Date:	Mon, 25 Feb 2013 15:54:56 +0100 (CET)
From:	Milos Vyletel <milos.vyletel@....cz>
To:	Asias He <asias@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mst@...hat.com,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio-blk: emit udev event when device is resized

----- Original Message -----
> On 02/22/2013 03:02 AM, Milos Vyletel wrote:
> > 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"
> > 
> > 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 };
> 
> event is not used again. Why not just
> 
> char *envp[] = { "RESIZE=1", NULL };
> 

You're right. This works too. I was looking at other modules in kernel
how they do it and this was commonly used. Take a look at block/genhd.c
media_change_notify_thread() function which does similar thing.

> 
> >  	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);
> >  }
> > 
> 
> I tried the following with your automatically resize udev rules.
> 
> (qemu) block_resize vd0 500
> Check the fs size in guest, it is 500Mb
> 
> (qemu) block_resize vd0 1200
> Check the fs size in guest, it is still 500Mb
> 
> Can you try resizing multiple times? Does it work?

Yep, works for me. After each block_resize call I get udev event. I
was running udevadm monitor at that time. I've also tried running
udevd in debug mode and even if I try to bump size twice in a row
I get two separate udev events and resize2fs is triggered. 

[root@...t ~]# lvresize -f -L +100M /dev/vgguests/evd2 && \
virsh blockresize resize vdb 1 && \
lvresize -f -L +100M /dev/vgguests/evd2 && \
virsh blockresize resize vdb 1
  Rounding size to boundary between physical extents: 128.00 MiB
  Extending logical volume evd2 to 31.38 GiB
  Logical volume evd2 successfully resized
Block device 'vdb' is resized
  Rounding size to boundary between physical extents: 128.00 MiB
  Extending logical volume evd2 to 31.50 GiB
  Logical volume evd2 successfully resized
Block device 'vdb' is resized

On guest I get this (from udevd --debug)
...
1361804003.724025 [4438] util_run_program: '/sbin/resize2fs /dev/vdb' started
1361804003.725215 [4438] util_run_program: '/sbin/resize2fs' (stderr) 'resize2fs 1.41.12 (17-May-2010)'
1361804004.129329 [4437] event_queue_insert: seq 2073 queued, 'change' 'block'
1361804006.577235 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'Filesystem at /dev/vdb is mounted on /mnt/backup; on-line resizing required'
1361804006.577251 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'old desc_blocks = 2, new_desc_blocks = 2'
1361804006.577254 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'Performing an on-line resize of /dev/vdb to 8224768 (4k) blocks.'
1361804006.577257 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'The filesystem on /dev/vdb is now 8224768 blocks long.'
1361804006.577260 [4438] util_run_program: '/sbin/resize2fs' (stdout) ''
1361804006.577544 [4438] util_run_program: '/sbin/resize2fs /dev/vdb' returned with exitcode 0
...
1361804006.702659 [4438] util_run_program: '/sbin/resize2fs /dev/vdb' started
1361804006.703841 [4438] util_run_program: '/sbin/resize2fs' (stderr) 'resize2fs 1.41.12 (17-May-2010)'
1361804009.343332 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'Filesystem at /dev/vdb is mounted on /mnt/backup; on-line resizing required'
1361804009.343351 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'old desc_blocks = 2, new_desc_blocks = 2'
1361804009.343356 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'Performing an on-line resize of /dev/vdb to 8257536 (4k) blocks.'
1361804009.343362 [4438] util_run_program: '/sbin/resize2fs' (stdout) 'The filesystem on /dev/vdb is now 8257536 blocks long.'
1361804009.343367 [4438] util_run_program: '/sbin/resize2fs' (stdout) ''
1361804009.343727 [4438] util_run_program: '/sbin/resize2fs /dev/vdb' returned with exitcode 0
1361804009.343740 [4438] udev_watch_begin: adding watch on '/dev/vdb'

Milos
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