Re: multipath-tools: add ANA support for NVMe device

Re: multipath-tools: add ANA support for NVMe device

[Mike Snitzer]

On Tue, Nov 13 2018 at 11:18am -0500,
Keith Busch <keith.busch@intel.com> wrote:

> On Mon, Nov 12, 2018 at 04:53:23PM -0500, Mike Snitzer wrote:
> > On Mon, Nov 12 2018 at 11:23am -0500,
> > Martin Wilck <mwilck@suse.com> wrote:
> > 
> > > Hello Lijie,
> > > 
> > > On Thu, 2018-11-08 at 14:09 +0800, lijie wrote:
> > > > Add support for Asynchronous Namespace Access as specified in NVMe
> > > > 1.3
> > > > TP 4004. The states are updated through reading the ANA log page.
> > > > 
> > > > By default, the native nvme multipath takes over the nvme device.
> > > > We can pass a false to the parameter 'multipath' of the nvme-core.ko
> > > > module,when we want to use multipath-tools.
> > > 
> > > Thank you for the patch. It looks quite good to me. I've tested it with
> > > a Linux target and found no problems so far.
> > > 
> > > I have a few questions and comments inline below.
> > > 
> > > I suggest you also have a look at detect_prio(); it seems to make sense
> > > to use the ana prioritizer for NVMe paths automatically if ANA is
> > > supported (with your patch, "detect_prio no" and "prio ana" have to be
> > > configured explicitly). But that can be done in a later patch.
> > 
> > I (and others) think it makes sense to at least triple check with the
> > NVMe developers (now cc'd) to see if we could get agreement on the nvme
> > driver providing the ANA state via sysfs (when modparam
> > nvme_core.multipath=N is set), like Hannes proposed here:
> > http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
> > 
> > Then the userspace multipath-tools ANA support could just read sysfs
> > rather than reinvent harvesting the ANA state via ioctl.
> 
> I'd prefer not duplicating the log page parsing. Maybe nvme's shouldn't
> even be tied to CONFIG_NVME_MULTIPATH so that the 'multipath' param
> isn't even an issue.

I like your instincts, we just need to take them a bit further.

Splitting out the kernel's ANA log page parsing won't buy us much given
it is userspace (multipath-tools) that needs to consume it.  The less
work userspace needs to do (because kernel has already done it) the
better.

If the NVMe driver is made to always track and export the ANA state via
sysfs [1] we'd avoid userspace parsing duplication "for free".  This
should occur regardless of what layer is reacting to the ANA state
changes (be it NVMe's native multipathing or multipath-tools).

ANA and NVMe multipathing really are disjoint, making them tightly
coupled only serves to force NVMe driver provided multipathing _or_
userspace ANA state tracking duplication that really isn't ideal [2].

We need a reasoned answer to the primary question of whether the NVMe
maintainers are willing to cooperate by providing this basic ANA sysfs
export even if nvme_core.multipath=N [1].

Christoph said "No" [3], but offered little _real_ justification for why
this isn't the right thing for NVMe in general -- even when asked the
question gets ignored [4].

The inability to provide proper justification for rejecting a patch
(that already had one co-maintainer's Reviewed-by [5]) _should_ render
that rejection baseless, and the patch applied (especially if there is
contributing subsystem developer interest in maintaining this support
over time, which there is).  At least that is what would happen in a
properly maintained kernel subsystem.

It'd really go a long way if senior Linux NVMe maintainers took steps to
accept reasonable changes.

Mike

[1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
[2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
[3]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020815.html
[4]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020846.html
[5]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020790.html

Re: multipath-tools: add ANA support for NVMe device

[Mike Snitzer]

On Tue, Nov 13 2018 at  1:00pm -0500,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Tue, Nov 13 2018 at 11:18am -0500,
> Keith Busch <keith.busch@intel.com> wrote:
> 
> > On Mon, Nov 12, 2018 at 04:53:23PM -0500, Mike Snitzer wrote:
> > > On Mon, Nov 12 2018 at 11:23am -0500,
> > > Martin Wilck <mwilck@suse.com> wrote:
> > > 
> > > > Hello Lijie,
> > > > 
> > > > On Thu, 2018-11-08 at 14:09 +0800, lijie wrote:
> > > > > Add support for Asynchronous Namespace Access as specified in NVMe
> > > > > 1.3
> > > > > TP 4004. The states are updated through reading the ANA log page.
> > > > > 
> > > > > By default, the native nvme multipath takes over the nvme device.
> > > > > We can pass a false to the parameter 'multipath' of the nvme-core.ko
> > > > > module,when we want to use multipath-tools.
> > > > 
> > > > Thank you for the patch. It looks quite good to me. I've tested it with
> > > > a Linux target and found no problems so far.
> > > > 
> > > > I have a few questions and comments inline below.
> > > > 
> > > > I suggest you also have a look at detect_prio(); it seems to make sense
> > > > to use the ana prioritizer for NVMe paths automatically if ANA is
> > > > supported (with your patch, "detect_prio no" and "prio ana" have to be
> > > > configured explicitly). But that can be done in a later patch.
> > > 
> > > I (and others) think it makes sense to at least triple check with the
> > > NVMe developers (now cc'd) to see if we could get agreement on the nvme
> > > driver providing the ANA state via sysfs (when modparam
> > > nvme_core.multipath=N is set), like Hannes proposed here:
> > > http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
> > > 
> > > Then the userspace multipath-tools ANA support could just read sysfs
> > > rather than reinvent harvesting the ANA state via ioctl.
> > 
> > I'd prefer not duplicating the log page parsing. Maybe nvme's shouldn't
> > even be tied to CONFIG_NVME_MULTIPATH so that the 'multipath' param
> > isn't even an issue.
> 
> I like your instincts, we just need to take them a bit further.
> 
> Splitting out the kernel's ANA log page parsing won't buy us much given
> it is userspace (multipath-tools) that needs to consume it.  The less
> work userspace needs to do (because kernel has already done it) the
> better.
> 
> If the NVMe driver is made to always track and export the ANA state via
> sysfs [1] we'd avoid userspace parsing duplication "for free".  This
> should occur regardless of what layer is reacting to the ANA state
> changes (be it NVMe's native multipathing or multipath-tools).
> 
> ANA and NVMe multipathing really are disjoint, making them tightly
> coupled only serves to force NVMe driver provided multipathing _or_
> userspace ANA state tracking duplication that really isn't ideal [2].
> 
> We need a reasoned answer to the primary question of whether the NVMe
> maintainers are willing to cooperate by providing this basic ANA sysfs
> export even if nvme_core.multipath=N [1].
> 
> Christoph said "No" [3], but offered little _real_ justification for why
> this isn't the right thing for NVMe in general.
...
> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
...

I knew there had to be a pretty tight coupling between the NVMe driver's
native multipathing and ANA support... and that the simplicity of
Hannes' patch [1] was too good to be true.

The real justification for not making Hannes' change is it'd effectively
be useless without first splitting out the ANA handling done during NVMe
request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
triggers re-reading the ANA log page accordingly.

So without the ability to drive the ANA workqueue to trigger
nvme_read_ana_log() from the nvme driver's completion path -- even if
nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
to have the NVMe driver export the ana state via sysfs, because that ANA
state will never get updated.

> The inability to provide proper justification for rejecting a patch
> (that already had one co-maintainer's Reviewed-by [5]) _should_ render
> that rejection baseless, and the patch applied (especially if there is
> contributing subsystem developer interest in maintaining this support
> over time, which there is).  At least that is what would happen in a
> properly maintained kernel subsystem.
> 
> It'd really go a long way if senior Linux NVMe maintainers took steps to
> accept reasonable changes.

Even though I'm frustrated I was clearly too harsh and regret my tone.
I promise to _try_ to suck less.

This dynamic of terse responses or no responses at all whenever NVMe
driver changes to ease multipath-tools NVMe support are floated is the
depressing gift that keeps on giving.  But enough excuses...

Not holding my breath BUT:
if decoupling the reading of ANA state from native NVMe multipathing
specific work during nvme request completion were an acceptable
advancement I'd gladly do the work.

