net: docs: document multiqueue tuntap API
Signed-off-by: Jason Wang <jasowang@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -105,6 +105,83 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
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Proto [2 bytes]
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Raw protocol(IP, IPv6, etc) frame.
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3.3 Multiqueue tuntap interface:
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From version 3.8, Linux supports multiqueue tuntap which can uses multiple
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file descriptors (queues) to parallelize packets sending or receiving. The
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device allocation is the same as before, and if user wants to create multiple
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queues, TUNSETIFF with the same device name must be called many times with
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IFF_MULTI_QUEUE flag.
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char *dev should be the name of the device, queues is the number of queues to
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be created, fds is used to store and return the file descriptors (queues)
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created to the caller. Each file descriptor were served as the interface of a
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queue which could be accessed by userspace.
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#include <linux/if.h>
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#include <linux/if_tun.h>
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int tun_alloc_mq(char *dev, int queues, int *fds)
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{
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struct ifreq ifr;
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int fd, err, i;
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if (!dev)
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return -1;
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memset(&ifr, 0, sizeof(ifr));
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/* Flags: IFF_TUN - TUN device (no Ethernet headers)
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* IFF_TAP - TAP device
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*
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* IFF_NO_PI - Do not provide packet information
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* IFF_MULTI_QUEUE - Create a queue of multiqueue device
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*/
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ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_MULTI_QUEUE;
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strcpy(ifr.ifr_name, dev);
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for (i = 0; i < queues; i++) {
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if ((fd = open("/dev/net/tun", O_RDWR)) < 0)
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goto err;
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err = ioctl(fd, TUNSETIFF, (void *)&ifr);
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if (err) {
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close(fd);
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goto err;
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}
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fds[i] = fd;
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}
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return 0;
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err:
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for (--i; i >= 0; i--)
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close(fds[i]);
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return err;
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}
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A new ioctl(TUNSETQUEUE) were introduced to enable or disable a queue. When
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calling it with IFF_DETACH_QUEUE flag, the queue were disabled. And when
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calling it with IFF_ATTACH_QUEUE flag, the queue were enabled. The queue were
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enabled by default after it was created through TUNSETIFF.
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fd is the file descriptor (queue) that we want to enable or disable, when
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enable is true we enable it, otherwise we disable it
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#include <linux/if.h>
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#include <linux/if_tun.h>
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int tun_set_queue(int fd, int enable)
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{
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struct ifreq ifr;
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memset(&ifr, 0, sizeof(ifr));
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if (enable)
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ifr.ifr_flags = IFF_ATTACH_QUEUE;
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else
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ifr.ifr_flags = IFF_DETACH_QUEUE;
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return ioctl(fd, TUNSETQUEUE, (void *)&ifr);
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}
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Universal TUN/TAP device driver Frequently Asked Question.
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1. What platforms are supported by TUN/TAP driver ?
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