Re: [PATCH] media: radio: Replace strlcat() with seq_buf in TEA drivers

[David Laight]

On Thu,  5 Nov 2026 23:46:39 -0800
Mariia Nikitash <nikitash.mariiaw@xxxxxxxxx> wrote:

> In preparation for removing the deprecated strlcat() API[1],
> replace the strscpy() and strlcat() calls used to construct
> V4L2 card names in the TEA5777 and TEA575x radio drivers.
> 
> seq_buf tracks the current write position and remaining capacity
> across appends, avoiding repeated scans of the destination buffer.
> This preserves the resulting strings, including truncation behavior.

seq_buf is just OTT.
Using to replace a single strcat() is just silly.
There is no point doing these patches until there is a sensible alternative.

> 
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Mariia Nikitash <nikitash.mariiaw@xxxxxxxxx>
> ---
>  drivers/media/radio/radio-tea5777.c | 10 ++++++++--
>  drivers/media/radio/tea575x.c       | 10 ++++++++--
>  2 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/radio/radio-tea5777.c b/drivers/media/radio/radio-tea5777.c
> index fb9de7bbcd19..2b1c7f6ddd60 100644
> --- a/drivers/media/radio/radio-tea5777.c
> +++ b/drivers/media/radio/radio-tea5777.c
> @@ -13,6 +13,7 @@
>  #include <linux/init.h>
>  #include <linux/module.h>
>  #include <linux/sched.h>
> +#include <linux/seq_buf.h>
>  #include <linux/slab.h>
>  #include <media/v4l2-device.h>
>  #include <media/v4l2-dev.h>
> @@ -255,10 +256,15 @@ static int vidioc_querycap(struct file *file, void  *priv,
>  					struct v4l2_capability *v)
>  {
>  	struct radio_tea5777 *tea = video_drvdata(file);
> +	struct seq_buf s;
>  
>  	strscpy(v->driver, tea->v4l2_dev->name, sizeof(v->driver));
> -	strscpy(v->card, tea->card, sizeof(v->card));
> -	strlcat(v->card, " TEA5777", sizeof(v->card));

What is wrong with (and almost OTT):
#define TEA5777 " TEA5777"
	BUILD_BUG_ON(sizeof(TEA5777) <= sizeof(v->card))

	len = strscpy(v->card, tea->card, sizeof(v->card) - sizeof(TEA5777) + 1);
	if (len < 0)
		goto fail;
	memcpy(v->card + len, TEA5777, sizeof(TEA5777);

What might be useful is a helper that would let you write:
	len = strscpy(v->card, tea->card);
	len = strscpy_at(v->card, len, " TEA5777" [, implied_length]);
	if (len < 0)
		goto fail;

David

> +
> +	seq_buf_init(&s, (char *)v->card, sizeof(v->card));
> +	seq_buf_puts(&s, (const char *)tea->card);
> +	seq_buf_puts(&s, " TEA5777");
> +	seq_buf_terminate(&s);
> +
>  	strscpy(v->bus_info, tea->bus_info, sizeof(v->bus_info));
>  	return 0;
>  }
> diff --git a/drivers/media/radio/tea575x.c b/drivers/media/radio/tea575x.c
> index c37315226c42..e49228eb7c46 100644
> --- a/drivers/media/radio/tea575x.c
> +++ b/drivers/media/radio/tea575x.c
> @@ -9,6 +9,7 @@
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> +#include <linux/seq_buf.h>
>  #include <linux/sched.h>
>  #include <asm/io.h>
>  #include <media/v4l2-device.h>
> @@ -221,10 +222,15 @@ static int vidioc_querycap(struct file *file, void  *priv,
>  					struct v4l2_capability *v)
>  {
>  	struct snd_tea575x *tea = video_drvdata(file);
> +	struct seq_buf s;
>  
>  	strscpy(v->driver, tea->v4l2_dev->name, sizeof(v->driver));
> -	strscpy(v->card, tea->card, sizeof(v->card));
> -	strlcat(v->card, tea->tea5759 ? " TEA5759" : " TEA5757", sizeof(v->card));
> +
> +	seq_buf_init(&s, (char *)v->card, sizeof(v->card));
> +	seq_buf_puts(&s, (const char *)tea->card);
> +	seq_buf_puts(&s, tea->tea5759 ? " TEA5759" : " TEA5757");
> +	seq_buf_terminate(&s);
> +
>  	strscpy(v->bus_info, tea->bus_info, sizeof(v->bus_info));
>  	return 0;
>  }