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Subject[PATCH] net: docs: document multiqueue tuntap API
Date
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Documentation/networking/tuntap.txt | 77 +++++++++++++++++++++++++++++++++++
1 files changed, 77 insertions(+), 0 deletions(-)

diff --git a/Documentation/networking/tuntap.txt b/Documentation/networking/tuntap.txt
index c0aab98..97423f5 100644
--- a/Documentation/networking/tuntap.txt
+++ b/Documentation/networking/tuntap.txt
@@ -105,6 +105,83 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
Proto [2 bytes]
Raw protocol(IP, IPv6, etc) frame.

+ 3.3 Multiqueue tuntap interface:
+
+ From version 3.8, Linux supports multiqueue tuntap which can uses multiple
+ file descriptors (queues) to parallelize packets sending or receiving. The
+ device allocation is the same as before, and if user wants to create multiple
+ queues, TUNSETIFF with the same device name must be called many times with
+ IFF_MULTI_QUEUE flag.
+
+ char *dev should be the name of the device, queues is the number of queues to
+ be created, fds is used to store and return the file descriptors (queues)
+ created to the caller. Each file descriptor were served as the interface of a
+ queue which could be accessed by userspace.
+
+ #include <linux/if.h>
+ #include <linux/if_tun.h>
+
+ int tun_alloc_mq(char *dev, int queues, int *fds)
+ {
+ struct ifreq ifr;
+ int fd, err, i;
+
+ if (!dev)
+ return -1;
+
+ memset(&ifr, 0, sizeof(ifr));
+ /* Flags: IFF_TUN - TUN device (no Ethernet headers)
+ * IFF_TAP - TAP device
+ *
+ * IFF_NO_PI - Do not provide packet information
+ * IFF_MULTI_QUEUE - Create a multiqueue devices
+ */
+ ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_MULTI_QUEUE;
+ strcpy(ifr.ifr_name, dev);
+
+ for (i = 0; i < queues; i++) {
+ if ((fd = open("/dev/net/tun", O_RDWR)) < 0)
+ goto err;
+ err = ioctl(fd, TUNSETIFF, (void *)&ifr);
+ if (err) {
+ close(fd);
+ goto err;
+ }
+ fds[i] = fd;
+ }
+
+ return 0;
+ err:
+ for (--i; i >= 0; i--)
+ close(fds[i]);
+ return err;
+ }
+
+ A new ioctl(TUNSETQUEUE) were introduced to enable or disable a queue. When
+ calling it with IFF_DETACH_QUEUE flag, the queue were disabled. And when
+ calling it with IFF_ATTACH_QUEUE flag, the queue were enabled. The queue were
+ enabled by default after it was created through TUNSETIFF.
+
+ fd is the file descriptor (queue) that we want to enable or disable, when
+ enable is true we enable it, otherwise we disable it
+
+ #include <linux/if.h>
+ #include <linux/if_tun.h>
+
+ int tun_set_queue(int fd, int enable)
+ {
+ struct ifreq ifr;
+
+ memset(&ifr, 0, sizeof(ifr));
+
+ if (enable)
+ ifr.ifr_flags = IFF_ATTACH_QUEUE;
+ else
+ ifr.ifr_flags = IFF_DETACH_QUEUE;
+
+ return ioctl(fd, TUNSETQUEUE, (void *)&ifr);
+ }
+
Universal TUN/TAP device driver Frequently Asked Question.

1. What platforms are supported by TUN/TAP driver ?
--
1.7.1


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