Mike

Re: multipath-tools: add ANA support for NVMe device

[Hannes Reinecke]

On 11/14/18 6:38 AM, Mike Snitzer wrote:
> On Tue, Nov 13 2018 at  1:00pm -0500,
> Mike Snitzer <snitzer@redhat.com> wrote:
> 
>> On Tue, Nov 13 2018 at 11:18am -0500,
>> Keith Busch <keith.busch@intel.com> wrote:
>>
>>> On Mon, Nov 12, 2018 at 04:53:23PM -0500, Mike Snitzer wrote:
>>>> On Mon, Nov 12 2018 at 11:23am -0500,
>>>> Martin Wilck <mwilck@suse.com> wrote:
>>>>
>>>>> Hello Lijie,
>>>>>
>>>>> On Thu, 2018-11-08 at 14:09 +0800, lijie wrote:
>>>>>> Add support for Asynchronous Namespace Access as specified in NVMe
>>>>>> 1.3
>>>>>> TP 4004. The states are updated through reading the ANA log page.
>>>>>>
>>>>>> By default, the native nvme multipath takes over the nvme device.
>>>>>> We can pass a false to the parameter 'multipath' of the nvme-core.ko
>>>>>> module,when we want to use multipath-tools.
>>>>>
>>>>> Thank you for the patch. It looks quite good to me. I've tested it with
>>>>> a Linux target and found no problems so far.
>>>>>
>>>>> I have a few questions and comments inline below.
>>>>>
>>>>> I suggest you also have a look at detect_prio(); it seems to make sense
>>>>> to use the ana prioritizer for NVMe paths automatically if ANA is
>>>>> supported (with your patch, "detect_prio no" and "prio ana" have to be
>>>>> configured explicitly). But that can be done in a later patch.
>>>>
>>>> I (and others) think it makes sense to at least triple check with the
>>>> NVMe developers (now cc'd) to see if we could get agreement on the nvme
>>>> driver providing the ANA state via sysfs (when modparam
>>>> nvme_core.multipath=N is set), like Hannes proposed here:
>>>> http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
>>>>
>>>> Then the userspace multipath-tools ANA support could just read sysfs
>>>> rather than reinvent harvesting the ANA state via ioctl.
>>>
>>> I'd prefer not duplicating the log page parsing. Maybe nvme's shouldn't
>>> even be tied to CONFIG_NVME_MULTIPATH so that the 'multipath' param
>>> isn't even an issue.
>>
>> I like your instincts, we just need to take them a bit further.
>>
>> Splitting out the kernel's ANA log page parsing won't buy us much given
>> it is userspace (multipath-tools) that needs to consume it.  The less
>> work userspace needs to do (because kernel has already done it) the
>> better.
>>
>> If the NVMe driver is made to always track and export the ANA state via
>> sysfs [1] we'd avoid userspace parsing duplication "for free".  This
>> should occur regardless of what layer is reacting to the ANA state
>> changes (be it NVMe's native multipathing or multipath-tools).
>>
>> ANA and NVMe multipathing really are disjoint, making them tightly
>> coupled only serves to force NVMe driver provided multipathing _or_
>> userspace ANA state tracking duplication that really isn't ideal [2].
>>
>> We need a reasoned answer to the primary question of whether the NVMe
>> maintainers are willing to cooperate by providing this basic ANA sysfs
>> export even if nvme_core.multipath=N [1].
>>
>> Christoph said "No" [3], but offered little _real_ justification for why
>> this isn't the right thing for NVMe in general.
> ...
>> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
>> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
> ...
> 
> I knew there had to be a pretty tight coupling between the NVMe driver's
> native multipathing and ANA support... and that the simplicity of
> Hannes' patch [1] was too good to be true.
> 
> The real justification for not making Hannes' change is it'd effectively
> be useless without first splitting out the ANA handling done during NVMe
> request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
> triggers re-reading the ANA log page accordingly.
> 
> So without the ability to drive the ANA workqueue to trigger
> nvme_read_ana_log() from the nvme driver's completion path -- even if
> nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
> to have the NVMe driver export the ana state via sysfs, because that ANA
> state will never get updated.
> 
Hmm. Indeed, I was more focussed on having the sysfs attributes 
displayed, so yes, indeed it needs some more work.

>> The inability to provide proper justification for rejecting a patch
>> (that already had one co-maintainer's Reviewed-by [5]) _should_ render
>> that rejection baseless, and the patch applied (especially if there is
>> contributing subsystem developer interest in maintaining this support
>> over time, which there is).  At least that is what would happen in a
>> properly maintained kernel subsystem.
>>
>> It'd really go a long way if senior Linux NVMe maintainers took steps to
>> accept reasonable changes.
> 
> Even though I'm frustrated I was clearly too harsh and regret my tone.
> I promise to _try_ to suck less.
> 
> This dynamic of terse responses or no responses at all whenever NVMe
> driver changes to ease multipath-tools NVMe support are floated is the
> depressing gift that keeps on giving.  But enough excuses...
> 
> Not holding my breath BUT:
> if decoupling the reading of ANA state from native NVMe multipathing
> specific work during nvme request completion were an acceptable
> advancement I'd gladly do the work.
> 
I'd be happy to work on that, given that we'll have to have 'real' ANA 
support for device-mapper anyway for SLE12 SP4 etc.

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: [dm-devel] multipath-tools: add ANA support for NVMe device

[Martin Wilck]

On Wed, 2018-11-14 at 08:49 +0100, Hannes Reinecke wrote:
> On 11/14/18 6:38 AM, Mike Snitzer wrote:
> > 
> > Not holding my breath BUT:
> > if decoupling the reading of ANA state from native NVMe
> > multipathing
> > specific work during nvme request completion were an acceptable
> > advancement I'd gladly do the work.
> > 
> I'd be happy to work on that, given that we'll have to have 'real'
> ANA 
> support for device-mapper anyway for SLE12 SP4 etc.

So, what's the way ahead for multipath-tools? 

Given that, IIUC, at least one official kernel (4.19) has been released
with ANA support but without the ANA sysfs attributes exported to user
space, multipath-tools can't rely on them being present. I for one have
no issue with copying code from nvme-cli and doing NVMe ioctls from
multipath-tools, as in Lijie's patch. When those sysfs attributes are
added (and work as expected), we will use them, but IMO we'll need to
fall back to ioctls until then, and also afterwards, because we can't
assume to be always running on the latest kernel.

Best,
Martin

Re: multipath-tools: add ANA support for NVMe device

[Mike Snitzer]

On Wed, Nov 14 2018 at  2:49am -0500,
Hannes Reinecke <hare@suse.de> wrote:

> On 11/14/18 6:38 AM, Mike Snitzer wrote:
> >On Tue, Nov 13 2018 at  1:00pm -0500,
> >Mike Snitzer <snitzer@redhat.com> wrote:
> >
> >>[1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
> >>[2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
> >...
> >
> >I knew there had to be a pretty tight coupling between the NVMe driver's
> >native multipathing and ANA support... and that the simplicity of
> >Hannes' patch [1] was too good to be true.
> >
> >The real justification for not making Hannes' change is it'd effectively
> >be useless without first splitting out the ANA handling done during NVMe
> >request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
> >triggers re-reading the ANA log page accordingly.
> >
> >So without the ability to drive the ANA workqueue to trigger
> >nvme_read_ana_log() from the nvme driver's completion path -- even if
> >nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
> >to have the NVMe driver export the ana state via sysfs, because that ANA
> >state will never get updated.
> >
> Hmm. Indeed, I was more focussed on having the sysfs attributes
> displayed, so yes, indeed it needs some more work.
...
> >Not holding my breath BUT:
> >if decoupling the reading of ANA state from native NVMe multipathing
> >specific work during nvme request completion were an acceptable
> >advancement I'd gladly do the work.
> >
> I'd be happy to work on that, given that we'll have to have 'real'
> ANA support for device-mapper anyway for SLE12 SP4 etc.

I had a close enough look yesterday that I figured I'd just implement
what I reasoned through as one way forward, compile tested only (patch
relative to Jens' for-4.21/block):

 drivers/nvme/host/core.c      | 14 +++++++---
 drivers/nvme/host/multipath.c | 65 ++++++++++++++++++++++++++-----------------
 drivers/nvme/host/nvme.h      |  4 +++
 3 files changed, 54 insertions(+), 29 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f172d63db2b5..05313ab5d91e 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -252,10 +252,16 @@ void nvme_complete_rq(struct request *req)
 	trace_nvme_complete_rq(req);
 
 	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
-		if ((req->cmd_flags & REQ_NVME_MPATH) &&
-		    blk_path_error(status)) {
-			nvme_failover_req(req);
-			return;
+		if (blk_path_error(status)) {
+			struct nvme_ns *ns = req->q->queuedata;
+			u16 nvme_status = nvme_req(req)->status;
+
+			if (req->cmd_flags & REQ_NVME_MPATH) {
+				nvme_failover_req(req);
+				nvme_update_ana(ns, nvme_status);
+				return;
+			}
+			nvme_update_ana(ns, nvme_status);
 		}
 
 		if (!blk_queue_dying(req->q)) {
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 5e3cc8c59a39..f7fbc161dc8c 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
 
 inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
 {
-	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
+	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
 }
 
 /*
@@ -47,6 +47,17 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 	}
 }
 
+static bool nvme_ana_error(u16 status)
+{
+	switch (status & 0x7ff) {
+	case NVME_SC_ANA_TRANSITION:
+	case NVME_SC_ANA_INACCESSIBLE:
+	case NVME_SC_ANA_PERSISTENT_LOSS:
+		return true;
+	}
+	return false;
+}
+
 void nvme_failover_req(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
@@ -58,10 +69,7 @@ void nvme_failover_req(struct request *req)
 	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
 	blk_mq_end_request(req, 0);
 
