[PATCH v2 16/18] scsi: sd: add mpath_dev file

[John Garry <john.g.garry@oracle.com>]

Since per-path gendisk is hidden, we have no /dev/ file.

Add a mpath_dev file so that the multipath disk can be looked up from
per-path gendisk directory.

The following is an example of this usage:

$ ls -l /dev/sdc
brw-rw----    1 root     disk        8,  32 Feb 24 16:08 /dev/sdc
$ cat /sys/class/scsi_mpath_disk/scsi_mpath_disk0/sdc/multipath/sdc:0/mpath_dev
8:32

This can be used by a util like lsscsi, which would find that the gendisk
for the per-path scsi_device is missing.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 drivers/scsi/sd.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b1cf35194895e..380da0b0298bb 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -4017,6 +4017,52 @@ static int sd_mpath_revalidate_head(struct scsi_disk *sdkp)
 
 	return ret;
 }
+
+static ssize_t sd_mpath_dev_show(struct device *dev,
+			struct device_attribute *attr, char *page)
+{
+	struct gendisk *gd = dev_to_disk(dev);
+	struct scsi_disk *sdkp = gd->private_data;
+	struct sd_mpath_disk *sd_mpath_disk = sdkp->sd_mpath_disk;
+	struct scsi_mpath_head *scsi_mpath_head = sd_mpath_disk->scsi_mpath_head;
+	struct mpath_head *mpath_head = scsi_mpath_head->mpath_head;
+	struct gendisk *disk = mpath_head->disk;
+	struct device *disk_dev = disk_to_dev(disk);
+
+	return print_dev_t(page, disk_dev->devt);
+}
+static DEVICE_ATTR(mpath_dev, 0444, sd_mpath_dev_show, NULL);
+
+static struct attribute *sd_mpath_dev_attrs[] = {
+	&dev_attr_mpath_dev.attr,
+	NULL
+};
+
+static umode_t sd_mpath_dev_attr_is_visible(struct kobject *kobj,
+				struct attribute *attr, int i)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct gendisk *gd = dev_to_disk(dev);
+	struct scsi_disk *sdkp = gd->private_data;
+	struct scsi_device *sdev = sdkp->device;
+	struct scsi_mpath_device *scsi_mpath_device = sdev->scsi_mpath_dev;
+
+	if (!scsi_mpath_device)
+		return 0;
+
+	return attr->mode;
+}
+
+static const struct attribute_group sd_mpath_dev_attr_group = {
+	.is_visible = sd_mpath_dev_attr_is_visible,
+	.attrs = sd_mpath_dev_attrs,
+};
+
+static const struct attribute_group *sd_mpath_dev_groups[] = {
+	&sd_mpath_dev_attr_group,
+	NULL
+};
+
 static int sd_mpath_get_disk(struct sd_mpath_disk *sd_mpath_disk)
 {
 	if (!get_device(&sd_mpath_disk->dev))
@@ -4334,6 +4380,8 @@ static int sd_mpath_revalidate_head(struct scsi_disk *sdkp)
 static void sd_mpath_add_disk(struct scsi_disk *sdkp)
 {
 }
+
+#define sd_mpath_dev_groups NULL
 #endif
 /**
  *	sd_probe - called during driver initialization and whenever a
@@ -4475,7 +4523,7 @@ static int sd_probe(struct scsi_device *sdp)
 			sdp->host->rpm_autosuspend_delay);
 	}
 
-	error = device_add_disk(dev, gd, NULL);
+	error = device_add_disk(dev, gd, sd_mpath_dev_groups);
 	if (error) {
 		sd_mpath_fail_probe(sdkp);
 		device_unregister(&sdkp->disk_dev);
-- 
2.43.5