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

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Date:	Tue, 26 Feb 2013 14:05:47 +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 02/25/2013 10:54 PM, Milos Vyletel wrote:
> > ----- 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.
> 
> Well, which kernel version are you looking at.
> media_change_notify_thread() is gone back in 2010. See commit: dddd9dc340.
>

Oh, you're right. I was looking at the rhel 6.3 kernel (2.6.32-279.19.1.el6)
before I switched to upstream branch and did the changes. Sorry about the
confusion.

Milos
 
> >>
> >>>  	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.
> 
> Turned on the debug info and looked into it again. It works for me now
> and the udev event is seen.
> 
> Tested-by: Asias He <asias@...hat.com>
> 
> > [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
> > 
> 
> 
> --
> Asias
> 
--
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