Nouveau - Oct 2022 - [PATCH v5 12/22] drm/connector: Add a function to lookup a TV mode by its name

On Tue, Oct 18, 2022 at 02:29:00PM +0200, Noralf Tr?nnes
wrote:
> 
> 
> Den 18.10.2022 11.33, skrev Maxime Ripard:
> > On Mon, Oct 17, 2022 at 12:44:45PM +0200, Noralf Tr?nnes wrote:
> >> Den 13.10.2022 15.18, skrev Maxime Ripard:
> >>> As part of the command line parsing rework coming in the next
patches,
> >>> we'll need to lookup drm_connector_tv_mode values by their
name, already
> >>> defined in drm_tv_mode_enum_list.
> >>>
> >>> In order to avoid any code duplication, let's do a
function that will
> >>> perform a lookup of a TV mode name and return its value.
> >>>
> >>> Signed-off-by: Maxime Ripard <maxime at cerno.tech>
> >>> ---
> >>>  drivers/gpu/drm/drm_connector.c | 24 ++++++++++++++++++++++++
> >>>  include/drm/drm_connector.h     |  2 ++
> >>>  2 files changed, 26 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/drm_connector.c
b/drivers/gpu/drm/drm_connector.c
> >>> index 820f4c730b38..30611c616435 100644
> >>> --- a/drivers/gpu/drm/drm_connector.c
> >>> +++ b/drivers/gpu/drm/drm_connector.c
> >>> @@ -991,6 +991,30 @@ static const struct drm_prop_enum_list
drm_tv_mode_enum_list[] = {
> >>>  };
> >>>  DRM_ENUM_NAME_FN(drm_get_tv_mode_name, drm_tv_mode_enum_list)
> >>>  
> >>> +/**
> >>> + * drm_get_tv_mode_from_name - Translates a TV mode name into
its enum value
> >>> + * @name: TV Mode name we want to convert
> >>> + * @len: Length of @name
> >>> + *
> >>> + * Translates @name into an enum drm_connector_tv_mode.
> >>> + *
> >>> + * Returns: the enum value on success, a negative errno
otherwise.
> >>> + */
> >>> +int drm_get_tv_mode_from_name(const char *name, size_t len)
> >>
> >> Do we really need to pass in length here? item->name has to
always be
> >> NUL terminated otherwise things would break elsewhere, so it
shouldn't
> >> be necessary AFAICS.
> > 
> > The only user so far is the command-line parsing code, and we might
very
> > well have an option after the tv_mode, something like
> > 720x480i,tv_mode=NTSC,rotate=180
> > 
> > In this case, we won't get a NULL-terminated name.
>
> My point is that item->name will always be NUL terminated so strcmp()
> will never look past that.
Right, but we don't have the guarantee that strlen(item->name) <
strlen(name), and we could thus just access after the end of our name

Maxime
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Den 19.10.2022 10.48, skrev Maxime Ripard:
> On Tue, Oct 18, 2022 at 02:29:00PM +0200, Noralf Tr?nnes wrote:
>>
>>
>> Den 18.10.2022 11.33, skrev Maxime Ripard:
>>> On Mon, Oct 17, 2022 at 12:44:45PM +0200, Noralf Tr?nnes wrote:
>>>> Den 13.10.2022 15.18, skrev Maxime Ripard:
>>>>> As part of the command line parsing rework coming in the
next patches,
>>>>> we'll need to lookup drm_connector_tv_mode values by
their name, already
>>>>> defined in drm_tv_mode_enum_list.
>>>>>
>>>>> In order to avoid any code duplication, let's do a
function that will
>>>>> perform a lookup of a TV mode name and return its value.
>>>>>
>>>>> Signed-off-by: Maxime Ripard <maxime at cerno.tech>
>>>>> ---
>>>>>  drivers/gpu/drm/drm_connector.c | 24
++++++++++++++++++++++++
>>>>>  include/drm/drm_connector.h     |  2 ++
>>>>>  2 files changed, 26 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/drm_connector.c
b/drivers/gpu/drm/drm_connector.c
>>>>> index 820f4c730b38..30611c616435 100644
>>>>> --- a/drivers/gpu/drm/drm_connector.c
>>>>> +++ b/drivers/gpu/drm/drm_connector.c
>>>>> @@ -991,6 +991,30 @@ static const struct drm_prop_enum_list
drm_tv_mode_enum_list[] = {
>>>>>  };
>>>>>  DRM_ENUM_NAME_FN(drm_get_tv_mode_name,
drm_tv_mode_enum_list)
>>>>>  
>>>>> +/**
>>>>> + * drm_get_tv_mode_from_name - Translates a TV mode name
into its enum value
>>>>> + * @name: TV Mode name we want to convert
>>>>> + * @len: Length of @name
>>>>> + *
>>>>> + * Translates @name into an enum drm_connector_tv_mode.
>>>>> + *
>>>>> + * Returns: the enum value on success, a negative errno
otherwise.
>>>>> + */
>>>>> +int drm_get_tv_mode_from_name(const char *name, size_t
len)
>>>>
>>>> Do we really need to pass in length here? item->name has to
always be
>>>> NUL terminated otherwise things would break elsewhere, so it
shouldn't
>>>> be necessary AFAICS.
>>>
>>> The only user so far is the command-line parsing code, and we might
very
>>> well have an option after the tv_mode, something like
>>> 720x480i,tv_mode=NTSC,rotate=180
>>>
>>> In this case, we won't get a NULL-terminated name.
>>
>> My point is that item->name will always be NUL terminated so
strcmp()
>> will never look past that.
> 
> Right, but we don't have the guarantee that strlen(item->name) <
> strlen(name), and we could thus just access after the end of our name
> 
Ok, using the length limiting str funtions is the safe thing to do, so
len needs to stay. But I don't get the 'strlen(item->name) ==
len'
check. strncmp() will stop when it reaches a NUL in either string so no
need for the length check?

Anyways:

Reviewed-by: Noralf Tr?nnes <noralf at tronnes.org>