Re: [PATCH 7/8] scsi: scsi-multipath: Issue a periodic TUR per path

[Hannes Reinecke <hare@suse.com>]

On 3/10/26 12:49, John Garry wrote:
> To allow the initiator know of any ALUA configuration changes, issue a
> periodic TUR.
> 
> multipathd does something similar for dm-multipath in terms of issuing
> a periodic read per path.
> 
> The purpose of the TUR is that the target can update UA info in the TUR
> response and the INI can handle it, but currently we don't for SCSI
> multipath.
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>   drivers/scsi/scsi_multipath.c | 36 +++++++++++++++++++++++++++++++++++
>   include/scsi/scsi_multipath.h |  1 +
>   2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
> index 0c34b1151f5bf..2b916c7af4bd7 100644
> --- a/drivers/scsi/scsi_multipath.c
> +++ b/drivers/scsi/scsi_multipath.c
> @@ -4,6 +4,7 @@
>    *
>    */
>   
> +#include <linux/kthread.h>
>   #include <scsi/scsi_alua.h>
>   #include <scsi/scsi_cmnd.h>
>   #include <scsi/scsi_driver.h>
> @@ -124,6 +125,7 @@ static void scsi_mpath_head_release(struct device *dev)
>   		container_of(dev, struct scsi_mpath_head, dev);
>   	struct mpath_head *mpath_head = scsi_mpath_head->mpath_head;
>   
> +	WARN_ON_ONCE(kthread_stop(scsi_mpath_head->kua));
>   	scsi_mpath_delete_head(scsi_mpath_head);
>   	bioset_exit(&scsi_mpath_head->bio_pool);
>   	ida_free(&scsi_multipath_dev_ida, scsi_mpath_head->index);
> @@ -514,6 +516,29 @@ struct mpath_head_template smpdt_pr = {
>   	.device_groups = mpath_device_groups,
>   };
>   
> +static void scsi_mpath_cb_ua_thread(struct mpath_device *mpath_device)
> +{
> +	struct scsi_mpath_device *scsi_mpath_dev =
> +			to_scsi_mpath_device(mpath_device);
> +
> +	if (alua_tur(scsi_mpath_dev->sdev))
> +		sdev_printk(KERN_NOTICE, scsi_mpath_dev->sdev,
> +			    "%s: No target port descriptors found\n",
> +			    __func__);
> +}
> +
> +static int scsi_mpath_ua_thread(void *data)
> +{
> +	struct scsi_mpath_head *scsi_mpath_head = data;
> +
> +	while (!kthread_should_stop()) {
> +		mpath_call_for_all_devices(scsi_mpath_head->mpath_head,
> +			scsi_mpath_cb_ua_thread);
> +		msleep(5000);
> +	}
> +	return 0;
> +}
> +
>   static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
>   {
>   	struct scsi_mpath_head *scsi_mpath_head;
> @@ -548,6 +573,17 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
>   		goto out_free_ida;
>   	}
>   
> +	scsi_mpath_head->kua = kthread_create(scsi_mpath_ua_thread,
> +			scsi_mpath_head, "scsi-multipath-kua-%d",
> +			scsi_mpath_head->index);
> +	if (IS_ERR(scsi_mpath_head->kua)) {
> +		put_device(&scsi_mpath_head->dev);
> +		goto out_free_ida;
> +	}
> +
> +	set_user_nice(scsi_mpath_head->kua, 10);
> +	wake_up_process(scsi_mpath_head->kua);
> +
>   	return scsi_mpath_head;
>   
>   out_free_ida:
> diff --git a/include/scsi/scsi_multipath.h b/include/scsi/scsi_multipath.h
> index 7c7ee2fb7def7..d30f2c41e17de 100644
> --- a/include/scsi/scsi_multipath.h
> +++ b/include/scsi/scsi_multipath.h
> @@ -30,6 +30,7 @@ struct scsi_mpath_head {
>   	struct mpath_head	*mpath_head;
>   	struct device		dev;
>   	int			index;
> +	struct task_struct	*kua;
>   };
>   
>   struct scsi_mpath_device {

Please, don't. We should _not_ go into the business of doing TUR path 
checkers.
Path checkers turned out to be a major issue for multipathing, and
are mostly pointless for things like FC where you get reliable
path information via RSCNs.
Additionally I would advocate for scsi-multipath to be a _simple_
implementation, restricting to the most common scenarios. Namely
implicit ALUA only and reliable fabric notifications.
If you have anything else, fine, use dm-multipath.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.com                               +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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