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

[Tal Zussman]

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@xxxxxxxxx>
>> Link: https://lore.kernel.org/all/82978d5c-3e08-48e9-bf0a-7913e1cd0507@xxxxxxxxx/
>> Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
> 
> Reviewed-by: John Garry <john.garry@xxxxxxxxx>
> 

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.

>> ---
>>   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;
>> 
>