Re: [PATCH 2/2] iomap: remove the atomic write length check in iomap_dio_bio_iter_one()

[John Garry <john.garry@linux.dev>]

On 11/9/26 18:34, Tal Zussman wrote:
> 
> 
> On 11/8/26 12:06 PM, John Garry wrote:
>> On 11/8/26 04:24, Tal Zussman wrote:
>>> bio_iov_iter_get_pages() and bio_iov_iter_bounce_write() now fail a
>>> REQ_ATOMIC bio that doesn't cover the whole iterator, so the bio here
>>> always covers iomap_length() and the check can't trigger. Remove the
>>> check.
>>>
>>> Suggested-by: John Garry <john.garry@linux.dev>
>>> Link: https://lore.kernel.org/all/82978d5c-3e08-48e9-bf0a-7913e1cd0507@linux.dev/
>>> Signed-off-by: Tal Zussman <tz2294@columbia.edu>
>>
>> Reviewed-by: John Garry <john.garry@linux.dev>
>>
> 
> Thanks!
> 
>> This looks ok. But I am just thinking that a CoW-based atomic write does
>> not have the single bio restriction, so we don't need to fail the atomic
>> in this case. However, we should have consistent rules for iovec's
>> whether it's a block device or regular file for ext4 or xfs, so this
>> makes sense.
>>
>> thanks
>>
>> BTW, you could be a real hero and add an xfstests case for this also.
>>
> 
> What specifically would you want to see tested? I can do an atomic write with
> a partially unmapped buffer, with and without stable writes, and check that it
> fails and that nothing is written.

Just something similar to the blktests case which you added.

BTW, have you tested this partially-unmapped case for CoW-based atomics 
on xfs? You can just do that by setting atomic_wr=0

Thanks,
John

> 
>>> ---
>>>    fs/iomap/direct-io.c | 14 --------------
>>>    1 file changed, 14 deletions(-)
>>>
>>> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
>>> index ad041ac3252a..aca7cbaea4af 100644
>>> --- a/fs/iomap/direct-io.c
>>> +++ b/fs/iomap/direct-io.c
>>> @@ -370,15 +370,6 @@ static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,
>>>    		goto out_put_bio;
>>>    	ret = bio->bi_iter.bi_size;
>>>    
>>> -	/*
>>> -	 * An atomic write bio must cover the complete length.  If it doesn't,
>>> -	 * error out.
>>> -	 */
>>> -	if ((op & REQ_ATOMIC) && WARN_ON_ONCE(ret != iomap_length(iter))) {
>>> -		ret = -EINVAL;
>>> -		goto out_bio_release_pages;
>>> -	}
>>> -
>>>    	if (dio->flags & IOMAP_DIO_WRITE)
>>>    		task_io_account_write(ret);
>>>    	else if ((dio->flags & IOMAP_DIO_USER_BACKED) &&
>>> @@ -393,11 +384,6 @@ static ssize_t iomap_dio_bio_iter_one(struct iomap_iter *iter,
>>>    	iomap_dio_submit_bio(iter, dio, bio, pos);
>>>    	return ret;
>>>    
>>> -out_bio_release_pages:
>>> -	if (dio->flags & IOMAP_DIO_BOUNCE)
>>> -		bio_free_folios(bio);
>>> -	else
>>> -		bio_release_pages(bio, false);
>>>    out_put_bio:
>>>    	bio_put(bio);
>>>    	return ret;
>>>
>>
>