Re: [PATCH v1 1/2] string: Add strprefix(), and deprecate str_has_prefix()

[Andy Shevchenko]

On Thu, Nov 5, 2026 at 1:13 PM Alejandro Colomar <alx@xxxxxxxxxx> wrote:
>
> As Bartosz reported, str_has_prefix() has a bug: it can't differentiate
> between an empty prefix matching an empty string from a non-matching
> prefix.  This is a fundamental design flaw in this API, and not
> something that can be fixed.
>
> As always, this is a consequence of choosing sizes instead of pointers.
> Sizes are often the wrong choice.  In this specific case, pointers are
> more capable of differentiating these cases, as NULL is a special
> sentinel value that doesn't need to overload a valid value.
>
> Let's implement strprefix(), a function that returns a pointer
> right after the prefix if found, and a null pointer if not found.
>
> We'll slowly migrate existing code from str_has_prefix() to strprefix().
>
> Reported-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>

Ouch!

> Cc: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Andy Shevchenko <andy@xxxxxxxxxx>
> Cc: Bartosz Golaszewski <brgl@xxxxxxxxxx>
> Cc: Daniel Scally <djrscally@xxxxxxxxx>
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> Cc: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: Johan Hovold <johan@xxxxxxxxxx>
> Cc: Kees Cook <kees@xxxxxxxxxx>
> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Cc: Len Brown <lenb@xxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Walleij <linusw@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Rob Herring <robh@xxxxxxxxxx>
> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Tom Zanussi <zanussi@xxxxxxxxxx
> Cc: linux-acpi@xxxxxxxxxxxxxxx
> Cc: driver-core@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Cc: devicetree@xxxxxxxxxxxxxxx
> Cc: linux-gpio@xxxxxxxxxxxxxxx

This list is twice as long as the commit message! That's why I highly
recommend moving it under the '---' line below. The email headers will
get all the listed Cc and git history will be clean from this rather
noisy list.

-- 
With Best Regards,
Andy Shevchenko