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

[Asias He]

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@xxxxxx>
>>> ---
>>>  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.

>>
>>>  	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@xxxxxxxxxx>

> [root@host ~]# 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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