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From:   Xie He <xie.he.0141@gmail.com>
To:     Krzysztof Halasa <khc@pm.waw.pl>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Xie He <xie.he.0141@gmail.com>, Martin Schiller <ms@dev.tdt.de>
Subject: [PATCH net v2] drivers/net/wan/hdlc_fr: Add needed_headroom for PVC devices
Date:   Wed,  2 Sep 2020 17:06:58 -0700
Message-Id: <20200903000658.89944-1-xie.he.0141@gmail.com>
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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 <khc@pm.waw.pl>
Cc: Martin Schiller <ms@dev.tdt.de>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---

Change from v1:

English language fix for the commit message.

Changed "Ethernet-emulated" to "Ethernet-emulating" because the device
is emulating an Ethernet device, rather than being emulated by an
Ethernet device.

I'm sorry for my poor English.

---
 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 9acad651ea1f..12b35404cd8e 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -1041,7 +1041,7 @@ 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;
 	netif_keep_dst(dev);
 }
@@ -1093,6 +1093,7 @@ 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;
 
-- 
2.25.1