Re: [PATCH 04/24] scsi-multipath: introduce scsi_mpath_device_class

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, Feb 25, 2026 at 03:36:07PM +0000, John Garry wrote:
> Introduce a new class for multipathed devices, scsi_mpath_device_class.
> 
> The purpose of this class is for managing the scsi_mpath_head.dev member.
> 
> The naming for the scsi_device structure is in form H:C:I:L,
> where H is host, C is channel, I is ID, and L is lun.
> 
> However, for a multipathed scsi_device, all the naming members may be
> different between member scsi_device's. As such, just use a simple
> single-number naming index for each scsi_mpath_head.
> 
> The sysfs device folder will have links to the scsi_device's so, it will
> be possible to lookup the member scsi_device's.
> 
> An example sysfs entry is as follows:
> # ls -l /sys/class/scsi_mpath_device/0/
> total 0
> drwxr-xr-x    2 root     root             0 Feb 24 11:56 power
> lrwxrwxrwx    1 root     root             0 Feb 24 11:56 subsystem -> ../../../../class/scsi_mpath_device
> -rw-r--r--    1 root     root          4096 Feb 24 11:55 uevent
> -r--r--r--    1 root     root          4096 Feb 24 11:56 wwid
> # cat /sys/class/scsi_mpath_device/0/wwid
> naa.600140505200a986f0043c9afa1fd077
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>  drivers/scsi/scsi_multipath.c | 67 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
> index 49316269fad8e..05af178921cb4 100644
> --- a/drivers/scsi/scsi_multipath.c
> +++ b/drivers/scsi/scsi_multipath.c
> @@ -85,6 +85,69 @@ static int scsi_mpath_unique_lun_id(struct scsi_device *sdev)
>  	return 0;
>  }
>  
> +static void scsi_mpath_delete_head(struct scsi_mpath_head *scsi_mpath_head)
> +{
> +	mutex_lock(&scsi_mpath_heads_lock);
> +	list_del_init(&scsi_mpath_head->entry);
> +	mutex_unlock(&scsi_mpath_heads_lock);
> +}
> +
> +static void scsi_mpath_head_release(struct device *dev)
> +{
> +	struct scsi_mpath_head *scsi_mpath_head =
> +		container_of(dev, struct scsi_mpath_head, dev);
> +	struct mpath_head *mpath_head = scsi_mpath_head->mpath_head;
> +
> +	scsi_mpath_delete_head(scsi_mpath_head);
> +	ida_free(&scsi_multipath_dev_ida, scsi_mpath_head->index);
> +	mpath_put_head(mpath_head);
> +	kfree(scsi_mpath_head);
> +}
> +
> +static ssize_t scsi_mpath_device_wwid_show(struct device *dev,
> +			struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct scsi_mpath_head *scsi_mpath_head =
> +		container_of(dev, struct scsi_mpath_head, dev);
> +
> +	return sysfs_emit(buf, "%s\n", scsi_mpath_head->wwid);
> +}
> +
> +static DEVICE_ATTR(wwid, S_IRUGO, scsi_mpath_device_wwid_show, NULL);
> +
> +static struct attribute *scsi_mpath_device_attrs[] = {
> +	&dev_attr_wwid.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group scsi_mpath_device_attrs_group = {
> +	.attrs = scsi_mpath_device_attrs,
> +};
> +
> +static bool scsi_multipath_sysfs_group_visible(struct kobject *kobj)
> +{
> +	return true;
> +}
> +
> +static bool scsi_multipath_sysfs_attr_visible(struct kobject *kobj,
> +		struct attribute *attr, int n)

The return for this is actually a umode_t.

> +{
> +	return false;
> +}
> +DEFINE_SYSFS_GROUP_VISIBLE(scsi_multipath_sysfs)

Nitpick again: This could just use DEFINE_SIMPLE_SYSFS_GROUP_VISIBLE()
Also, this code would make more sense in the next patch.

-Ben

> +
> +const struct attribute_group *scsi_mpath_device_groups[] = {
> +	&scsi_mpath_device_attrs_group,
> +	NULL
> +};
> +
> +static const struct class scsi_mpath_device_class = {
> +	.name = "scsi_mpath_device",
> +	.dev_groups = scsi_mpath_device_groups,
> +	.dev_release = scsi_mpath_head_release,
> +};
> +
>  static int scsi_multipath_sdev_init(struct scsi_device *sdev)
>  {
>  	struct Scsi_Host *shost = sdev->host;
> @@ -129,6 +192,7 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
>  		goto out_put_head;
>  
>  	device_initialize(&scsi_mpath_head->dev);
> +	scsi_mpath_head->dev.class = &scsi_mpath_device_class;
>  	ret = dev_set_name(&scsi_mpath_head->dev, "%d", scsi_mpath_head->index);
>  	if (ret) {
>  		put_device(&scsi_mpath_head->dev);
> @@ -294,11 +358,12 @@ EXPORT_SYMBOL_GPL(scsi_mpath_put_head);
>  
>  int __init scsi_multipath_init(void)
>  {
> -	return 0;
> +	return class_register(&scsi_mpath_device_class);
>  }
>  
>  void __exit scsi_multipath_exit(void)
>  {
> +	class_unregister(&scsi_mpath_device_class);
>  }
>  
>  MODULE_LICENSE("GPL");
> -- 
> 2.43.5