linux-kernel - Re: [PATCH] virtio-blk: emit udev event when device is resized

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Message-ID: <20130225221238.GA10575@kroah.com>
Date:	Mon, 25 Feb 2013 14:12:38 -0800
From:	Greg KH <greg@...ah.com>
To:	Rusty Russell <rusty@...tcorp.com.au>, Kay Sievers <kay@...y.org>
Cc:	Milos Vyletel <milos.vyletel@....cz>, linux-kernel@...r.kernel.org,
	linux-hotplug@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, mst@...hat.com
Subject: Re: [PATCH] virtio-blk: emit udev event when device is resized

On Fri, Feb 22, 2013 at 10:14:49AM +1030, Rusty Russell wrote:
> Milos Vyletel <milos.vyletel@....cz> writes:
> 
> > When virtio-blk device is resized from host (using block_resize from QEMU) emit
> > KOBJ_CHANGE uevent to notify guest about such change. This allows user to have
> > custom udev rules which would take whatever action if such event occurs. As a
> > proof of concept I've created simple udev rule that automatically resize
> > filesystem on virtio-blk device.
> >
> > ACTION=="change", KERNEL=="vd*", \
> >         ENV{RESIZE}=="1", \
> >         ENV{ID_FS_TYPE}=="ext[3-4]", \
> >         RUN+="/sbin/resize2fs /dev/%k"
> > ACTION=="change", KERNEL=="vd*", \
> >         ENV{RESIZE}=="1", \
> >         ENV{ID_FS_TYPE}=="LVM2_member", \
> >         RUN+="/sbin/pvresize /dev/%k"
> 
> This looks fine to me, but I like to check with Greg before adding udev
> callouts.... Greg?

Hm, I thought we were frowning apon running binaries from udev rules
these days, especially ones that might have big consequences (like
resizing a disk image) like this.

Kay, am I right?

We already emit KOBJECT_CHANGE events when block devices change, from
within the block core code.  Why is the patch below needed instead of
using these events that are already generated?  How are virtio block
devices special?

> BTW, if this is good, it's good for stable IMHO.

What bug does it fix?

thanks,

greg k-h

> Cheers,
> Rusty.
> 
> > Signed-off-by: Milos Vyletel <milos.vyletel@....cz>
> > ---
> >  drivers/block/virtio_blk.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 8ad21a2..5990382 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -539,6 +539,8 @@ static void virtblk_config_changed_work(struct work_struct *work)
> >  	struct virtio_device *vdev = vblk->vdev;
> >  	struct request_queue *q = vblk->disk->queue;
> >  	char cap_str_2[10], cap_str_10[10];
> > +	char event[] = "RESIZE=1";
> > +	char *envp[] = { event, NULL };
> >  	u64 capacity, size;
> >  
> >  	mutex_lock(&vblk->config_lock);
> > @@ -568,6 +570,7 @@ static void virtblk_config_changed_work(struct work_struct *work)
> >  
> >  	set_capacity(vblk->disk, capacity);
> >  	revalidate_disk(vblk->disk);
> > +	kobject_uevent_env(&disk_to_dev(vblk->disk)->kobj, KOBJ_CHANGE, envp);
> >  done:
> >  	mutex_unlock(&vblk->config_lock);
> >  }
> > -- 
> > 1.7.1
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