On Thu, Feb 08, 2024 at 02:32:11PM -0500, Stefan Hajnoczi wrote:
> Alyssa Ross <hi@xxxxxxxxx> requested that virtiofs notifies userspace
> when filesytems become available. This can be used to detect when a
> filesystem with a given tag is hotplugged, for example. uevents allow
> userspace to detect changes without resorting to polling.
>
> The tag is included as a uevent property so it's easy for userspace to
> identify the filesystem in question even when the sysfs directory goes
> away during removal.
>
> Here are example uevents:
>
> # udevadm monitor -k -p
>
> KERNEL[111.113221] add /fs/virtiofs/2 (virtiofs)
> ACTION=add
> DEVPATH=/fs/virtiofs/2
> SUBSYSTEM=virtiofs
> TAG=test
>
> KERNEL[165.527167] remove /fs/virtiofs/2 (virtiofs)
> ACTION=remove
> DEVPATH=/fs/virtiofs/2
> SUBSYSTEM=virtiofs
> TAG=test
>
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> ---
> fs/fuse/virtio_fs.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 28e96b7cde00..18a8f531e5d4 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -270,6 +270,17 @@ static void virtio_fs_start_all_queues(struct virtio_fs *fs)
> }
> }
>
> +static void virtio_fs_uevent(struct virtio_fs *fs, enum kobject_action action)
> +{
> + char tag_str[sizeof("TAG=") +
> + sizeof_field(struct virtio_fs_config, tag) + 1];
> + char *envp[] = {tag_str, NULL};
> +
> + snprintf(tag_str, sizeof(tag_str), "TAG=%s", fs->tag);
> +
> + kobject_uevent_env(&fs->kobj, action, envp);
> +}
> +
> /* Add a new instance to the list or return -EEXIST if tag name exists*/
> static int virtio_fs_add_instance(struct virtio_device *vdev,
> struct virtio_fs *fs)
> @@ -309,6 +320,8 @@ static int virtio_fs_add_instance(struct virtio_device *vdev,
>
> mutex_unlock(&virtio_fs_mutex);
>
> + virtio_fs_uevent(fs, KOBJ_ADD);
Why do you have to explicitly ask for the event? Doesn't sysfs trigger
this for you automatically? Set the kset uevent callback for this,
right?
thanks,
greg k-h
