Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

2 files changed, 259 insertions, 0 deletions

diff --git a/docs/user/index.rst b/docs/user/index.rst
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+-------------------
+User Mode Emulation
+-------------------
+
+This section of the manual is the overall guide for users using QEMU
+for user-mode emulation.  In this mode, QEMU can launch
+processes compiled for one CPU on another CPU.
+
+.. toctree::
+   :maxdepth: 2
+
+   main
diff --git a/docs/user/main.rst b/docs/user/main.rst
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+QEMU User space emulator
+========================
+
+Supported Operating Systems
+---------------------------
+
+The following OS are supported in user space emulation:
+
+-  Linux (referred as qemu-linux-user)
+
+-  BSD (referred as qemu-bsd-user)
+
+Features
+--------
+
+QEMU user space emulation has the following notable features:
+
+**System call translation:**
+   QEMU includes a generic system call translator. This means that the
+   parameters of the system calls can be converted to fix endianness and
+   32/64-bit mismatches between hosts and targets. IOCTLs can be
+   converted too.
+
+**POSIX signal handling:**
+   QEMU can redirect to the running program all signals coming from the
+   host (such as ``SIGALRM``), as well as synthesize signals from
+   virtual CPU exceptions (for example ``SIGFPE`` when the program
+   executes a division by zero).
+
+   QEMU relies on the host kernel to emulate most signal system calls,
+   for example to emulate the signal mask. On Linux, QEMU supports both
+   normal and real-time signals.
+
+**Threading:**
+   On Linux, QEMU can emulate the ``clone`` syscall and create a real
+   host thread (with a separate virtual CPU) for each emulated thread.
+   Note that not all targets currently emulate atomic operations
+   correctly. x86 and Arm use a global lock in order to preserve their
+   semantics.
+
+QEMU was conceived so that ultimately it can emulate itself. Although it
+is not very useful, it is an important test to show the power of the
+emulator.
+
+Linux User space emulator
+-------------------------
+
+Command line options
+~~~~~~~~~~~~~~~~~~~~
+
+::
+
+   qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] [-B offset] [-R size] program [arguments...]
+
+``-h``
+   Print the help
+
+``-L path``
+   Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
+
+``-s size``
+   Set the x86 stack size in bytes (default=524288)
+
+``-cpu model``
+   Select CPU model (-cpu help for list and additional feature
+   selection)
+
+``-E var=value``
+   Set environment var to value.
+
+``-U var``
+   Remove var from the environment.
+
+``-B offset``
+   Offset guest address by the specified number of bytes. This is useful
+   when the address region required by guest applications is reserved on
+   the host. This option is currently only supported on some hosts.
+
+``-R size``
+   Pre-allocate a guest virtual address space of the given size (in
+   bytes). \"G\", \"M\", and \"k\" suffixes may be used when specifying
+   the size.
+
+Debug options:
+
+``-d item1,...``
+   Activate logging of the specified items (use '-d help' for a list of
+   log items)
+
+``-p pagesize``
+   Act as if the host page size was 'pagesize' bytes
+
+``-g port``
+   Wait gdb connection to port
+
+``-singlestep``
+   Run the emulation in single step mode.
+
+Environment variables:
+
+QEMU_STRACE
+   Print system calls and arguments similar to the 'strace' program
+   (NOTE: the actual 'strace' program will not work because the user
+   space emulator hasn't implemented ptrace). At the moment this is
+   incomplete. All system calls that don't have a specific argument
+   format are printed with information for six arguments. Many
+   flag-style arguments don't have decoders and will show up as numbers.
+
+Other binaries
+~~~~~~~~~~~~~~
+
+-  user mode (Alpha)
+
+   * ``qemu-alpha`` TODO.
+
+-  user mode (Arm)
+
+   * ``qemu-armeb`` TODO.
