[PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Hannes Reinecke]

The device handler needs to check if a given queue belongs to
a scsi device; only then does it make sense to attach a device
handler.

Signed-off-by: Hannes Reinecke <hare@suse.com>
---
 drivers/scsi/scsi_dh.c     | 22 ++++------------------
 drivers/scsi/scsi_lib.c    | 26 ++++++++++++++++++++++++++
 include/scsi/scsi_device.h |  1 +
 3 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/drivers/scsi/scsi_dh.c b/drivers/scsi/scsi_dh.c
index b8d3b97..84addee 100644
--- a/drivers/scsi/scsi_dh.c
+++ b/drivers/scsi/scsi_dh.c
@@ -219,20 +219,6 @@ int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh)
 }
 EXPORT_SYMBOL_GPL(scsi_unregister_device_handler);
 
-static struct scsi_device *get_sdev_from_queue(struct request_queue *q)
-{
-	struct scsi_device *sdev;
-	unsigned long flags;
-
-	spin_lock_irqsave(q->queue_lock, flags);
-	sdev = q->queuedata;
-	if (!sdev || !get_device(&sdev->sdev_gendev))
-		sdev = NULL;
-	spin_unlock_irqrestore(q->queue_lock, flags);
-
-	return sdev;
-}
-
 /*
  * scsi_dh_activate - activate the path associated with the scsi_device
  *      corresponding to the given request queue.
@@ -251,7 +237,7 @@ int scsi_dh_activate(struct request_queue *q, activate_complete fn, void *data)
 	struct scsi_device *sdev;
 	int err = SCSI_DH_NOSYS;
 
-	sdev = get_sdev_from_queue(q);
+	sdev = scsi_device_from_queue(q);
 	if (!sdev) {
 		if (fn)
 			fn(data, err);
@@ -298,7 +284,7 @@ int scsi_dh_set_params(struct request_queue *q, const char *params)
 	struct scsi_device *sdev;
 	int err = -SCSI_DH_NOSYS;
 
-	sdev = get_sdev_from_queue(q);
+	sdev = scsi_device_from_queue(q);
 	if (!sdev)
 		return err;
 
@@ -321,7 +307,7 @@ int scsi_dh_attach(struct request_queue *q, const char *name)
 	struct scsi_device_handler *scsi_dh;
 	int err = 0;
 
-	sdev = get_sdev_from_queue(q);
+	sdev = scsi_device_from_queue(q);
 	if (!sdev)
 		return -ENODEV;
 
@@ -359,7 +345,7 @@ const char *scsi_dh_attached_handler_name(struct request_queue *q, gfp_t gfp)
 	struct scsi_device *sdev;
 	const char *handler_name = NULL;
 
-	sdev = get_sdev_from_queue(q);
+	sdev = scsi_device_from_queue(q);
 	if (!sdev)
 		return NULL;
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9d6aed5..1a81ef9 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2145,6 +2145,32 @@ void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 	blk_mq_free_tag_set(&shost->tag_set);
 }
 
+/**
+ * scsi_device_from_queue - return sdev associated with a request_queue
+ * @q: The request queue to return the sdev from
+ *
+ * Return the sdev associated with a request queue or NULL if the
+ * request_queue does not reference a SCSI device.
+ */
+struct scsi_device *scsi_device_from_queue(struct request_queue *q)
+{
+	struct scsi_device *sdev = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	if (q->mq_ops) {
+		if (q->mq_ops == &scsi_mq_ops)
+			sdev = q->queuedata;
+	} else if (q->request_fn == scsi_request_fn)
+		sdev = q->queuedata;
+	if (!sdev || !get_device(&sdev->sdev_gendev))
+		sdev = NULL;
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	return sdev;
+}
+EXPORT_SYMBOL_GPL(scsi_device_from_queue);
+
 /*
  * Function:    scsi_block_requests()
  *
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 8990e58..be41c76 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -315,6 +315,7 @@ extern int scsi_add_device(struct Scsi_Host *host, uint channel,
 extern int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh);
 void scsi_attach_vpd(struct scsi_device *sdev);
 
+extern struct scsi_device *scsi_device_from_queue(struct request_queue *q);
 extern int scsi_device_get(struct scsi_device *);
 extern void scsi_device_put(struct scsi_device *);
 extern struct scsi_device *scsi_device_lookup(struct Scsi_Host *,
-- 
1.8.5.6

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Bart Van Assche]

