1a3ec8c156
Compatibility properties started life as a qdev property thing: we supported them only for qdev properties, and implemented them with the machinery backing command line option -global. Recent commit fa0cb34d221 put them to use (tacitly) with memory backend objects (subtypes of TYPE_MEMORY_BACKEND). To make that possible, we first moved the work of applying them from the -global machinery into TYPE_DEVICE's .instance_post_init() method device_post_init(), in commits ea9ce8934c5 and b66bbee39f6, then made it available to TYPE_MEMORY_BACKEND's .instance_post_init() method host_memory_backend_post_init() as object_apply_compat_props(), in commit 1c3994f6d2a. Note the code smell: we now have function name starting with object_ in hw/core/qdev.c. It has to be there rather than in qom/, because it calls qdev_get_machine() to find the current accelerator's and machine's compat_props. Turns out calling qdev_get_machine() there is problematic. If we qdev_create() from a machine's .instance_init() method, we call device_post_init() and thus qdev_get_machine() before main() can create "/machine" in QOM. qdev_get_machine() tries to get it with container_get(), which "helpfully" creates it as "container" object, and returns that. object_apply_compat_props() tries to paper over the problem by doing nothing when the value of qdev_get_machine() isn't a TYPE_MACHINE. But the damage is done already: when main() later attempts to create the real "/machine", it fails with "attempt to add duplicate property 'machine' to object (type 'container')", and aborts. Since no machine .instance_init() calls qdev_create() so far, the bug is latent. But since I want to do that, I get to fix the bug first. Observe that object_apply_compat_props() doesn't actually need the MachineState, only its the compat_props member of its MachineClass and AccelClass. This permits a simple fix: register MachineClass and AccelClass compat_props with the object_apply_compat_props() machinery right after these classes get selected. This is actually similar to how things worked before commits ea9ce8934c5 and b66bbee39f6, except we now register much earlier. The old code registered them only after the machine's .instance_init() ran, which would've broken compatibility properties for any devices created there. Cc: Marc-André Lureau <marcandre.lureau@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-Id: <20190308131445.17502-2-armbru@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
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 https://git.qemu.org/git/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 https://git.qemu.org/git/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