f2fs: fix to adjust appropriate length for fiemap

If user give a file size as "length" parameter for fiemap
operations, but if this size is non-block size aligned,
it will show 2 segments fiemap results even this whole file
is contiguous on disk, such as the following results:

 ./f2fs_io fiemap 0 19034 ylog/analyzer.py
Fiemap: offset = 0 len = 19034
        logical addr.    physical addr.   length           flags
0       0000000000000000 0000000020baa000 0000000000004000 00001000
1       0000000000004000 0000000020bae000 0000000000001000 00001001

after this patch:
./f2fs_io fiemap 0 19034 ylog/analyzer.py
Fiemap: offset = 0 len = 19034
    logical addr.    physical addr.   length           flags
0    0000000000000000 00000000315f3000 0000000000005000 00001001

Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: Zhiguo Niu

fs/f2fs/data.c

@@ -1938,12 +1938,12 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			goto out;
 	}
 
-	if (F2FS_BYTES_TO_BLK(len) == 0)
-		len = F2FS_BLKSIZE;
-
 	start_blk = F2FS_BYTES_TO_BLK(start);
 	last_blk = F2FS_BYTES_TO_BLK(start + len - 1);
 
+	if (len & F2FS_BLKSIZE_MASK)
+		len = round_up(len, F2FS_BLKSIZE);
+
 next:
 	memset(&map, 0, sizeof(map));
 	map.m_lblk = start_blk;

include/linux/f2fs_fs.h

@@ -24,6 +24,7 @@
 #define NEW_ADDR		((block_t)-1)	/* used as block_t addresses */
 #define COMPRESS_ADDR		((block_t)-2)	/* used as compressed data flag */
 
+#define F2FS_BLKSIZE_MASK		(F2FS_BLKSIZE - 1)
 #define F2FS_BYTES_TO_BLK(bytes)	((unsigned long long)(bytes) >> F2FS_BLKSIZE_BITS)
 #define F2FS_BLK_TO_BYTES(blk)		((unsigned long long)(blk) << F2FS_BLKSIZE_BITS)
 #define F2FS_BLK_END_BYTES(blk)		(F2FS_BLK_TO_BYTES(blk + 1) - 1)