Re: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree

Cornelia Huck
2019-08-27T10:47:18Z

On Mon, 26 Aug 2019 15:41:18 -0500
Parav Pandit <parav@mellanox.com> wrote:

> Expose mdev alias as string in a sysfs tree so that such attribute can
> be used to generate netdevice name by systemd/udev or can be used to
> match other kernel objects based on the alias of the mdev.

What about

"Expose the optional alias for an mdev device as a sysfs attribute.
This way, userspace tools such as udev may make use of the alias, for
example to create a netdevice name for the mdev."

>
> Signed-off-by: Parav Pandit <parav@mellanox.com>
> ---
> drivers/vfio/mdev/mdev_sysfs.c | 13 +++++++++++++

I think the documentation should be updated as well.

> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c
> index 43afe0e80b76..59f4e3cc5233 100644
> --- a/drivers/vfio/mdev/mdev_sysfs.c
> +++ b/drivers/vfio/mdev/mdev_sysfs.c
> @@ -246,7 +246,20 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
>
> static DEVICE_ATTR_WO(remove);
>
> +static ssize_t alias_show(struct device *device,
> + struct device_attribute *attr, char *buf)
> +{
> + struct mdev_device *dev = mdev_from_dev(device);
> +
> + if (!dev->alias)
> + return -EOPNOTSUPP;

I'm wondering how to make this consumable by userspace in the easiest way.
- As you do now (userspace gets an error when trying to read)?
- Returning an empty value (nothing to see here, move along)?
- Or not creating the attribute at all? That would match what userspace
sees on older kernels, so it needs to be able to deal with that
anyway.

> +
> + return sprintf(buf, "%s\n", dev->alias);
> +}
> +static DEVICE_ATTR_RO(alias);
> +
> static const struct attribute *mdev_device_attrs[] = {
> + &dev_attr_alias.attr,
> &dev_attr_remove.attr,
> NULL,
> };