linux-kernel - Re: [PATCH v2] nbd: Issue a uevent when disconnecting

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Date:	Fri, 5 Feb 2016 10:42:41 +0100
From:	Wouter Verhelst <w@...r.be>
To:	Markus Pargmann <mpa@...gutronix.de>
Cc:	nbd-general <nbd-general@...ts.sourceforge.net>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] nbd: Issue a uevent when disconnecting

Hi Markus,

On Fri, Feb 05, 2016 at 10:03:41AM +0100, Markus Pargmann wrote:
> Hi Wouter,
> 
> On Tuesday, February 02, 2016 04:27:00 PM Wouter Verhelst wrote:
> > There already is a uevent by default when closing a device upon connect
> > of the device. However, the same isn't true on disconnect.
> > 
> > This makes it hard for userspace to keep track of whether a device is
> > connected, since we are notified when the connection is created, but not
> > when it is removed again.
> > 
> > Explicitly issue a "change" uevent to remedy.
> > 
> > [v2: incorporate feedback from udev maintainer and make sure that we
> > issue a uevent upon connect as well as disconnect, rather than connect
> > only]
> 
> The systemd people had the same feedback.

Well, the systemd people and the udev people are the same people these
days :-)

> Basically the device is not marked as ready until a uevent is received. My
> idea was to use the size property consistently. If the device is connected
> the size is correctly changed and a uevent is created. On disconnect the size
> is set to 0 with another uevent.
> 
> Does this work for you as well? I will send the patch as reply.

Sure. What matters most is that the uevent is done; how it's done, less
so.

I should add that this was meant to go with systemd #2422. I wasn't
aware of #358, or I would've talked to you more :-)

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