[PATCH v9 23/29] scsi-multipath: add delayed disk removal support

[John Garry <john.garry@linux.dev>]

Add support in core code for delayed disk removal support. In this, the
callback calls into the scsi_driver to do the necessary removal work.

The scsi_disk driver (sd) must ensure that the scsi_mpath_device does not
go away while the delayed removal work is active, i.e. it must keep a
reference.

No reference to the scsi_disk multipath structures are kept outside that
driver, so that driver needs to provide a scsi_driver.mpath_remove_head
callback to do the necessary work.

Signed-off-by: John Garry <john.garry@linux.dev>
---
 drivers/scsi/scsi_multipath.c | 27 +++++++++++++++++++++++++++
 include/scsi/scsi_driver.h    |  4 ++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
index bec6dd94f3be..58b0be88a952 100644
--- a/drivers/scsi/scsi_multipath.c
+++ b/drivers/scsi/scsi_multipath.c
@@ -344,7 +344,34 @@ static bool scsi_mpath_available_path(struct mpath_device *mpath_device)
 	return false;
 }
 
+static int scsi_mpath_remove_head_drv(struct device_driver *drv, void *data)
+{
+	struct scsi_mpath_head *scsi_mpath_head = data;
+	struct scsi_driver *scsi_driver = to_scsi_driver(drv);
+
+	if (scsi_driver->mpath_remove_head)
+		scsi_driver->mpath_remove_head(scsi_mpath_head);
+
+	return 0;
+}
+
+static void scsi_mpath_remove_head_work(struct mpath_head *mpath_head)
+{
+	struct scsi_mpath_head *scsi_mpath_head = to_scsi_mpath_head(mpath_head);
+
+	/*
+	 * scsi_mpath_remove_head_drv() could drop the final reference to
+	 * scsi_mpath_head, meaning that we pass a free'd pointer further
+	 * drivers - take a reference so that won't happen.
+	 */
+	scsi_mpath_get_head(scsi_mpath_head);
+	bus_for_each_drv(&scsi_bus_type, NULL, scsi_mpath_head,
+		scsi_mpath_remove_head_drv);
+	scsi_mpath_put_head(scsi_mpath_head);
+}
+
 static struct mpath_head_template smpdt = {
+	.remove_head = scsi_mpath_remove_head_work,
 	.is_disabled = scsi_mpath_is_disabled,
 	.is_optimized = scsi_mpath_is_optimized,
 	.available_path = scsi_mpath_available_path,
diff --git a/include/scsi/scsi_driver.h b/include/scsi/scsi_driver.h
index 249cea724abd..d92b63d357f2 100644
--- a/include/scsi/scsi_driver.h
+++ b/include/scsi/scsi_driver.h
@@ -8,6 +8,7 @@
 
 struct module;
 struct request;
+struct scsi_mpath_head;
 
 struct scsi_driver {
 	struct device_driver	gendrv;
@@ -22,6 +23,9 @@ struct scsi_driver {
 	int (*done)(struct scsi_cmnd *);
 	int (*eh_action)(struct scsi_cmnd *, int);
 	void (*eh_reset)(struct scsi_cmnd *);
+	#ifdef CONFIG_SCSI_MULTIPATH
+	void (*mpath_remove_head)(struct scsi_mpath_head *);
+	#endif
 };
 #define to_scsi_driver(drv) \
 	container_of((drv), struct scsi_driver, gendrv)
-- 
2.43.0