-	switch (status & 0x7ff) {
-	case NVME_SC_ANA_TRANSITION:
-	case NVME_SC_ANA_INACCESSIBLE:
-	case NVME_SC_ANA_PERSISTENT_LOSS:
+	if (nvme_ana_error(status)) {
 		/*
 		 * If we got back an ANA error we know the controller is alive,
 		 * but not ready to serve this namespaces.  The spec suggests
@@ -69,31 +77,38 @@ void nvme_failover_req(struct request *req)
 		 * that the admin and I/O queues are not serialized that is
 		 * fundamentally racy.  So instead just clear the current path,
 		 * mark the the path as pending and kick of a re-read of the ANA
-		 * log page ASAP.
+		 * log page ASAP (see nvme_update_ana() below).
 		 */
 		nvme_mpath_clear_current_path(ns);
-		if (ns->ctrl->ana_log_buf) {
-			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
-			queue_work(nvme_wq, &ns->ctrl->ana_work);
+	} else {
+		switch (status & 0x7ff) {
+		case NVME_SC_HOST_PATH_ERROR:
+			/*
+			 * Temporary transport disruption in talking to the
+			 * controller.  Try to send on a new path.
+			 */
+			nvme_mpath_clear_current_path(ns);
+			break;
+		default:
+			/*
+			 * Reset the controller for any non-ANA error as we
+			 * don't know what caused the error.
+			 */
+			nvme_reset_ctrl(ns->ctrl);
+			break;
 		}
-		break;
-	case NVME_SC_HOST_PATH_ERROR:
-		/*
-		 * Temporary transport disruption in talking to the controller.
-		 * Try to send on a new path.
-		 */
-		nvme_mpath_clear_current_path(ns);
-		break;
-	default:
-		/*
-		 * Reset the controller for any non-ANA error as we don't know
-		 * what caused the error.
-		 */
-		nvme_reset_ctrl(ns->ctrl);
-		break;
 	}
+}
 
-	kblockd_schedule_work(&ns->head->requeue_work);
+void nvme_update_ana(struct nvme_ns *ns, u16 status)
+{
+	if (nvme_ana_error(status) && ns->ctrl->ana_log_buf) {
+		set_bit(NVME_NS_ANA_PENDING, &ns->flags);
+		queue_work(nvme_wq, &ns->ctrl->ana_work);
+	}
+
+	if (multipath)
+		kblockd_schedule_work(&ns->head->requeue_work);
 }
 
 void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 32a1f1cfdfb4..8b4bc2054b7a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -468,6 +468,7 @@ bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl);
 void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 			struct nvme_ctrl *ctrl, int *flags);
 void nvme_failover_req(struct request *req);
+void nvme_update_ana(struct nvme_ns *ns, u16 status);
 void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl);
 int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl,struct nvme_ns_head *head);
 void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
@@ -507,6 +508,9 @@ static inline void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 static inline void nvme_failover_req(struct request *req)
 {
 }
+static inline void nvme_update_ana(struct nvme_ns *ns, u16 status)
+{
+}
 static inline void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
 {
 }

Re: multipath-tools: add ANA support for NVMe device

[Hannes Reinecke]

On 11/14/18 6:47 PM, Mike Snitzer wrote:
> On Wed, Nov 14 2018 at  2:49am -0500,
> Hannes Reinecke <hare@suse.de> wrote:
> 
>> On 11/14/18 6:38 AM, Mike Snitzer wrote:
>>> On Tue, Nov 13 2018 at  1:00pm -0500,
>>> Mike Snitzer <snitzer@redhat.com> wrote:
>>>
>>>> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
>>>> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
>>> ...
>>>
>>> I knew there had to be a pretty tight coupling between the NVMe driver's
>>> native multipathing and ANA support... and that the simplicity of
>>> Hannes' patch [1] was too good to be true.
>>>
>>> The real justification for not making Hannes' change is it'd effectively
>>> be useless without first splitting out the ANA handling done during NVMe
>>> request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
>>> triggers re-reading the ANA log page accordingly.
>>>
>>> So without the ability to drive the ANA workqueue to trigger
>>> nvme_read_ana_log() from the nvme driver's completion path -- even if
>>> nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
>>> to have the NVMe driver export the ana state via sysfs, because that ANA
>>> state will never get updated.
>>>
>> Hmm. Indeed, I was more focussed on having the sysfs attributes
>> displayed, so yes, indeed it needs some more work.
> ...
>>> Not holding my breath BUT:
>>> if decoupling the reading of ANA state from native NVMe multipathing
>>> specific work during nvme request completion were an acceptable
>>> advancement I'd gladly do the work.
>>>
>> I'd be happy to work on that, given that we'll have to have 'real'
>> ANA support for device-mapper anyway for SLE12 SP4 etc.
> 
> I had a close enough look yesterday that I figured I'd just implement
> what I reasoned through as one way forward, compile tested only (patch
> relative to Jens' for-4.21/block):
> 
>  drivers/nvme/host/core.c      | 14 +++++++---
>  drivers/nvme/host/multipath.c | 65 ++++++++++++++++++++++++++-----------------
>  drivers/nvme/host/nvme.h      |  4 +++
>  3 files changed, 54 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index f172d63db2b5..05313ab5d91e 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -252,10 +252,16 @@ void nvme_complete_rq(struct request *req)
>  	trace_nvme_complete_rq(req);
>  
>  	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
> -		if ((req->cmd_flags & REQ_NVME_MPATH) &&
> -		    blk_path_error(status)) {
> -			nvme_failover_req(req);
> -			return;
> +		if (blk_path_error(status)) {
> +			struct nvme_ns *ns = req->q->queuedata;
> +			u16 nvme_status = nvme_req(req)->status;
> +
> +			if (req->cmd_flags & REQ_NVME_MPATH) {
> +				nvme_failover_req(req);
> +				nvme_update_ana(ns, nvme_status);
> +				return;
> +			}
> +			nvme_update_ana(ns, nvme_status);
>  		}
>  
>  		if (!blk_queue_dying(req->q)) {
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 5e3cc8c59a39..f7fbc161dc8c 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
>  
>  inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
>  {
> -	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
> +	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
>  }
>  
>  /*
> @@ -47,6 +47,17 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
>  	}
>  }
>  
> +static bool nvme_ana_error(u16 status)
> +{
> +	switch (status & 0x7ff) {
> +	case NVME_SC_ANA_TRANSITION:
> +	case NVME_SC_ANA_INACCESSIBLE:
> +	case NVME_SC_ANA_PERSISTENT_LOSS:
> +		return true;
> +	}
> +	return false;
> +}
> +
>  void nvme_failover_req(struct request *req)
>  {
>  	struct nvme_ns *ns = req->q->queuedata;
> @@ -58,10 +69,7 @@ void nvme_failover_req(struct request *req)
>  	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
>  	blk_mq_end_request(req, 0);
>  
> -	switch (status & 0x7ff) {
> -	case NVME_SC_ANA_TRANSITION:
> -	case NVME_SC_ANA_INACCESSIBLE:
> -	case NVME_SC_ANA_PERSISTENT_LOSS:
> +	if (nvme_ana_error(status)) {
>  		/*
>  		 * If we got back an ANA error we know the controller is alive,
>  		 * but not ready to serve this namespaces.  The spec suggests
> @@ -69,31 +77,38 @@ void nvme_failover_req(struct request *req)
>  		 * that the admin and I/O queues are not serialized that is
>  		 * fundamentally racy.  So instead just clear the current path,
>  		 * mark the the path as pending and kick of a re-read of the ANA
> -		 * log page ASAP.
> +		 * log page ASAP (see nvme_update_ana() below).
>  		 */
>  		nvme_mpath_clear_current_path(ns);
> -		if (ns->ctrl->ana_log_buf) {
> -			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> -			queue_work(nvme_wq, &ns->ctrl->ana_work);
> +	} else {
> +		switch (status & 0x7ff) {
> +		case NVME_SC_HOST_PATH_ERROR:
> +			/*
> +			 * Temporary transport disruption in talking to the
> +			 * controller.  Try to send on a new path.
> +			 */
> +			nvme_mpath_clear_current_path(ns);
> +			break;
> +		default:
> +			/*
> +			 * Reset the controller for any non-ANA error as we
> +			 * don't know what caused the error.
> +			 */
> +			nvme_reset_ctrl(ns->ctrl);
> +			break;
>  		}
> -		break;
> -	case NVME_SC_HOST_PATH_ERROR:
> -		/*
> -		 * Temporary transport disruption in talking to the controller.
> -		 * Try to send on a new path.
> -		 */
> -		nvme_mpath_clear_current_path(ns);
> -		break;
> -	default:
> -		/*
> -		 * Reset the controller for any non-ANA error as we don't know
> -		 * what caused the error.
> -		 */
> -		nvme_reset_ctrl(ns->ctrl);
> -		break;
>  	}
Maybe move nvme_mpath_clear_current_path() out of the loop (it wouldn't
matter if we clear the path if we reset the controller afterwards); that
might even clean up the code even more.

> +}
>  
> -	kblockd_schedule_work(&ns->head->requeue_work);
> +void nvme_update_ana(struct nvme_ns *ns, u16 status)
> +{
> +	if (nvme_ana_error(status) && ns->ctrl->ana_log_buf) {
> +		set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> +		queue_work(nvme_wq, &ns->ctrl->ana_work);
> +	}
> +
> +	if (multipath)
> +		kblockd_schedule_work(&ns->head->requeue_work);
>  }

maybe use 'ns->head->disk' here; we only need to call this if we have a
multipath disk.

