Re: [PATCH V2] f2fs: fix to adjust appropriate length for fiemap

From: Chao Yu
Date: Wed Nov 06 2024 - 01:45:39 EST


On 2024/11/6 10:54, Zhiguo Niu wrote:
Chao Yu <chao@xxxxxxxxxx> 于2024年11月6日周三 10:40写道:

On 2024/11/6 10:26, Zhiguo Niu wrote:
Chao Yu <chao@xxxxxxxxxx> 于2024年11月6日周三 10:16写道:

On 2024/11/5 19:02, Zhiguo Niu wrote:
Chao Yu <chao@xxxxxxxxxx> 于2024年11月5日周二 18:39写道:

On 2024/11/5 15:28, Zhiguo Niu wrote:
Chao Yu <chao@xxxxxxxxxx> 于2024年11月5日周二 15:04写道:

On 2024/11/4 9:56, Zhiguo Niu wrote:
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@xxxxxxxxxx>
---
V2: correct commit msg according to Chao's questions
f2fs_io has been modified for testing, the length for fiemap is
real file size, not block number
---
fs/f2fs/data.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 306b86b0..9fc229d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1966,8 +1966,8 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
goto out;
}

- if (bytes_to_blks(inode, len) == 0)
- len = blks_to_bytes(inode, 1);
+ if (len & (blks_to_bytes(inode, 1) - 1))
+ len = round_up(len, blks_to_bytes(inode, 1));

How do you think of getting rid of above alignment for len?


start_blk = bytes_to_blks(inode, start);
last_blk = bytes_to_blks(inode, start + len - 1);

And round up end position w/:

last_blk = bytes_to_blks(inode, round_up(start + len - 1, F2FS_BLKSIZE));
Hi Chao,
I think this will change the current code logic
-------------
if (start_blk > last_blk)
goto out;
-------------
for example, a file with size 19006, but the length from the user is 16384.
before this modification, last_blk = bytes_to_blks(inode, start +
len - 1) = (inode, 16383) = 3
after the first f2fs_map_blocks(). start_blk change to be 4,
after the second f2fs_map_blocks(), fiemap_fill_nex_exten will be
called to fill user parameter and then
will goto out because start_blk > last_blk, then fiemap flow finishes.
but after this modification, last_blk will be 4
will do f2fs_map_blocks() until reach the max_file_blocks(inode)

Yes, you're right, however, w/ this patch, it may change last_blk, e.g.

xfs_io file -c "fiemap -v 0 19006" vs xfs_io file -c "fiemap -v 2 19006"
start_blk and last_blk will be: 0, 4 and 0, 5.
Hi Chao,
yes, but w/o this patch , the original code still has the same situation??
for example
xfs_io file -c "fiemap -v 0 16384" vs xfs_io file -c "fiemap -v 2 16384"
start_blk and last_blk will be: 0, 3 and 0, 4.

For the case "fiemap -v 2 19006", offset is 2, and length is 19006, so last_offset
is 19008, and last_blk should be 4 rather than 5, right?
hi Chao,
it is right w/o my patch.

And for you case, it calculates last_blk correctly.
So you suggest that "Should we round_up len after start_blk & last_blk
calculation?"

Zhiguo,

Yes, I think alignment of len should not affect calculation of last_blk.

I mean this,

---
fs/f2fs/data.c | 6 +++---
include/linux/f2fs_fs.h | 3 ++-
2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7d1bb9518a40..cbbb956f420d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1967,12 +1967,12 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
goto out;
}

- if (bytes_to_blks(inode, len) == 0)
- len = blks_to_bytes(inode, 1);
-
start_blk = bytes_to_blks(inode, start);
last_blk = bytes_to_blks(inode, start + len - 1);

+ if (len & F2FS_BLKSIZE_MASK)
+ len = round_up(len, F2FS_BLKSIZE);
+
Hi Chao,
It looks well and clear, Let me verify this.
another unimportant questions, do we need to use macor
F2FS_BLKSIZE_xxx for round_up?

Zhiguo,

Well, f2fs doesn't support different blksize in one instance, so
bytes_to_blks() is equal to F2FS_BYTES_TO_BLK(), I guess we can
use F2FS_BYTES_TO_BLK() instead of bytes_to_blks() for cleanup,
let me figure out a patch for that.

Thanks,

because in fiemap, it all use bytes_to_blks(inode, xxx) /
blks_to_bytes(inode, xxx)
thanks!
next:
memset(&map, 0, sizeof(map));
map.m_lblk = start_blk;
diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
index b0b821edfd97..954e8e8344b7 100644
--- a/include/linux/f2fs_fs.h
+++ b/include/linux/f2fs_fs.h
@@ -24,10 +24,11 @@
#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) ((bytes) >> F2FS_BLKSIZE_BITS)
#define F2FS_BLK_TO_BYTES(blk) ((blk) << F2FS_BLKSIZE_BITS)
#define F2FS_BLK_END_BYTES(blk) (F2FS_BLK_TO_BYTES(blk + 1) - 1)
-#define F2FS_BLK_ALIGN(x) (F2FS_BYTES_TO_BLK((x) + F2FS_BLKSIZE - 1))
+#define F2FS_BLK_ALIGN(x) (F2FS_BYTES_TO_BLK((x) + F2FS_BLKSIZE - 1))

/* 0, 1(node nid), 2(meta nid) are reserved node id */
#define F2FS_RESERVED_NODE_NUM 3
--
2.40.1



Thanks

Thanks,

but overall last_blk will change loop counts but has not affect on the results.

Should we round_up len after start_blk & last_blk calculation?
I thinks it is ok ,but just a little bit redundant with the following
handling about len.

if (bytes_to_blks(inode, len) == 0)
len = blks_to_bytes(inode, 1);

Based on the above situation,
do you have any other good suggestions? ^^
thanks!


Thanks,

thanks!

Thanks,