On Wed, Sep 3, 2025 at 5:13 AM Willem de Bruijn
<[email protected]> wrote:
>
> Simon Schippers wrote:
> > The implementation is inspired by ptr_ring_empty.
> >
> > Co-developed-by: Tim Gebauer <[email protected]>
> > Signed-off-by: Tim Gebauer <[email protected]>
> > Signed-off-by: Simon Schippers <[email protected]>
> > ---
> > include/linux/ptr_ring.h | 71 ++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 71 insertions(+)
> >
> > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > index 551329220e4f..6b8cfaecf478 100644
> > --- a/include/linux/ptr_ring.h
> > +++ b/include/linux/ptr_ring.h
> > @@ -243,6 +243,77 @@ static inline bool ptr_ring_empty_bh(struct ptr_ring
> > *r)
> > return ret;
> > }
> >
> > +/*
> > + * Check if a spare capacity of cnt is available without taking any locks.
> > + *
> > + * If cnt==0 or cnt > r->size it acts the same as __ptr_ring_empty.
>
> cnt >= r->size?
>
> > + *
> > + * The same requirements apply as described for __ptr_ring_empty.
> > + */
> > +static inline bool __ptr_ring_spare(struct ptr_ring *r, int cnt)
> > +{
> > + int size = r->size;
> > + int to_check;
> > +
> > + if (unlikely(!size || cnt < 0))
> > + return true;
>
> Does !size ever happen.
Yes, see 982fb490c298 ("ptr_ring: support zero length ring"). The
reason is tun reuse dev->tx_queue_len for ptr_ring size.
> Also no need for preconditions for trivial
> errors that never happen, like passing negative values. Or prefer
> an unsigned type.
+1.
Thanks
