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docs: networking: convert tuntap.txt to ReST

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- add SPDX header;
- use copyright symbol;
- adjust titles and chapters, adding proper markups;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines where needed;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Mauro Carvalho Chehab
2020-05-01 16:44:23 +02:00
committed by David S. Miller
parent ef891284b1
commit 973d55e590
4 changed files with 119 additions and 86 deletions
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1
Documentation/networking/index.rst
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@@ -111,6 +111,7 @@ Contents:
team team
timestamping timestamping
tproxy tproxy
tuntap
.. only:: subproject and html .. only:: subproject and html

200
Documentation/networking/tuntap.txt → Documentation/networking/tuntap.rst
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@@ -1,20 +1,28 @@
Universal TUN/TAP device driver. .. SPDX-License-Identifier: GPL-2.0
Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com> .. include:: <isonum.txt>
Linux, Solaris drivers ===============================
Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com> Universal TUN/TAP device driver
===============================
FreeBSD TAP driver Copyright |copy| 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
Copyright (c) 1999-2000 Maksim Yevmenkin <m_evmenkin@yahoo.com>
Linux, Solaris drivers
Copyright |copy| 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
FreeBSD TAP driver
Copyright |copy| 1999-2000 Maksim Yevmenkin <m_evmenkin@yahoo.com>
Revision of this document 2002 by Florian Thiel <florian.thiel@gmx.net> Revision of this document 2002 by Florian Thiel <florian.thiel@gmx.net>
1. Description 1. Description
TUN/TAP provides packet reception and transmission for user space programs. ==============
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, It can be seen as a simple Point-to-Point or Ethernet device, which,
instead of receiving packets from physical media, receives them from instead of receiving packets from physical media, receives them from
user space program and instead of sending packets via physical media user space program and instead of sending packets via physical media
writes them to the user space program. writes them to the user space program.
In order to use the driver a program has to open /dev/net/tun and issue a 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 corresponding ioctl() to register a network device with the kernel. A network
@@ -33,41 +41,51 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
br_sigio.c - bridge based on async io and SIGIO signal. br_sigio.c - bridge based on async io and SIGIO signal.
However, the best example is VTun http://vtun.sourceforge.net :)) However, the best example is VTun http://vtun.sourceforge.net :))
2. Configuration 2. Configuration
Create device node: ================
Create device node::
mkdir /dev/net (if it doesn't exist already) mkdir /dev/net (if it doesn't exist already)
mknod /dev/net/tun c 10 200 mknod /dev/net/tun c 10 200
Set permissions: Set permissions::
e.g. chmod 0666 /dev/net/tun 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 There's no harm in allowing the device to be accessible by non-root users,
connecting to network devices which aren't owned by the user in question. since CAP_NET_ADMIN is required for creating network devices or for
If you want to create persistent devices and give ownership of them to connecting to network devices which aren't owned by the user in question.
unprivileged users, then you need the /dev/net/tun device to be usable by If you want to create persistent devices and give ownership of them to
those users. unprivileged users, then you need the /dev/net/tun device to be usable by
those users.
Driver module autoloading Driver module autoloading
Make sure that "Kernel module loader" - module auto-loading Make sure that "Kernel module loader" - module auto-loading
support is enabled in your kernel. The kernel should load it on support is enabled in your kernel. The kernel should load it on
first access. first access.
Manual loading Manual loading
insert the module by hand:
modprobe tun insert the module by hand::
modprobe tun
If you do it the latter way, you have to load the module every time you 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 need it, if you do it the other way it will be automatically loaded when
/dev/net/tun is being opened. /dev/net/tun is being opened.
