[PATCH v3 4/4] nvme: decouple basic ANA log page re-read support from 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 is achieved by factoring out nvme_update_ana() and calling it in
nvme_complete_rq() for all FAILOVER requests.

This affords userspace access to the current ANA state independent of
which layer might be doing multipathing. This makes 'nvme list-subsys'
show ANA state for all NVMe subsystems with multiple controllers. It
also allows userspace multipath-tools to rely on the NVMe driver for
ANA support while dm-multipath takes care of multipathing.

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 at redhat.com>
---
 drivers/nvme/host/core.c      |  2 ++
 drivers/nvme/host/multipath.c | 16 +++++++++++-----
 drivers/nvme/host/nvme.h      |  4 ++++
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 605ffba6835f..9a878a599897 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -349,6 +349,8 @@ static void nvme_failup_req(struct request *req)
 {
 	blk_status_t status = nvme_error_status(nvme_req(req)->status);
 
+	nvme_update_ana(req);
+
 	/* Ensure a retryable path error is returned */
 	if (WARN_ON_ONCE(!blk_path_error(status))) {
 		/*
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index a1d476e1ac02..7d94250264aa 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -65,23 +65,29 @@ void nvme_set_disk_name(char *disk_name, struct nvme_ns *ns,
 	}
 }
 
-void nvme_failover_req(struct request *req)
+void nvme_update_ana(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
 	u16 status = nvme_req(req)->status & 0x7ff;
-	unsigned long flags;
-
-	nvme_mpath_clear_current_path(ns);
 
 	/*
 	 * If we got back an ANA error, we know the controller is alive but not
-	 * ready to serve this namespace.  Kick of a re-read of the ANA
+	 * ready to serve this namespace.  Kick off a re-read of the ANA
 	 * information page, and just try any other available path for now.
 	 */
 	if (nvme_is_ana_error(status) && ns->ctrl->ana_log_buf) {
 		set_bit(NVME_NS_ANA_PENDING, &ns->flags);
 		queue_work(nvme_wq, &ns->ctrl->ana_work);
 	}
+}
+
+void nvme_failover_req(struct request *req)
+{
+	struct nvme_ns *ns = req->q->queuedata;
+	unsigned long flags;
+
+	nvme_mpath_clear_current_path(ns);
+	nvme_update_ana(req);
 
 	spin_lock_irqsave(&ns->head->requeue_lock, flags);
 	blk_steal_bios(&ns->head->requeue_list, req);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 07b34175c6ce..4eed8536625c 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -664,6 +664,7 @@ void nvme_mpath_start_freeze(struct nvme_subsystem *subsys);
 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);
@@ -714,6 +715,9 @@ 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