+
+   * ``qemu-arm`` is also capable of running Arm \"Angel\" semihosted ELF
+     binaries (as implemented by the arm-elf and arm-eabi Newlib/GDB
+     configurations), and arm-uclinux bFLT format binaries.
+
+-  user mode (ColdFire)
+
+-  user mode (M68K)
+
+   * ``qemu-m68k`` is capable of running semihosted binaries using the BDM
+     (m5xxx-ram-hosted.ld) or m68k-sim (sim.ld) syscall interfaces, and
+     coldfire uClinux bFLT format binaries.
+
+   The binary format is detected automatically.
+
+-  user mode (Cris)
+
+   * ``qemu-cris`` TODO.
+
+-  user mode (i386)
+
+   * ``qemu-i386`` TODO.
+   * ``qemu-x86_64`` TODO.
+
+-  user mode (Microblaze)
+
+   * ``qemu-microblaze`` TODO.
+
+-  user mode (MIPS)
+
+   * ``qemu-mips`` executes 32-bit big endian MIPS binaries (MIPS O32 ABI).
+
+   * ``qemu-mipsel`` executes 32-bit little endian MIPS binaries (MIPS O32 ABI).
+
+   * ``qemu-mips64`` executes 64-bit big endian MIPS binaries (MIPS N64 ABI).
+
+   * ``qemu-mips64el`` executes 64-bit little endian MIPS binaries (MIPS N64
+     ABI).
+
+   * ``qemu-mipsn32`` executes 32-bit big endian MIPS binaries (MIPS N32 ABI).
+
+   * ``qemu-mipsn32el`` executes 32-bit little endian MIPS binaries (MIPS N32
+     ABI).
+
+-  user mode (NiosII)
+
+   * ``qemu-nios2`` TODO.
+
+-  user mode (PowerPC)
+
+   * ``qemu-ppc64abi32`` TODO.
+   * ``qemu-ppc64`` TODO.
+   * ``qemu-ppc`` TODO.
+
+-  user mode (SH4)
+
+   * ``qemu-sh4eb`` TODO.
+   * ``qemu-sh4`` TODO.
+
+-  user mode (SPARC)
+
+   * ``qemu-sparc`` can execute Sparc32 binaries (Sparc32 CPU, 32 bit ABI).
+
+   * ``qemu-sparc32plus`` can execute Sparc32 and SPARC32PLUS binaries
+     (Sparc64 CPU, 32 bit ABI).
+
+   * ``qemu-sparc64`` can execute some Sparc64 (Sparc64 CPU, 64 bit ABI) and
+     SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).
+
+BSD User space emulator
+-----------------------
+
+BSD Status
+~~~~~~~~~~
+
+-  target Sparc64 on Sparc64: Some trivial programs work.
+
+Quick Start
+~~~~~~~~~~~
+
+In order to launch a BSD process, QEMU needs the process executable
+itself and all the target dynamic libraries used by it.
+
+-  On Sparc64, you can just try to launch any process by using the
+   native libraries::
+
+      qemu-sparc64 /bin/ls
+
+Command line options
+~~~~~~~~~~~~~~~~~~~~
+
+::
+
+   qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
+
+``-h``
+   Print the help
+
+``-L path``
+   Set the library root path (default=/)
+
+``-s size``
+   Set the stack size in bytes (default=524288)
+
+``-ignore-environment``
+   Start with an empty environment. Without this option, the initial
+   environment is a copy of the caller's environment.
+
+``-E var=value``
+   Set environment var to value.
+
+``-U var``
+   Remove var from the environment.
+
+``-bsd type``
+   Set the type of the emulated BSD Operating system. Valid values are
+   FreeBSD, NetBSD and OpenBSD (default).
+
+Debug options:
+
+``-d item1,...``
+   Activate logging of the specified items (use '-d help' for a list of
+   log items)
+
+``-p pagesize``
+   Act as if the host page size was 'pagesize' bytes
+
+``-singlestep``
+   Run the emulation in single step mode.