linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: change the way of handling range.len in F2FS_IOC_SEC_TRIM

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Date:   Fri, 10 Jul 2020 14:31:03 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     Daeho Jeong <daeho43@...il.com>,
        Daeho Jeong <daehojeong@...gle.com>, <kernel-team@...roid.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] f2fs: change the way of handling range.len in
 F2FS_IOC_SEC_TRIM_FILE

On 2020/7/10 11:52, Jaegeuk Kim wrote:
> On 07/10, Chao Yu wrote:
>> On 2020/7/10 11:31, Jaegeuk Kim wrote:
>>> On 07/10, Chao Yu wrote:
>>>> On 2020/7/10 11:02, Jaegeuk Kim wrote:
>>>>> On 07/10, Daeho Jeong wrote:
>>>>>> From: Daeho Jeong <daehojeong@...gle.com>
>>>>>>
>>>>>> Changed the way of handling range.len of F2FS_IOC_SEC_TRIM_FILE.
>>>>>>  1. Added -1 value support for range.len to signify the end of file.
>>>>>>  2. If the end of the range passes over the end of file, it means until
>>>>>>     the end of file.
>>>>>>  3. ignored the case of that range.len is zero to prevent the function
>>>>>>     from making end_addr zero and triggering different behaviour of
>>>>>>     the function.
>>>>>>
>>>>>> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
>>>>>> ---
>>>>>>  fs/f2fs/file.c | 16 +++++++---------
>>>>>>  1 file changed, 7 insertions(+), 9 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>>> index 368c80f8e2a1..1c4601f99326 100644
>>>>>> --- a/fs/f2fs/file.c
>>>>>> +++ b/fs/f2fs/file.c
>>>>>> @@ -3813,21 +3813,19 @@ static int f2fs_sec_trim_file(struct file *filp, unsigned long arg)
>>>>>>  	file_start_write(filp);
>>>>>>  	inode_lock(inode);
>>>>>>  
>>>>>> -	if (f2fs_is_atomic_file(inode) || f2fs_compressed_file(inode)) {
>>>>>> +	if (f2fs_is_atomic_file(inode) || f2fs_compressed_file(inode) ||
>>>>>> +			range.start >= inode->i_size) {
>>>>>>  		ret = -EINVAL;
>>>>>>  		goto err;
>>>>>>  	}
>>>>>>  
>>>>>> -	if (range.start >= inode->i_size) {
>>>>>> -		ret = -EINVAL;
>>>>>> +	if (range.len == 0)
>>>>>>  		goto err;
>>>>>> -	}
>>>>>>  
>>>>>> -	if (inode->i_size - range.start < range.len) {
>>>>>> -		ret = -E2BIG;
>>>>>> -		goto err;
>>>>>> -	}
>>>>>> -	end_addr = range.start + range.len;
>>>>>> +	if (range.len == (u64)-1 || inode->i_size - range.start < range.len)
>>>>>> +		end_addr = inode->i_size;
>>>>
>>>> We can remove 'range.len == (u64)-1' condition since later condition can cover
>>>> this?
>>>>
>>>>>
>>>>> Hmm, what if there are blocks beyond i_size? Do we need to check i_blocks for
>>>>
>>>> The blocks beyond i_size will never be written, there won't be any valid message
>>>> there, so we don't need to worry about that.
>>>
>>> I don't think we have a way to guarantee the order of i_size and block
>>> allocation in f2fs. See f2fs_write_begin and f2fs_write_end.
>>
>> However, write_begin & write_end are covered by inode_lock, it could not be
>> racy with inode size check in f2fs_sec_trim_file() as it hold inode_lock as
>> well?
> 
> Like Daeho said, write_begin -> checkpoint -> power-cut can give bigger i_blocks
> than i_size.

The path won't, cp only persists reserved block in dnode rather than written
data block in segment, because data will be copied to page cache after write_begin.

I think truncation path could as Daeho said:

1. truncate -> i_size update however blocks wasn't truncated yet -> checkpoint -> recovery
2. truncate failed -> i_size update however partial blocks was truncated -> fsync

> 
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>> ending criteria?
>>>>>
>>>>>> +	else
>>>>>> +		end_addr = range.start + range.len;
>>>>>>  
>>>>>>  	to_end = (end_addr == inode->i_size);
>>>>>>  	if (!IS_ALIGNED(range.start, F2FS_BLKSIZE) ||
>>>>>> -- 
>>>>>> 2.27.0.383.g050319c2ae-goog
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Linux-f2fs-devel mailing list
>>>>>> Linux-f2fs-devel@...ts.sourceforge.net
>>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Linux-f2fs-devel mailing list
>>>>> Linux-f2fs-devel@...ts.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>> .
>>>>>
>>> .
>>>
> .
>