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SubjectRe: [PATCH v2 061/101] fbdev/ps3fb: Duplicate video-mode option string
From
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@suse.de> 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@suse.de>
>
> 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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