Re: [PATCH 1/2] staging: greybus: audio_topology: avoid -Wformat-truncation

[Dan Carpenter <dan.carpenter@linaro.org>]

On Sun, Aug 31, 2025 at 02:38:49AM +0900, Masaharu Noguchi wrote:
>     - Fix -Wformat-truncation when prefixing device id to widget/control
>       names.
>     - Write the prefix with scnprintf() and copy the remainder with
>       strscpy().
>     - This avoids potential truncation and satisfies W=1 builds in
>       drivers/staging/greybus.
> 
> Signed-off-by: Masaharu Noguchi <nogunix@gmail.com>
> ---
>  drivers/staging/greybus/audio_topology.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/greybus/audio_topology.c b/drivers/staging/greybus/audio_topology.c
> index 6ca938dca4fd..5bf8b5e29dd8 100644
> --- a/drivers/staging/greybus/audio_topology.c
> +++ b/drivers/staging/greybus/audio_topology.c
> @@ -1013,7 +1013,7 @@ static int gbaudio_tplg_create_widget(struct gbaudio_module_info *module,
>  				      struct snd_soc_dapm_widget *dw,
>  				      struct gb_audio_widget *w, int *w_size)
>  {
> -	int i, ret, csize;
> +	int i, ret, csize, n;
>  	struct snd_kcontrol_new *widget_kctls;
>  	struct gb_audio_control *curr;
>  	struct gbaudio_control *control, *_control;
> @@ -1087,7 +1087,8 @@ static int gbaudio_tplg_create_widget(struct gbaudio_module_info *module,
>  
>  	/* Prefix dev_id to widget control_name */
>  	strscpy(temp_name, w->name, sizeof(temp_name));
> -	snprintf(w->name, sizeof(w->name), "GB %d %s", module->dev_id, temp_name);
> +	n = scnprintf(w->name, sizeof(w->name), "GB %d ", module->dev_id);
> +	strscpy(w->name + n, temp_name, sizeof(w->name) - n);

The strscpy() doesn't make sense.  If the string doesn't fit then you
can't *force* it to fit with strscpy().  :P

Here we're taking a buffer w->name and adding a prefix at the beginning
of the exact same buffer.  Obviously the result is going to be larger.
The W=1 warning doesn't add any new information...

I feel like these W=1 warnings about string truncation are rarely useful.
These limits are not normally thought out that deeply.  Poeople just say,
"This is probably something like a company name.  Let's say that a
company name is probably 48 characters long."  But really very few company
names are that long.  It's just a rough estimate.

And really it's not the worst thing if these strings are truncated.  Kernel
messages are mostly error messages.  We'll still be able to debug the crash
even if the last couple characters in a really long name are chopped off.

regards,
dan carpenter