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

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On 4/23/20 4:13 PM, John Garry wrote:
On 07/04/2020 17:30, Christoph Hellwig wrote:
On Tue, Apr 07, 2020 at 04:00:10PM +0200, Hannes Reinecke wrote:
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.

But alright, I'll give it a go; let's see what I'll end up with.

But this shouldn't be exposed anywhere.  And I prefer that over having
magic requests/scsi_cmnd that do not have a valid ->device pointer.
.


(just looking at this again)

Hi Christoph,

So how would this look added in scsi_lib.c:

struct scsi_cmnd *scsi_get_reserved_cmd(struct Scsi_Host *shost)
{
     struct scsi_cmnd *scmd;
     struct request *rq;
     struct scsi_device *sdev = scsi_get_host_dev(shost);

     if (!sdev)
         return NULL;

     rq = blk_mq_alloc_request(sdev->request_queue,
                   REQ_OP_DRV_OUT | REQ_NOWAIT,
                   BLK_MQ_REQ_RESERVED);
     if (IS_ERR(rq)) // fix tidy-up
         return NULL;
     WARN_ON(rq->tag == -1);
     scmd = blk_mq_rq_to_pdu(rq);
     scmd->request = rq;
     scmd->device = sdev;

     return scmd;
}
EXPORT_SYMBOL_GPL(scsi_get_reserved_cmd);

void scsi_put_reserved_cmd(struct scsi_cmnd *scmd)
{
     struct request *rq = blk_mq_rq_from_pdu(scmd);

     if (blk_mq_rq_is_reserved(rq)) {
         struct scsi_device *sdev = scmd->device;
         blk_mq_free_request(rq);
         scsi_free_host_dev(sdev);
     }
}
EXPORT_SYMBOL_GPL(scsi_put_reserved_cmd);

Not sure if we want a static scsi_device per host, or alloc and free dynamically.

(@Hannes, I also have some proper patches for libsas if you want to add it)

Hold your horses.
I'm currently preparing a patchset implementing things by improving the current scsi_get_host_dev() etc.

RFC should be ready by the end of the week.

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
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