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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Subject: [PATCH net-next v4] ppp: enable TX scatter-gather Date: Thu, 29 Jan 2026 09:29:02 +0800 Message-ID: <20260129012902.941-1-dqfext@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" PPP channels using chan->direct_xmit prepend the PPP header to a skb and call dev_queue_xmit() directly. In this mode the skb does not need to be linear, but the PPP netdevice currently does not advertise scatter-gather features, causing unnecessary linearization and preventing GSO. Enable NETIF_F_SG and NETIF_F_FRAGLIST on PPP devices. In case a linear buffer is required (PPP compression, multilink, and channels without direct_xmit), call skb_linearize() explicitly. Signed-off-by: Qingfang Deng --- v3 -> v4: Always expose SG and FRAGLIST, and linearize the skb if necessary. - https://lore.kernel.org/linux-ppp/20260123014214.225278-1-dqfext@gmail.c= om/ drivers/net/ppp/ppp_generic.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index f9f0f16c41d1..f8814d7be6f1 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -1641,6 +1641,8 @@ static void ppp_setup(struct net_device *dev) dev->flags =3D IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST; dev->priv_destructor =3D ppp_dev_priv_destructor; dev->pcpu_stat_type =3D NETDEV_PCPU_STAT_TSTATS; + dev->features =3D NETIF_F_SG | NETIF_F_FRAGLIST; + dev->hw_features =3D dev->features; netif_keep_dst(dev); } =20 @@ -1710,6 +1712,10 @@ pad_compress_skb(struct ppp *ppp, struct sk_buff *sk= b) ppp->xcomp->comp_extra + ppp->dev->hard_header_len; int compressor_skb_size =3D ppp->dev->mtu + ppp->xcomp->comp_extra + PPP_HDRLEN; + + if (skb_linearize(skb)) + return NULL; + new_skb =3D alloc_skb(new_skb_size, GFP_ATOMIC); if (!new_skb) { if (net_ratelimit()) @@ -1797,6 +1803,10 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb) case PPP_IP: if (!ppp->vj || (ppp->flags & SC_COMP_TCP) =3D=3D 0) break; + + if (skb_linearize(skb)) + goto drop; + /* try to do VJ TCP header compression */ new_skb =3D alloc_skb(skb->len + ppp->dev->hard_header_len - 2, GFP_ATOMIC); @@ -1894,19 +1904,26 @@ ppp_push(struct ppp *ppp) } =20 if ((ppp->flags & SC_MULTILINK) =3D=3D 0) { + struct ppp_channel *chan; /* not doing multilink: send it down the first channel */ list =3D list->next; pch =3D list_entry(list, struct channel, clist); =20 spin_lock(&pch->downl); - if (pch->chan) { - if (pch->chan->ops->start_xmit(pch->chan, skb)) - ppp->xmit_pending =3D NULL; - } else { - /* channel got unregistered */ + chan =3D pch->chan; + if (unlikely(!chan || (!chan->direct_xmit && skb_linearize(skb)))) { + /* channel got unregistered, or it requires a linear + * skb but linearization failed + */ kfree_skb(skb); ppp->xmit_pending =3D NULL; + goto out; } + + if (chan->ops->start_xmit(chan, skb)) + ppp->xmit_pending =3D NULL; + +out: spin_unlock(&pch->downl); return; } @@ -1991,6 +2008,8 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_= buff *skb) return 0; /* can't take now, leave it in xmit_pending */ =20 /* Do protocol field compression */ + if (skb_linearize(skb)) + goto err_linearize; p =3D skb->data; len =3D skb->len; if (*p =3D=3D 0 && mp_protocol_compress) { @@ -2149,6 +2168,7 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_= buff *skb) =20 noskb: spin_unlock(&pch->downl); + err_linearize: if (ppp->debug & 1) netdev_err(ppp->dev, "PPP: no memory (fragment)\n"); ++ppp->dev->stats.tx_errors; --=20 2.43.0