diff mbox series

[RFC] docs: add a proper feature overview in "About QEMU"

Message ID 20230109170323.3796306-1-alex.bennee@linaro.org
State Superseded
Headers show
Series [RFC] docs: add a proper feature overview in "About QEMU" | expand

Commit Message

Alex Bennée Jan. 9, 2023, 5:03 p.m. UTC 
I decide to do this because I was looking for the best place to add a
reference to a document on semihosting and there didn't seem to be
an obvious place to do this. To do this I took the original pre-amble
to the about index and moved it to its own section, expanding the
description and giving a quick high level overview of some of the key
feature of QEMU.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 docs/about/features.rst       | 236 ++++++++++++++++++++++++++++++++++
 docs/about/index.rst          |  16 +--
 docs/devel/tcg-plugins.rst    |   2 +
 docs/system/arm/emulation.rst |   2 +
 docs/system/index.rst         |   2 +
 docs/system/multi-process.rst |   2 +
 docs/tools/index.rst          |   2 +
 docs/user/index.rst           |   2 +
 8 files changed, 249 insertions(+), 15 deletions(-)
 create mode 100644 docs/about/features.rst

Comments

Peter Maydell Jan. 12, 2023, 4:45 p.m. UTC | #1 
On Mon, 9 Jan 2023 at 17:04, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> I decide to do this because I was looking for the best place to add a
> reference to a document on semihosting and there didn't seem to be
> an obvious place to do this. To do this I took the original pre-amble
> to the about index and moved it to its own section, expanding the
> description and giving a quick high level overview of some of the key
> feature of QEMU.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

To summarise from our conversation on IRC:

(1) I like the current short summary and orientation that we
have at the top of https://www.qemu.org/docs/master/about/index.html
and would prefer not to delete it. We can add hyperlinks to cue
the user that they can go look at the top level sections
for system emulation etc for more detail.

(2) I think most of this text would be better at the start
of docs/system/index.rst and/or in a new subsection at the top
of docs/system (which would be more easily findable from
the top level if we added those hyperlinks).

(3) I don't think we should be mentioning TCI this prominently.

