From: Xie He <xie.he.0141@gmail.com>
To: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-x25@vger.kernel.org
Cc: Xie He <xie.he.0141@gmail.com>
Subject: [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len
Date: Sun, 26 Jul 2020 04:05:24 -0700 [thread overview]
Message-ID: <20200726110524.151957-1-xie.he.0141@gmail.com> (raw)
In net/packet/af_packet.c, the function packet_snd first reserves a
headroom of length (dev->hard_header_len + dev->needed_headroom).
Then if the socket is a SOCK_DGRAM socket, it calls dev_hard_header,
which calls dev->header_ops->create, to create the link layer header.
If the socket is a SOCK_RAW socket, it "un-reserves" a headroom of
length (dev->hard_header_len), and assumes the user to provide the
appropriate link layer header.
So according to the logic of af_packet.c, dev->hard_header_len should
be the length of the header that would be created by
dev->header_ops->create.
However, this driver doesn't provide dev->header_ops, so logically
dev->hard_header_len should be 0.
So we should use dev->needed_headroom instead of dev->hard_header_len
to request necessary headroom to be allocated.
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
drivers/net/wan/lapbether.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index b2868433718f..34cf6db89912 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -305,6 +305,7 @@ static void lapbeth_setup(struct net_device *dev)
dev->netdev_ops = &lapbeth_netdev_ops;
dev->needs_free_netdev = true;
dev->type = ARPHRD_X25;
+ dev->hard_header_len = 0;
dev->mtu = 1000;
dev->addr_len = 0;
}
@@ -331,7 +332,8 @@ static int lapbeth_new_device(struct net_device *dev)
* then this driver prepends a length field of 2 bytes,
* then the underlying Ethernet device prepends its own header.
*/
- ndev->hard_header_len = -1 + 3 + 2 + dev->hard_header_len;
+ ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len
+ + dev->needed_headroom;
lapbeth = netdev_priv(ndev);
lapbeth->axdev = ndev;
--
2.25.1
next reply other threads:[~2020-07-26 11:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-26 11:05 Xie He [this message]
2020-07-27 19:41 ` [PATCH] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len Xie He
2020-07-28 5:24 ` Cong Wang
2020-07-28 6:59 ` Xie He
2020-07-28 19:52 ` Brian Norris
2020-07-29 1:41 ` Xie He
2020-07-31 0:24 ` Brian Norris
2020-07-31 0:55 ` Xie He
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