Remaining bits are okay.

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: multipath-tools: add ANA support for NVMe device

[Mike Snitzer]

On Wed, Nov 14 2018 at  1:51pm -0500,
Hannes Reinecke <hare@suse.de> wrote:

> On 11/14/18 6:47 PM, Mike Snitzer wrote:
> > On Wed, Nov 14 2018 at  2:49am -0500,
> > Hannes Reinecke <hare@suse.de> wrote:
> > 
> >> On 11/14/18 6:38 AM, Mike Snitzer wrote:
> >>> On Tue, Nov 13 2018 at  1:00pm -0500,
> >>> Mike Snitzer <snitzer@redhat.com> wrote:
> >>>
> >>>> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html
> >>>> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html
> >>> ...
> >>>
> >>> I knew there had to be a pretty tight coupling between the NVMe driver's
> >>> native multipathing and ANA support... and that the simplicity of
> >>> Hannes' patch [1] was too good to be true.
> >>>
> >>> The real justification for not making Hannes' change is it'd effectively
> >>> be useless without first splitting out the ANA handling done during NVMe
> >>> request completion (NVME_SC_ANA_* cases in nvme_failover_req) that
> >>> triggers re-reading the ANA log page accordingly.
> >>>
> >>> So without the ability to drive the ANA workqueue to trigger
> >>> nvme_read_ana_log() from the nvme driver's completion path -- even if
> >>> nvme_core.multipath=N -- it really doesn't buy multipath-tools anything
> >>> to have the NVMe driver export the ana state via sysfs, because that ANA
> >>> state will never get updated.
> >>>
> >> Hmm. Indeed, I was more focussed on having the sysfs attributes
> >> displayed, so yes, indeed it needs some more work.
> > ...
> >>> Not holding my breath BUT:
> >>> if decoupling the reading of ANA state from native NVMe multipathing
> >>> specific work during nvme request completion were an acceptable
> >>> advancement I'd gladly do the work.
> >>>
> >> I'd be happy to work on that, given that we'll have to have 'real'
> >> ANA support for device-mapper anyway for SLE12 SP4 etc.
> > 
> > I had a close enough look yesterday that I figured I'd just implement
> > what I reasoned through as one way forward, compile tested only (patch
> > relative to Jens' for-4.21/block):
> > 
> >  drivers/nvme/host/core.c      | 14 +++++++---
> >  drivers/nvme/host/multipath.c | 65 ++++++++++++++++++++++++++-----------------
> >  drivers/nvme/host/nvme.h      |  4 +++
> >  3 files changed, 54 insertions(+), 29 deletions(-)
> > 
> > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > index f172d63db2b5..05313ab5d91e 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -252,10 +252,16 @@ void nvme_complete_rq(struct request *req)
> >  	trace_nvme_complete_rq(req);
> >  
> >  	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
> > -		if ((req->cmd_flags & REQ_NVME_MPATH) &&
> > -		    blk_path_error(status)) {
> > -			nvme_failover_req(req);
> > -			return;
> > +		if (blk_path_error(status)) {
> > +			struct nvme_ns *ns = req->q->queuedata;
> > +			u16 nvme_status = nvme_req(req)->status;
> > +
> > +			if (req->cmd_flags & REQ_NVME_MPATH) {
> > +				nvme_failover_req(req);
> > +				nvme_update_ana(ns, nvme_status);
> > +				return;
> > +			}
> > +			nvme_update_ana(ns, nvme_status);
> >  		}
> >  
> >  		if (!blk_queue_dying(req->q)) {
> > diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> > index 5e3cc8c59a39..f7fbc161dc8c 100644
> > --- a/drivers/nvme/host/multipath.c
> > +++ b/drivers/nvme/host/multipath.c
> > @@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
> >  
> >  inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
> >  {
> > -	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
> > +	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
> >  }
> >  
> >  /*
> > @@ -47,6 +47,17 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
> >  	}
> >  }
> >  
> > +static bool nvme_ana_error(u16 status)
> > +{
> > +	switch (status & 0x7ff) {
> > +	case NVME_SC_ANA_TRANSITION:
> > +	case NVME_SC_ANA_INACCESSIBLE:
> > +	case NVME_SC_ANA_PERSISTENT_LOSS:
> > +		return true;
> > +	}
> > +	return false;
> > +}
> > +
> >  void nvme_failover_req(struct request *req)
> >  {
> >  	struct nvme_ns *ns = req->q->queuedata;
> > @@ -58,10 +69,7 @@ void nvme_failover_req(struct request *req)
> >  	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
> >  	blk_mq_end_request(req, 0);
> >  
> > -	switch (status & 0x7ff) {
> > -	case NVME_SC_ANA_TRANSITION:
> > -	case NVME_SC_ANA_INACCESSIBLE:
> > -	case NVME_SC_ANA_PERSISTENT_LOSS:
> > +	if (nvme_ana_error(status)) {
> >  		/*
> >  		 * If we got back an ANA error we know the controller is alive,
> >  		 * but not ready to serve this namespaces.  The spec suggests
> > @@ -69,31 +77,38 @@ void nvme_failover_req(struct request *req)
> >  		 * that the admin and I/O queues are not serialized that is
> >  		 * fundamentally racy.  So instead just clear the current path,
> >  		 * mark the the path as pending and kick of a re-read of the ANA
> > -		 * log page ASAP.
> > +		 * log page ASAP (see nvme_update_ana() below).
> >  		 */
> >  		nvme_mpath_clear_current_path(ns);
> > -		if (ns->ctrl->ana_log_buf) {
> > -			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> > -			queue_work(nvme_wq, &ns->ctrl->ana_work);
> > +	} else {
> > +		switch (status & 0x7ff) {
> > +		case NVME_SC_HOST_PATH_ERROR:
> > +			/*
> > +			 * Temporary transport disruption in talking to the
> > +			 * controller.  Try to send on a new path.
> > +			 */
> > +			nvme_mpath_clear_current_path(ns);
> > +			break;
> > +		default:
> > +			/*
> > +			 * Reset the controller for any non-ANA error as we
> > +			 * don't know what caused the error.
> > +			 */
> > +			nvme_reset_ctrl(ns->ctrl);
> > +			break;
> >  		}
> > -		break;
> > -	case NVME_SC_HOST_PATH_ERROR:
> > -		/*
> > -		 * Temporary transport disruption in talking to the controller.
> > -		 * Try to send on a new path.
> > -		 */
> > -		nvme_mpath_clear_current_path(ns);
> > -		break;
> > -	default:
> > -		/*
> > -		 * Reset the controller for any non-ANA error as we don't know
> > -		 * what caused the error.
> > -		 */
> > -		nvme_reset_ctrl(ns->ctrl);
> > -		break;
> >  	}
> Maybe move nvme_mpath_clear_current_path() out of the loop (it wouldn't
> matter if we clear the path if we reset the controller afterwards); that
> might even clean up the code even more.

Not completely sure what you're suggesting.  But I was going for purely
functional equivalent of the existing upstream code -- just with
multipathing and ana split.

Could be that in future it wouldn't make sense to always
nvme_mpath_clear_current_path() for all cases?

> 
> > +}
> >  
> > -	kblockd_schedule_work(&ns->head->requeue_work);
> > +void nvme_update_ana(struct nvme_ns *ns, u16 status)
> > +{
> > +	if (nvme_ana_error(status) && ns->ctrl->ana_log_buf) {
> > +		set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> > +		queue_work(nvme_wq, &ns->ctrl->ana_work);
> > +	}
> > +
> > +	if (multipath)
> > +		kblockd_schedule_work(&ns->head->requeue_work);
> >  }
> 
> maybe use 'ns->head->disk' here; we only need to call this if we have a
> multipath disk.

Sure.

> Remaining bits are okay.

Thanks,
Mike

[PATCH] nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

Whether or not ANA is present is a choice of the target implementation;
the host (and whether it supports multipathing) has _zero_ influence on
this.  If the target declares a path as 'inaccessible' the path _is_
inaccessible to the host.  As such, ANA support should be functional
even if native multipathing is not.

Introduce ability to always re-read ANA log page as required due to ANA
error and make current ANA state available via sysfs -- even if native
multipathing is disabled on the host (e.g. nvme_core.multipath=N).

This affords userspace access to the current ANA state independent of
which layer might be doing multipathing.  It also allows multipath-tools
to rely on the NVMe driver for ANA support while dm-multipath takes care
of multipathing.

While implementing these changes care was taken to preserve the exact
ANA functionality and code sequence native multipathing has provided.
This manifests as native multipathing's nvme_failover_req() being
tweaked to call __nvme_update_ana() which was factored out to allow
nvme_update_ana() to be called independent of nvme_failover_req().

