Re: [PATCHv3] nvme: generate uevent once a multipath namespace is operational again

[Hannes Reinecke <hare@suse.de>]

On 5/18/21 9:05 AM, Christoph Hellwig wrote:
> On Tue, May 18, 2021 at 08:59:09AM +0200, Hannes Reinecke wrote:
>>> I asked this on v1, is this only needed for mpath devices?
>>
>> Yes; we need to send the KOBJ_CHANGE event on the mpath device as it's not
>> backed by hardware. The only non-multipathed devices I've seen so far are
>> PCI devices where events are generated by the PCI device itself.
> 
> Which really goes back to my repeated request to add a comment to the
> code to document why we need this uevent.  It surely looks out of place
> and it seems Hannes can tell a story of why it is required.  I'd really
> like to see that story next to the call.
> 
The issue here is that MD RAID will detect an I/O failure once the last 
path drops and fail the namespace, but will continue to work in degraded 
mode.
But upon reconnect the namespace will stay failed, and MD RAID will 
continue to operate in degraded mode even though the path it available 
again.
And without this patch there is no programmatic way on how MD RAID could 
re-assemble the degraded array as there is no indicator that the 
namespace is usable again.

Is this the information you are looking for?

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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