Messages in this thread | | | Subject | Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands | From | Hannes Reinecke <> | Date | Tue, 7 Apr 2020 16:45:04 +0200 |
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On 4/7/20 4:35 PM, John Garry wrote: > On 07/04/2020 15:00, Hannes Reinecke wrote: >> On 4/7/20 1:54 PM, John Garry wrote: >>> On 06/04/2020 10:05, Hannes Reinecke wrote: [ .. ] >>>> This would be okay if 'this_id' would have been defined by the driver; >>>> sadly, most drivers which are affected here do set 'this_id' to -1. >>>> So we wouldn't have a nice target ID to allocate the device from, let >>>> alone the problem that we would have to emulate a complete scsi device >>>> with all required minimal command support etc. >>>> And I'm not quite sure how well that would play with the exising SCSI >>>> host template; the device we'll be allocating would have basically >>>> nothing in common with the 'normal' SCSI devices. >>>> >>>> What we could do, though, is to try it the other way round: >>>> Lift the request queue from scsi_get_host_dev() into the scsi host >>>> itself, so that scsi_get_host_dev() can use that queue, but we also >>>> would be able to use it without a SCSI device attached. >>> >>> wouldn't that limit 1x scsi device per host, not that I know if any >>> more would ever be required? But it does still seem better to use the >>> request queue in the scsi device. >>> >> My concern is this: >> >> struct scsi_device *scsi_get_host_dev(struct Scsi_Host *shost) >> { >> [ .. ] >> starget = scsi_alloc_target(&shost->shost_gendev, 0, >> shost->this_id); >> [ .. ] >> >> and we have typically: >> >> drivers/scsi/hisi_sas/hisi_sas_v3_hw.c: .this_id = -1, >> >> It's _very_ uncommon to have a negative number as the SCSI target >> device; in fact, it _is_ an unsigned int already. >> > > FWIW, the only other driver (gdth) which I see uses this API has this_id > = -1 in the scsi host template. > >> But alright, I'll give it a go; let's see what I'll end up with. > > note: If we want a fixed scsi_device per host, calling > scsi_mq_setup_tags() -> scsi_get_host_dev() will fail as shost state is > not running. Maybe we need to juggle some things there to provide a > generic solution. > It might even get worse, as during device setup things like 'slave_alloc' etc is getting called, which has a fair chance of getting confused for non-existing devices. Cf qla2xxx:qla2xx_slave_alloc() is calling starget_to_rport(), which will get us a nice oops when accessing a target which is _not_ the child of a fc remote port. And this is why I'm not utterly keen on this approach; auditing all these callbacks is _not_ fun.
Cheers,
Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
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