Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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@xxxxxxx                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux