Linux Virtualization - Feb 2013 - [PATCH] virtio-blk: emit udev event when device is resized

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 at sde.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

Milos Vyletel <milos.vyletel at sde.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?

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

Cheers,
Rusty.
> Signed-off-by: Milos Vyletel <milos.vyletel at sde.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

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 at sde.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 };

>  	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?

-- 
Asias

Milos Vyletel <milos.vyletel at sde.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"
>
> Signed-off-by: Milos Vyletel <milos.vyletel at sde.cz>
OK, I collapsed the event[] line as suggested by Asias, and applied this.

Thanks,
Rusty.

From: Milos Vyletel <milos.vyletel at sde.cz>
Subject: virtio-blk: emit udev event when device is resized

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 at sde.cz>
Tested-by: Asias He <asias at redhat.com>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au> (minor
simplification)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 8ad21a2..922bcb9 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -539,6 +539,7 @@ 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 *envp[] = { "RESIZE=1", NULL };
 	u64 capacity, size;
 
 	mutex_lock(&vblk->config_lock);
@@ -568,6 +569,7 @@ 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);
 }