[PATCH net-next v4] ppp: enable TX scatter-gather
From: Qingfang Deng <dqfext@gmail.com>
Date: 2026-01-29 01:29:09
Also in:
lkml
Subsystem:
networking drivers, ppp protocol drivers and compressors, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <dqfext@gmail.com> --- v3 -> v4: Always expose SG and FRAGLIST, and linearize the skb if necessary. - https://lore.kernel.org/linux-ppp/20260123014214.225278-1-dqfext@gmail.com/ (local) 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 = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST; dev->priv_destructor = ppp_dev_priv_destructor; dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS; + dev->features = NETIF_F_SG | NETIF_F_FRAGLIST; + dev->hw_features = dev->features; netif_keep_dst(dev); }
@@ -1710,6 +1712,10 @@ pad_compress_skb(struct ppp *ppp, struct sk_buff *skb) ppp->xcomp->comp_extra + ppp->dev->hard_header_len; int compressor_skb_size = ppp->dev->mtu + ppp->xcomp->comp_extra + PPP_HDRLEN; + + if (skb_linearize(skb)) + return NULL; + new_skb = 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) == 0) break; + + if (skb_linearize(skb)) + goto drop; + /* try to do VJ TCP header compression */ new_skb = alloc_skb(skb->len + ppp->dev->hard_header_len - 2, GFP_ATOMIC);
@@ -1894,19 +1904,26 @@ ppp_push(struct ppp *ppp) } if ((ppp->flags & SC_MULTILINK) == 0) { + struct ppp_channel *chan; /* not doing multilink: send it down the first channel */ list = list->next; pch = list_entry(list, struct channel, clist); spin_lock(&pch->downl); - if (pch->chan) { - if (pch->chan->ops->start_xmit(pch->chan, skb)) - ppp->xmit_pending = NULL; - } else { - /* channel got unregistered */ + chan = 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 = NULL; + goto out; } + + if (chan->ops->start_xmit(chan, skb)) + ppp->xmit_pending = 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 */ /* Do protocol field compression */ + if (skb_linearize(skb)) + goto err_linearize; p = skb->data; len = skb->len; if (*p == 0 && mp_protocol_compress) {
@@ -2149,6 +2168,7 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb) 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;
--
2.43.0