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Tue, 02 Sep 2025 20:13:20 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGTcvOJVfQMP9AtXeCfqc3GqOtFGl+2YHKFjgvAyMuI4oaGeseIgP7UAQtunJbi2+5RUMMF8o50W85VET7Ldak= X-Received: by 2002:a17:90b:5867:b0:327:fd85:6cd2 with SMTP id 98e67ed59e1d1-328156c623emr18214850a91.24.1756869200081; Tue, 02 Sep 2025 20:13:20 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250902080957.47265-1-simon.schippers@tu-dortmund.de> <20250902080957.47265-2-simon.schippers@tu-dortmund.de> In-Reply-To: From: Jason Wang Date: Wed, 3 Sep 2025 11:13:07 +0800 X-Gm-Features: Ac12FXyivnmUX4HGcNjFfQl5uUVCs0KxooT46aj1-W0YWPU72YBI_ajqRuEAnwE Message-ID: Subject: Re: [PATCH 1/4] ptr_ring_spare: Helper to check if spare capacity of size cnt is available To: Willem de Bruijn Cc: Simon Schippers , mst@redhat.com, eperezma@redhat.com, stephen@networkplumber.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, Tim Gebauer Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Sep 3, 2025 at 5:13=E2=80=AFAM Willem de Bruijn wrote: > > Simon Schippers wrote: > > The implementation is inspired by ptr_ring_empty. > > > > Co-developed-by: Tim Gebauer > > Signed-off-by: Tim Gebauer > > Signed-off-by: Simon Schippers > > --- > > 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_ri= ng *r) > > return ret; > > } > > > > +/* > > + * Check if a spare capacity of cnt is available without taking any lo= cks. > > + * > > + * If cnt=3D=3D0 or cnt > r->size it acts the same as __ptr_ring_empty= . > > cnt >=3D 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 =3D 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