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

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Date:	Fri, 12 Feb 2016 15:49:32 +0100
From:	Markus Pargmann <mpa@...gutronix.de>
To:	Wouter Verhelst <w@...r.be>
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 Wouter,

On Friday, February 05, 2016 10:42:41 AM Wouter Verhelst wrote:
> 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 :-)

Ah I see, thanks.

I wrote some tests yesterday to ensure that I don't break other things
with the new size calculations. I will send the pull request with this
patch for 4.6.

Best Regards,

Markus

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