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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: Felix Fietkau Subject: [RFC PATCH net-next] ppp: enable TX scatter-gather Date: Thu, 4 Sep 2025 10:13:28 +0800 Message-ID: <20250904021328.24329-1-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" When chan->direct_xmit is true, and no compressors are in use, PPP prepends its header to a skb, and calls dev_queue_xmit directly. In this mode the skb does not need to be linearized. Enable NETIF_F_SG and NETIF_F_FRAGLIST if chan->direct_xmit is true, so the networking core can transmit non-linear skbs directly. The compressors still require a linear buffer so call skb_linearize() before passing skb->data to them. This is required to support PPPoE GSO. Signed-off-by: Qingfang Deng --- RFC: This depends on a pending fix: https://lore.kernel.org/netdev/20250903100726.269839-1-dqfext@gmail.com/ There are also alternative approaches: - set SG and FRAGLIST unconditionally, and use skb_linearize() on !chan->direct_xmit paths. - don't use skb_linearize(), instead fix the compressors to handle non-linear sk_buffs. - conditionally set SG and FRAGLIST based on whether compressors are in use. drivers/net/ppp/ppp_generic.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index f9f0f16c41d1..3bf37871a1aa 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -1710,6 +1710,12 @@ 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; + /* Until we fix the compressor need to make sure data portion is + * linear. + */ + if (skb_linearize(skb)) + return NULL; + new_skb =3D alloc_skb(new_skb_size, GFP_ATOMIC); if (!new_skb) { if (net_ratelimit()) @@ -1797,6 +1803,12 @@ 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; + /* Until we fix the compressor need to make sure data portion + * is linear. + */ + 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); @@ -3516,10 +3528,13 @@ ppp_connect_channel(struct channel *pch, int unit) ret =3D -ENOTCONN; goto outl; } - if (pch->chan->direct_xmit) + if (pch->chan->direct_xmit) { ppp->dev->priv_flags |=3D IFF_NO_QUEUE; - else + ppp->dev->features |=3D NETIF_F_SG | NETIF_F_FRAGLIST; + } else { ppp->dev->priv_flags &=3D ~IFF_NO_QUEUE; + ppp->dev->features &=3D ~(NETIF_F_SG | NETIF_F_FRAGLIST); + } spin_unlock_bh(&pch->downl); if (pch->file.hdrlen > ppp->file.hdrlen) ppp->file.hdrlen =3D pch->file.hdrlen; --=20 2.43.0