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Commit ae55e1aa authored by Tao Ma's avatar Tao Ma Committed by Linus Torvalds
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fs/direct-io.c: calculate fs_count correctly in get_more_blocks() 



In get_more_blocks(), we use dio_count to calcuate fs_count and do some
tricky things to increase fs_count if dio_count isn't aligned.  But
actually it still has some corner cases that can't be coverd.  See the
following example:

	dio_write foo -s 1024 -w 4096

(direct write 4096 bytes at offset 1024).  The same goes if the offset
isn't aligned to fs_blocksize.

In this case, the old calculation counts fs_count to be 1, but actually we
will write into 2 different blocks (if fs_blocksize=4096).  The old code
just works, since it will call get_block twice (and may have to allocate
and create extents twice for filesystems like ext4).  So we'd better call
get_block just once with the proper fs_count.

Signed-off-by: default avatarTao Ma <boyu.mt@taobao.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 45dac90f

fs/direct-io.c

+4 −7
Original line number Diff line number Diff line
@@ -580,9 +580,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, 
{

	int ret;

	sector_t fs_startblk;	/* Into file, in filesystem-sized blocks */

	sector_t fs_endblk;	/* Into file, in filesystem-sized blocks */

	unsigned long fs_count;	/* Number of filesystem-sized blocks */

	unsigned long dio_count;/* Number of dio_block-sized blocks */

	unsigned long blkmask;

	int create;



	/*
@@ -593,11 +592,9 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, 
	if (ret == 0) {

		BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);

		fs_startblk = sdio->block_in_file >> sdio->blkfactor;

		dio_count = sdio->final_block_in_request - sdio->block_in_file;

		fs_count = dio_count >> sdio->blkfactor;

		blkmask = (1 << sdio->blkfactor) - 1;

		if (dio_count & blkmask)	

			fs_count++;

		fs_endblk = (sdio->final_block_in_request - 1) >>

					sdio->blkfactor;

		fs_count = fs_endblk - fs_startblk + 1;



		map_bh->b_state = 0;

		map_bh->b_size = fs_count << dio->inode->i_blkbits;