3. Program interface 3. Program interface
3.1 Network device allocation: ====================
char *dev should be the name of the device with a format string (e.g. 3.1 Network device allocation
"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") ``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.h>
#include <linux/if_tun.h> #include <linux/if_tun.h>
@@ -78,45 +96,51 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
int fd, err; int fd, err;
if( (fd = open("/dev/net/tun", O_RDWR)) < 0 ) if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
return tun_alloc_old(dev); return tun_alloc_old(dev);
memset(&ifr, 0, sizeof(ifr)); memset(&ifr, 0, sizeof(ifr));
/* Flags: IFF_TUN - TUN device (no Ethernet headers) /* Flags: IFF_TUN - TUN device (no Ethernet headers)
* IFF_TAP - TAP device * IFF_TAP - TAP device
* *
* IFF_NO_PI - Do not provide packet information * IFF_NO_PI - Do not provide packet information
*/ */
ifr.ifr_flags = IFF_TUN; ifr.ifr_flags = IFF_TUN;
if( *dev ) if( *dev )
strncpy(ifr.ifr_name, dev, IFNAMSIZ); strncpy(ifr.ifr_name, dev, IFNAMSIZ);
if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){ if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
close(fd); close(fd);
return err; return err;
} }
strcpy(dev, ifr.ifr_name); strcpy(dev, ifr.ifr_name);
return fd; return fd;
} }
3.2 Frame format: 3.2 Frame format
If flag IFF_NO_PI is not set each frame format is: ----------------
If flag IFF_NO_PI is not set each frame format is::
Flags [2 bytes] Flags [2 bytes]
Proto [2 bytes] Proto [2 bytes]
Raw protocol(IP, IPv6, etc) frame. Raw protocol(IP, IPv6, etc) frame.
3.3 Multiqueue tuntap interface: 3.3 Multiqueue tuntap interface
-------------------------------
From version 3.8, Linux supports multiqueue tuntap which can uses multiple From version 3.8, Linux supports multiqueue tuntap which can uses multiple
file descriptors (queues) to parallelize packets sending or receiving. The file descriptors (queues) to parallelize packets sending or receiving. The
device allocation is the same as before, and if user wants to create multiple 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 queues, TUNSETIFF with the same device name must be called many times with
IFF_MULTI_QUEUE flag. IFF_MULTI_QUEUE flag.
char *dev should be the name of the device, queues is the number of queues to ``char *dev`` should be the name of the device, queues is the number of queues
be created, fds is used to store and return the file descriptors (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 created to the caller. Each file descriptor were served as the interface of a
queue which could be accessed by userspace. queue which could be accessed by userspace.
::
#include <linux/if.h> #include <linux/if.h>
#include <linux/if_tun.h> #include <linux/if_tun.h>
@@ -127,7 +151,7 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
int fd, err, i; int fd, err, i;
if (!dev) if (!dev)
return -1; return -1;
memset(&ifr, 0, sizeof(ifr)); memset(&ifr, 0, sizeof(ifr));
/* Flags: IFF_TUN - TUN device (no Ethernet headers) /* Flags: IFF_TUN - TUN device (no Ethernet headers)
@@ -140,30 +164,30 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
strcpy(ifr.ifr_name, dev); strcpy(ifr.ifr_name, dev);
for (i = 0; i < queues; i++) { for (i = 0; i < queues; i++) {
if ((fd = open("/dev/net/tun", O_RDWR)) < 0) if ((fd = open("/dev/net/tun", O_RDWR)) < 0)
goto err; goto err;
err = ioctl(fd, TUNSETIFF, (void *)&ifr); err = ioctl(fd, TUNSETIFF, (void *)&ifr);
if (err) { if (err) {
close(fd); close(fd);
goto err; goto err;
} }
fds[i] = fd; fds[i] = fd;
} }
return 0; return 0;
err: err:
for (--i; i >= 0; i--) for (--i; i >= 0; i--)
close(fds[i]); close(fds[i]);
return err; return err;
} }
A new ioctl(TUNSETQUEUE) were introduced to enable or disable a queue. When 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_DETACH_QUEUE flag, the queue were disabled. And when
calling it with IFF_ATTACH_QUEUE flag, the queue were enabled. The queue were calling it with IFF_ATTACH_QUEUE flag, the queue were enabled. The queue were
enabled by default after it was created through TUNSETIFF. enabled by default after it was created through TUNSETIFF.
fd is the file descriptor (queue) that we want to enable or disable, when fd is the file descriptor (queue) that we want to enable or disable, when
enable is true we enable it, otherwise we disable it enable is true we enable it, otherwise we disable it::
#include <linux/if.h> #include <linux/if.h>
#include <linux/if_tun.h> #include <linux/if_tun.h>
@@ -175,53 +199,61 @@ Copyright (C) 1999-2000 Maxim Krasnyansky <max_mk@yahoo.com>
memset(&ifr, 0, sizeof(ifr)); memset(&ifr, 0, sizeof(ifr));
if (enable) if (enable)
ifr.ifr_flags = IFF_ATTACH_QUEUE; ifr.ifr_flags = IFF_ATTACH_QUEUE;
else else
ifr.ifr_flags = IFF_DETACH_QUEUE; ifr.ifr_flags = IFF_DETACH_QUEUE;
return ioctl(fd, TUNSETQUEUE, (void *)&ifr); return ioctl(fd, TUNSETQUEUE, (void *)&ifr);
} }
Universal TUN/TAP device driver Frequently Asked Question. Universal TUN/TAP device driver Frequently Asked Question
