[PATCH 2/7] xfs: fix min bufsize bugs in two places

[Alex Elder <aelder@xxxxxxx>]

This fixes a bug in two places that I found by inspection.  In
xlog_find_verify_cycle() and xlog_write_log_records(), the code
attempts to allocate a buffer to hold as many blocks as possible.
It gives up if the number of blocks to be allocated gets too small.
Right now it uses log->l_sectbb_log as that lower bound, but I'm
sure it's supposed to be the actual log sector size instead.  That
is, the lower bound should be (1 << log->l_sectbb_log).

Also define a simple macro xlog_sectbb(log) to represent the number
of basic blocks in a sector for the given log.

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

---
 fs/xfs/xfs_log_recover.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

Index: b/fs/xfs/xfs_log_recover.c
===================================================================
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -66,6 +66,9 @@ STATIC void   xlog_recover_check_summary(x
        ((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)
+
 STATIC xfs_buf_t *
 xlog_get_bp(
        xlog_t          *log,
@@ -376,12 +379,16 @@ xlog_find_verify_cycle(
        xfs_caddr_t     buf = NULL;
        int             error = 0;
 
+       /*
+        * Greedily allocate a buffer big enough to handle the full
+        * range of basic blocks we'll be examining.  If that fails,
+        * try a smaller size.  We need to be able to read at least
+        * a log sector, or we're out of luck.
+        */
        bufblks = 1 << ffs(nbblks);
-
        while (!(bp = xlog_get_bp(log, bufblks))) {
-               /* can't get enough memory to do everything in one big buffer */
                bufblks >>= 1;
-               if (bufblks <= log->l_sectbb_log)
+               if (bufblks < xlog_sectbb(log))
                        return ENOMEM;
        }
 
@@ -1158,10 +1165,16 @@ xlog_write_log_records(
        int             error = 0;
        int             i, j = 0;
 
+       /*
+        * Greedily allocate a buffer big enough to handle the full
+        * range of basic blocks to be written.  If that fails, try
+        * a smaller size.  We need to be able to write at least a
+        * log sector, or we're out of luck.
+        */
        bufblks = 1 << ffs(blocks);
        while (!(bp = xlog_get_bp(log, bufblks))) {
                bufblks >>= 1;
-               if (bufblks <= log->l_sectbb_log)
+               if (bufblks < xlog_sectbb(log))
                        return ENOMEM;
        }