On Thu, 2017-02-16 at 16:12 +0100, Hannes Reinecke wrote:
> +struct scsi_device *scsi_device_from_queue(struct request_queue *q)
> +{
> +	struct scsi_device *sdev = NULL;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(q->queue_lock, flags);
> +	if (q->mq_ops) {
> +		if (q->mq_ops == &scsi_mq_ops)
> +			sdev = q->queuedata;
> +	} else if (q->request_fn == scsi_request_fn)
> +		sdev = q->queuedata;
> +	if (!sdev || !get_device(&sdev->sdev_gendev))
> +		sdev = NULL;
> +	spin_unlock_irqrestore(q->queue_lock, flags);
> +
> +	return sdev;
> +}

Hello Hannes,

Do we need to take the queue lock? Neither q->mq_ops nor q->request_fn are
modified after a block device has been created. q->queuedata is not modified
by any SCSI driver after it has been set. And since the caller of
scsi_device_from_queue() has to guarantee that the queue does not disappear
while this function is in progress, the queue lock does not have to be held
around the get_device() call either. Otherwise this patch looks fine to me.

Bart.

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Keith Busch]

On Thu, Feb 16, 2017 at 04:12:23PM +0100, Hannes Reinecke wrote:
> The device handler needs to check if a given queue belongs to
> a scsi device; only then does it make sense to attach a device
> handler.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.com>

The thing I don't like is that this still has dm-mpath directly calling
into scsi. I don't think dm-mpath has any business calling protocol
specific APIs, and doesn't help other protocols with similar needs.

Can we solve this with an indirection layer instead? 

(untested; just checking if this direction is preferable)
---
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 3570bcb..28310a2 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -847,7 +847,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 
 	if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags)) {
 retain:
-		attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
+		attached_handler_name = blk_dh_attached_handler_name(q, GFP_KERNEL);
 		if (attached_handler_name) {
 			/*
 			 * Clear any hw_handler_params associated with a
@@ -870,7 +870,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 	}
 
 	if (m->hw_handler_name) {
-		r = scsi_dh_attach(q, m->hw_handler_name);
+		r = blk_dh_attach(q, m->hw_handler_name);
 		if (r == -EBUSY) {
 			char b[BDEVNAME_SIZE];
 
@@ -885,7 +885,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 		}
 
 		if (m->hw_handler_params) {
-			r = scsi_dh_set_params(q, m->hw_handler_params);
+			r = blk_dh_set_params(q, m->hw_handler_params);
 			if (r < 0) {
 				ti->error = "unable to set hardware "
 							"handler parameters";
@@ -1526,7 +1526,7 @@ static void activate_path(struct work_struct *work)
 	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
 
 	if (pgpath->is_active && !blk_queue_dying(q))
-		scsi_dh_activate(q, pg_init_done, pgpath);
+		blk_dh_activate(q, pg_init_done, pgpath);
 	else
 		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
 }
diff --git a/drivers/pci/pcie/pcie-dpc.c b/drivers/pci/pcie/pcie-dpc.c
index 06d2ed4..49a061a 100644
--- a/drivers/pci/pcie/pcie-dpc.c
+++ b/drivers/pci/pcie/pcie-dpc.c
@@ -107,7 +107,7 @@ static int dpc_probe(struct pcie_device *dev)
 	int status;
 	u16 ctl, cap;
 
-	dpc = kzalloc(&dev->device, sizeof(*dpc), GFP_KERNEL);
+	dpc = kzalloc(sizeof(*dpc), GFP_KERNEL);
 	if (!dpc)
 		return -ENOMEM;
 
@@ -116,7 +116,7 @@ static int dpc_probe(struct pcie_device *dev)
 	INIT_WORK(&dpc->work, interrupt_event_handler);
 	set_service_data(dev, dpc);
 
-	status = request_irq(&dev->device, dev->irq, dpc_irq, IRQF_SHARED,
+	status = request_irq(dev->irq, dpc_irq, IRQF_SHARED,
 				  "pcie-dpc", dpc);
 	if (status) {
 		dev_warn(&dev->device, "request IRQ%d failed: %d\n", dev->irq,
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9e1e14..e23c7d5 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2028,6 +2028,13 @@ static u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
 	return bounce_limit;
 }
 
