docs/system: convert Texinfo documentation to rST

Apart from targets.rst, which was written by hand, this is an automated
conversion obtained with the following command:

  makeinfo --force -o - --docbook \
    -D 'qemu_system_x86 QEMU_SYSTEM_X86_MACRO' \
    -D 'qemu_system     QEMU_SYSTEM_MACRO' \
    $texi | pandoc -f docbook -t rst+smart | perl -e '
      $/=undef;
      $_ = <>;
      s/^-  − /-  /gm;
      s/QEMU_SYSTEM_MACRO/|qemu_system|/g;
      s/QEMU_SYSTEM_X86_MACRO/|qemu_system_x86|/g;
      s/(?=::\n\n +\|qemu)/.. parsed-literal/g;
      s/:\n\n::$/::/gm;
      print' > $rst

In addition, the following changes were made manually:

- target-i386.rst and target-mips.rst: replace CPU model documentation with
  an include directive

- monitor.rst: replace the command section with a comment

- images.rst: add toctree

- target-arm.rst: Replace use of :math: (which Sphinx complains
  about) with :sup:, and hide it behind |I2C| and |I2C| substitutions.

Content that is not @included remains exclusive to qemu-doc.texi.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200228153619.9906-20-peter.maydell@linaro.org
Message-id: 20200226113034.6741-19-pbonzini@redhat.com
[PMM: Fixed target-arm.rst use of :math:; remove out of date
 note about images.rst from commit message; fixed expansion
 of |qemu_system_x86|; use parsed-literal in invocation.rst
 when we want to use |qemu_system_x86|; fix incorrect subsection
 level for "OS requirements" in target-i386.rst; fix incorrect
 syntax for making links to other sections of the manual]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 100 insertions, 0 deletions

diff --git a/docs/system/net.rst b/docs/system/net.rst
new file mode 100644
index 0000000000..4b2640c448
--- /dev/null
+++ b/docs/system/net.rst
@@ -0,0 +1,100 @@
+.. _pcsys_005fnetwork:
+
+Network emulation
+-----------------
+
+QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC
+target) and can connect them to a network backend on the host or an
+emulated hub. The various host network backends can either be used to
+connect the NIC of the guest to a real network (e.g. by using a TAP
+devices or the non-privileged user mode network stack), or to other
+guest instances running in another QEMU process (e.g. by using the
+socket host network backend).
+
+Using TAP network interfaces
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the standard way to connect QEMU to a real network. QEMU adds a
+virtual network device on your host (called ``tapN``), and you can then
+configure it as if it was a real ethernet card.
+
+Linux host
+^^^^^^^^^^
+
+As an example, you can download the ``linux-test-xxx.tar.gz`` archive
+and copy the script ``qemu-ifup`` in ``/etc`` and configure properly
+``sudo`` so that the command ``ifconfig`` contained in ``qemu-ifup`` can
+be executed as root. You must verify that your host kernel supports the
+TAP network interfaces: the device ``/dev/net/tun`` must be present.
+
+See :ref:`sec_005finvocation` to have examples of command
+lines using the TAP network interfaces.
+
+Windows host
+^^^^^^^^^^^^
+
+There is a virtual ethernet driver for Windows 2000/XP systems, called
+TAP-Win32. But it is not included in standard QEMU for Windows, so you
+will need to get it separately. It is part of OpenVPN package, so
+download OpenVPN from : https://openvpn.net/.
+
+Using the user mode network stack
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+By using the option ``-net user`` (default configuration if no ``-net``
+option is specified), QEMU uses a completely user mode network stack
+(you don't need root privilege to use the virtual network). The virtual
+network configuration is the following::
+
+        guest (10.0.2.15)  <------>  Firewall/DHCP server <-----> Internet
+                              |          (10.0.2.2)
+                              |
+                              ---->  DNS server (10.0.2.3)
+                              |
+                              ---->  SMB server (10.0.2.4)
+
+The QEMU VM behaves as if it was behind a firewall which blocks all
+incoming connections. You can use a DHCP client to automatically
+configure the network in the QEMU VM. The DHCP server assign addresses
+to the hosts starting from 10.0.2.15.
+
+In order to check that the user mode network is working, you can ping
+the address 10.0.2.2 and verify that you got an address in the range
+10.0.2.x from the QEMU virtual DHCP server.
+
+Note that ICMP traffic in general does not work with user mode
+networking. ``ping``, aka. ICMP echo, to the local router (10.0.2.2)
+shall work, however. If you're using QEMU on Linux >= 3.0, it can use
+unprivileged ICMP ping sockets to allow ``ping`` to the Internet. The
+host admin has to set the ping_group_range in order to grant access to
+those sockets. To allow ping for GID 100 (usually users group)::
+
+   echo 100 100 > /proc/sys/net/ipv4/ping_group_range
+
+When using the built-in TFTP server, the router is also the TFTP server.
+
+When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP
+connections can be redirected from the host to the guest. It allows for
+example to redirect X11, telnet or SSH connections.
+
+Hubs
+~~~~
+
+QEMU can simulate several hubs. A hub can be thought of as a virtual
+connection between several network devices. These devices can be for
+example QEMU virtual ethernet cards or virtual Host ethernet devices
+(TAP devices). You can connect guest NICs or host network backends to
+such a hub using the ``-netdev
+hubport`` or ``-nic hubport`` options. The legacy ``-net`` option also
+connects the given device to the emulated hub with ID 0 (i.e. the
+default hub) unless you specify a netdev with ``-net nic,netdev=xxx``
+here.
+
+Connecting emulated networks between QEMU instances
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Using the ``-netdev socket`` (or ``-nic socket`` or ``-net socket``)
+option, it is possible to create emulated networks that span several
+QEMU instances. See the description of the ``-netdev socket`` option in
+:ref:`sec_005finvocation` to have a basic
+example.