Hi Geert

Am 07.03.23 um 08:53 schrieb Geert Uytterhoeven:

Hi Thomas,

On Mon, Mar 6, 2023 at 5:00 PM Thomas Zimmermann [off-list ref] wrote:

quoted

Introduce struct option_iter and helpers to parse command-line
options with comma-separated key-value pairs. Then convert fbdev
drivers to the new interface. Fixes a memory leak in the parsing of
the video= option.

Before commit 73ce73c30ba9 ("fbdev: Transfer video= option strings to
caller; clarify ownership"), a call to fb_get_options() either
returned an internal string or a duplicated string; hence ownership of
the string's memory buffer was not well defined, but depended on how
users specified the video= option on the kernel command line. For
global settings, the caller owned the returned memory and for per-driver
settings, fb_get_options() owned the memory. As calling drivers were
unable to detect the case, the memory was leaked.

Commit 73ce73c30ba9 ("fbdev: Transfer video= option strings to caller;
clarify ownership") changed sematics to caller-owned strings. Drivers
still leaked the memory, but at least ownership was clear.

This patchset fixes the memory leak and changes string ownership back
to fb_get_options(). Patch 1 introduces struct option_iter and a few
helpers. The interface takes an option string, such as video=, in the
common form value1,key2:value2,value3 etc and returns the individial
comma-separated pairs. Various modules use this pattern, so the code
is located under lib/.

Patches 2 to 98 go through fbdev drivers and convert them to the new
interface. This often requires a number of cleanups. A driver would
typically refer to the option string's video mode. Such strings are now
copied to driver-allocated memory so that drivers don't refer directly
to the option string's memory. The option iterator then replaces manual
parsing loops based on strsep(",").

Thanks for your series!

Unfortunately I cannot say I'm thrilled about this: you are replacing
a single small dynamic memory leak by 36 larger static memory leaks.

That's fair enough.

Am I missing something?

The current size of the videomode buffers is ridiculously large. I just 
needed something that could hold the string. A long mode description 
might look like

   1920x1080MR-32@120ime

which has 21 characters. 32-byte buffers would probably be more than enough.

I think it should also be possible to do a simple kstrdup() on the given 
videomode string and free the copy in the module's _fini function.

That also brings up the question of these MODULE ifdefs. Almost all of 
the fbdev drivers only parse the command-line option if they are not 
build as a module. Do you know why? Because of the awkward semantics of 
the old fb_get_options()?  I think this should be changed so that they 
always respect the video= parameter.

Best regards
Thomas

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