[34-longterm 052/196] ext4: fix credits computing for indirect mapped files

[Paul Gortmaker]

From: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 5b41395fcc0265fc9f193aef9df39ce49d64677c upstream.

When writing a contiguous set of blocks, two indirect blocks could be
needed depending on how the blocks are aligned, so we need to increase
the number of credits needed by one.

[ Also fixed a another bug which could further underestimate the
  number of journal credits needed by 1; the code was using integer
  division instead of DIV_ROUND_UP() -- tytso]

Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 fs/ext4/inode.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4eced51..904f3e4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5573,13 +5573,12 @@ static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
 	/* if nrblocks are contiguous */
 	if (chunk) {
 		/*
-		 * With N contiguous data blocks, it need at most
-		 * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) indirect blocks
-		 * 2 dindirect blocks
-		 * 1 tindirect block
+		 * With N contiguous data blocks, we need at most
+		 * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) + 1 indirect blocks,
+		 * 2 dindirect blocks, and 1 tindirect block
 		 */
-		indirects = nrblocks / EXT4_ADDR_PER_BLOCK(inode->i_sb);
-		return indirects + 3;
+		return DIV_ROUND_UP(nrblocks,
+				    EXT4_ADDR_PER_BLOCK(inode->i_sb)) + 4;
 	}
 	/*
 	 * if nrblocks are not contiguous, worse case, each block touch
-- 
1.7.9.3

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