linux-kernel - Re: [PATCH v2 3/3] nvme: fire discovery log page change events to userspace

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Date:   Fri, 30 Aug 2019 11:08:19 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-nvme@...ts.infradead.org,
        Keith Busch <keith.busch@...el.com>,
        James Smart <james.smart@...adcom.com>,
        linux-kernel@...r.kernel.org, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH v2 3/3] nvme: fire discovery log page change events to
 userspace


>>> Yes we do, userspace should use it to order events.  Does udev not
>>> handle that properly today?
>>
>> The problem is not ordering of events, its really about the fact that
>> the chardev can be removed and reallocated for a different controller
>> (could be a completely different discovery controller) by the time
>> that userspace handles the event.
> 
> The same is generally true for lot of kernel devices.  We could reduce
> the chance by using the idr cyclic allocator.

Well, it was raised by Hannes and James, so I'll ask them respond here
because I don't mind having it this way. I personally think that this
is a better approach than having a cyclic idr allocator. In general, I
don't necessarily think that this is a good idea to have cyclic
controller enumerations if we don't absolutely have to...