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[PATCH 6/7] xfs: nothing special about 1-block log sector

To: xfs@xxxxxxxxxxx
Subject: [PATCH 6/7] xfs: nothing special about 1-block log sector
From: Alex Elder <aelder@xxxxxxx>
Date: Thu, 18 Mar 2010 17:54:11 -0500
User-agent: Heirloom mailx 12.4 7/29/08
There are a number of places where a log sector size of 1 uses
special case code.  The round_up() and round_down() macros
produce the correct result even when the log sector size is 1, and
this eliminates the need for treating this as a special case.

Signed-off-by: Alex Elder <aelder@xxxxxxx>

---
 fs/xfs/xfs_log_recover.c |   42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

Index: b/fs/xfs/xfs_log_recover.c
===================================================================
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -89,6 +89,11 @@ _xlog_buf_bbcount_valid(
        return 0;       /* Basic block count out of log's range */
 }
 
+/*
+ * Allocate a buffer to hold log data.  The buffer needs to be able
+ * to map to a range of nbblks basic blocks at any valid (basic
+ * block) offset within the log.
+ */
 STATIC xfs_buf_t *
 xlog_get_bp(
        xlog_t          *log,
@@ -97,11 +102,26 @@ xlog_get_bp(
        if (!xlog_buf_bbcount_valid(log, nbblks))
                return NULL;
 
-       if (log->l_sectbb_log) {
-               if (nbblks > 1)
-                       nbblks += xlog_sectbb(log);
-               nbblks = round_up(nbblks, xlog_sectbb(log));
-       }
+       /*
+        * We do log I/O in units of log sectors (a power-of-2
+        * multiple of the basic block size), so we round up the
+        * requested size to acommodate the basic blocks required
+        * for complete log sectors.
+        *
+        * In addition, the buffer may be used for a non-sector-
+        * aligned block offset, in which case an I/O of the
+        * requested size could extend beyond the end of the
+        * buffer.  If the requested size is only 1 basic block it
+        * will never straddle a sector boundary, so this won't be
+        * an issue.  Nor will this be a problem if the log I/O is
+        * done in basic blocks (sector size 1).  But otherwise we
+        * extend the buffer by one extra log sector to ensure
+        * there's space to accomodate this possiblility.
+        */
+       if (nbblks > 1 && log->l_sectbb_log)
+               nbblks += xlog_sectbb(log);
+       nbblks = round_up(nbblks, xlog_sectbb(log));
+
        return xfs_buf_get_noaddr(BBTOB(nbblks), log->l_mp->m_logdev_targp);
 }
 
@@ -146,10 +166,8 @@ xlog_bread_noalign(
        if (!xlog_buf_bbcount_valid(log, nbblks))
                return EFSCORRUPTED;
 
-       if (log->l_sectbb_log) {
-               blk_no = round_down(blk_no, xlog_sectbb(log));
-               nbblks = round_up(nbblks, xlog_sectbb(log));
-       }
+       blk_no = round_down(blk_no, xlog_sectbb(log));
+       nbblks = round_up(nbblks, xlog_sectbb(log));
 
        ASSERT(nbblks > 0);
        ASSERT(BBTOB(nbblks) <= XFS_BUF_SIZE(bp));
@@ -204,10 +222,8 @@ xlog_bwrite(
        if (!xlog_buf_bbcount_valid(log, nbblks))
                return EFSCORRUPTED;
 
-       if (log->l_sectbb_log) {
-               blk_no = round_down(blk_no, xlog_sectbb(log));
-               nbblks = round_up(nbblks, xlog_sectbb(log));
-       }
+       blk_no = round_down(blk_no, xlog_sectbb(log));
+       nbblks = round_up(nbblks, xlog_sectbb(log));
 
        ASSERT(nbblks > 0);
        ASSERT(BBTOB(nbblks) <= XFS_BUF_SIZE(bp));

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