 0..n-1 set. The condition in this case occurs when none of
those mask bits is set in the value v provided. If that is the
case, subtracting 1 from v will have 1's in all those lower bits (at
least). Therefore, OR-ing the mask with that decremented value has
no effect, so adding the 1 back again will just translate the v to
itself. This handles case (2).
Otherwise, the value v is greater than some multiple of p, and
decrementing it will produce a result greater than or equal to that
multiple. OR-ing in the mask will produce a value 1 less than the
next multiple of p, so finally adding 1 back will result in the
desired rounded-up value. This handles case (3).
Hopefully this is convincing.
While I was at it, I converted XLOG_SECTOR_ROUNDDOWN_BLKNO() to use
the round_down() macro.
Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Diffstat (limited to 'fs/xfs')
-rw-r--r-- | fs/xfs/xfs_log_recover.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c index 0d81a90..2813a6e 100644 --- a/fs/xfs/xfs_log_recover.c +++ b/fs/xfs/xfs_log_recover.c @@ -61,14 +61,13 @@ STATIC void xlog_recover_check_summary(xlog_t *); * Sector aligned buffer routines for buffer create/read/write/access */ -#define XLOG_SECTOR_ROUNDUP_BBCOUNT(log, bbs) \ - ( ((log)->l_sectbb_mask && (bbs & (log)->l_sectbb_mask)) ? \ - ((bbs + (log)->l_sectbb_mask + 1) & ~(log)->l_sectbb_mask) : (bbs) ) -#define XLOG_SECTOR_ROUNDDOWN_BLKNO(log, bno) ((bno) & ~(log)->l_sectbb_mask) - /* Number of basic blocks in a log sector */ #define xlog_sectbb(log) (1 << (log)->l_sectbb_log) +#define XLOG_SECTOR_ROUNDUP_BBCOUNT(log, bbs) round_up((bbs), xlog_sectbb(log)) +#define XLOG_SECTOR_ROUNDDOWN_BLKNO(log, bno) \ + round_down((bno), xlog_sectbb(log)) + STATIC xfs_buf_t * xlog_get_bp( xlog_t *log, |