Re: [PATCH v2 1/1] usb: gadget: add raw-gadget interface

Alan Stern
2019-11-15T15:38:43Z

On Fri, 15 Nov 2019, Andrey Konovalov wrote:

> USB Raw Gadget is a kernel module that provides a userspace interface for
> the USB Gadget subsystem. Essentially it allows to emulate USB devices
> from userspace. Enabled with CONFIG_USB_RAW_GADGET. Raw Gadget is
> currently a strictly debugging feature and shouldn't be used in
> production.
>
> Raw Gadget is similar to GadgetFS, but provides a more low-level and
> direct access to the USB Gadget layer for the userspace. The key
> differences are:
>
> 1. Every USB request is passed to the userspace to get a response, while
> GadgetFS responds to some USB requests internally based on the provided
> descriptors. However note, that the UDC driver might respond to some
> requests on its own and never forward them to the Gadget layer.
>
> 2. GadgetFS performs some sanity checks on the provided USB descriptors,
> while Raw Gadget allows you to provide arbitrary data as responses to
> USB requests.
>
> 3. Raw Gadget provides a way to select a UDC device/driver to bind to,
> while GadgetFS currently binds to the first available UDC.
>
> 4. Raw Gadget uses predictable endpoint names (handles) across different
> UDCs (as long as UDCs have enough endpoints of each required transfer
> type).
>
> 5. Raw Gadget has ioctl-based interface instead of a filesystem-based one.

...

> --- /dev/null
> +++ b/Documentation/usb/raw-gadget.rst

> +Userspace interface
> +~~~~~~~~~~~~~~~~~~~
> +
> +To create a Raw Gadget instance open /sys/kernel/debug/usb/raw-gadget
> +(debugfs should be enabled and mounted). Multiple raw-gadget instances

Looks like the documentation hasn't kept up with the more recent
changes to the driver.

> --- /dev/null
> +++ b/drivers/usb/gadget/legacy/raw.c
> @@ -0,0 +1,1057 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * USB Raw Gadget driver.
> + * See Documentation/usb/raw-gadget.rst for more details.
> + *
> + * Andrey Konovalov <andreyknvl@gmail.com>
> + */
> +
> +#define pr_fmt(fmt) "raw: %s: " fmt, __func__

This macro isn't used anywhere now.

Alan Stern