Re: [PATCH v2] nvme-multipath: add fail_if_no_path sysfs attribute

[Nilay Shroff]

On 9/18/26 4:46 AM, Krishna Iyer wrote:
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 3d46c4f28a47..23aeb1737ab5 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -499,6 +499,8 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
>   static bool nvme_available_path(struct nvme_ns_head *head)
>   	__must_hold_shared(&head->srcu)
>   {
> +	bool fail_if_no_path = test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH,
> +					&head->flags);
>   	struct nvme_ns *ns;
>   
>   	if (!test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags))
> @@ -510,14 +512,25 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>   			continue;
>   		switch (nvme_ctrl_state(ns->ctrl)) {
>   		case NVME_CTRL_LIVE:
> +			if (fail_if_no_path &&
> +			    (ns->ana_state == NVME_ANA_INACCESSIBLE ||
> +			     ns->ana_state == NVME_ANA_PERSISTENT_LOSS))
> +				continue;
I think we have helper nvme_state_is_live() which could be used here.
 [...]

> +static ssize_t fail_if_no_path_store(struct device *dev,
> +		struct device_attribute *attr, const char *buf, size_t count)
> +{
> +	struct gendisk *disk = dev_to_disk(dev);
> +	struct nvme_ns_head *head = disk->private_data;
> +	bool enable;
> +	int ret;
> +
> +	ret = kstrtobool(buf, &enable);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (enable)
> +		set_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags);
> +	else
> +		clear_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags);
> +
> +	/*
> +	 * Ensure that update to NVME_NSHEAD_FAIL_IF_NO_PATH is seen
> +	 * by its reader.
> +	 */
> +	synchronize_srcu(&head->srcu);
> +
> +	/* Make already-queued I/O re-evaluate path availability. */
> +	if (enable)
> +		kblockd_schedule_work(&head->requeue_work);
> +
If the user stores the same value as the current setting, we could
return immediately instead of waiting for synchronize_srcu() and
scheduling the requeue work.

Otherwise changes look good.

Thanks,
--Nilay