linux-kernel - Re: [PATCH] virtio-blk: Generate uevent after attribute available

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Date:	Wed, 29 Jun 2016 09:24:15 +0800
From:	Fam Zheng <famz@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio-blk: Generate uevent after attribute available

On Tue, 06/28 04:45, Christoph Hellwig wrote:
> On Tue, Jun 28, 2016 at 10:39:15AM +0800, Fam Zheng wrote:
> > Userspace listens to the KOBJ_ADD uevent generated in add_disk. At that
> > point we haven't created the serial attribute file, therefore depending
> > on how fast udev reacts, the /dev/disk/by-id/ entry doesn't always get
> > created.
> > 
> > This race condition can be easily reproduced by hot plugging a number of
> > virtio-blk disks.
> > 
> > Also in systemd, there used to be a related workaround in udev rules
> > called 'WAIT_FOR="serial"', but it is removed in later versions.
> > 
> > Now let's generate a KOBJ_CHANGE event after the attributes are ready.
> 
> The same race is present in other drivers as well, e.g. nvme.  Please
> find a way to make this work properly without needing to hack every
> driver to send events manually.

OK, I'll take a look today!

Fam