+static struct dh_ops scsi_dh_ops = {
+	.dh_activate = scsi_dh_activate,
+	.dh_attach = scsi_dh_attach,
+	.dh_attached_handler_name = scsi_dh_attached_handler_name,
+	.dh_set_params = scsi_dh_set_params,
+};
+
 static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 {
 	struct device *dev = shost->dma_dev;
@@ -2062,6 +2069,8 @@ static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 	 * blk_queue_update_dma_alignment() later.
 	 */
 	blk_queue_dma_alignment(q, 0x03);
+
+	q->dh_ops = &scsi_dh_ops;
 }
 
 struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ca8e8f..5899768 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -378,6 +378,14 @@ static inline int blkdev_reset_zones_ioctl(struct block_device *bdev,
 
 #endif /* CONFIG_BLK_DEV_ZONED */
 
+typedef void (*activate_complete)(void *, int);
+struct dh_ops {
+	int (*dh_activate)(struct request_queue *, activate_complete, void *);
+	int (*dh_attach)(struct request_queue *, const char *);
+	const char *(*dh_attached_handler_name)(struct request_queue *, gfp_t);
+	int (*dh_set_params)(struct request_queue *, const char *);
+};
+
 struct request_queue {
 	/*
 	 * Together with queue_head for cacheline sharing
@@ -408,6 +416,7 @@ struct request_queue {
 	lld_busy_fn		*lld_busy_fn;
 
 	struct blk_mq_ops	*mq_ops;
+	struct dh_ops 		*dh_ops;
 
 	unsigned int		*mq_map;
 
@@ -572,6 +581,35 @@ struct request_queue {
 	bool			mq_sysfs_init_done;
 };
 
+static inline int blk_dh_activate(struct request_queue *q, activate_complete fn, void *data)
+{
+	if (q->dh_ops && q->dh_ops->dh_activate)
+		return q->dh_ops->dh_activate(q, fn, data);
+	fn(data, 0);
+	return 0;
+}
+
+static inline int blk_dh_attach(struct request_queue *q, const char *name)
+{
+	if (q->dh_ops && q->dh_ops->dh_attach)
+		return q->dh_ops->dh_attach(q, name);
+	return 0;
+}
+
+static inline const char *blk_dh_attached_handler_name(struct request_queue *q, gfp_t gfp)
+{
+	if (q->dh_ops && q->dh_ops->dh_attached_handler_name)
+		return q->dh_ops->dh_attached_handler_name(q, gfp);
+	return NULL;
+}
+
+static inline int blk_dh_set_params(struct request_queue *q, const char *params)
+{
+	if (q->dh_ops && q->dh_ops->dh_set_params)
+		return q->dh_ops->dh_set_params(q, params);
+	return 0;
+}
+
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
 #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
 #define	QUEUE_FLAG_SYNCFULL	3	/* read queue has been filled */
diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
index c7bba2b..9169a66 100644
--- a/include/scsi/scsi_dh.h
+++ b/include/scsi/scsi_dh.h
@@ -57,7 +57,6 @@ enum {
 	SCSI_DH_DRIVER_MAX,
 };
 
-typedef void (*activate_complete)(void *, int);
 struct scsi_device_handler {
 	/* Used by the infrastructure */
 	struct list_head list; /* list of scsi_device_handlers */
--

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Keith Busch]

On Thu, Feb 16, 2017 at 12:05:19PM -0500, Keith Busch wrote:
> On Thu, Feb 16, 2017 at 04:12:23PM +0100, Hannes Reinecke wrote:
> > The device handler needs to check if a given queue belongs to
> > a scsi device; only then does it make sense to attach a device
> > handler.
> > 
> > Signed-off-by: Hannes Reinecke <hare@suse.com>
> 
> The thing I don't like is that this still has dm-mpath directly calling
> into scsi. I don't think dm-mpath has any business calling protocol
> specific APIs, and doesn't help other protocols with similar needs.
> 
> Can we solve this with an indirection layer instead? 
> 
> (untested; just checking if this direction is preferable)

Eh osrry, I accidently included unrelated stuff in the previous. Here's
what I meant to send:

---
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 3570bcb..28310a2 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -847,7 +847,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 
 	if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags)) {
 retain:
-		attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
+		attached_handler_name = blk_dh_attached_handler_name(q, GFP_KERNEL);
 		if (attached_handler_name) {
 			/*
 			 * Clear any hw_handler_params associated with a
@@ -870,7 +870,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 	}
 
 	if (m->hw_handler_name) {
-		r = scsi_dh_attach(q, m->hw_handler_name);
+		r = blk_dh_attach(q, m->hw_handler_name);
 		if (r == -EBUSY) {
 			char b[BDEVNAME_SIZE];
 
