#include <linux/in.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>

#include <net/datalink.h>

static int pEII_request(struct datalink_proto *dl,
			struct sk_buff *skb, unsigned char *dest_node)
{
	struct net_device *dev = skb->dev;

	skb->protocol = htons(ETH_P_IPX);
	dev_hard_header(skb, dev, ETH_P_IPX, dest_node, NULL, skb->len);
	return dev_queue_xmit(skb);
}

struct datalink_proto *make_EII_client(void)
{
	struct datalink_proto *proto = kmalloc(sizeof(*proto), GFP_ATOMIC);

	if (proto) {
		proto->header_length = 0;
		proto->request = pEII_request;
	}

	return proto;
}

void destroy_EII_client(struct datalink_proto *dl)
{
	kfree(dl);
}
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<tr class='logheader'><td><span title='2017-02-02 21:58:02 -0500'>2017-02-02</span></td><td class='logsubject'><a href='/cgit.cgi/linux/net-next.git/commit/net/unix?id=ba94f3088b792b16ea576a256a6030feddc87f24'>unix: add ioctl to open a unix socket file with O_PATH</a></td><td>Andrey Vagin</td><td>1</td><td><span class='deletions'>-0</span>/<span class='insertions'>+41</span></td></tr>
<tr class='nohover-highlight'><td/><td colspan='5' class='logmsg'>
This ioctl opens a file to which a socket is bound and
returns a file descriptor. The caller has to have CAP_NET_ADMIN
in the socket network namespace.

Currently it is impossible to get a path and a mount point
for a socket file. socket_diag reports address, device ID and inode
number for unix sockets. An address can contain a relative path or
a file may be moved somewhere. And these properties say nothing about
a mount namespace and a mount point of a socket file.

With the introduced ioctl, we can get a path by reading
/proc/self/fd/X and get mnt_id from /proc/self/fdinfo/X.

In CRIU we are going to use this ioctl to dump and restore unix socket.

Here is an example how it can be used:

$ strace -e socket,bind,ioctl ./test /tmp/test_sock
socket(AF_UNIX, SOCK_STREAM, 0)         = 3
bind(3, {sa_family=AF_UNIX, sun_path="test_sock"}, 11) = 0
ioctl(3, SIOCUNIXFILE, 0)           = 4
^Z

$ ss -a | grep test_sock
u_str  LISTEN     0      1      test_sock 17798                 * 0

$ ls -l /proc/760/fd/{3,4}
lrwx------ 1 root root 64 Feb  1 09:41 3 -&gt; 'socket:[17798]'
l--------- 1 root root 64 Feb  1 09:41 4 -&gt; /tmp/test_sock

$ cat /proc/760/fdinfo/4
pos:	0
flags:	012000000
mnt_id:	40

$ cat /proc/self/mountinfo | grep "^40\s"
40 19 0:37 / /tmp rw shared:23 - tmpfs tmpfs rw

Signed-off-by: Andrei Vagin &lt;avagin@openvz.org&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;


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