docs: add a glossary

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20241209183104.365796-7-pierrick.bouvier@linaro.org>
[AJB: update MAINTAINERS]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-37-alex.bennee@linaro.org>

MAINTAINERS

@@ -79,6 +79,7 @@ F: docs/devel/conflict-resolution.rst
 F: docs/devel/style.rst
 F: docs/devel/submitting-a-patch.rst
 F: docs/devel/submitting-a-pull-request.rst
+F: docs/glossary.rst
 
 Responsible Disclosure, Reporting Security Issues
 -------------------------------------------------

docs/devel/control-flow-integrity.rst

@@ -1,3 +1,5 @@
+.. _cfi:
+
 ============================
 Control-Flow Integrity (CFI)
 ============================

docs/devel/multi-thread-tcg.rst

@@ -4,6 +4,8 @@
   This work is licensed under the terms of the GNU GPL, version 2 or
   later. See the COPYING file in the top-level directory.
 
+.. _mttcg:
+
 ==================
 Multi-threaded TCG
 ==================

docs/glossary.rst

@@ -0,0 +1,280 @@
+.. _Glossary:
+
+--------
+Glossary
+--------
+
+This section of the manual presents brief definitions of acronyms and terms used
+by QEMU developers.
+
+Accelerator
+-----------
+
+A specific API used to accelerate execution of guest instructions. It can be
+hardware-based, through a virtualization API provided by the host OS (kvm, hvf,
+whpx, ...), or software-based (tcg). See this description of `supported
+accelerators<Accelerators>`.
+
+Board
+-----
+
+Another name for :ref:`machine`.
+
+Block
+-----
+
+Block drivers are the available `disk formats and front-ends
+<block-drivers>` available, and block devices `(see Block device section on
+options page)<sec_005finvocation>` are using them to implement disks for a
+virtual machine.
+
+CFI
+---
+
+Control Flow Integrity is a hardening technique used to prevent exploits
+targeting QEMU by detecting unexpected branches during execution. QEMU `actively
+supports<cfi>` being compiled with CFI enabled.
+
+Device
+------
+
+In QEMU, a device is a piece of hardware visible to the guest. Examples include
+UARTs, PCI controllers, PCI cards, VGA controllers, and many more.
+
+QEMU is able to emulate a CPU, and all the hardware interacting with it,
+including `many devices<device-emulation>`. When QEMU runs a virtual machine
+using a hardware-based accelerator, it is responsible for emulating, using
+software, all devices.
+
+EDK2
+----
+
+EDK2, as known as `TianoCore <https://www.tianocore.org/>`_, is an open source
+implementation of UEFI standard. QEMU virtual machines that boot a UEFI firmware
+usually use EDK2.
+
+gdbstub
+-------
+
+QEMU implements a `gdb server <GDB usage>`, allowing gdb to attach to it and
+debug a running virtual machine, or a program in user-mode. This allows
+debugging the guest code that is running inside QEMU.
+
+glib2
+-----
+
+`GLib2 <https://docs.gtk.org/glib/>`_ is one of the most important libraries we
+are using through the codebase. It provides many data structures, macros, string
+and thread utilities and portable functions across different OS. It's required
+to build QEMU.
+
+Guest agent
+-----------
+
+The `QEMU Guest Agent <qemu-ga>` is a daemon intended to be run within virtual
+machines. It provides various services to help QEMU to interact with it.
+
+.. _guest:
+
+Guest
+-----
+
+Guest is the architecture of the virtual machine, which is emulated.
+See also :ref:`host`.
+
+Sometimes this is called the :ref:`target` architecture, but that term
+can be ambiguous.
+
+.. _host:
+
+Host
+----
+
+Host is the architecture on which QEMU is running on, which is native.
+See also :ref:`guest`.
+
+Hypervisor
+----------
+
+The formal definition of an hypervisor is a program or API than can be used to
+manage a virtual machine. QEMU is a virtualizer, that interacts with various
+hypervisors.
+
+In the context of QEMU, an hypervisor is an API, provided by the Host OS,
+allowing to execute virtual machines. Linux implementation is KVM (and supports
+Xen as well). For MacOS, it's HVF. Windows defines WHPX. And NetBSD provides
+NVMM.
+
+.. _machine:
+
+Machine
+-------
+
+QEMU's system emulation models many different types of hardware. A machine model
+(sometimes called a board model) is the model of a complete virtual system with
+RAM, one or more CPUs, and various devices. It can be selected with the option
+``-machine`` of qemu-system. Our machine models can be found on this `page
+<system-targets-ref>`.
+
+Migration
+---------
+
+QEMU can save and restore the execution of a virtual machine between different
+host systems. This is provided by the `Migration framework<migration>`.
+
+NBD
+---
+
+The `QEMU Network Block Device server <qemu-nbd>` is a tool that can be used to
+mount and access QEMU images, providing functionality similar to a loop device.
+
+Mailing List
+------------
+
+This is `where <https://wiki.qemu.org/Contribute/MailingLists>`_ all the
+development happens! Changes are posted as series, that all developers can
+review and share feedback for.
+
+For reporting issues, our `GitLab
+<https://gitlab.com/qemu-project/qemu/-/issues>`_ tracker is the best place.
+
+.. _softmmu:
+
+MMU / softmmu
+-------------
+
