Re: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb_ringbuffer.c

[Hans Petter Selasky]

On 8/31/22 15:45, 유용수 wrote:
> Dear All,
>
> Can you share how this patch is going ?
>
> 2022년 8월 18일 (목) 오후 9:55, 유용수 <yongsuyoo0215@xxxxxxxxx>님이 작성:
> > Dear All,
> >
> > Can you pay your attention to this patch ?
> > This is a very simple modification.
> > But, too much time has already passed since I sent the first E-mail.
> >
> > 2022년 8월 3일 (수) 오후 9:04, 유용수 <yongsuyoo0215@xxxxxxxxx>님이 작성:
> > > Dear All.
> > > Too much time has already passed since I first sent this Email.
> > > Can you share how this patch is going ?
> > >
> > > 2022년 6월 23일 (목) 오후 6:11, 유용수 <yongsuyoo0215@xxxxxxxxx>님이 작성:
> > > > Dear Kieran Bingham
> > > >
> > > > I sent E-mail again by Linux terminal by using the command " ... git
> > > > send-email .."
> > > > I believe that you will surely get the diff file.
> > > >
> > > > Thank you
> > > >
> > > > 2022년 6월 22일 (수) 오후 10:12, Hans Petter Selasky <hps@xxxxxxxxxxx>님이 작성:
> > > > > Hi Kieran,
> > > > >
> > > > > The consumed variable should not be negative. This bug has been there
> > > > > since the beginning of the GIT at Linux from what I can see.
> > > > >
> > > > > +1
> > > > >
> > > > > --HPS
> > > > >
> > > > >   From 108c6acb2cc4bc4314b96f6f254a04b2873a096c Mon Sep 17 00:00:00 2001
> > > > > From: YongSu Yoo <yongsuyoo0215@xxxxxxxxx>
> > > > > Date: Sun, 22 May 2022 04:53:12 +0000
> > > > > Subject: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb_ringbuffer.c
> > > > >
> > > > > Signed-off-by:Yongsu Yoo <yongsuyoo0215@xxxxxxxxx>
> > > > >
> > > > > The function dvb_ringbuffer_pkt_next in
> > > > > /linux-next/drviers/media/dvb-core/dvb_ringbuffer.c,
> > > > > which searches the idx of the next valid packet in the ring
> > > > > buffer of the ca->slot_info[slot].rx_buffer at
> > > > > /linux-next/drivers/media/dvb-core/dvb_ca_en50221.c,
> > > > > has the following problem.
> > > > > In calculating the amounts of the consumed address of the ring
> > > > > buffer, if the read address(rbuf->pread) of the ring buffer is
> > > > > smaller than the idx, the amounts of the searched address
> > > > > should be (idx - rbuf->pread),
> > > > > whereas if the read address(rbuf->pread) of the ring buffer is
> > > > > larger than the idx, the amounts of the consumed address should
> > > > > be (idx - rbuf->pread + rbug->size). But there exists an
> > > > > incorrect logic that the rbug-size was not properly added on
> > > > > (idx - rbug->pread) in the later case. With this commit, we
> > > > > fixed this bug.
> > > > > ---
> > > > >    drivers/media/dvb-core/dvb_ringbuffer.c | 4 +++-
> > > > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c
> > > > > b/drivers/media/dvb-core/dvb_ringbuffer.c
> > > > > index d1d471af0636..7d4558de8e83 100644
> > > > > --- a/drivers/media/dvb-core/dvb_ringbuffer.c
> > > > > +++ b/drivers/media/dvb-core/dvb_ringbuffer.c
> > > > > @@ -335,7 +335,9 @@ ssize_t dvb_ringbuffer_pkt_next(struct
> > > > > dvb_ringbuffer *rbuf, size_t idx, size_t*
> > > > >                  idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
> > > > >          }
> > > > >
> > > > > -       consumed = (idx - rbuf->pread) % rbuf->size;
> > > > > +       consumed = (idx - rbuf->pread);
> > > > > +       if (consumed < 0)
> > > > > +               consumed += rbuf->size;
> > > > >
> > > > >          while((dvb_ringbuffer_avail(rbuf) - consumed) >
> > > > > DVB_RINGBUFFER_PKTHDRSIZE) {
> > > > >
> > > > > --
> > > > > 2.17.1

Maybe it will help if you write a test C-program to show the bad numbers 
computed?

--HPS