Re: [PATCH 1/2] nvme: add 'fail_if_no_path' sysfs attribute

[Minwoo Im <minwoo.im.dev@gmail.com>]

On 21-02-23 12:59:21, Hannes Reinecke wrote:
> In some setups like RAID or cluster we need to return an I/O error
> once all paths are unavailable to allow the upper layers to start
> their own error recovery (like redirecting I/O to other mirrors).
> This patch adds a sysfs attribute 'fail_if_no_path' to allow the
> admin to enable that behaviour instead of the current 'queue until
> a path becomes available' policy.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/nvme/host/core.c      |  5 ++++
>  drivers/nvme/host/multipath.c | 43 +++++++++++++++++++++++++++++++++--
>  drivers/nvme/host/nvme.h      |  2 ++
>  3 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 4de6a3a13575..2fb3ecc0c53b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3464,6 +3464,7 @@ static struct attribute *nvme_ns_id_attrs[] = {
>  #ifdef CONFIG_NVME_MULTIPATH
>  	&dev_attr_ana_grpid.attr,
>  	&dev_attr_ana_state.attr,
> +	&dev_attr_fail_if_no_path.attr,
>  #endif
>  	NULL,
>  };
> @@ -3494,6 +3495,10 @@ static umode_t nvme_ns_id_attrs_are_visible(struct kobject *kobj,
>  		if (!nvme_ctrl_use_ana(nvme_get_ns_from_dev(dev)->ctrl))
>  			return 0;
>  	}
> +	if (a == &dev_attr_fail_if_no_path.attr) {
> +		if (dev_to_disk(dev)->fops == &nvme_bdev_ops)
> +			return 0;
> +	}
>  #endif
>  	return a->mode;
>  }
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 0696319adaf6..d5773ea105b1 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -283,10 +283,18 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>  			continue;
>  		switch (ns->ctrl->state) {
>  		case NVME_CTRL_LIVE:
> +			if (!test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH,
> +				      &head->flags))
> +				return true;
> +			if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
> +			    ns->ana_state != NVME_ANA_PERSISTENT_LOSS)
> +				return true;

It looks like it needs to prevent fallthru here with return false.  It
causes following warning:

  drivers/nvme/host/multipath.c: In function ‘nvme_available_path’:
  drivers/nvme/host/multipath.c:289:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    289 |    if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
        |       ^
  drivers/nvme/host/multipath.c:292:3: note: here
    292 |   case NVME_CTRL_RESETTING:
        |   ^~~~


diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index f995b8234622..d692eab3d483 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -289,6 +289,7 @@ static bool nvme_available_path(struct nvme_ns_head *head)
                        if (ns->ana_state != NVME_ANA_INACCESSIBLE &&
                            ns->ana_state != NVME_ANA_PERSISTENT_LOSS)
                                return true;
+                       return false;
                case NVME_CTRL_RESETTING:

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