Re: [PATCHv2] nvme: add 'fail_if_no_path' sysfs attribute

[Hannes Reinecke <hare@suse.de>]

On 2/22/21 11:15 AM, Minwoo Im wrote:
> On 21-02-22 07:41:55, Hannes Reinecke wrote:
>> In some setups like RAID 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 | 38 +++++++++++++++++++++++++++++++++--
>>   drivers/nvme/host/nvme.h      |  2 ++
>>   3 files changed, 43 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 5c1ec3bfb9d3..ef20029a46b2 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -3466,6 +3466,7 @@ 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,
>>   };
>> @@ -3496,6 +3497,10 @@ 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..35ed2f6d431b 100644
>> --- a/drivers/nvme/host/multipath.c
>> +++ b/drivers/nvme/host/multipath.c
>> @@ -283,10 +283,13 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>>   			continue;
>>   		switch (ns->ctrl->state) {
>>   		case NVME_CTRL_LIVE:
>> +			return true;
> 
> Hello Hannes,
> 
> May I ask there's any reason why LIVE state is not covered by the sysfs
> attribute that this patch introduced ?  Wouldn't it be possible to have
> no available paths (inaccessible) in LIVE state ?
> 
> Thanks! :)
> 
Ah, you mean ANA inaccessible?
Hmm. Technically, yes, this might be the case.
I'll be updating the patch.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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