Re: [PATCH] nvme: honour O_NONBLOCK during resetting

[Hannes Reinecke <hare@suse.de>]

On 11/16/21 2:40 AM, Chaitanya Kulkarni wrote:
> On 11/11/2021 2:59 AM, Hannes Reinecke wrote:
>> When opening a controller device node we should honour the O_NONBLOCK
>> flag to allow the device to be openend even if it's in state 'resetting'
>> or 'connecting'. This allows user-space applications to use a call to 'open'
>> to figure out if the controller is present, even if it's currently
>> undergoing a reset.
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.de>
> 
> Will resetting and connecting ever result is deleting the controller due
> to error cases present in that path ?
> 
Yes, of course this might happen.

> If yes then application will have handle for something that might
> go away in the future, should allow such a semantic ?
> I am not sure I follow.
Even today an application can open the device, and even now error 
recovery can result in the device now going away.
And even today it'll be possible that error recovery sets the device
to 'RESETTING' after the open call.

So I don't think that we need to treat things special because of this patch.

Whether or not the call to nvme_dev_ioctl() should be protected by an 
explicit state check is a different point, though; that does have some 
benefits seeing that the timing between open() and ioctl() is pretty 
much up to the application, and hence we shouldn't assume that the state 
doesn't change in between.
But really it should be done in a different patch.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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