[PATCH v2 4/6] usb: Add environment based device blocklist

[Marek Vasut]

On 3/17/24 12:07 PM, Janne Grunau via B4 Relay wrote:
> From: Janne Grunau <j at jannau.net>
> 
> Add the environment variable "usb_blocklist" to prevent USB devices
> listed in it from being used. This allows to ignore devices which
> trigger bugs in u-boot's USB stack or are undesirable for other reasons.
> Devices emulating keyboards are one example. U-boot currently supports
> only one USB keyboard device. Most commonly, people run into this with
> Yubikeys, so let's ignore those in the default environment.
> 
> Based on previous USB keyboard specific patches for the same purpose.
> 
> Link: https://lore.kernel.org/u-boot/7ab604fb-0fec-4f5e-8708-7a3a7e2cb568@denx.de/
> Signed-off-by: Janne Grunau <j at jannau.net>
> ---
>   common/usb.c              | 56 +++++++++++++++++++++++++++++++++++++++++++++++
>   doc/usage/environment.rst | 12 ++++++++++
>   include/env_default.h     | 11 ++++++++++
>   3 files changed, 79 insertions(+)
> 
> diff --git a/common/usb.c b/common/usb.c
> index 836506dcd9..73af5be066 100644
> --- a/common/usb.c
> +++ b/common/usb.c
> @@ -1084,6 +1084,57 @@ static int usb_prepare_device(struct usb_device *dev, int addr, bool do_read,
>   	return 0;
>   }
>   
> +static int usb_blocklist_parse_error(const char *blocklist, size_t pos)
> +{
> +	printf("usb_blocklist parse error at char %zu in \"%s\"\n", pos,
> +	       blocklist);
> +	return 0;

This could be static void without return 0 at the end.

> +}
> +
> +static int usb_device_is_blocked(u16 id_vendor, u16 id_product)
> +{
> +	ulong vid, pid;
> +	char *end;
> +	const char *block_str = env_get("usb_blocklist");
> +	const char *cur = block_str;
> +
> +	/* parse "usb_blocklist" strictly */
> +	while (cur && cur[0] != '\0') {

Have a look at strsep() , namely strsep(block_str, ","); This will split 
the string up for you at "," delimiters.

Example is in drivers/dfu/dfu.c dfu_config_interfaces() .

And then, on each token, you can try and run sscanf(token, "%04x:%04x", 
vid, pid);, that will parse the token format for you. See e.g. 
test/lib/sscanf.c for further examples.

That should simplify the parsing a lot.

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