linux-ext4 - Re: [PATCH] ext4: use vmtruncate() instead of ext4_truncate() in ext4

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Date:	Wed, 18 May 2011 11:27:24 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Jiaying Zhang <jiayingz@...gle.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: use vmtruncate() instead of ext4_truncate() in ext4_setattr()

On Wed, May 18, 2011 at 10:56 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> On Wed, May 18, 2011 at 6:59 AM, Jiaying Zhang <jiayingz@...gle.com> 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.
>>
>> 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@...gle.com>
>>
>> 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;
>> +               }
>>        }
> Another question, does vmtruncate() write zeros to blocks beyond old
> EOF?  I had a rough look and could not find the code doing this, maybe
> due to my density.
Sorry, ignore this, the extent is unwritten, no need to zero.
>
> Yongqiang.
>>
>>        if ((attr->ia_valid & ATTR_SIZE) &&
>> --
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>
>
>
> --
> Best Wishes
> Yongqiang Yang
>



-- 
Best Wishes
Yongqiang Yang
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