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 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".