[PATCHv2] ublk: persistent device links

[Hannes Reinecke <hare@kernel.org>]

Implement a 'uuid' parameter to export a device UUID in a sysfs
attribute 'uuid'. The ublk server is required to set the uuid
parameter when creating the device.
This allows udev to create persistent device links for ublk devices
eg with this rule:

KERNEL=="ublk*", ATTRS{uuid}=="?*", SYMLINK+="disk/by-id/ublk-$attr{uuid}"

Signed-off-by: Hannes Reinecke <hare@kernel.org>
---
 drivers/block/ublk_drv.c      | 55 +++++++++++++++++++++++++++++++++--
 include/uapi/linux/ublk_cmd.h |  6 ++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index aaf94d2fb789..ffbd5acda36b 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -89,7 +89,7 @@
 	(UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD | \
 	 UBLK_PARAM_TYPE_DEVT | UBLK_PARAM_TYPE_ZONED |    \
 	 UBLK_PARAM_TYPE_DMA_ALIGN | UBLK_PARAM_TYPE_SEGMENT | \
-	 UBLK_PARAM_TYPE_INTEGRITY)
+	 UBLK_PARAM_TYPE_INTEGRITY | UBLK_PARAM_TYPE_UUID)
 
 struct ublk_uring_cmd_pdu {
 	/*
@@ -761,6 +761,14 @@ static int ublk_validate_params(const struct ublk_device *ub)
 			return -EINVAL;
 	}
 
+	if (ub->params.types & UBLK_PARAM_TYPE_UUID) {
+		const struct ublk_param_uuid *p = &ub->params.uuid;
+		uuid_t uuid;
+
+		import_uuid(&uuid, p->uuid);
+		if (uuid_is_null(&uuid))
+			return -EINVAL;
+	}
 	return 0;
 }
 
@@ -2971,6 +2979,49 @@ static int ublk_add_chdev(struct ublk_device *ub)
 	return ret;
 }
 
+static ssize_t uuid_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct ublk_device *ub = disk->private_data;
+	const struct ublk_param_uuid *p = &ub->params.uuid;
+	uuid_t uuid;
+
+	import_uuid(&uuid, p->uuid);
+	return sprintf(buf, "%pU\n", &uuid);
+}
+
+static DEVICE_ATTR_RO(uuid);
+
+static struct attribute *ublk_attrs[] = {
+	&dev_attr_uuid.attr,
+	NULL,
+};
+
+static umode_t ublk_attrs_are_visible(struct kobject *kobj,
+		struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct gendisk *disk = dev_to_disk(dev);
+	struct ublk_device *ub = disk->private_data;
+
+	if (a == &dev_attr_uuid.attr &&
+	    (ub->params.types & UBLK_PARAM_TYPE_UUID))
+		return S_IRUGO;
+
+	return a->mode;
+}
+
+static const struct attribute_group ublk_attr_group = {
+	.attrs = ublk_attrs,
+	.is_visible = ublk_attrs_are_visible,
+};
+
+static const struct attribute_group *ublk_attr_groups[] = {
+	&ublk_attr_group,
+	NULL,
+};
+
 /* align max io buffer size with PAGE_SIZE */
 static void ublk_align_max_io_size(struct ublk_device *ub)
 {
@@ -3149,7 +3200,7 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
 			goto out_put_cdev;
 	}
 
-	ret = add_disk(disk);
+	ret = device_add_disk(NULL, disk, ublk_attr_groups);
 	if (ret)
 		goto out_put_cdev;
 
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 90f47da4f435..b30a0de44b85 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -630,6 +630,10 @@ struct ublk_param_integrity {
 	__u8	pad[5];
 };
 
+struct ublk_param_uuid {
+	__u8	uuid[16];
+};
+
 struct ublk_params {
 	/*
 	 * Total length of parameters, userspace has to set 'len' for both
@@ -645,6 +649,7 @@ struct ublk_params {
 #define UBLK_PARAM_TYPE_DMA_ALIGN       (1 << 4)
 #define UBLK_PARAM_TYPE_SEGMENT         (1 << 5)
 #define UBLK_PARAM_TYPE_INTEGRITY       (1 << 6) /* requires UBLK_F_INTEGRITY */
+#define UBLK_PARAM_TYPE_UUID            (1 << 7)
 	__u32	types;			/* types of parameter included */
 
 	struct ublk_param_basic		basic;
@@ -654,6 +659,7 @@ struct ublk_params {
 	struct ublk_param_dma_align	dma;
 	struct ublk_param_segment	seg;
 	struct ublk_param_integrity	integrity;
+	struct ublk_param_uuid		uuid;
 };
 
 #endif
-- 
2.43.0