@@ -885,7 +885,7 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 		}
 
 		if (m->hw_handler_params) {
-			r = scsi_dh_set_params(q, m->hw_handler_params);
+			r = blk_dh_set_params(q, m->hw_handler_params);
 			if (r < 0) {
 				ti->error = "unable to set hardware "
 							"handler parameters";
@@ -1526,7 +1526,7 @@ static void activate_path(struct work_struct *work)
 	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
 
 	if (pgpath->is_active && !blk_queue_dying(q))
-		scsi_dh_activate(q, pg_init_done, pgpath);
+		blk_dh_activate(q, pg_init_done, pgpath);
 	else
 		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
 }
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9e1e14..e23c7d5 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2028,6 +2028,13 @@ static u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
 	return bounce_limit;
 }
 
+static struct dh_ops scsi_dh_ops = {
+	.dh_activate = scsi_dh_activate,
+	.dh_attach = scsi_dh_attach,
+	.dh_attached_handler_name = scsi_dh_attached_handler_name,
+	.dh_set_params = scsi_dh_set_params,
+};
+
 static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 {
 	struct device *dev = shost->dma_dev;
@@ -2062,6 +2069,8 @@ static void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 	 * blk_queue_update_dma_alignment() later.
 	 */
 	blk_queue_dma_alignment(q, 0x03);
+
+	q->dh_ops = &scsi_dh_ops;
 }
 
 struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ca8e8f..5899768 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -378,6 +378,14 @@ static inline int blkdev_reset_zones_ioctl(struct block_device *bdev,
 
 #endif /* CONFIG_BLK_DEV_ZONED */
 
+typedef void (*activate_complete)(void *, int);
+struct dh_ops {
+	int (*dh_activate)(struct request_queue *, activate_complete, void *);
+	int (*dh_attach)(struct request_queue *, const char *);
+	const char *(*dh_attached_handler_name)(struct request_queue *, gfp_t);
+	int (*dh_set_params)(struct request_queue *, const char *);
+};
+
 struct request_queue {
 	/*
 	 * Together with queue_head for cacheline sharing
@@ -408,6 +416,7 @@ struct request_queue {
 	lld_busy_fn		*lld_busy_fn;
 
 	struct blk_mq_ops	*mq_ops;
+	struct dh_ops 		*dh_ops;
 
 	unsigned int		*mq_map;
 
@@ -572,6 +581,35 @@ struct request_queue {
 	bool			mq_sysfs_init_done;
 };
 
+static inline int blk_dh_activate(struct request_queue *q, activate_complete fn, void *data)
+{
+	if (q->dh_ops && q->dh_ops->dh_activate)
+		return q->dh_ops->dh_activate(q, fn, data);
+	fn(data, 0);
+	return 0;
+}
+
+static inline int blk_dh_attach(struct request_queue *q, const char *name)
+{
+	if (q->dh_ops && q->dh_ops->dh_attach)
+		return q->dh_ops->dh_attach(q, name);
+	return 0;
+}
+
+static inline const char *blk_dh_attached_handler_name(struct request_queue *q, gfp_t gfp)
+{
+	if (q->dh_ops && q->dh_ops->dh_attached_handler_name)
+		return q->dh_ops->dh_attached_handler_name(q, gfp);
+	return NULL;
+}
+
+static inline int blk_dh_set_params(struct request_queue *q, const char *params)
+{
+	if (q->dh_ops && q->dh_ops->dh_set_params)
+		return q->dh_ops->dh_set_params(q, params);
+	return 0;
+}
+
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
 #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
 #define	QUEUE_FLAG_SYNCFULL	3	/* read queue has been filled */
diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
index c7bba2b..9169a66 100644
--- a/include/scsi/scsi_dh.h
+++ b/include/scsi/scsi_dh.h
@@ -57,7 +57,6 @@ enum {
 	SCSI_DH_DRIVER_MAX,
 };
 
-typedef void (*activate_complete)(void *, int);
 struct scsi_device_handler {
 	/* Used by the infrastructure */
 	struct list_head list; /* list of scsi_device_handlers */
--

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Hannes Reinecke]

