Re: [PATCH-v2 0/6] vhost/scsi: Add T10 PI SGL passthrough support

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 10, 2014 at 12:05:12AM -0700, Nicholas A. Bellinger wrote:
> On Mon, 2014-06-09 at 16:30 +0300, Michael S. Tsirkin wrote:
> > On Thu, May 22, 2014 at 02:26:16AM +0000, Nicholas A. Bellinger wrote:
> > > From: Nicholas Bellinger <nab@linux-iscsi.org>
> > > 
> > > Hi MST, MKP, Paolo & Co,
> > > 
> > > Here is the v2 patch series for adding T1O protection information (PI)
> > > SGL passthrough support between virtio-scsi LLD + vhost-scsi fabric
> > > endpoints.
> > > 
> > > Following MST's recommendation, it includes the changes for using
> > > bytes intead of number of iovecs in virtio_scsi_cmd_req_pi along with
> > > the associated changes to virtio-scsi + vhost/scsi code.
> > > 
> > > For vhost/scsi, this includes walking the leading iovec's length(s)
> > > to determine where protection payload ends, and real data payload 
> > > starts.  For virtio-scsi LLD code, this includes locating struct
> > > blk_integrity for using blk_rq_sectors + ->tuple_size to calculate
> > > the total bytes for outgoing cmd_pi->pi_bytes[out,in] values.
> > > 
> > > The full list of changes from last series include:
> > > 
> > >   - Use pi_bytesout + pi_bytesin instead of niovs in virtio-scsi PI
> > >     header (mst + paolo)
> > >   - Add prot_pto=1 in tcm_vhost_submission_work() when no PI buffer
> > >     exists (nab)
> > >   - Get rid of req + cdb pointer casts in vhost_scsi_handle_vq (mst)
> > >   - Ensure that virtio_scsi_cmd_req_pi processing happens regardless
> > >     of data_num in vhost_scsi_handle_vq (nab)
> > >   - Pass TARGET_PROT_ALL into transport_init_session_tags() (nab)
> > >   - Convert vhost_scsi_handle_vq to use memcpy_fromiovecend() (mst)
> > >   - Convert vhost_scsi_handle_vq to use pi_bytesout + pi_bytesin (nab)
> > >   - Convert virtio_scsi_init_hdr_pi() to use pi_bytesout + pi_bytesin
> > >     (mst + paolo + nab)
> > >   - Use blk_integrity->tuple_size to calculate pi bytes (nab)
> > > 
> > > Please review for v3.16-rc1 code.
> > > 
> > > Thanks!
> > > 
> > > --nab
> > 
> > OK since this conflicts with my vhost locking
> > patches, I have rebased this and parked at vhost-review
> > branch in my tree.
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git vhost-review
> > 
> > Nicholas could you please take a look at the patches and confirm this is
> > OK ASAP?
> > 
> > If yes I will pack it all up and send to Linus.
> 
> >From my experience, Linus prefers to fix this type of conflict on his
> own at merge time, instead of having subsystem maintainers rebase their
> for-next branches to include other's commits.

Cross-device type changes is exactly what vhost tree is there to allow
so I don't see a problem.

What Linus does not want is same patch in two trees.

So I see two options:
- I go ahead with my changes and you with yours and let Linus resolve
  the conflict.  This means bisect build will be broken since the
  breakage will likely not be noticed until after the merge.
- I pick up vhost scsi PI patches on my tree and you drop them from yours.

I prefer option 2 because it's cleaner wrt bisect.
But if you see a problem, pls let me know.

> Stephen (CC'ed) has included a fix in today's linux-next for the merge
> conflict here:
> 
> https://lkml.org/lkml/2014/6/10/3
> 
> Please confirm, as it will be a pointer to Linus within the
> target-pending/for-next PULL request.
> 
> --nab


Yes but this does mean people trying to bisect will
hit build breakages, not nice.

-- 
MST