thanks
-- PMM
diff mbox series

Patch

diff --git a/docs/about/features.rst b/docs/about/features.rst
new file mode 100644
index 0000000000..037234c10a
--- /dev/null
+++ b/docs/about/features.rst
@@ -0,0 +1,236 @@ 
+Features
+========
+
+Virtualisation
+--------------
+
+The most common use case for QEMU is to provide a virtual model of a
+machine (CPU, memory and emulated devices) to run a guest OS. It
+supports a number of hypervisors (known as accelerators) as well as a
+dynamic JIT known as the Tiny Code Generator (TCG) capable of
+emulating many CPUs.
+
+.. list-table:: Supported Accelerators
+  :header-rows: 1
+
+  * - Accelerator
+    - Host OS
+    - Host Architectures
+  * - KVM
+    - Linux
+    - Arm (64 bit only), MIPS, PPC, RISC-V, s390x, x86
+  * - Xen
+    - Linux (as dom0)
+    - Arm, x86
+  * - Intel HAXM (hax)
+    - Linux, Windows
+    - x86
+  * - Hypervisor Framework (hvf)
+    - MacOS
+    - x86 (64 bit only), Arm (64 bit only)
+  * - Windows Hypervisor Platform (wphx)
+    - Windows
+    - x86
+  * - NetBSD Virtual Machine Monitor (nvmm)
+    - NetBSD
+    - x86
+  * - Tiny Code Generator (tcg)
+    - Linux, other POSIX, Windows, MacOS
+    - Arm, x86, Loongarch64, MIPS, PPC, s390x, Sparc64, TCI [#tci]_
+
+.. [#tci] The Tiny Code Interpreter (TCI) can be used where there is no
+          explicit support for a processor backend. It will be even
+          slower than normal TCG guests.
+
+Related features
+~~~~~~~~~~~~~~~~
+
+System emulation provides a wide range of device models to emulate
+various hardware components you may want to add to your machine. This
+includes a wide number of VirtIO devices which are specifically tuned
+for efficient operation under virtualisation. Some of the device
+emulation can be offloaded from the main QEMU process using either
+vhost-user (for VirtIO) or :ref:`Multi-process QEMU`. If the platform
+supports it QEMU also supports directly passing devices through to
+guest VMs to eliminate the device emulation overhead. See
+:ref:`device-emulation` for more details.
+
+There is a full featured block layer allows for construction of
+complex storage typologies which can be stacked across multiple layers
+supporting redirection, networking, snapshots and migration support.
+
+The flexible ``chardev`` system allows for handling IO from character
+like devices using stdio, files, unix sockets and TCP networking.
+
+QEMU provides a number of management interfaces including a line based
+Human Monitor Protocol (HMP) that allows you to dynamically add and
+remove devices as well as introspect the system state. The QEMU
+Monitor Protocol (QMP) is a well defined, versioned, machine usable
+API that presents a rich interface to other tools to create, control
+and manage Virtual Machines. This is the interface used by higher
+level tools interfaces such as `Virt Manager
+<https://virt-manager.org/>`_ using the `libvirt framework
+<https://libvirt.org>`_. Using some sort of management layer to
+configure complex QEMU setups is recommended.
+
+For the common accelerators QEMU supported debugging with its
+:ref:`gdbstub<GDB usage>` which allows users to connect GDB and debug
+system software images.
+
+See the :ref:`System Emulation` section of the manual for full details
+of how to run QEMU as a VMM.
+
+Emulation
+---------
+
+As alluded to above QEMU's Tiny Code Generator (TCG) also has the
+ability to emulate a number of CPU architectures on any supported
+platform. This can either be using full system emulation or using its
+"user mode emulation" support to run user space processes compiled for
+one CPU on another CPU.
+
+See `User Mode Emulation` for more details on running in this mode.
+
+.. list-table:: Supported Guest Architectures for Emulation
+  :widths: 30 10 10 50
+  :header-rows: 1
+
+  * - Architecture (qemu name)
+    - System
+    - User-mode
+    - Notes
+  * - Alpha
+    - Yes
+    - Yes
+    - Legacy 64 bit RISC ISA developed by DEC
+  * - Arm (arm, aarch64)
+    - Yes
+    - Yes
+    - Wide range of features, see :ref:`Arm Emulation` for details
+  * - AVR
+    - Yes
+    - No
+    - 8 bit micro controller, often used in maker projects
+  * - Cris
+    - Yes
+    - Yes
+    - Embedded RISC chip developed by AXIS
+  * - Hexagon
+    - No
+    - Yes
+    - Family of DSPs by Qualcomm
+  * - PA-RISC (hppa)
+    - Yes
+    - Yes
+    - A legacy RISC system used in HPs old minicomputers
+  * - x86 (i386, x86_64)
+    - Yes
+    - Yes
+    - The ubiquitous desktop PC CPU architecture, 32 and 64 bit.
+  * - Loongarch
+    - Yes
+    - Yes
+    - A MIPs-like 64bit RISC architecture developed in China
+  * - m68k
+    - Yes
+    - Yes
+    - Motorola 68000 variants and ColdFire
+  * - Microblaze
+    - Yes
+    - Yes
+    - RISC based soft-core by Xilinx
+  * - MIPS (mips, mipsel, mips64, mips64el)
+    - Yes
+    - Yes
+    - Venerable RISC architecture originally out of Stanford University
+  * - Nios2
+    - Yes
+    - Yes
+    - 32 bit embedded soft-core by Altera
+  * - OpenRISC
+    - Yes
+    - Yes
+    - Open source RISC architecture developed by the OpenRISC community
+  * - Power (ppc, ppc64)
+    - Yes
+    - Yes
+    - A general purpose RISC architecture now managed by IBM
+  * - RISC-V
+    - Yes
+    - Yes
+    - An open standard RISC ISA maintained by RISC-V International
+  * - RX
+    - Yes
+    - No
+    - A 32 bit micro controller developed by Renesas
+  * - s390x
+    - Yes
+    - Yes
+    - A 64 bit CPU found in IBM's System Z mainframes
+  * - sh4
+    - Yes
+    - Yes
+    - A 32 bit RISC embedded CPU developed by Hitachi
+  * - SPARC (sparc, sparc64)
+    - Yes
+    - Yes
+    - A RISC ISA originally developed by Sun Microsystems
+  * - Tricore
+    - Yes
+    - No
+    - A 32 bit RISC/uController/DSP developed by Infineon
+  * - Xtensa
+    - Yes
+    - Yes
+    - A configurable 32 bit soft core now owned by Cadence
+
+Semi-hosting
+~~~~~~~~~~~~
+
+A number of guest architecture support semi-hosting which provides a
+way for guest programs to access the host system though a POSIX-like
+system call layer. This has applications for early software bring-up
+making it easy for a guest to dump data or read configuration files
+before a full operating system is implemented.
+
+Some of those guest architectures also support semi-hosting in
+user-mode making the testing of "bare-metal" micro-controller code
+easy in a user-mode environment that doesn't have a full libc port.
+
+Deterministic Execution with Record/Replay
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For system emulation QEMU offers a execution mode called ``icount``
+which allows for guest time to be purely a function of the number of
+instructions executed. Combined with snapshots and a logging of HW
+events a deterministic execution can be recorded and played back at
+will.
+
+gdbstub
+~~~~~~~
+
+Under emulation the :ref:`gdbstub<GDB usage>` is fully supported and
+takes advantage of the implementation to support unlimited breakpoints
+in the guest code. For system emulation we also support an unlimited
+number of memory based watchpoints as well as integration with
+record/replay to support reverse debugging.
+
+
+TCG Plugins
+~~~~~~~~~~~
+
+In any emulation execution mode you can write :ref:`TCG Plugins` which
+can instrument the guest code as it executes to a per-instruction
+granularity. This is useful for writing tools to analyse the real
+world execution behaviour of your programs.
+
+Tools
+-----
+
+QEMU also provides a number of standalone commandline utilities, such
+as the ``qemu-img`` disk image utility that allows you to create,
+convert and modify disk images. While most are expected to be used in
+conjunction with QEMU itself some can also be used with other VMMs
+that support the same interfaces.
+
+See :ref:`Tools` for more details.
diff --git a/docs/about/index.rst b/docs/about/index.rst
index 5bea653c07..6949e6dc93 100644
--- a/docs/about/index.rst
+++ b/docs/about/index.rst
@@ -4,24 +4,10 @@  About QEMU
 