+The Memory Management Unit is responsible for translating virtual addresses to
+physical addresses and managing memory protection. QEMU system mode is named
+"softmmu" precisely because it implements this in software, including a TLB
+(Translation lookaside buffer), for the guest virtual machine.
+
+QEMU user-mode does not implement a full software MMU, but "simply" translates
+virtual addresses by adding a specific offset, and relying on host MMU/OS
+instead.
+
+Monitor / QMP / HMP
+-------------------
+
+The `QEMU Monitor <QEMU monitor>` is a text interface which can be used to interact
+with a running virtual machine.
+
+QMP stands for QEMU Monitor Protocol and is a json based interface.
+HMP stands for Human Monitor Protocol and is a set of text commands available
+for users who prefer natural language to json.
+
+MTTCG
+-----
+
+Multiple CPU support was first implemented using a round-robin algorithm
+running on a single thread. Later on, `Multi-threaded TCG <mttcg>` was developed
+to benefit from multiple cores to speed up execution.
+
+Plugins
+-------
+
+`TCG Plugins <TCG Plugins>` is an API used to instrument guest code, in system
+and user mode. The end goal is to have a similar set of functionality compared
+to `DynamoRIO <https://dynamorio.org/>`_ or `valgrind <https://valgrind.org/>`_.
+
+One key advantage of QEMU plugins is that they can be used to perform
+architecture agnostic instrumentation.
+
+Patchew
+-------
+
+`Patchew <https://patchew.org/QEMU/>`_ is a website that tracks patches on the
+Mailing List.
+
+PR
+--
+
+Once a series is reviewed and accepted by a subsystem maintainer, it will be
+included in a PR (Pull Request) that the project maintainer will merge into QEMU
+main branch, after running tests.
+
+The QEMU project doesn't currently expect most developers to directly submit
+pull requests.
+
+QCOW2
+-----
+
+QEMU Copy On Write is a disk format developed by QEMU. It provides transparent
+compression, automatic extension, and many other advantages over a raw image.
+
+qcow2 is the recommended format to use.
+
+QEMU
+----
+
+`QEMU (Quick Emulator) <https://www.qemu.org/>`_ is a generic and open source
+machine emulator and virtualizer.
+
+QOM
+---
+
+`QEMU Object Model <qom>` is an object oriented API used to define various
+devices and hardware in the QEMU codebase.
+
+Record/replay
+-------------
+
+`Record/replay <replay>` is a feature of QEMU allowing to have a deterministic
+and reproducible execution of a virtual machine.
+
+Rust
+----
+
+`A new programming language <https://www.rust-lang.org/>`_, memory safe by
+default. There is a work in progress to integrate it in QEMU codebase for
+various subsystems.
+
+System mode
+-----------
+
+QEMU System mode provides a virtual model of an entire machine (CPU, memory and
+emulated devices) to run a guest OS. In this mode the CPU may be fully emulated,
+or it may work with a hypervisor such as KVM, Xen or Hypervisor.Framework to
+allow the guest to run directly on the host CPU.
+
+QEMU System mode is called :ref:`softmmu <softmmu>` as well.
+
+.. _target:
+
+Target
+------
+
+The term "target" can be ambiguous. In most places in QEMU it is used as a
+synonym for :ref:`guest`. For example the code for emulating Arm CPUs is in
+``target/arm/``. However in the :ref:`TCG subsystem <tcg>` "target" refers to the
+architecture which QEMU is running on, i.e. the :ref:`host`.
+
+TCG
+---
+
+TCG is the QEMU `Tiny Code Generator <tcg>`. It is the JIT (just-in-time)
+compiler we use to emulate a guest CPU in software.
+
+It is one of the accelerators supported by QEMU, and supports a lot of
+guest/host architectures.
+
+User mode
+---------
+
+QEMU User mode can launch processes compiled for one CPU on another CPU. In this
+mode the CPU is always emulated. In this mode, QEMU translate system calls from
+guest to host kernel. It is available for Linux and BSD.
+
+VirtIO
+------
+
+VirtIO is an open standard used to define and implement virtual devices with a
+minimal overhead, defining a set of data structures and hypercalls (similar to
+system calls, but targeting an hypervisor, which happens to be QEMU in our
+case). It's designed to be more efficient than emulating a real device, by
+minimizing the amount of interactions between a guest VM and its hypervisor.
+
+vhost-user
+----------
+
+`Vhost-user <vhost_user>` is an interface used to implement VirtIO devices
+outside of QEMU itself.

docs/index.rst

@@ -20,3 +20,4 @@ Welcome to QEMU's documentation!
    interop/index
    specs/index
    devel/index
+   glossary

docs/system/arm/virt.rst

@@ -1,3 +1,5 @@
+.. _arm-virt:
+
 'virt' generic virtual platform (``virt``)
 ==========================================
 

docs/system/images.rst

@@ -82,4 +82,6 @@ VM snapshots currently have the following known limitations:
 -  A few device drivers still have incomplete snapshot support so their
    state is not saved or restored properly (in particular USB).
 
+.. _block-drivers:
+
 .. include:: qemu-block-drivers.rst.inc

docs/tools/qemu-nbd.rst

@@ -1,3 +1,5 @@
+.. _qemu-nbd:
+
 =====================================
 QEMU Disk Network Block Device Server
 =====================================