Re: [PATCH v2 1/2] fs,block: Introduce RWF_ZONE_APPEND and handling in direct IO path

[Kanchan Joshi]

On Tue, Jun 30, 2020 at 07:56:46AM +0000, Damien Le Moal wrote:
> On 2020/06/30 16:53, Damien Le Moal wrote:
> > On 2020/06/30 16:43, Kanchan Joshi wrote:
> > > On Tue, Jun 30, 2020 at 12:37:07AM +0000, Damien Le Moal wrote:
> > > > On 2020/06/30 3:35, Kanchan Joshi wrote:
> > > > > On Fri, Jun 26, 2020 at 02:50:20AM +0000, Damien Le Moal wrote:
> > > > > > On 2020/06/26 2:18, Kanchan Joshi wrote:
> > > > > > > Introduce RWF_ZONE_APPEND flag to represent zone-append. User-space
> > > > > > > sends this with write. Add IOCB_ZONE_APPEND which is set in
> > > > > > > kiocb->ki_flags on receiving RWF_ZONE_APPEND.
> > > > > > > Make direct IO submission path use IOCB_ZONE_APPEND to send bio with
> > > > > > > append op. Direct IO completion returns zone-relative offset, in sector
> > > > > > > unit, to upper layer using kiocb->ki_complete interface.
> > > > > > > Report error if zone-append is requested on regular file or on sync
> > > > > > > kiocb (i.e. one without ki_complete).
> > > > > > >
> > > > > > > Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
> > > > > > > Signed-off-by: SelvaKumar S <selvakuma.s1@xxxxxxxxxxx>
> > > > > > > Signed-off-by: Arnav Dawn <a.dawn@xxxxxxxxxxx>
> > > > > > > Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> > > > > > > Signed-off-by: Javier Gonzalez <javier.gonz@xxxxxxxxxxx>
> > > > > > > ---
> > > > > > >  fs/block_dev.c          | 28 ++++++++++++++++++++++++----
> > > > > > >  include/linux/fs.h      |  9 +++++++++
> > > > > > >  include/uapi/linux/fs.h |  5 ++++-
> > > > > > >  3 files changed, 37 insertions(+), 5 deletions(-)
> > > > > > >
> > > > > > > diff --git a/fs/block_dev.c b/fs/block_dev.c
> > > > > > > index 47860e5..5180268 100644
> > > > > > > --- a/fs/block_dev.c
> > > > > > > +++ b/fs/block_dev.c
> > > > > > > @@ -185,6 +185,10 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb)
> > > > > > >  	/* avoid the need for a I/O completion work item */
> > > > > > >  	if (iocb->ki_flags & IOCB_DSYNC)
> > > > > > >  		op |= REQ_FUA;
> > > > > > > +
> > > > > > > +	if (iocb->ki_flags & IOCB_ZONE_APPEND)
> > > > > > > +		op |= REQ_OP_ZONE_APPEND;
> > > > > >
> > > > > > This is wrong. REQ_OP_WRITE is already set in the declaration of "op". How can
> > > > > > this work ?
> > > > > REQ_OP_ZONE_APPEND will override the REQ_WRITE op, while previously set op
> > > > > flags (REQ_FUA etc.) will be retained. But yes, this can be made to look
> > > > > cleaner.
> > > > > V3 will include the other changes you pointed out. Thanks for the review.
> > > >
> > > > REQ_OP_WRITE and REQ_OP_ZONE_APPEND are different bits, so there is no
> > > > "override". A well formed BIO bi_opf is one op+flags. Specifying multiple OP
> > > > codes does not make sense.
> > >
> > > one op+flags behavior is retained here. OP is not about bits (op flags are).
> > > Had it been, REQ_OP_WRITE (value 1) can not be differentiated from
> > > REQ_OP_ZONE_APPEND (value 13).
> > > We do not do "bio_op(bio) & REQ_OP_WRITE", rather we look at the
> > > absolute value "bio_op(bio) == REQ_OP_WRITE".
> >
> > Sure, the ops are not bits like the flags, but (excluding the flags) doing:
> >
> > op |= REQ_OP_ZONE_APPEND;
> >
> > will give you op == (REQ_OP_WRITE | REQ_OP_ZONE_APPEND). That's not what you want...
>
> And yes, REQ_OP_WRITE | REQ_OP_ZONE_APPEND == REQ_OP_ZONE_APPEND... But still
> not a reason for not setting the op correctly :)
Right, this is what op override was about, and intent was to minimize
the changes in the existing function. As said before, completely agree about
changing, code should not draw suspicion.