On 02/16/2017 05:09 PM, Bart Van Assche wrote:
> On Thu, 2017-02-16 at 16:12 +0100, Hannes Reinecke wrote:
>> +struct scsi_device *scsi_device_from_queue(struct request_queue *q)
>> +{
>> +	struct scsi_device *sdev = NULL;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(q->queue_lock, flags);
>> +	if (q->mq_ops) {
>> +		if (q->mq_ops == &scsi_mq_ops)
>> +			sdev = q->queuedata;
>> +	} else if (q->request_fn == scsi_request_fn)
>> +		sdev = q->queuedata;
>> +	if (!sdev || !get_device(&sdev->sdev_gendev))
>> +		sdev = NULL;
>> +	spin_unlock_irqrestore(q->queue_lock, flags);
>> +
>> +	return sdev;
>> +}
> 
> Hello Hannes,
> 
> Do we need to take the queue lock? Neither q->mq_ops nor q->request_fn are
> modified after a block device has been created. q->queuedata is not modified
> by any SCSI driver after it has been set. And since the caller of
> scsi_device_from_queue() has to guarantee that the queue does not disappear
> while this function is in progress, the queue lock does not have to be held
> around the get_device() call either. Otherwise this patch looks fine to me.
> 
Well, we did for the original code path, so I assumed that it'd be
prudent to do so.
And it's hardly time-critical anyway.
But yes, I guess we could do without the lock.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Hannes Reinecke]

On 02/16/2017 06:05 PM, Keith Busch wrote:
> On Thu, Feb 16, 2017 at 04:12:23PM +0100, Hannes Reinecke wrote:
>> The device handler needs to check if a given queue belongs to
>> a scsi device; only then does it make sense to attach a device
>> handler.
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.com>
> 
> The thing I don't like is that this still has dm-mpath directly calling
> into scsi. I don't think dm-mpath has any business calling protocol
> specific APIs, and doesn't help other protocols with similar needs.
> 
> Can we solve this with an indirection layer instead? 
> 
> (untested; just checking if this direction is preferable)

We could, but why?
ATM we're only having SCSI devices able to use device handler; adding
another layer of indirection doesn't solve anything here.
Moving the infrastructure one level up will only make sense if we're
getting non-SCSI device handler (ANA?), but until then I'd think it's
just overengineering.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Christoph Hellwig]

On Fri, Feb 17, 2017 at 09:06:14AM +0100, Hannes Reinecke wrote:
> We could, but why?
> ATM we're only having SCSI devices able to use device handler; adding
> another layer of indirection doesn't solve anything here.
> Moving the infrastructure one level up will only make sense if we're
> getting non-SCSI device handler (ANA?), but until then I'd think it's
> just overengineering.

Agreed.  Independent of what does the balancing between queues hardware
handler should be attached by the low-level driver for any future
transport without any control from DM.

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Mike Snitzer]

On Fri, Feb 17, 2017 at 3:27 AM, Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Feb 17, 2017 at 09:06:14AM +0100, Hannes Reinecke wrote:
> > We could, but why?
> > ATM we're only having SCSI devices able to use device handler; adding
> > another layer of indirection doesn't solve anything here.
> > Moving the infrastructure one level up will only make sense if we're
> > getting non-SCSI device handler (ANA?), but until then I'd think it's
> > just overengineering.
>
> Agreed.  Independent of what does the balancing between queues hardware
> handler should be attached by the low-level driver for any future
> transport without any control from DM.

But doesn't Keith's abstraction makes a lot of sense given that you're
providing a device handler interface for NVMe?

The most important part of scsi_dh that DM uses is its calls to
scsi_dh_activate.  Attachment isn't interesting or the issue (DM's
call to scsi_dh_attach is purely legacy now that SCSI attaches the
proper scsi_dh during SCSI's device scan).

Re: [PATCHv2] scsi: use 'scsi_device_from_queue()' for scsi_dh

[Mike Snitzer]

On Fri, Feb 17, 2017 at 3:27 AM, Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Feb 17, 2017 at 09:06:14AM +0100, Hannes Reinecke wrote:
> > We could, but why?
> > ATM we're only having SCSI devices able to use device handler; adding
> > another layer of indirection doesn't solve anything here.
> > Moving the infrastructure one level up will only make sense if we're
> > getting non-SCSI device handler (ANA?), but until then I'd think it's
> > just overengineering.
>
> Agreed.  Independent of what does the balancing between queues hardware
> handler should be attached by the low-level driver for any future
> transport without any control from DM.

But doesn't Keith's abstraction makes a lot of sense given that you're
providing a device handler interface for NVMe?

The most important part of scsi_dh that DM uses is its calls to
scsi_dh_activate.  Attachment isn't interesting or the issue (DM's
call to scsi_dh_attach is purely legacy now that SCSI attaches the
proper scsi_dh during SCSI's device scan).