ppp: enable TX scatter-gather

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>
Link: https://patch.msgid.link/20260129012902.941-1-dqfext@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index f9f0f16c41d10f6091fffa9f558d23c336c1caf0..f8814d7be6f1e9a32fd81ed5303c963a84848d2e 100644 (file)
--- 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;