linux-ext4 - [PATCH v2] filefrag: fix wrong extent count calculation when using FIBMAP

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Date:	Tue, 7 Oct 2014 16:31:17 +0800
From:	Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
To:	<linux-ext4@...r.kernel.org>
CC:	<tytso@....edu>, <darrick.wong@...cle.com>,
	Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
Subject: [PATCH v2] filefrag: fix wrong extent count calculation when using FIBMAP

When using FIBMAP and '-e' option is specified, the calculation for fiemap_extent
is wrong, we wrongly updated fm_ext.fe_logical for every iteration, please see the
code in the end of 'for' loop in fm_ext.fe_logical().

In an ext2 file system(block size is 1024 bytes),
  dd if=/dev/zero of=testfile bs=1k count=15
  Using debugfs, corresponding physical blocks are "2049 2050 2051 2052 2053 2054
2055 2056 2057 2058 2059 2060 1025 2061 2062 2063",  1025 is this indirect block.
Before this patch, filefrag's output would be:
  filefrag -B -e testfile
  Filesystem type is: ef53
  Filesystem cylinder groups approximately 16
  File size of testfile is 15360 (15 blocks of 1024 bytes)
   ext:     logical_offset:        physical_offset: length:   expected: flags:
     0:        1..       2:       2050..      2051:      2:       2051: merged
     1:        3..       4:       2052..      2053:      2:       2053: merged
     2:        5..       6:       2054..      2055:      2:       2055: merged
     3:        7..       8:       2056..      2057:      2:       2057: merged
     4:        9..      10:       2058..      2059:      2:       2059: merged
     5:       11..      12:       2060..      2061:      2:       2062: merged
     6:       13..      14:       2062..      2063:      2:       2063: merged,eof
     7:       14..      14:       2063..      2063:      1:       2063: merged,eof
This output is not reasonable.

Fix this bug and try to make it readable. With this patch, the output would be:
  ./filefrag -B -e mntpoint/testfile
  Filesystem type is: ef53
  Filesystem cylinder groups approximately 16
  File size of mntpoint/testfile is 15360 (15 blocks of 1024 bytes)
   ext:     logical_offset:        physical_offset: length:   expected: flags:
     0:        0..      11:       2049..      2060:     12:       2062: merged
     1:       12..      14:       2061..      2063:      3:       2063: merged,eof
  mntpoint/testfile: 2 extents found, perfection would be 1 extent

Changes since v1->v2
 - remove the unnecessary {} for if statement.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 misc/filefrag.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/misc/filefrag.c b/misc/filefrag.c
index c1a8684..76e613f 100644
--- a/misc/filefrag.c
+++ b/misc/filefrag.c
@@ -315,32 +315,40 @@ static int filefrag_fibmap(int fd, int blk_shift, int *num_extents,
 			return rc;
 		if (block == 0)
 			continue;
+		count++;
+
 		if (*num_extents == 0) {
 			(*num_extents)++;
 			if (force_extent) {
 				print_extent_header();
+				fm_ext.fe_logical = logical;
 				fm_ext.fe_physical = block * st->st_blksize;
+				fm_ext.fe_length = st->st_blksize;
 			}
+			last_block = block;
+			continue;
 		}
-		count++;
-		if (force_extent && last_block != 0 &&
-		    (block != last_block + 1 ||
-		     fm_ext.fe_logical + fm_ext.fe_length != logical)) {
-			print_extent_info(&fm_ext, *num_extents - 1,
-					  (last_block + 1) * st->st_blksize,
-					  blk_shift, st);
-			fm_ext.fe_length = 0;
-			(*num_extents)++;
+
+		if (force_extent) {
+			if (block != last_block + 1 ||
+			    fm_ext.fe_length + fm_ext.fe_logical != logical) {
+				print_extent_info(&fm_ext, *num_extents - 1,
+						  (last_block + 1) *
+						  st->st_blksize,
+						  blk_shift, st);
+				fm_ext.fe_logical = logical;
+				fm_ext.fe_physical = block * st->st_blksize;
+				fm_ext.fe_length = st->st_blksize;
+				(*num_extents)++;
+			} else {
+				fm_ext.fe_length += st->st_blksize;
+			}
 		} else if (last_block && (block != last_block + 1)) {
 			if (verbose)
 				printf("Discontinuity: Block %ld is at %lu (was "
 				       "%lu)\n", i, block, last_block + 1);
-			fm_ext.fe_length = 0;
 			(*num_extents)++;
 		}
-		fm_ext.fe_logical = logical;
-		fm_ext.fe_physical = block * st->st_blksize;
-		fm_ext.fe_length += st->st_blksize;
 		last_block = block;
 	}
 
-- 
1.8.2.1

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