Re: [PATCH v2 1/6] USB: add usb_make_subpath() for formatted device subpaths

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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Hi Shihuang,

> Date: 2026-10-21 20:31:41+0800
> From: Shihuang Liu <shlomojune6@gmail.com>
>
> USB drivers often build device paths by calling usb_make_path() :and
> then appending a subpath. Several callers use the deprecated strlcat()
> API for this.
> 
> In preparation for removing the deprecated strlcat() API[1], add
> usb_make_subpath() to format the USB device path.
> 
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Shihuang Liu <shlomojune6@gmail.com>
> ---
>  include/linux/usb.h | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 1da4ad1610bca..c90ccea0cdbf6 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -14,6 +14,7 @@
>  #include <linux/errno.h>        /* for -ENODEV */
>  #include <linux/delay.h>	/* for mdelay() */
>  #include <linux/interrupt.h>	/* for in_interrupt() */
> +#include <linux/stdarg.h>	/* for va_list */
>  #include <linux/list.h>		/* for struct list_head */
>  #include <linux/kref.h>		/* for struct kref */
>  #include <linux/device.h>	/* for struct device */
> @@ -987,6 +988,34 @@ static inline int usb_make_path(struct usb_device *dev, char *buf, size_t size)
>  	return (actual >= (int)size) ? -1 : actual;
>  }
>  
> +/**
> + * usb_make_subpath - returns a stable device path and formatted subpath
> + * @dev: the device whose path is being constructed
> + * @buf: where to put the string
> + * @size: how big is "buf"?
> + * @fmt: format string for the subpath, without the leading slash
> + * @...: arguments for @fmt
> + *
> + * Return: Length of the string (> 0) or negative if size was too small.
> + */
> +static inline __printf(4, 5)
> +int usb_make_subpath(struct usb_device *dev, char *buf, size_t size,
> +		     const char *fmt, ...)
> +{
> +	struct va_format vaf;
> +	va_list args;
> +	int actual;
> +
> +	va_start(args, fmt);
> +	vaf.fmt = fmt;
> +	vaf.va = &args;
> +	actual = snprintf(buf, size, "usb-%s-%s/%pV", dev->bus->bus_name,
> +			  dev->devpath, &vaf);
> +	va_end(args);
> +
> +	return (actual >= (int)size) ? -1 : actual;

Why are you open-coding usb_make_path() here instead of calling it?


Have a lovely day!
Alex

> +}
> +
>  /*-------------------------------------------------------------------------*/
>  
>  #define USB_DEVICE_ID_MATCH_DEVICE \
> -- 
> 2.43.0
> 
> 

-- 
<https://www.alejandro-colomar.es>

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