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

[Mariia Nikitash]

On Tue, Nov 10, 2026 at 5:54 AM David Laight
<david.laight.linux@xxxxxxxxx> wrote:
>
> On Tue, 10 Nov 2026 11:08:30 +0100
> Hans Verkuil <hverkuil+cisco@xxxxxxxxxx> wrote:
>
> > On 06/11/2026 08:46, Mariia Nikitash 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.
> > >
> > > Link: https://github.com/KSPP/linux/issues/370 [1]
> > > Signed-off-by: Mariia Nikitash <nikitash.mariiaw@xxxxxxxxx>
> >
> > Nacked-by: Hans Verkuil <hverkuil+cisco@xxxxxxxxxx>
> >

Hi,



> > This is silly. Just use scnprintf().
>
> Or wait for someone to add a call that just does what is needed.
> In this case the first stscpy() returns the length (and it is often
> known).
> So you could have:
>         len = strscpy(buf, tea->card[, buflen]);
>         len = strscpy_at(buf, len, " TEA5777"[, buflen]);
> or:
>         len = strscat(buf, buflen, tea->card, " TEA5777", ....);
> or some variant that will do a strnlen(buf, buflen) to get the offset.
>
> But it really is best to leave the strlcat() calls in there for now.
>

Thanks Hans and David for the feedback.

I agree that seq_buf is too complex here. I'll look into using
scnprintf() as Hans suggested.

David, I also see your point about leaving strlcat() in place until a
more suitable append helper is available. I'll revisit the approach
before deciding on a v2.


Best,
Mariia

> David
>
> >
> > Regards,
> >
> >       Hans
> >
> > > ---
> > >  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));
> > > +
> > > +   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;
> > >  }
> >
> >
>