[PATCH V2] nvme: introduce nvme_disk_is_ns_head helper

[PATCH V2] nvme: introduce nvme_disk_is_ns_head helper

[Guixin Liu]

We currently rely on gendisk's file operations (fops) to distinguish
between a namespace head (ns_head) and a regular namespace. To enhance
code readability, introduce a helper function.
Additionally, we must ensure that the device is not an ns_head before
calling nvme_get_ns_from_dev(). To enforce this, add a WARN_ON check
within the nvme_get_ns_from_dev().

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
Changes from v1 to v2:
- change helper name from nvme_gendisk_is_ns_head to
  nvme_disk_is_ns_head.
- remove redundant comment.

 drivers/nvme/host/nvme.h  | 12 +++++++++++-
 drivers/nvme/host/pr.c    |  2 +-
 drivers/nvme/host/sysfs.c |  9 +++++----
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index e7411dac00f7..ceddf01b2d66 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -1029,9 +1029,19 @@ static inline int nvme_update_zone_info(struct nvme_ns *ns, unsigned lbaf)
 }
 #endif
 
+static inline bool nvme_disk_is_ns_head(struct gendisk *disk)
+{
+	if (disk->fops == &nvme_ns_head_ops)
+		return true;
+	return false;
+}
+
 static inline struct nvme_ns *nvme_get_ns_from_dev(struct device *dev)
 {
-	return dev_to_disk(dev)->private_data;
+	struct gendisk *disk = dev_to_disk(dev);
+
+	WARN_ON(nvme_disk_is_ns_head(disk));
+	return disk->private_data;
 }
 
 #ifdef CONFIG_NVME_HWMON
diff --git a/drivers/nvme/host/pr.c b/drivers/nvme/host/pr.c
index 391b1465ebfd..fc3eed00f9ff 100644
--- a/drivers/nvme/host/pr.c
+++ b/drivers/nvme/host/pr.c
@@ -98,7 +98,7 @@ static int nvme_send_pr_command(struct block_device *bdev,
 		struct nvme_command *c, void *data, unsigned int data_len)
 {
 	if (IS_ENABLED(CONFIG_NVME_MULTIPATH) &&
-	    bdev->bd_disk->fops == &nvme_ns_head_ops)
+	    nvme_disk_is_ns_head(bdev->bd_disk))
 		return nvme_send_ns_head_pr_command(bdev, c, data, data_len);
 
 	return nvme_send_ns_pr_command(bdev->bd_disk->private_data, c, data,
diff --git a/drivers/nvme/host/sysfs.c b/drivers/nvme/host/sysfs.c
index c6b7fbd4d34d..925042ca728b 100644
--- a/drivers/nvme/host/sysfs.c
+++ b/drivers/nvme/host/sysfs.c
@@ -39,10 +39,10 @@ static inline struct nvme_ns_head *dev_to_ns_head(struct device *dev)
 {
 	struct gendisk *disk = dev_to_disk(dev);
 
-	if (disk->fops == &nvme_bdev_ops)
-		return nvme_get_ns_from_dev(dev)->head;
-	else
+	if (nvme_disk_is_ns_head(disk))
 		return disk->private_data;
+	else
+		return nvme_get_ns_from_dev(dev)->head;
 }
 
 static ssize_t wwid_show(struct device *dev, struct device_attribute *attr,
@@ -148,7 +148,8 @@ static umode_t nvme_ns_id_attrs_are_visible(struct kobject *kobj,
 	}
 #ifdef CONFIG_NVME_MULTIPATH
 	if (a == &dev_attr_ana_grpid.attr || a == &dev_attr_ana_state.attr) {
-		if (dev_to_disk(dev)->fops != &nvme_bdev_ops) /* per-path attr */
+		/* per-path attr */
+		if (nvme_disk_is_ns_head(dev_to_disk(dev)))
 			return 0;
 		if (!nvme_ctrl_use_ana(nvme_get_ns_from_dev(dev)->ctrl))
 			return 0;
-- 
2.43.0

Re: [PATCH V2] nvme: introduce nvme_disk_is_ns_head helper

[Christoph Hellwig]

On Wed, Dec 27, 2023 at 05:05:25PM +0800, Guixin Liu wrote:
>  
> +static inline bool nvme_disk_is_ns_head(struct gendisk *disk)
> +{
> +	if (disk->fops == &nvme_ns_head_ops)
> +		return true;
> +	return false;

I would still keep it simple here:

	return disk->fops == &nvme_ns_head_ops;

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH V2] nvme: introduce nvme_disk_is_ns_head helper

[Sagi Grimberg]

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>