And as always, if embedded NVMe users do not want any performance
overhead associated with ANA or native NVMe multipathing they can
disable CONFIG_NVME_MULTIPATH.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/nvme/host/core.c      | 10 +++++----
 drivers/nvme/host/multipath.c | 49 +++++++++++++++++++++++++++++++++----------
 drivers/nvme/host/nvme.h      |  4 ++++
 3 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index fe957166c4a9..3df607905628 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -255,10 +255,12 @@ void nvme_complete_rq(struct request *req)
 		nvme_req(req)->ctrl->comp_seen = true;
 
 	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
-		if ((req->cmd_flags & REQ_NVME_MPATH) &&
-		    blk_path_error(status)) {
-			nvme_failover_req(req);
-			return;
+		if (blk_path_error(status)) {
+			if (req->cmd_flags & REQ_NVME_MPATH) {
+				nvme_failover_req(req);
+				return;
+			}
+			nvme_update_ana(req);
 		}
 
 		if (!blk_queue_dying(req->q)) {
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 8e03cda770c5..0adbcff5fba2 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
 
 inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
 {
-	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
+	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
 }
 
 /*
@@ -47,6 +47,35 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 	}
 }
 
+static bool nvme_ana_error(u16 status)
+{
+	switch (status & 0x7ff) {
+	case NVME_SC_ANA_TRANSITION:
+	case NVME_SC_ANA_INACCESSIBLE:
+	case NVME_SC_ANA_PERSISTENT_LOSS:
+		return true;
+	}
+	return false;
+}
+
+static void __nvme_update_ana(struct nvme_ns *ns)
+{
+	if (!ns->ctrl->ana_log_buf)
+		return;
+
+	set_bit(NVME_NS_ANA_PENDING, &ns->flags);
+	queue_work(nvme_wq, &ns->ctrl->ana_work);
+}
+
+void nvme_update_ana(struct request *req)
+{
+	struct nvme_ns *ns = req->q->queuedata;
+	u16 status = nvme_req(req)->status;
+
+	if (nvme_ana_error(status))
+		__nvme_update_ana(ns);
+}
+
 void nvme_failover_req(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
@@ -58,25 +87,22 @@ void nvme_failover_req(struct request *req)
 	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
 	blk_mq_end_request(req, 0);
 
-	switch (status & 0x7ff) {
-	case NVME_SC_ANA_TRANSITION:
-	case NVME_SC_ANA_INACCESSIBLE:
-	case NVME_SC_ANA_PERSISTENT_LOSS:
+	if (nvme_ana_error(status)) {
 		/*
 		 * If we got back an ANA error we know the controller is alive,
 		 * but not ready to serve this namespaces.  The spec suggests
 		 * we should update our general state here, but due to the fact
 		 * that the admin and I/O queues are not serialized that is
 		 * fundamentally racy.  So instead just clear the current path,
-		 * mark the the path as pending and kick of a re-read of the ANA
+		 * mark the path as pending and kick off a re-read of the ANA
 		 * log page ASAP.
 		 */
 		nvme_mpath_clear_current_path(ns);
-		if (ns->ctrl->ana_log_buf) {
-			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
-			queue_work(nvme_wq, &ns->ctrl->ana_work);
-		}
-		break;
+		__nvme_update_ana(ns);
+		goto kick_requeue;
+	}
+
+	switch (status & 0x7ff) {
 	case NVME_SC_HOST_PATH_ERROR:
 		/*
 		 * Temporary transport disruption in talking to the controller.
@@ -93,6 +119,7 @@ void nvme_failover_req(struct request *req)
 		break;
 	}
 
+kick_requeue:
 	kblockd_schedule_work(&ns->head->requeue_work);
 }
 
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 27663ce3044e..cbe4253f2d02 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -471,6 +471,7 @@ bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl);
 void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 			struct nvme_ctrl *ctrl, int *flags);
 void nvme_failover_req(struct request *req);
+void nvme_update_ana(struct request *req);
 void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl);
 int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl,struct nvme_ns_head *head);
 void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
@@ -510,6 +511,9 @@ static inline void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 static inline void nvme_failover_req(struct request *req)
 {
 }
+static inline void nvme_update_ana(struct request *req)
+{
+}
 static inline void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
 {
 }
-- 
2.15.0

Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Hannes Reinecke]

On 11/15/18 6:46 PM, Mike Snitzer wrote:
> Whether or not ANA is present is a choice of the target implementation;
> the host (and whether it supports multipathing) has _zero_ influence on
> this.  If the target declares a path as 'inaccessible' the path _is_
> inaccessible to the host.  As such, ANA support should be functional
> even if native multipathing is not.
> 
> Introduce ability to always re-read ANA log page as required due to ANA
> error and make current ANA state available via sysfs -- even if native
> multipathing is disabled on the host (e.g. nvme_core.multipath=N).
> 
> This affords userspace access to the current ANA state independent of
> which layer might be doing multipathing.  It also allows multipath-tools
> to rely on the NVMe driver for ANA support while dm-multipath takes care
> of multipathing.
> 
> While implementing these changes care was taken to preserve the exact
> ANA functionality and code sequence native multipathing has provided.
> This manifests as native multipathing's nvme_failover_req() being
> tweaked to call __nvme_update_ana() which was factored out to allow
> nvme_update_ana() to be called independent of nvme_failover_req().
> 
> And as always, if embedded NVMe users do not want any performance
> overhead associated with ANA or native NVMe multipathing they can
> disable CONFIG_NVME_MULTIPATH.
> 
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>   drivers/nvme/host/core.c      | 10 +++++----
>   drivers/nvme/host/multipath.c | 49 +++++++++++++++++++++++++++++++++----------
>   drivers/nvme/host/nvme.h      |  4 ++++
>   3 files changed, 48 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index fe957166c4a9..3df607905628 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -255,10 +255,12 @@ void nvme_complete_rq(struct request *req)
>   		nvme_req(req)->ctrl->comp_seen = true;
>   
>   	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
> -		if ((req->cmd_flags & REQ_NVME_MPATH) &&
> -		    blk_path_error(status)) {
> -			nvme_failover_req(req);
> -			return;
> +		if (blk_path_error(status)) {
> +			if (req->cmd_flags & REQ_NVME_MPATH) {
> +				nvme_failover_req(req);
> +				return;
> +			}
> +			nvme_update_ana(req);
>   		}
>   
>   		if (!blk_queue_dying(req->q)) {
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 8e03cda770c5..0adbcff5fba2 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -22,7 +22,7 @@ MODULE_PARM_DESC(multipath,
>   
>   inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
>   {
> -	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
> +	return ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
>   }
>   
>   /*
> @@ -47,6 +47,35 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
>   	}
>   }
>   
> +static bool nvme_ana_error(u16 status)
> +{
> +	switch (status & 0x7ff) {
> +	case NVME_SC_ANA_TRANSITION:
> +	case NVME_SC_ANA_INACCESSIBLE:
> +	case NVME_SC_ANA_PERSISTENT_LOSS:
> +		return true;
> +	}
> +	return false;
> +}
> +
> +static void __nvme_update_ana(struct nvme_ns *ns)
> +{
> +	if (!ns->ctrl->ana_log_buf)
> +		return;
> +
> +	set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> +	queue_work(nvme_wq, &ns->ctrl->ana_work);
> +}
> +
> +void nvme_update_ana(struct request *req)
> +{
> +	struct nvme_ns *ns = req->q->queuedata;
> +	u16 status = nvme_req(req)->status;
> +
> +	if (nvme_ana_error(status))
> +		__nvme_update_ana(ns);
> +}
> +
>   void nvme_failover_req(struct request *req)
>   {
>   	struct nvme_ns *ns = req->q->queuedata;
> @@ -58,25 +87,22 @@ void nvme_failover_req(struct request *req)
>   	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
>   	blk_mq_end_request(req, 0);
>   
> -	switch (status & 0x7ff) {
> -	case NVME_SC_ANA_TRANSITION:
> -	case NVME_SC_ANA_INACCESSIBLE:
> -	case NVME_SC_ANA_PERSISTENT_LOSS:
> +	if (nvme_ana_error(status)) {
>   		/*
>   		 * If we got back an ANA error we know the controller is alive,
>   		 * but not ready to serve this namespaces.  The spec suggests
>   		 * we should update our general state here, but due to the fact
>   		 * that the admin and I/O queues are not serialized that is
>   		 * fundamentally racy.  So instead just clear the current path,
> -		 * mark the the path as pending and kick of a re-read of the ANA
> +		 * mark the path as pending and kick off a re-read of the ANA
>   		 * log page ASAP.
>   		 */
>   		nvme_mpath_clear_current_path(ns);
> -		if (ns->ctrl->ana_log_buf) {
> -			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> -			queue_work(nvme_wq, &ns->ctrl->ana_work);
> -		}
> -		break;
> +		__nvme_update_ana(ns);
> +		goto kick_requeue;
> +	}
> +
> +	switch (status & 0x7ff) {
>   	case NVME_SC_HOST_PATH_ERROR:
>   		/*
>   		 * Temporary transport disruption in talking to the controller.
> @@ -93,6 +119,7 @@ void nvme_failover_req(struct request *req)
>   		break;
>   	}
>   
> +kick_requeue:
>   	kblockd_schedule_work(&ns->head->requeue_work);
>   }
>   
Doesn't the need to be protected by 'if (ns->head->disk)' or somesuch?

