[PATCH net-next] drivers/net/wan/hdlc_fr: Move the skb_headroom check out of fr_hard_header

From: Xie He
Date: Wed Oct 07 2020 - 14:32:19 EST


Move the skb_headroom check out of fr_hard_header and into pvc_xmit.
This has two benefits:

1. Originally we only do this check for skbs sent by users on Ethernet-
emulating PVC devices. After the change we do this check for skbs sent on
normal PVC devices, too.
(Also add a comment to make it clear that this is only a protection
against upper layers that don't take dev->needed_headroom into account.
Such upper layers should be rare and I believe they should be fixed.)

2. After the change we can simplify the parameter list of fr_hard_header.
We no longer need to use a pointer to pointers (skb_p) because we no
longer need to replace the skb inside fr_hard_header.

Cc: Krzysztof Halasa <khc@xxxxxxxxx>
Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
---
drivers/net/wan/hdlc_fr.c | 30 +++++++++++++++++-------------
1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 4dfdbca54296..409e5a7ad8e2 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -271,10 +271,8 @@ static inline struct net_device **get_dev_p(struct pvc_device *pvc,
}


-static int fr_hard_header(struct sk_buff **skb_p, u16 dlci)
+static int fr_hard_header(struct sk_buff *skb, u16 dlci)
{
- struct sk_buff *skb = *skb_p;
-
if (!skb->dev) { /* Control packets */
switch (dlci) {
case LMI_CCITT_ANSI_DLCI:
@@ -316,13 +314,6 @@ static int fr_hard_header(struct sk_buff **skb_p, u16 dlci)
}

} else if (skb->dev->type == ARPHRD_ETHER) {
- if (skb_headroom(skb) < 10) {
- struct sk_buff *skb2 = skb_realloc_headroom(skb, 10);
- if (!skb2)
- return -ENOBUFS;
- dev_kfree_skb(skb);
- skb = *skb_p = skb2;
- }
skb_push(skb, 10);
skb->data[3] = FR_PAD;
skb->data[4] = NLPID_SNAP;
@@ -429,8 +420,21 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
}
}

+ /* We already requested the header space with dev->needed_headroom.
+ * So this is just a protection in case the upper layer didn't take
+ * dev->needed_headroom into consideration.
+ */
+ if (skb_headroom(skb) < 10) {
+ struct sk_buff *skb2 = skb_realloc_headroom(skb, 10);
+
+ if (!skb2)
+ goto drop;
+ dev_kfree_skb(skb);
+ skb = skb2;
+ }
+
skb->dev = dev;
- if (fr_hard_header(&skb, pvc->dlci))
+ if (fr_hard_header(skb, pvc->dlci))
goto drop;

dev->stats.tx_bytes += skb->len;
@@ -498,9 +502,9 @@ static void fr_lmi_send(struct net_device *dev, int fullrep)
memset(skb->data, 0, len);
skb_reserve(skb, 4);
if (lmi == LMI_CISCO) {
- fr_hard_header(&skb, LMI_CISCO_DLCI);
+ fr_hard_header(skb, LMI_CISCO_DLCI);
} else {
- fr_hard_header(&skb, LMI_CCITT_ANSI_DLCI);
+ fr_hard_header(skb, LMI_CCITT_ANSI_DLCI);
}
data = skb_tail_pointer(skb);
data[i++] = LMI_CALLREF;
--
2.25.1