On Tue, Jun 15 2021 at 6:54P -0400, Martin Wilck <mwilck@xxxxxxxx> wrote: > Hi Mike, > > On Mo, 2021-06-14 at 11:15 -0400, Mike Snitzer wrote: > > > > This work offers a proof-of-concept but it needs further refinement > > for sure. > > Thanks for looking into it again. I need some more guidance from your > part in order to be able to resubmit the set in a form that you > consider ready for merging. > > > The proposed open-coded SCSI code (in patch 2's drivers/md/dm- > > scsi_ioctl.c) > > is well beyond what I'm willing to take in DM. > > I'm not sure what code you're referring to. Is it the processing of the > bytes of the SCSI result code? If yes, please note that I had changed > that to open-coded form in response to Bart's review of my v2 > submission. If it's something else, please point it out to me. > > To minimize the special-casing for this code path, Hannes suggested to > use a target-specific unprepare_ioctl() callback to to tell the generic > dm code whether a given ioctl could be retried. The logic that I've put > into dm-scsi_ioctl.c could then be moved into the unprepare_ioctl() > callback of dm-mpath. dm_blk_ioctl() would need to check the callback's > return value and possibly retry the ioctl. Would hat appeal to you? > > > If this type of > > functionality is still needed (for kvm's SCSI passthru snafu) then > > more work is needed to negotiate proper interfaces with the SCSI > > subsystem (added linux-scsi to cc, odd they weren't engaged on this). > > Not cc'ing linux-scsi was my oversight, sorry about that. > > But I don't quite understand what interfaces you have in mind. SCSI > needs to expose the SG_IO interface to dm, which it does; I just needed > to export sg_io() to get access to the sg_io_hdr fields. The question > whether a given IO can be retried is decided on the dm (-mpath) layer, > based on blk_status_t; no additional interface on the SCSI side is > necessary for that. > > > Does it make sense to extend the SCSI device handler interface to add > > the required enablement? (I think it'd have to if this line of work > > is > > to ultimately get upstream). > > My current code uses the device handler indirectly for activating paths > during priority group switching, via the dm-mpath prepare_ioctl() > method and __pg_init_all_paths(). This is what I intended - to use > exactly the same logic for SG_IO which is used for regular read/write > IO on the block device. What additional functionality for the device > handler do you have in mind? > > Regards and thanks, > Martin I just replied to patch 2 with detailed suggestions. Thanks, Mike