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: nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

On Fri, Nov 16 2018 at  2:25am -0500,
Hannes Reinecke <hare@suse.de> wrote:

> On 11/15/18 6:46 PM, Mike Snitzer wrote:
> >Whether or not ANA is present is a choice of the target implementation;
> >the host (and whether it supports multipathing) has _zero_ influence on
> >this.  If the target declares a path as 'inaccessible' the path _is_
> >inaccessible to the host.  As such, ANA support should be functional
> >even if native multipathing is not.
> >
> >Introduce ability to always re-read ANA log page as required due to ANA
> >error and make current ANA state available via sysfs -- even if native
> >multipathing is disabled on the host (e.g. nvme_core.multipath=N).
> >
> >This affords userspace access to the current ANA state independent of
> >which layer might be doing multipathing.  It also allows multipath-tools
> >to rely on the NVMe driver for ANA support while dm-multipath takes care
> >of multipathing.
> >
> >While implementing these changes care was taken to preserve the exact
> >ANA functionality and code sequence native multipathing has provided.
> >This manifests as native multipathing's nvme_failover_req() being
> >tweaked to call __nvme_update_ana() which was factored out to allow
> >nvme_update_ana() to be called independent of nvme_failover_req().
> >
> >And as always, if embedded NVMe users do not want any performance
> >overhead associated with ANA or native NVMe multipathing they can
> >disable CONFIG_NVME_MULTIPATH.
> >
> >Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> >---
> >  drivers/nvme/host/core.c      | 10 +++++----
> >  drivers/nvme/host/multipath.c | 49 +++++++++++++++++++++++++++++++++----------
> >  drivers/nvme/host/nvme.h      |  4 ++++
> >  3 files changed, 48 insertions(+), 15 deletions(-)
> >
> >diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> >index fe957166c4a9..3df607905628 100644
> >--- a/drivers/nvme/host/core.c
> >+++ b/drivers/nvme/host/core.c
> >@@ -255,10 +255,12 @@ void nvme_complete_rq(struct request *req)
> >  		nvme_req(req)->ctrl->comp_seen = true;
> >  	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
> >-		if ((req->cmd_flags & REQ_NVME_MPATH) &&
> >-		    blk_path_error(status)) {
> >-			nvme_failover_req(req);
> >-			return;
> >+		if (blk_path_error(status)) {
> >+			if (req->cmd_flags & REQ_NVME_MPATH) {
> >+				nvme_failover_req(req);
> >+				return;
> >+			}
> >+			nvme_update_ana(req);
> >  		}
> >  		if (!blk_queue_dying(req->q)) {

...

> >diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> >index 8e03cda770c5..0adbcff5fba2 100644
> >--- a/drivers/nvme/host/multipath.c
> >+++ b/drivers/nvme/host/multipath.c
> >@@ -58,25 +87,22 @@ void nvme_failover_req(struct request *req)
> >  	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
> >  	blk_mq_end_request(req, 0);
> >-	switch (status & 0x7ff) {
> >-	case NVME_SC_ANA_TRANSITION:
> >-	case NVME_SC_ANA_INACCESSIBLE:
> >-	case NVME_SC_ANA_PERSISTENT_LOSS:
> >+	if (nvme_ana_error(status)) {
> >  		/*
> >  		 * If we got back an ANA error we know the controller is alive,
> >  		 * but not ready to serve this namespaces.  The spec suggests
> >  		 * we should update our general state here, but due to the fact
> >  		 * that the admin and I/O queues are not serialized that is
> >  		 * fundamentally racy.  So instead just clear the current path,
> >-		 * mark the the path as pending and kick of a re-read of the ANA
> >+		 * mark the path as pending and kick off a re-read of the ANA
> >  		 * log page ASAP.
> >  		 */
> >  		nvme_mpath_clear_current_path(ns);
> >-		if (ns->ctrl->ana_log_buf) {
> >-			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
> >-			queue_work(nvme_wq, &ns->ctrl->ana_work);
> >-		}
> >-		break;
> >+		__nvme_update_ana(ns);
> >+		goto kick_requeue;
> >+	}
> >+
> >+	switch (status & 0x7ff) {
> >  	case NVME_SC_HOST_PATH_ERROR:
> >  		/*
> >  		 * Temporary transport disruption in talking to the controller.
> >@@ -93,6 +119,7 @@ void nvme_failover_req(struct request *req)
> >  		break;
> >  	}
> >+kick_requeue:
> >  	kblockd_schedule_work(&ns->head->requeue_work);
> >  }
> Doesn't the need to be protected by 'if (ns->head->disk)' or somesuch?

No.  nvme_failover_req() is only ever called by native multipathing; see
nvme_complete_rq()'s check for req->cmd_flags & REQ_NVME_MPATH as the
condition for calling nvme_complete_rq().

The previos RFC-style patch I posted muddled ANA and multipathing in
nvme_update_ana() but this final patch submission was fixed because I
saw a cleaner way forward by having nvme_failover_req() also do ANA work
just like it always has -- albeit with new helpers that
nvme_update_ana() also calls.

Mike

Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Thu, Nov 15, 2018 at 12:46:05PM -0500, Mike Snitzer wrote:
> Whether or not ANA is present is a choice of the target implementation;
> the host (and whether it supports multipathing) has _zero_ influence on
> this.  If the target declares a path as 'inaccessible' the path _is_
> inaccessible to the host.  As such, ANA support should be functional
> even if native multipathing is not.
> 
> Introduce ability to always re-read ANA log page as required due to ANA
> error and make current ANA state available via sysfs -- even if native
> multipathing is disabled on the host (e.g. nvme_core.multipath=N).

The first part I could see, but I still want to make it conditional
in some way as nvme is going into deeply embedded setups, and I don't
want to carry the weight of the ANA code around for everyone.

The second I fundamentally disagree with.  And even if you found agreement
it would have to be in a separate patch as it is a separate feature.

Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Hannes Reinecke]

On 11/16/18 10:14 AM, Christoph Hellwig wrote:
> On Thu, Nov 15, 2018 at 12:46:05PM -0500, Mike Snitzer wrote:
>> Whether or not ANA is present is a choice of the target implementation;
>> the host (and whether it supports multipathing) has _zero_ influence on
>> this.  If the target declares a path as 'inaccessible' the path _is_
>> inaccessible to the host.  As such, ANA support should be functional
>> even if native multipathing is not.
>>
>> Introduce ability to always re-read ANA log page as required due to ANA
>> error and make current ANA state available via sysfs -- even if native
>> multipathing is disabled on the host (e.g. nvme_core.multipath=N).
> 
> The first part I could see, but I still want to make it conditional
> in some way as nvme is going into deeply embedded setups, and I don't
> want to carry the weight of the ANA code around for everyone.
> 
Can you clarify this a bit?
We _do_ have the NVME multipath config option to deconfigure the whole 
thing during compile time; that isn't influenced with this patch.
So are you worried about the size of the ANA implementation itself?
Or are you worried about the size of the ANA structures?

> The second I fundamentally disagree with.  And even if you found agreement
> it would have to be in a separate patch as it is a separate feature.
> 
Why? Where's the problem with re-reading the ANA log pages if we get an 
event indicating that we should?

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: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Fri, Nov 16, 2018 at 10:40:40AM +0100, Hannes Reinecke wrote:
>>> Introduce ability to always re-read ANA log page as required due to ANA
>>> error and make current ANA state available via sysfs -- even if native
>>> multipathing is disabled on the host (e.g. nvme_core.multipath=N).
>>
>> The first part I could see, but I still want to make it conditional
>> in some way as nvme is going into deeply embedded setups, and I don't
>> want to carry the weight of the ANA code around for everyone.
>>
> Can you clarify this a bit?
> We _do_ have the NVME multipath config option to deconfigure the whole 
> thing during compile time; that isn't influenced with this patch.
> So are you worried about the size of the ANA implementation itself?
> Or are you worried about the size of the ANA structures?

I just see the next step of wanting to move ANA code into the core
which is implied above.
>
>> The second I fundamentally disagree with.  And even if you found agreement
>> it would have to be in a separate patch as it is a separate feature.
>>
> Why? Where's the problem with re-reading the ANA log pages if we get an 
> event indicating that we should?

"second" here means the sysfs file.

Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Hannes Reinecke]

On 11/16/18 10:49 AM, Christoph Hellwig wrote:
> On Fri, Nov 16, 2018 at 10:40:40AM +0100, Hannes Reinecke wrote:
>>>> Introduce ability to always re-read ANA log page as required due to ANA
>>>> error and make current ANA state available via sysfs -- even if native
>>>> multipathing is disabled on the host (e.g. nvme_core.multipath=N).
>>>
>>> The first part I could see, but I still want to make it conditional
>>> in some way as nvme is going into deeply embedded setups, and I don't
>>> want to carry the weight of the ANA code around for everyone.
>>>
>> Can you clarify this a bit?
>> We _do_ have the NVME multipath config option to deconfigure the whole
>> thing during compile time; that isn't influenced with this patch.
>> So are you worried about the size of the ANA implementation itself?
>> Or are you worried about the size of the ANA structures?
> 
> I just see the next step of wanting to move ANA code into the core
> which is implied above.

