c0644771eb
Alternates are sum types like unions, but use the JSON type on the wire / QType in QObject instead of an explicit tag. That's why we require alternate members to have distinct QTypes. The recently introduced keyval_parse() (commit d454dbe) can only produce string scalars. The qobject_input_visitor_new_keyval() input visitor mostly hides the difference, so code using a QObject input visitor doesn't have to care whether its input was parsed from JSON or KEY=VALUE,... The difference leaks for alternates, as noted in commit 0ee9ae7: a non-string, non-enum scalar alternate value can't currently be expressed. In part, this is just our insufficiently sophisticated implementation. Consider alternate type 'GuestFileWhence'. It has an integer member and a 'QGASeek' member. The latter is an enumeration with values 'set', 'cur', 'end'. The meaning of b=set, b=cur, b=end, b=0, b=1 and so forth is perfectly obvious. However, our current implementation falls apart at run time for b=0, b=1, and so forth. Fixable, but not today; add a test case and a TODO comment. Now consider an alternate type with a string and an integer member. What's the meaning of a=42? Is it the string "42" or the integer 42? Whichever meaning you pick makes the other inexpressible. This isn't just an implementation problem, it's fundamental. Our current implementation will pick string. So far, we haven't needed such alternates. To make sure we stop and think before we add one that cannot sanely work with keyval_parse(), let's require alternate members to have sufficiently distinct representation in KEY=VALUE,... syntax: * A string member clashes with any other scalar member * An enumeration member clashes with bool members when it has value 'on' or 'off'. * An enumeration member clashes with numeric members when it has a value that starts with '-', '+', or a decimal digit. This is a rather lazy approximation of the actual number syntax accepted by the visitor. Note that enumeration values starting with '-' and '+' are rejected elsewhere already, but better safe than sorry. Signed-off-by: Markus Armbruster <armbru@redhat.com> Message-Id: <1495471335-23707-5-git-send-email-armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@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:
http://qemu-project.org/Hosts/Linux
http://qemu-project.org/Hosts/Mac
http://qemu-project.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu-project.org/qemu.git
When submitting patches, the preferred 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
http://qemu-project.org/Contribute/SubmitAPatch
http://qemu-project.org/Contribute/TrivialPatches
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:
http://qemu-project.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
http://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:
http://qemu-project.org/Contribute/StartHere
-- End