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Date:   Mon, 28 Sep 2020 21:31:19 -0400
From:   Sasha Levin <>
Cc:     Xie He <>, Krzysztof Halasa <>,
        Martin Schiller <>,
        Jakub Kicinski <>,
        Sasha Levin <>,
Subject: [PATCH AUTOSEL 4.19 01/11] drivers/net/wan/hdlc_fr: Add needed_headroom for PVC devices

From: Xie He <>

[ Upstream commit 44a049c42681de71c783d75cd6e56b4e339488b0 ]

PVC devices are virtual devices in this driver stacked on top of the
actual HDLC device. They are the devices normal users would use.
PVC devices have two types: normal PVC devices and Ethernet-emulating
PVC devices.

When transmitting data with PVC devices, the ndo_start_xmit function
will prepend a header of 4 or 10 bytes. Currently this driver requests
this headroom to be reserved for normal PVC devices by setting their
hard_header_len to 10. However, this does not work when these devices
are used with AF_PACKET/RAW sockets. Also, this driver does not request
this headroom for Ethernet-emulating PVC devices (but deals with this
problem by reallocating the skb when needed, which is not optimal).

This patch replaces hard_header_len with needed_headroom, and set
needed_headroom for Ethernet-emulating PVC devices, too. This makes
the driver to request headroom for all PVC devices in all cases.

Cc: Krzysztof Halasa <>
Cc: Martin Schiller <>
Signed-off-by: Xie He <>
Signed-off-by: Jakub Kicinski <>
Signed-off-by: Sasha Levin <>
 drivers/net/wan/hdlc_fr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 038236a9c60ee..67f89917277ce 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -1044,7 +1044,7 @@ static void pvc_setup(struct net_device *dev)
 	dev->type = ARPHRD_DLCI;
 	dev->flags = IFF_POINTOPOINT;
-	dev->hard_header_len = 10;
+	dev->hard_header_len = 0;
 	dev->addr_len = 2;
@@ -1096,6 +1096,7 @@ static int fr_add_pvc(struct net_device *frad, unsigned int dlci, int type)
 	dev->mtu = HDLC_MAX_MTU;
 	dev->min_mtu = 68;
 	dev->max_mtu = HDLC_MAX_MTU;
+	dev->needed_headroom = 10;
 	dev->priv_flags |= IFF_NO_QUEUE;
 	dev->ml_priv = pvc;

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