Re: [PATCH 2/6] virtio: add register_virtio_root_device()

Cornelia Huck
2008-12-11T12:59:39Z

On Wed, 10 Dec 2008 17:45:35 +0000,
Mark McLoughlin <markmc@redhat.com> wrote:

> Add a function to allocate a root device object to group the
> devices from a given virtio implementation.
>
> Also add a 'module' sysfs symlink to allow so that userspace
> can generically determine which virtio implementation a
> device is associated with. This will be used by Fedora
> mkinitrd to generically determine e.g. that virtio_pci is
> needed to mount a given root filesystem.

Nothing about this is really virtio-specific (just as
s390_root_dev_register() is not really s390-specific), and a 'module'
symlink doesn't really hurt in a generic implementation, even if it is
unneeded. I'm voting to put this in some generic, always built-in code
(or have the users select it) so we could also use it from s390.

>
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> ---
> drivers/virtio/virtio.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/virtio.h | 10 ++++++
> 2 files changed, 81 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 018c070..61e6597 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -1,6 +1,7 @@
> #include <linux/virtio.h>
> #include <linux/spinlock.h>
> #include <linux/virtio_config.h>
> +#include <linux/err.h>
>
> /* Unique numbering for virtio devices. */
> static unsigned int dev_index;
> @@ -200,6 +201,76 @@ void unregister_virtio_device(struct virtio_device *dev)
> }
> EXPORT_SYMBOL_GPL(unregister_virtio_device);
>
> +/* A root device for virtio devices from a given backend. This makes them
> + * appear as /sys/devices/{name}/0,1,2 not /sys/devices/0,1,2. It also allows
> + * us to have a /sys/devices/{name}/module symlink to the backend module. */
> +struct virtio_root_device
> +{
> + struct device dev;
> + struct module *owner;
> +};
> +
> +static struct virtio_root_device *to_virtio_root(struct device *dev)
> +{
> + return container_of(dev, struct virtio_root_device, dev);
> +}
> +
> +static void release_virtio_root_device(struct device *dev)
> +{
> + struct virtio_root_device *root = to_virtio_root(dev);
> + if (root->owner)
> + sysfs_remove_link(&root->dev.kobj, "module");
> + kfree(root);
> +}

Can this code be a module? If yes, move the release callback to a
build-in as there are races with release-functions in modules.

> +
> +struct device *__register_virtio_root_device(const char *name,
> + struct module *owner)
> +{
> + struct virtio_root_device *root;
> + int err = -ENOMEM;
> +
> + root = kzalloc(sizeof(struct virtio_root_device), GFP_KERNEL);
> + if (!root)
> + goto out;
> +
> + err = dev_set_name(&root->dev, name);
> + if (err)
> + goto free_root;
> +
> + err = device_register(&root->dev);
> + if (err)
> + goto free_root;
> +
> + root->dev.parent = NULL;
> + root->dev.release = release_virtio_root_device;

You must set ->release before calling device_register(), and setting
the parent is unneeded.

> +
> + if (owner) {
> + struct module_kobject *mk = &owner->mkobj;
> +
> + err = sysfs_create_link(&root->dev.kobj, &mk->kobj, "module");
> + if (err) {
> + device_unregister(&root->dev);
> + return ERR_PTR(err);
> + }
> +
> + root->owner = owner;
> + }
> +
> + return &root->dev;
> +
> +free_root:
> + kfree(root);

You need to call device_put() if you called device_register().

> +out:
> + return ERR_PTR(err);
> +}
> +EXPORT_SYMBOL_GPL(__register_virtio_root_device);
> +
> +void unregister_virtio_root_device(struct device *root)
> +{
> + device_unregister(root);
> +}
> +EXPORT_SYMBOL_GPL(unregister_virtio_root_device);
> +
> static int virtio_init(void)
> {
> if (bus_register(&virtio_bus) != 0)
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 06005fa..66e6c67 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -93,6 +93,16 @@ struct virtio_device
> int register_virtio_device(struct virtio_device *dev);
> void unregister_virtio_device(struct virtio_device *dev);
>
> +/* A root device is a dummy device used to group virtio devices from each
> + * implementation. */
> +struct device *__register_virtio_root_device(const char *name,
> + struct module *owner);
> +static inline struct device *register_virtio_root_device(const char *name)
> +{
> + return __register_virtio_root_device(name, THIS_MODULE);
> +}
> +void unregister_virtio_root_device(struct device *root);
> +
> /**
> * virtio_driver - operations for a virtio I/O driver
> * @driver: underlying device driver (populate name and owner).
> --
> 1.5.4.3