=========================================================
1. What platforms are supported by TUN/TAP driver ? 1. What platforms are supported by TUN/TAP driver ?
Currently driver has been written for 3 Unices: Currently driver has been written for 3 Unices:
Linux kernels 2.2.x, 2.4.x
FreeBSD 3.x, 4.x, 5.x - Linux kernels 2.2.x, 2.4.x
Solaris 2.6, 7.0, 8.0 - FreeBSD 3.x, 4.x, 5.x
- Solaris 2.6, 7.0, 8.0
2. What is TUN/TAP driver used for? 2. What is TUN/TAP driver used for?
As mentioned above, main purpose of TUN/TAP driver is tunneling.
As mentioned above, main purpose of TUN/TAP driver is tunneling.
It is used by VTun (http://vtun.sourceforge.net). It is used by VTun (http://vtun.sourceforge.net).
Another interesting application using TUN/TAP is pipsecd Another interesting application using TUN/TAP is pipsecd
(http://perso.enst.fr/~beyssac/pipsec/), a userspace IPSec (http://perso.enst.fr/~beyssac/pipsec/), a userspace IPSec
implementation that can use complete kernel routing (unlike FreeS/WAN). implementation that can use complete kernel routing (unlike FreeS/WAN).
3. How does Virtual network device actually work ? 3. How does Virtual network device actually work ?
Virtual network device can be viewed as a simple Point-to-Point or Virtual network device can be viewed as a simple Point-to-Point or
Ethernet device, which instead of receiving packets from a physical Ethernet device, which instead of receiving packets from a physical
media, receives them from user space program and instead of sending media, receives them from user space program and instead of sending
packets via physical media sends them to the user space program. packets via physical media sends them to the user space program.
Let's say that you configured IPv6 on the tap0, then whenever Let's say that you configured IPv6 on the tap0, then whenever
the kernel sends an IPv6 packet to tap0, it is passed to the application the kernel sends an IPv6 packet to tap0, it is passed to the application
(VTun for example). The application encrypts, compresses and sends it to (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 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, 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. the kernel handles the packet like it came from real physical device.
4. What is the difference between TUN driver and TAP driver? 4. What is the difference between TUN driver and TAP driver?
TUN works with IP frames. TAP works with Ethernet frames. 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 This means that you have to read/write IP packets when you are using tun and
ethernet frames when using tap. ethernet frames when using tap.
5. What is the difference between BPF and TUN/TAP driver? 5. What is the difference between BPF and TUN/TAP driver?
BPF is an advanced packet filter. It can be attached to existing BPF is an advanced packet filter. It can be attached to existing
network interface. It does not provide a virtual network interface. network interface. It does not provide a virtual network interface.
A TUN/TAP driver does provide a virtual network interface and it is possible A TUN/TAP driver does provide a virtual network interface and it is possible
to attach BPF to this interface. to attach BPF to this interface.
6. Does TAP driver support kernel Ethernet bridging? 6. Does TAP driver support kernel Ethernet bridging?
Yes. Linux and FreeBSD drivers support Ethernet bridging.
Yes. Linux and FreeBSD drivers support Ethernet bridging.

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MAINTAINERS
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@@ -17161,7 +17161,7 @@ TUN/TAP driver
M: Maxim Krasnyansky <maxk@qti.qualcomm.com> M: Maxim Krasnyansky <maxk@qti.qualcomm.com>
S: Maintained S: Maintained
W: http://vtun.sourceforge.net/tun W: http://vtun.sourceforge.net/tun
F: Documentation/networking/tuntap.txt F: Documentation/networking/tuntap.rst
F: arch/um/os-Linux/drivers/ F: arch/um/os-Linux/drivers/
TURBOCHANNEL SUBSYSTEM TURBOCHANNEL SUBSYSTEM

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drivers/net/Kconfig
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@@ -355,7 +355,7 @@ config TUN
devices, driver will automatically delete tunXX or tapXX device and devices, driver will automatically delete tunXX or tapXX device and
all routes corresponding to it. all routes corresponding to it.
Please read <file:Documentation/networking/tuntap.txt> for more Please read <file:Documentation/networking/tuntap.rst> for more
information. information.
To compile this driver as a module, choose M here: the module To compile this driver as a module, choose M here: the module