Really, I couldn't care less _where_ the ANA code lives.
If the size of which is any concern we can even make it configurable of 
sorts.

>>
>>> The second I fundamentally disagree with.  And even if you found agreement
>>> it would have to be in a separate patch as it is a separate feature.
>>>
>> Why? Where's the problem with re-reading the ANA log pages if we get an
>> event indicating that we should?
> 
> "second" here means the sysfs file.
> 
Ok, so would you be happy with making ANA support configurable?

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: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Fri, Nov 16, 2018 at 11:06:32AM +0100, Hannes Reinecke wrote:
> Ok, so would you be happy with making ANA support configurable?

I've looked a bit over the whole situation, and what I think we need
to do is:

 a) warn if we see a ANA capable device without multipath support
    so people know it is not going to work properly.
 b) deprecate the multipath module option.  It was only intended as
    a migration for any pre-existing PCIe multipath user if there
    were any, not to support any new functionality.  So for 4.20
    put in a patch that prints a clear warning when it is used,
    including a link to the nvme list, and then for 4.25 or so
    remove it entirely unless something unexpected come up.

This whole drama of optional multipath use has wasted way too much
of everyones time already.

Re: nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

On Fri, Nov 16 2018 at  5:17am -0500,
Christoph Hellwig <hch@lst.de> wrote:

> On Fri, Nov 16, 2018 at 11:06:32AM +0100, Hannes Reinecke wrote:
> > Ok, so would you be happy with making ANA support configurable?
> 
> I've looked a bit over the whole situation, and what I think we need
> to do is:
> 
>  a) warn if we see a ANA capable device without multipath support
>     so people know it is not going to work properly.

I disagree with your cynicism but v2 of this patch now emits a warning
accordingly.

>  b) deprecate the multipath module option.  It was only intended as
>     a migration for any pre-existing PCIe multipath user if there
>     were any, not to support any new functionality.  So for 4.20
>     put in a patch that prints a clear warning when it is used,
>     including a link to the nvme list, and then for 4.25 or so
>     remove it entirely unless something unexpected come up.

You rejected the idea of allowing fine-grained control over whether
native NVMe multipathing is enabled or not on a per-namespace basis.
All we have is the coarse-grained nvme_core.multipath=N knob.  Now
you're forecasting removing even that.  Please don't do that.

> This whole drama of optional multipath use has wasted way too much
> of everyones time already.

It has wasted _way_ too much time.

But the drama is born out of you rejecting that we need to preserve
multipath-tools and dm-multipath's ability to work across any
transport.  You don't need to do that work: Hannes, myself and others
have always been willing and able -- if you'd let us.

IIRC it was at 2016's LSF in Boston where Ewan Milne and I had a
face-to-face conversation with you in the hallway track where you agreed
that ANA support would be activated if the capability was advertised by
the target.  The model we discussed is that it would be comparable to
how ALUA gets enabled during SCSI LUN discovery.

I hope you can see your way forward to be more accommodating now.
Especially given the proposed changes are backed by NVMe standards.

Please, PLEASE take v2 of this patch.. please? ;)

Thanks,
Mike

Re: nvme: allow ANA support to be independent of native multipathing

[Laurence Oberman]

On Fri, 2018-11-16 at 14:28 -0500, Mike Snitzer wrote:
> On Fri, Nov 16 2018 at  5:17am -0500,
> Christoph Hellwig <hch@lst.de> wrote:
> 
> > On Fri, Nov 16, 2018 at 11:06:32AM +0100, Hannes Reinecke wrote:
> > > Ok, so would you be happy with making ANA support configurable?
> > 
> > I've looked a bit over the whole situation, and what I think we
> > need
> > to do is:
> > 
> >  a) warn if we see a ANA capable device without multipath support
> >     so people know it is not going to work properly.
> 
> I disagree with your cynicism but v2 of this patch now emits a
> warning
> accordingly.
> 
> >  b) deprecate the multipath module option.  It was only intended as
> >     a migration for any pre-existing PCIe multipath user if there
> >     were any, not to support any new functionality.  So for 4.20
> >     put in a patch that prints a clear warning when it is used,
> >     including a link to the nvme list, and then for 4.25 or so
> >     remove it entirely unless something unexpected come up.
> 
> You rejected the idea of allowing fine-grained control over whether
> native NVMe multipathing is enabled or not on a per-namespace basis.
> All we have is the coarse-grained nvme_core.multipath=N knob.  Now
> you're forecasting removing even that.  Please don't do that.
> 
> > This whole drama of optional multipath use has wasted way too much
> > of everyones time already.
> 
> It has wasted _way_ too much time.
> 
> But the drama is born out of you rejecting that we need to preserve
> multipath-tools and dm-multipath's ability to work across any
> transport.  You don't need to do that work: Hannes, myself and others
> have always been willing and able -- if you'd let us.
> 
> IIRC it was at 2016's LSF in Boston where Ewan Milne and I had a
> face-to-face conversation with you in the hallway track where you
> agreed
> that ANA support would be activated if the capability was advertised
> by
> the target.  The model we discussed is that it would be comparable to
> how ALUA gets enabled during SCSI LUN discovery.
> 
> I hope you can see your way forward to be more accommodating now.
> Especially given the proposed changes are backed by NVMe standards.
> 
> Please, PLEASE take v2 of this patch.. please? ;)
> 
> Thanks,
> Mike

I am begging you take it too please 
Thanks
Laurence

Re: nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Fri, Nov 16, 2018 at 02:28:02PM -0500, Mike Snitzer wrote:
> You rejected the idea of allowing fine-grained control over whether
> native NVMe multipathing is enabled or not on a per-namespace basis.
> All we have is the coarse-grained nvme_core.multipath=N knob.  Now
> you're forecasting removing even that.  Please don't do that.

The whole point is that this hook was intended as a band aid for the
hypothetical pre-existing setups.  Not ever for new development.

> Please, PLEASE take v2 of this patch.. please? ;)

See the previous mail for the plan ahead.   I'm sick and tired of you
trying to sneak your new developemts back in.

Re: nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

On Mon, Nov 19 2018 at  4:39am -0500,
Christoph Hellwig <hch@lst.de> wrote:

> On Fri, Nov 16, 2018 at 02:28:02PM -0500, Mike Snitzer wrote:
> > You rejected the idea of allowing fine-grained control over whether
> > native NVMe multipathing is enabled or not on a per-namespace basis.
> > All we have is the coarse-grained nvme_core.multipath=N knob.  Now
> > you're forecasting removing even that.  Please don't do that.
> 
> The whole point is that this hook was intended as a band aid for the
> hypothetical pre-existing setups.  Not ever for new development.

It pains me that you're marching us towards increased conflict that
needs resolution through more formal means.  And that now I'm going to
have to document the timeline of your authoritarian approach to
stifling another Linux maintainer's freedom to do his job of delivering
on functionality I've been depended on for many years.

> > Please, PLEASE take v2 of this patch.. please? ;)
> 
> See the previous mail for the plan ahead.   I'm sick and tired of you
> trying to sneak your new developemts back in.

I've only ever posted patches in the open and never has it been with the
idea of sneaking anything in.  Miscategorizing my actions as such is a
gross abuse that I will not tolerate.

If we were to confine ourselves to this v2 patch I pleaded with you to
take: https://lkml.org/lkml/2018/11/17/4

1) Hannes proposed a simplistic patch that didn't account for the fact
   that NVMe's ana workqueue wouldn't get kicked, his intent was to make
   ANA work independent of your native multipathing.  (The fact he or I
   even need to post such patches, to unwind your tight-coupling of ANA
   and multipathing, speaks to how you've calculatingly undermined any
   effort to implement proper NVMe multipathing outside of the NVMe
   driver)

2) ANA and multipathing are completely disjoint on an NVMe spec level.
   You know this.

SO: will you be taking my v2 patch for 4.21 or not?

Please advise, thanks.
Mike

Re: nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Mon, Nov 19, 2018 at 09:56:50AM -0500, Mike Snitzer wrote:
> SO: will you be taking my v2 patch for 4.21 or not?

No.

Re: nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

On Tue, Nov 20 2018 at  4:42am -0500,
Christoph Hellwig <hch@lst.de> wrote:

> On Mon, Nov 19, 2018 at 09:56:50AM -0500, Mike Snitzer wrote:
> > SO: will you be taking my v2 patch for 4.21 or not?
> 
> No.

This isn't how a Linux maintainer engages in technical discussion.

You _clearly_ just want to prevent further use of multipath-tools and
DM-multipath.  You will resort to rejecting a patch that improves the
NVMe driver's standards compliance if it allows you hijack NVMe
multipathing because you think you have the best way and nobody else
should be allowed to use a well established competing _open_ _Linux_
solution.  Simple as that.

You haven't made a single technical argument against my v2 patch, yet
you're rejecting it.  Purely on the basis that having NVMe's ANA updates
work independent on native NVMe multipathing happens to benefit an
alternative (and that benefit is just to not have multipath-tools to be
so crude with a pure userspace ANA state tracking).

Jens, this entire situation has gotten well beyond acceptable and you or
other NVMe co-maintainers need to step in.  We need reasoned _technical_
discussion or this entire process falls apart.

