On 11/2/22 00:09, Christoph Hellwig wrote:
> On Mon, Oct 31, 2022 at 11:26:36AM +0900, Damien Le Moal wrote:
>> + /*
>> + * REQ_FUA does not apply to read requests because:
>> + * - There is no way to reliably force media access for read operations
>> + * with a block device that does not support FUA.
>> + * - Not all block devices support FUA for read operations (e.g. ATA
>> + * devices with NCQ support turned off).
>> + */
>> + if (!op_is_write(rq->cmd_flags) && (rq->cmd_flags & REQ_FUA)) {
>> + blk_mq_end_request(rq, BLK_STS_NOTSUPP);
>
> How could this even happen? If we want a debug check, I think it
> should be in submit_bio and a WARN_ON_ONCE.
I have not found any code that issues a FUA read. So I do not think this
can happen at all currently. The check is about making sure that it
*never* happens.
I thought of having the check higher up in the submit path but I wanted to
avoid adding yet another check in the very hot path. But if you are OK
with that, I will move it.
--
Damien Le Moal
Western Digital Research
