linux-ext4 - Re: [PATCH v2 3/4] ext4: factor out write end code of inline file

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Date:   Fri, 16 Jul 2021 20:04:19 +0800
From:   Zhang Yi <yi.zhang@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <yukuai3@...wei.com>
Subject: Re: [PATCH v2 3/4] ext4: factor out write end code of inline file

On 2021/7/16 18:08, Jan Kara wrote:
> On Fri 16-07-21 11:56:06, Zhang Yi wrote:
>> On 2021/7/15 20:08, Jan Kara wrote:
>>> On Thu 15-07-21 09:54:51, Zhang Yi wrote:
>>>> Now that the inline_data file write end procedure are falled into the
>>>> common write end functions, it is not clear. Factor them out and do
>>>> some cleanup. This patch also drop ext4_da_write_inline_data_end()
>>>> and switch to use ext4_write_inline_data_end() instead because we also
>>>> need to do the same error processing if we failed to write data into
>>>> inline entry.
>>>>
>>>> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
>>>
>>> Just two small comments below.
>>>
>>>> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
>>>> index 28b666f25ac2..3d227b32b21c 100644
>>>> --- a/fs/ext4/inline.c
>>>> +++ b/fs/ext4/inline.c
>>> ...
>>>> +out:
>>>> +	/*
>>>> +	 * If we have allocated more blocks and copied less. We will have
>>>> +	 * blocks allocated outside inode->i_size, so truncate them.
>>>> +	 */
>>>> +	if (pos + len > inode->i_size && ext4_can_truncate(inode))
>>>> +		ext4_orphan_add(handle, inode);
>>>
>>> I don't think we need this error handling here. For inline data we never
>>> allocate any blocks so shorter writes don't need any cleanup.
>>>
>>>> -	return copied;
>>>> +	ret2 = ext4_journal_stop(handle);
>>>> +	if (!ret)
>>>> +		ret = ret2;
>>>> +	if (pos + len > inode->i_size) {
>>>> +		ext4_truncate_failed_write(inode);
>>>> +		/*
>>>> +		 * If truncate failed early the inode might still be
>>>> +		 * on the orphan list; we need to make sure the inode
>>>> +		 * is removed from the orphan list in that case.
>>>> +		 */
>>>> +		if (inode->i_nlink)
>>>> +			ext4_orphan_del(NULL, inode);
>>>> +	}
>>>
>>> And this can go away as well...
>>>
>>
>> Yeah, but if we don't call ext4_truncate_failed_write()->..->
>> ext4_inline_data_truncate(), it will lead to incorrect larger i_inline_size
>> and data entry. Although it seems harmless (i_size can prevent read zero
>> data), I think it's better to restore the data entry(the comments need
>> change later), or else it will occupy more xattr space. What do you think ?
> 
> Good point. I've found this out last time when I was reviewing your patches
> and then forgot again. So please leave the code there but fix this
> misleading comment:
> 
> /*
>  * If we have allocated more blocks and copied less. We will have
>  * blocks allocated outside inode->i_size, so truncate them.
>  */
> 
> Something like:
> 
> /*
>  * If we didn't copy as much data as expected, we need to trim back size of
>  * xattr containing inline data.
>  */
> 

OK.

Thanks,
Yi.