Re: [PATCH 5/8] nowait aio: return on congested block device

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed 19-04-17 10:21:39, Goldwyn Rodrigues wrote:
> 
> 
> On 04/19/2017 01:45 AM, Christoph Hellwig wrote:
> > 
> >> +	if (bio->bi_opf & REQ_NOWAIT) {
> >> +		if (!blk_queue_nowait(q)) {
> >> +			err = -EOPNOTSUPP;
> >> +			goto end_io;
> >> +		}
> >> +		if (!(bio->bi_opf & REQ_SYNC)) {
> > 
> > I don't understand this check at all..
> 
> It is to ensure at the block layer that NOWAIT comes only for DIRECT
> calls only. I should probably change it to REQ_SYNC | REQ_IDLE.

Ouch. Checking 'REQ_SYNC' for this is

a) unreliable hack
b) layering violation

You just don't care why someone marked bio with REQ_NOWAIT at this place.
Just obey the request if you can, return error if you cannot, but advisory
REQ_SYNC or REQ_IDLE flags have nothing to do with the ability of the block
layer to submit the bio without blocking...

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux