According to commit 047f7038f5, option --preconfig
[...] allows pausing QEMU in the new RUN_STATE_PRECONFIG state,
allowing the configuration of QEMU from QMP before the machine
jumps into board initialization code of machine_run_board_init()
The intent is to allow management to query machine state and
additionally configure it using previous query results within one
QEMU instance (i.e. eliminate the need to start QEMU twice, 1st to
query board specific parameters and 2nd for actual VM start using
query results for additional parameters).
The implementation is a bit of a hack: it splices in an additional
main loop before machine creation, in special runstate preconfig. New
command exit-preconfig exits that main loop. QEMU continues
initializing, creates the machine, and runs the good old main loop.
The replacement of the main loop is transparent to monitors.
Sadly, some commands expect initialization to be complete. Running
them in --preconfig's main loop violates their preconditions. Since
we don't really know which commands are safe, we use a whitelist.
This drags the concept of run state into the QMP core.
The whitelist is done as a command flag in the QAPI schema (commit
d6fe3d02e9). Drags the concept of run state further into the QAPI
language.
The command flag is exposed in query-qmp-schema (also commit
d6fe3d02e9). This makes it ABI.
I consider the whole thing an offensively ugly hack, but sometimes an
ugly hack is the best we can do to solve a problem people have.
The need described by the commit message quote above is genuine. The
proper solution would be a main loop that permits complete
configuration via QMP. This is out of reach, thus the hack.
However, even though the need is genuine, it isn't urgent: libvirt is
not going to use this anytime soon. Baking a hack into ABI before it
has any users is a bad idea.
This commit reverts the parts of commit d6fe3d02e9 that affect ABI
via query-qmp-schema. The commit did the following:
(1) Add command flag 'allow-preconfig' to the QAPI schema language
(2) Pass it to code generators
(3) Have the commands.py code generator pass it to the command
registry (so commit 047f7038f5 can use it as whitelist)
(4) Add 'allow-preconfig' to SchemaInfoCommand (neglecting to update
qapi-code-gen.txt section "Client JSON Protocol introspection")
(5) Set 'allow-preconfig': true for commands qmp_capabilities,
query-commands, query-command-line-options, query-status
Revert exactly (4), plus a bit of documentation added to
qemu-tech.info in commit 047f7038f5.
Shrinks query-qmp-schema's output from 126.5KiB to 121.8KiB for me.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180705091402.26244-2-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
[Straightforward conflict with commit d626b6c1ae resolved]
QEMU README
===========
QEMU is a generic and open source machine & userspace emulator and
virtualizer.
QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).
QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.
QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.
QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.
Building
========
QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:
mkdir build
cd build
../configure
make
Additional information can also be found online via the QEMU website:
https://qemu.org/Hosts/Linux
https://qemu.org/Hosts/Mac
https://qemu.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu.org/qemu.git
When submitting patches, one common approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
https://qemu.org/Contribute/SubmitAPatch
https://qemu.org/Contribute/TrivialPatches
The QEMU website is also maintained under source control.
git clone git://git.qemu.org/qemu-web.git
https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/
A 'git-publish' utility was created to make above process less
cumbersome, and is highly recommended for making regular contributions,
or even just for sending consecutive patch series revisions. It also
requires a working 'git send-email' setup, and by default doesn't
automate everything, so you may want to go through the above steps
manually for once.
For installation instructions, please go to
https://github.com/stefanha/git-publish
The workflow with 'git-publish' is:
$ git checkout master -b my-feature
$ # work on new commits, add your 'Signed-off-by' lines to each
$ git publish
Your patch series will be sent and tagged as my-feature-v1 if you need to refer
back to it in the future.
Sending v2:
$ git checkout my-feature # same topic branch
$ # making changes to the commits (using 'git rebase', for example)
$ git publish
Your patch series will be sent with 'v2' tag in the subject and the git tip
will be tagged as my-feature-v2.
Bug reporting
=============
The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:
https://bugs.launchpad.net/qemu/
If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via launchpad.
For additional information on bug reporting consult:
https://qemu.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
https://lists.nongnu.org/mailman/listinfo/qemu-devel
- #qemu on irc.oftc.net
Information on additional methods of contacting the community can be
found online via the QEMU website:
https://qemu.org/Contribute/StartHere
-- End