 QEMU is a generic and open source machine emulator and virtualizer.
 
-QEMU can be used in several different ways. The most common is for
-"system emulation", where it 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, Hax or Hypervisor.Framework to
-allow the guest to run directly on the host CPU.
-
-The second supported way to use QEMU is "user mode emulation",
-where QEMU can launch processes compiled for one CPU on another CPU.
-In this mode the CPU is always emulated.
-
-QEMU also provides a number of standalone commandline utilities,
-such as the ``qemu-img`` disk image utility that allows you to create,
-convert and modify disk images.
-
 .. toctree::
    :maxdepth: 2
 
+   features
    build-platforms
    deprecated
    removed-features
diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
index 9740a70406..81dcd43a61 100644
--- a/docs/devel/tcg-plugins.rst
+++ b/docs/devel/tcg-plugins.rst
@@ -3,6 +3,8 @@ 
    Copyright (c) 2019, Linaro Limited
    Written by Emilio Cota and Alex Bennée
 
+.. _TCG Plugins:
+
 QEMU TCG Plugins
 ================
 
diff --git a/docs/system/arm/emulation.rst b/docs/system/arm/emulation.rst
index b33d7c28dc..b87e064d9d 100644
--- a/docs/system/arm/emulation.rst
+++ b/docs/system/arm/emulation.rst
@@ -1,3 +1,5 @@ 
+.. _Arm Emulation:
+
 A-profile CPU architecture support
 ==================================
 
diff --git a/docs/system/index.rst b/docs/system/index.rst
index e3695649c5..282b6ffb56 100644
--- a/docs/system/index.rst
+++ b/docs/system/index.rst
@@ -1,3 +1,5 @@ 
+.. _System Emulation:
+
 ----------------
 System Emulation
 ----------------
diff --git a/docs/system/multi-process.rst b/docs/system/multi-process.rst
index 210531ee17..16f0352416 100644
--- a/docs/system/multi-process.rst
+++ b/docs/system/multi-process.rst
@@ -1,3 +1,5 @@ 
+.. _Multi-process QEMU:
+
 Multi-process QEMU
 ==================
 
diff --git a/docs/tools/index.rst b/docs/tools/index.rst
index 1edd5a8054..2151adcf78 100644
--- a/docs/tools/index.rst
+++ b/docs/tools/index.rst
@@ -1,3 +1,5 @@ 
+.. _Tools:
+
 -----
 Tools
 -----
diff --git a/docs/user/index.rst b/docs/user/index.rst
index 2c4e29f3db..782d27cda2 100644
--- a/docs/user/index.rst
+++ b/docs/user/index.rst
@@ -1,3 +1,5 @@ 
+.. _User Mode Emulation:
+
 -------------------
 User Mode Emulation
 -------------------