Mike

Re: nvme: allow ANA support to be independent of native multipathing

[Christoph Hellwig]

On Tue, Nov 20, 2018 at 08:37:19AM -0500, Mike Snitzer wrote:
> This isn't how a Linux maintainer engages in technical discussion.

And this isn't a technical discussion.   As told before the only
reason to not build the multipath code is to save space, and
the only reason to disable multipath at runtime is for potential
pre-existing setups, which obviously are not ANA capable.

The right fix is to warn users if they use a driver without
CONFIG_NVME_MULTIPATH on a multi-port device and to phase out the
multipath=0 option in the long run, again with a warning.  Any new
additions to "improve" these cases simply don't make sense.

Re: nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

On Fri, Nov 16 2018 at  4:14am -0500,
Christoph Hellwig <hch@lst.de> wrote:

> On Thu, Nov 15, 2018 at 12:46:05PM -0500, Mike Snitzer wrote:
> > Whether or not ANA is present is a choice of the target implementation;
> > the host (and whether it supports multipathing) has _zero_ influence on
> > this.  If the target declares a path as 'inaccessible' the path _is_
> > inaccessible to the host.  As such, ANA support should be functional
> > even if native multipathing is not.
> > 
> > Introduce ability to always re-read ANA log page as required due to ANA
> > error and make current ANA state available via sysfs -- even if native
> > multipathing is disabled on the host (e.g. nvme_core.multipath=N).
> 
> The first part I could see, but I still want to make it conditional
> in some way as nvme is going into deeply embedded setups, and I don't
> want to carry the weight of the ANA code around for everyone.

So disabling CONFIG_NVME_MULTIPATH isn't adequate?  You see a need for
enabling CONFIG_NVME_MULTIPATH but disallowing consideration of ANA
state management for these embedded cases?  That doesn't make much sense
in that ANA won't be enabled on the target, and if it is then shouldn't
the NVMe host enable ANA support?
 
> The second I fundamentally disagree with.  And even if you found agreement
> it would have to be in a separate patch as it is a separate feature.

In a later mail you clarified that by "second" you meant the sysfs
export.

nvme_ns_id_attrs_are_visible() calls nvme_ctrl_use_ana() to know whether
to export the ana state via sysfs.  Makes no sense to enable ANA to
work, independent of native multipathing, and then even though ANA is
active disallow exporting the associated ANA state.  We need
consistency.. if the sysfs file exists it means ANA state is being
managed.

All I can figure is that what you're suggesting is born out of
disallowing uses you fundamentally disagree with (e.g. multipath-tools
reading the ANA state from this sysfs file).

Mike

[PATCH v2] nvme: allow ANA support to be independent of native multipathing

[Mike Snitzer]

Whether or not ANA is present is a choice of the target implementation;
the host (and whether it supports multipathing) has _zero_ influence on
this.  If the target declares a path as 'inaccessible' the path _is_
inaccessible to the host.  As such, ANA support should be functional
even if native multipathing is not.

Introduce ability to always re-read ANA log page as required due to ANA
error and make current ANA state available via sysfs -- even if native
multipathing is disabled on the host (via nvme_core.multipath=N).

While implementing these changes care was taken to preserve the exact
ANA functionality and code sequence native multipathing has provided.
This manifests as native multipathing's nvme_failover_req() being
tweaked to call __nvme_update_ana() which was factored out to allow
nvme_update_ana() to be called independent of nvme_failover_req().

Add new module param to allow ANA to be disabled via nvme_core.ana=N.
Also, emit warning if ANA is enabled but native multipathing isn't.

And as always, if embedded NVMe users do not want any performance
overhead associated with ANA or native NVMe multipathing they can
disable CONFIG_NVME_MULTIPATH.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/nvme/host/core.c      | 10 +++++---
 drivers/nvme/host/multipath.c | 59 ++++++++++++++++++++++++++++++++++---------
 drivers/nvme/host/nvme.h      |  4 +++
 3 files changed, 57 insertions(+), 16 deletions(-)

v2: add nvme_core.ana modparam and emit warning if ana but !multipath

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index fe957166c4a9..3df607905628 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -255,10 +255,12 @@ void nvme_complete_rq(struct request *req)
 		nvme_req(req)->ctrl->comp_seen = true;
 
 	if (unlikely(status != BLK_STS_OK && nvme_req_needs_retry(req))) {
-		if ((req->cmd_flags & REQ_NVME_MPATH) &&
-		    blk_path_error(status)) {
-			nvme_failover_req(req);
-			return;
+		if (blk_path_error(status)) {
+			if (req->cmd_flags & REQ_NVME_MPATH) {
+				nvme_failover_req(req);
+				return;
+			}
+			nvme_update_ana(req);
 		}
 
 		if (!blk_queue_dying(req->q)) {
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 8e03cda770c5..8b45cad2734d 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -18,11 +18,16 @@
 static bool multipath = true;
 module_param(multipath, bool, 0444);
 MODULE_PARM_DESC(multipath,
-	"turn on native support for multiple controllers per subsystem");
+	"toggle native support for multiple controllers per subsystem");
+
+static bool ana = true;
+module_param(ana, bool, 0444);
+MODULE_PARM_DESC(ana,
+	"toggle support for Asynchronous Namespace Access");
 
 inline bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl)
 {
-	return multipath && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
+	return ana && ctrl->subsys && (ctrl->subsys->cmic & (1 << 3));
 }
 
 /*
@@ -47,6 +52,35 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 	}
 }
 
+static bool nvme_ana_error(u16 status)
+{
+	switch (status & 0x7ff) {
+	case NVME_SC_ANA_TRANSITION:
+	case NVME_SC_ANA_INACCESSIBLE:
+	case NVME_SC_ANA_PERSISTENT_LOSS:
+		return true;
+	}
+	return false;
+}
+
+static void __nvme_update_ana(struct nvme_ns *ns)
+{
+	if (!ns->ctrl->ana_log_buf)
+		return;
+
+	set_bit(NVME_NS_ANA_PENDING, &ns->flags);
+	queue_work(nvme_wq, &ns->ctrl->ana_work);
+}
+
+void nvme_update_ana(struct request *req)
+{
+	struct nvme_ns *ns = req->q->queuedata;
+	u16 status = nvme_req(req)->status;
+
+	if (nvme_ana_error(status))
+		__nvme_update_ana(ns);
+}
+
 void nvme_failover_req(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
@@ -58,25 +92,22 @@ void nvme_failover_req(struct request *req)
 	spin_unlock_irqrestore(&ns->head->requeue_lock, flags);
 	blk_mq_end_request(req, 0);
 
-	switch (status & 0x7ff) {
-	case NVME_SC_ANA_TRANSITION:
-	case NVME_SC_ANA_INACCESSIBLE:
-	case NVME_SC_ANA_PERSISTENT_LOSS:
+	if (nvme_ana_error(status)) {
 		/*
 		 * If we got back an ANA error we know the controller is alive,
 		 * but not ready to serve this namespaces.  The spec suggests
 		 * we should update our general state here, but due to the fact
 		 * that the admin and I/O queues are not serialized that is
 		 * fundamentally racy.  So instead just clear the current path,
-		 * mark the the path as pending and kick of a re-read of the ANA
+		 * mark the path as pending and kick off a re-read of the ANA
 		 * log page ASAP.
 		 */
 		nvme_mpath_clear_current_path(ns);
-		if (ns->ctrl->ana_log_buf) {
-			set_bit(NVME_NS_ANA_PENDING, &ns->flags);
-			queue_work(nvme_wq, &ns->ctrl->ana_work);
-		}
-		break;
+		__nvme_update_ana(ns);
+		goto kick_requeue;
+	}
+
+	switch (status & 0x7ff) {
 	case NVME_SC_HOST_PATH_ERROR:
 		/*
 		 * Temporary transport disruption in talking to the controller.
@@ -93,6 +124,7 @@ void nvme_failover_req(struct request *req)
 		break;
 	}
 
+kick_requeue:
 	kblockd_schedule_work(&ns->head->requeue_work);
 }
 
@@ -551,6 +583,9 @@ int nvme_mpath_init(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
 	if (!nvme_ctrl_use_ana(ctrl))
 		return 0;
 
+	if (!multipath)
+		dev_warn(ctrl->device, "allowing ANA without native multipathing due to nvme_core.multipath=N\n");
+
 	ctrl->anacap = id->anacap;
 	ctrl->anatt = id->anatt;
 	ctrl->nanagrpid = le32_to_cpu(id->nanagrpid);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 27663ce3044e..cbe4253f2d02 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -471,6 +471,7 @@ bool nvme_ctrl_use_ana(struct nvme_ctrl *ctrl);
 void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 			struct nvme_ctrl *ctrl, int *flags);
 void nvme_failover_req(struct request *req);
+void nvme_update_ana(struct request *req);
 void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl);
 int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl,struct nvme_ns_head *head);
 void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
@@ -510,6 +511,9 @@ static inline void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 static inline void nvme_failover_req(struct request *req)
 {
 }
+static inline void nvme_update_ana(struct request *req)
+{
+}
 static inline void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
 {
 }
-- 
2.15.0