[RFC PATCH net-next] ppp: enable TX scatter-gather
From: Qingfang Deng <dqfext@gmail.com>
Date: 2025-09-04 02:13:44
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
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 <dqfext@gmail.com> --- RFC: This depends on a pending fix: https://lore.kernel.org/netdev/20250903100726.269839-1-dqfext@gmail.com/ (local) 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 *skb) ppp->xcomp->comp_extra + ppp->dev->hard_header_len; int compressor_skb_size = 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 = 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) == 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 = 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 = -ENOTCONN; goto outl; } - if (pch->chan->direct_xmit) + if (pch->chan->direct_xmit) { ppp->dev->priv_flags |= IFF_NO_QUEUE; - else + ppp->dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; + } else { ppp->dev->priv_flags &= ~IFF_NO_QUEUE; + ppp->dev->features &= ~(NETIF_F_SG | NETIF_F_FRAGLIST); + } spin_unlock_bh(&pch->downl); if (pch->file.hdrlen > ppp->file.hdrlen) ppp->file.hdrlen = pch->file.hdrlen;
--
2.43.0