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

On Feb 25, 2013, at 5:12 PM, Greg KH [off-list ref] wrote:

On Fri, Feb 22, 2013 at 10:14:49AM +1030, Rusty Russell wrote:

quoted

Milos Vyletel [off-list ref] writes:

quoted

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?

quoted

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

What bug does it fix?

It is not really a bug but it definitely is useful enhancement to have in stable too. I
can imagine lots of people can benefit from this.

Milos

thanks,

greg k-h

quoted

Cheers,
Rusty.

quoted

Signed-off-by: Milos Vyletel <redacted>
---
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