Re: [PATCH 10/24] scsi: allocate separate queue for reserved commands

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On 5/30/19 5:28 PM, John Garry wrote:
On 29/05/2019 14:28, Hannes Reinecke wrote:
From: Hannes Reinecke <hare@xxxxxxxx>

Allocate a separate 'reserved_cmd_q' for sending reserved commands.

Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
---
 drivers/scsi/scsi_lib.c  | 15 ++++++++++++++-
 include/scsi/scsi_host.h |  4 ++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e17153a9ce7c..076459853622 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1831,6 +1831,7 @@ struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev)
 int scsi_mq_setup_tags(struct Scsi_Host *shost)
 {
     unsigned int cmd_size, sgl_size;
+    int ret;

     sgl_size = scsi_mq_inline_sgl_size(shost);
     cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
@@ -1850,11 +1851,23 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
         BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
     shost->tag_set.driver_data = shost;

-    return blk_mq_alloc_tag_set(&shost->tag_set);
+    ret = blk_mq_alloc_tag_set(&shost->tag_set);
+    if (ret)
+        return ret;
+
+    if (shost->nr_reserved_cmds && shost->use_reserved_cmd_q) {
+        shost->reserved_cmd_q = blk_mq_init_queue(&shost->tag_set);
+        if (IS_ERR(shost->reserved_cmd_q)) {
+            blk_mq_free_tag_set(&shost->tag_set);
+            ret = PTR_ERR(shost->reserved_cmd_q);
+        }
+    }
+    return ret;
 }

 void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 {
+    blk_cleanup_queue(shost->reserved_cmd_q);
     blk_mq_free_tag_set(&shost->tag_set);
 }

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 89998b6bee04..a2bab5f07eff 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -600,6 +600,7 @@ struct Scsi_Host {
      * Number of reserved commands, if any.
      */
     unsigned nr_reserved_cmds;
+    struct request_queue *reserved_cmd_q;

     unsigned active_mode:2;
     unsigned unchecked_isa_dma:1;
@@ -637,6 +638,9 @@ struct Scsi_Host {
     /* The transport requires the LUN bits NOT to be stored in CDB[1] */
     unsigned no_scsi2_lun_in_cdb:1;

+    /* Host requires a separate reserved_cmd_q */
+    unsigned use_reserved_cmd_q:1;

Is this really required? I would think that a non-zero value for shost->nr_reserved_cmds means the same thing in practice.
;
My implementation actually allows for per-device reserved tags (eg for virtio). But some drivers require to use internal commands prior to any device setup, so they have to use a separate reserved command queue just to be able to allocate tags.

So yes, they are required.

Cheers,

Hannes



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