Re: [PATCH 1/3] driver core: generalize driver_override in struct device

[Geert Uytterhoeven]

Hi Danilo,

On Mon, 2 Mar 2026 at 11:26, Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> On Mon Mar 2, 2026 at 11:00 AM CET, Geert Uytterhoeven wrote:
> >> --- a/drivers/base/dd.c
> >> +++ b/drivers/base/dd.c
> >> @@ -381,6 +381,66 @@ static void __exit deferred_probe_exit(void)
> >>  }
> >>  __exitcall(deferred_probe_exit);
> >>
> >> +int __device_set_driver_override(struct device *dev, const char *s, size_t len)
> >> +{
> >> +       const char *new, *old;
> >> +       char *cp;
> >> +
> >> +       if (!s)
> >> +               return -EINVAL;
> >> +
> >> +       /*
> >> +        * The stored value will be used in sysfs show callback (sysfs_emit()),
> >> +        * which has a length limit of PAGE_SIZE and adds a trailing newline.
> >> +        * Thus we can store one character less to avoid truncation during sysfs
> >> +        * show.
> >> +        */
> >> +       if (len >= (PAGE_SIZE - 1))
> >> +               return -EINVAL;
> >> +
> >> +       /*
> >> +        * Compute the real length of the string in case userspace sends us a
> >> +        * bunch of \0 characters like python likes to do.
> >> +        */
> >> +       len = strlen(s);
> >> +
> >
> > The newline case below is is basically the same case as the empty
> > string.  Hence if you would move the newline check here:
> >
> >     if (len) {
> >             cp = strnchr(s, len, '\n');
> >             if (cp)
> >                     len = cp - s;
> >     }
> >
> > then the "cp != s" check below is no longer needed.
> >
> >> +       if (!len) {
> >> +               /* Empty string passed - clear override */
> >> +               spin_lock(&dev->driver_override.lock);
> >> +               old = dev->driver_override.name;
> >> +               dev->driver_override.name = NULL;
> >> +               spin_unlock(&dev->driver_override.lock);
> >> +               kfree(old);
> >> +
> >> +               return 0;
> >> +       }
> >
> > Also, this block can be eliminated completely...
> >
> >> +
> >> +       cp = strnchr(s, len, '\n');
> >> +       if (cp)
> >> +               len = cp - s;
> >> +
> >> +       new = kstrndup(s, len, GFP_KERNEL);
> >> +       if (!new)
> >> +               return -ENOMEM;
> >
> > ... by pre-initializing new to NULL, and making the allocation of new
> > conditional on len being non-zero.
> >
> >> +
> >> +       spin_lock(&dev->driver_override.lock);
> >> +       old = dev->driver_override.name;
> >> +       if (cp != s) {
> >> +               dev->driver_override.name = new;
> >> +               spin_unlock(&dev->driver_override.lock);
> >> +       } else {
> >> +               /* "\n" passed - clear override */
> >> +               dev->driver_override.name = NULL;
> >> +               spin_unlock(&dev->driver_override.lock);
> >> +
> >> +               kfree(new);
> >> +       }
> >> +       kfree(old);
> >> +
> >> +       return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(__device_set_driver_override);
>
> This is essentially a copy of driver_set_override(). Except for the required
> minor changes I intentionally kept it "as is" as it will go through -fixes and
> we know it works properly.

So I will have two to fix? ;-)

> Do you mind sending a follow-up patch with your suggested improvements?

Adding it to my TODO list, if this patch makes it as-is.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds