Re: [PATCH v2 061/101] fbdev/ps3fb: Duplicate video-mode option string

[Thomas Zimmermann]

Hi Geert

Am 10.03.23 um 09:18 schrieb Geert Uytterhoeven:
> Hi Thomas,
>
> On Thu, Mar 9, 2023 at 5:02 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > Assume that the driver does not own the option string or its substrings
> > and hence duplicate the option string for the video mode. Allocate the
> > copy's memory with kstrdup() and free it in the module's exit function.
> >
> > Done in preparation of switching the driver to struct option_iter and
> > constifying the option string.
> >
> > v2:
> >          * replace static memory with kstrdup()/kfree() (Geert)
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
>
> Thanks for the upodate!
>
> > --- a/drivers/video/fbdev/ps3fb.c
> > +++ b/drivers/video/fbdev/ps3fb.c
> > @@ -260,6 +260,7 @@ static const struct fb_videomode ps3fb_modedb[] = {
> >   static int ps3fb_mode;
> >   module_param(ps3fb_mode, int, 0);
> >
> > +static char *mode_option_buf;
>
> Do you really need this variable? It contains the same value
> as mode_option below.
> This is a common pattern in several patches.

In most cases, the extra variable is necessary. mode_option, or a 
similar variable, is often also used to store module parameters or is 
initialized from a static string. In those cases we obviously cannot 
free the memory. Hence the additional variable for the freeing the 
allocation.

I reviewed the patches and it looks like kyrofb, ps3fb, and sm712fb 
might be able to work without the _buf variable. I'll try to update those.

Best regards
Thomas

> >   static char *mode_option;
> >
> >   static int ps3fb_cmp_mode(const struct fb_videomode *vmode,
> > @@ -1276,8 +1277,11 @@ static int __init ps3fb_setup(void)
> >                          continue;
> >                  if (!strncmp(this_opt, "mode:", 5))
> >                          ps3fb_mode = simple_strtoul(this_opt + 5, NULL, 0);
> > -               else
> > -                       mode_option = this_opt;
> > +               else {
> > +                       kfree(mode_option_buf);
> > +                       mode_option_buf = kstrdup(this_opt, GFP_KERNEL); // ignore errors
> > +                       mode_option = mode_option_buf;
> > +               }
> >          }
> >          return 0;
> >   }
> > @@ -1294,6 +1298,7 @@ static void __exit ps3fb_exit(void)
> >   {
> >          pr_debug(" -> %s:%d\n", __func__, __LINE__);
> >          ps3_system_bus_driver_unregister(&ps3fb_driver);
> > +       kfree(mode_option_buf);
> >          pr_debug(" <- %s:%d\n", __func__, __LINE__);
> >   }
>
> Gr{oetje,eeting}s,
>
>                          Geert

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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