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Change-Id: I8a9ee2aea93cd29c52c847d0ce33091a73ae6afe
diff --git a/Documentation/networking/tuntap.txt b/Documentation/networking/tuntap.txt
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+Universal TUN/TAP device driver.
+Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
+
+ Linux, Solaris drivers
+ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
+
+ FreeBSD TAP driver
+ Copyright (c) 1999-2000 Maksim Yevmenkin <m_evmenkin@yahoo.com>
+
+ Revision of this document 2002 by Florian Thiel <florian.thiel@gmx.net>
+
+1. Description
+ TUN/TAP provides packet reception and transmission for user space programs.
+ It can be seen as a simple Point-to-Point or Ethernet device, which,
+ instead of receiving packets from physical media, receives them from
+ user space program and instead of sending packets via physical media
+ writes them to the user space program.
+
+ In order to use the driver a program has to open /dev/net/tun and issue a
+ corresponding ioctl() to register a network device with the kernel. A network
+ device will appear as tunXX or tapXX, depending on the options chosen. When
+ the program closes the file descriptor, the network device and all
+ corresponding routes will disappear.
+
+ Depending on the type of device chosen the userspace program has to read/write
+ IP packets (with tun) or ethernet frames (with tap). Which one is being used
+ depends on the flags given with the ioctl().
+
+ The package from http://vtun.sourceforge.net/tun contains two simple examples
+ for how to use tun and tap devices. Both programs work like a bridge between
+ two network interfaces.
+ br_select.c - bridge based on select system call.
+ br_sigio.c - bridge based on async io and SIGIO signal.
+ However, the best example is VTun http://vtun.sourceforge.net :))
+
+2. Configuration
+ Create device node:
+ mkdir /dev/net (if it doesn't exist already)
+ mknod /dev/net/tun c 10 200
+
+ Set permissions:
+ e.g. chmod 0666 /dev/net/tun
+ There's no harm in allowing the device to be accessible by non-root users,
+ since CAP_NET_ADMIN is required for creating network devices or for
+ connecting to network devices which aren't owned by the user in question.
+ If you want to create persistent devices and give ownership of them to
+ unprivileged users, then you need the /dev/net/tun device to be usable by
+ those users.
+
+ Driver module autoloading
+
+ Make sure that "Kernel module loader" - module auto-loading
+ support is enabled in your kernel. The kernel should load it on
+ first access.
+
+ Manual loading
+ insert the module by hand:
+ modprobe tun
+
+ If you do it the latter way, you have to load the module every time you
+ need it, if you do it the other way it will be automatically loaded when
+ /dev/net/tun is being opened.
+
+3. Program interface
+ 3.1 Network device allocation:
+
+ char *dev should be the name of the device with a format string (e.g.
+ "tun%d"), but (as far as I can see) this can be any valid network device name.
+ Note that the character pointer becomes overwritten with the real device name
+ (e.g. "tun0")
+
+ #include <linux/if.h>
+ #include <linux/if_tun.h>
+
+ int tun_alloc(char *dev)
+ {
+ struct ifreq ifr;
+ int fd, err;
+
+ if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
+ return tun_alloc_old(dev);
+
+ 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
+ */
+ ifr.ifr_flags = IFF_TUN;
+ if( *dev )
+ strncpy(ifr.ifr_name, dev, IFNAMSIZ);
+
+ if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
+ close(fd);
+ return err;
+ }
+ strcpy(dev, ifr.ifr_name);
+ return fd;
+ }
+
+ 3.2 Frame format:
+ If flag IFF_NO_PI is not set each frame format is:
+ Flags [2 bytes]
+ 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 queue of multiqueue device
+ */
+ 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 ?
+Currently driver has been written for 3 Unices:
+ Linux kernels 2.2.x, 2.4.x
+ FreeBSD 3.x, 4.x, 5.x
+ Solaris 2.6, 7.0, 8.0
+
+2. What is TUN/TAP driver used for?
+As mentioned above, main purpose of TUN/TAP driver is tunneling.
+It is used by VTun (http://vtun.sourceforge.net).
+
+Another interesting application using TUN/TAP is pipsecd
+(http://perso.enst.fr/~beyssac/pipsec/), a userspace IPSec
+implementation that can use complete kernel routing (unlike FreeS/WAN).
+
+3. How does Virtual network device actually work ?
+Virtual network device can be viewed as a simple Point-to-Point or
+Ethernet device, which instead of receiving packets from a physical
+media, receives them from user space program and instead of sending
+packets via physical media sends them to the user space program.
+
+Let's say that you configured IPX on the tap0, then whenever
+the kernel sends an IPX packet to tap0, it is passed to the application
+(VTun for example). The application encrypts, compresses and sends it to
+the other side over TCP or UDP. The application on the other side decompresses
+and decrypts the data received and writes the packet to the TAP device,
+the kernel handles the packet like it came from real physical device.
+
+4. What is the difference between TUN driver and TAP driver?
+TUN works with IP frames. TAP works with Ethernet frames.
+
+This means that you have to read/write IP packets when you are using tun and
+ethernet frames when using tap.
+
+5. What is the difference between BPF and TUN/TAP driver?
+BPF is an advanced packet filter. It can be attached to existing
+network interface. It does not provide a virtual network interface.
+A TUN/TAP driver does provide a virtual network interface and it is possible
+to attach BPF to this interface.
+
+6. Does TAP driver support kernel Ethernet bridging?
+Yes. Linux and FreeBSD drivers support Ethernet bridging.