On 5/17/11 5:59 PM, Jiaying Zhang wrote:
> There is a bug in commit c8d46e41 "ext4: Add flag to files with blocks
> intentionally past EOF" that if we fallocate a file with FALLOC_FL_KEEP_SIZE
> flag and then ftruncate the file to a size larger than the file's i_size,
> any allocated but unwritten blocks will be freed but the file size is set
> to the size that ftruncate specifies.
>
> Here is a simple test to reproduce the problem:
> 1. fallocate a 12k size file with KEEP_SIZE flag
> 2. write the first 4k
> 3. ftruncate the file to 8k
> Then 'ls -l' shows that the i_size of the file becomes 8k but debugfs
> shows the file has only the first written block left.
To be honest I'm not 100% certain what the fiesystem -should- do in this case.
If I go through that same sequence on xfs, I get 4k written / 8k unwritten:
# xfs_bmap -vp testfile
testfile:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS
0: [0..7]: 2648750760..2648750767 3 (356066400..356066407) 8 00000
1: [8..23]: 2648750768..2648750783 3 (356066408..356066423) 16 10000
size 8k:
# ls -l testfile
-rw-r--r-- 1 root root 8192 May 17 22:33 testfile
and diskspace used 12k:
# du -hc testfile
12K testfile
12K total
I think this is a different result from ext4, either with or without your patch.
On ext4 I get size 8k, but only the first 4k mapped, as you say.
I don't recall when truncate is supposed to free fallocated blocks, and from what point?
-Eric
> Below is the proposed patch to fix the bug:
>
> ext4: use vmtruncate() instead of ext4_truncate() in ext4_setattr().
>
> Change ext4_setattr() to use vmtruncate(inode, attr->ia_size) instead
> of ext4_truncate(inode) when it needs to truncate an inode so that
> if the inode has EXT4_EOFBLOCKS_FL flag set and we are trying to truncate
> to a size larger than the inode's i_size, we will only truncate the blocks
> beyond the specified truncate size instead of all of blocks beyond i_size.
>
> Signed-off-by: Jiaying Zhang <jiayingz@xxxxxxxxxx>
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 3424e82..3bfad57 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5347,8 +5347,11 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
> }
> }
> /* ext4_truncate will clear the flag */
> - if ((ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS)))
> - ext4_truncate(inode);
> + if ((ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS))) {
> + rc = vmtruncate(inode, attr->ia_size);
> + if (rc)
> + goto err_out;
> + }
> }
>
> if ((attr->ia_valid & ATTR_SIZE) &&
> --
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