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

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Message-ID: <20190826065639.GA11036@lst.de>
Date:   Mon, 26 Aug 2019 08:56:39 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Christoph Hellwig <hch@....de>, linux-nvme@...ts.infradead.org,
        Keith Busch <keith.busch@...el.com>,
        James Smart <james.smart@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 3/3] nvme: fire discovery log page change events to
 userspace

On Thu, Aug 22, 2019 at 12:10:23PM -0700, Sagi Grimberg wrote:
>> You are correct that this information can be derived from sysfs, but the
>> main reason why we add these here, is because in udev rule we can't
>> just go ahead and start looking these up and parsing these..
>>
>> We could send the discovery aen with NVME_CTRL_NAME and have
>> then have systemd run something like:
>>
>> nvme connect-all -d nvme0 --sysfs
>>
>> and have nvme-cli retrieve all this stuff from sysfs?
>
> Actually that may be a problem.
>
> There could be a hypothetical case where after the event was fired
> and before it was handled, the discovery controller went away and
> came back again with a different controller instance, and the old
> instance is now a different discovery controller.
>
> This is why we need this information in the event. And we verify this
> information in sysfs in nvme-cli.

Well, that must be a usual issue with uevents, right?  Don't we usually
have a increasing serial number for that or something?

If I look at other callers of kobject_uevent_env none throws in such
a huge context.

>
> Makes sense?
---end quoted text---