[PATCH] NVMe: Defer namespace add_disk() until after char device creation

[Keith Busch]

On Fri, 14 Nov 2014, Jens Axboe wrote:
> On 2014-11-04 17:18, Sam Bradshaw wrote:
>> In the current probe flow, each namespace gets an add_disk() then the
>> char device for the controller is registered.  For misbehaving devices
>> or namespace(s) that are not yet ready when add_disk() is called (eg.
>> namespace accesses that return NVME_SC_NS_NOT_READY and are requeued),
>> it can take time to disposition all the accesses.
>> 
>> This change moves add_disk() after the char device is created to give
>> manageability stacks an interface to query as IO flushes out.
>> 
>> (I also considered deferring the nvme_ns_add() to an async context but
>> that requires some sort of mutex between probe and remove to handle the
>> surprise remove during add_disk condition and was messier than this
>> patch)
>
> I'd love to see this get added. You need the control char dev to fixup such 
> bad situations, and it may never get created if we get stuck on trying to 
> setup and probe the block parts.

Would it be much trouble to make "add_disk" non-blocking? If it's not
too bad, then all storage drivers might benefit from that and we don't
have to do things like this in a driver. I haven't really looked into it,
so asking out of curiosity and not a serious suggestion yet.