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

Noralf Trønnes
2022-10-19T10:44:39Z

Den 19.10.2022 10.48, skrev Maxime Ripard:
> On Tue, Oct 18, 2022 at 02:29:00PM +0200, Noralf Trønnes wrote:
>>
>>
>> Den 18.10.2022 11.33, skrev Maxime Ripard:
>>> On Mon, Oct 17, 2022 at 12:44:45PM +0200, Noralf Trønnes 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@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 Trønnes <noralf@tronnes.org>