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Entity checking goes back to commit ac88219a6c "qapi: New QAPISchema intermediate representation", v2.5.0. It's designed to work as follows: QAPISchema.check() calls .check() for all the schema's entities. An entity's .check() recurses into another entity's .check() only if the C struct generated for the former contains the C struct generated for the latter (pointers don't count). This is used to detect "object contains itself". There are two instances of this: * An object's C struct contains its base's C struct QAPISchemaObjectType.check() calls self.base.check() * An object's C struct contains its variants' C structs QAPISchemaObjectTypeVariants().check calls v.type.check(). Since commit b807a1e1e3 "qapi: Check for QAPI collisions involving variant members", v2.6.0. Thus, only object types can participate in recursion. QAPISchemaObjectType.check() is made for that: it checks @self when called the first time, recursing into base and variants, it reports an "contains itself" error when this recursion reaches an object being checked, and does nothing it reaches an object that has been checked already. The other .check() may safely assume they get called exactly once. Sadly, this design has since eroded: * QAPISchemaCommand.check() and QAPISchemaEvent.check() call .args_type.check(). Since commit c818408e44 "qapi: Implement boxed types for commands/events", v2.7.0. Harmless, since args_type can only be an object type. * QAPISchemaEntity.check() calls ._ifcond.check() when inheriting the condition from another type. Since commit 4fca21c1b0 qapi: leave the ifcond attribute undefined until check(), v3.0.0. This makes simple union wrapper types recurse into the wrapped type (nothing else uses this condition inheritance). The .check() of types used as simple union branch type get called multiple times. * QAPISchemaObjectType.check() calls its super type's .check() *before* the conditional handling multiple calls. Also since commit 4fca21c1b0. QAPISchemaObjectType.check()'s guard against multiple checking doesn't protect QAPISchemaEntity.check(). * QAPISchemaArrayType.check() calls .element_type.check(). Also since commit 4fca21c1b0. The .check() of types used as array element types get called multiple times. Commit 56a4689582 "qapi: Fix array first used in a different module" (v4.0.0) added more code relying on this .element_type.check(). The absence of explosions suggests the .check() involved happen to be effectively idempotent. Fix the unwanted recursion anyway: * QAPISchemaCommand.check() and QAPISchemaEvent.check() calling .args_type.check() is unnecessary. Delete the calls. * Fix QAPISchemaObjectType.check() to call its super type's .check() after the conditional handling multiple calls. * A QAPISchemaEntity's .ifcond becomes valid at .check(). This is due to arrays and simple unions. Most types get ifcond and info passed to their constructor. Array types don't: they get it from their element type, which becomes known only in .element_type.check(). The implicit wrapper object types for simple union branches don't: they get it from the wrapped type, which might be an array. Ditch the idea to set .ifcond in .check(). Instead, turn it into a property and compute it on demand. Safe because it's only used after the schema has been checked. Most types simply return the ifcond passed to their constructor. Array types forward to their .element_type instead, and the wrapper types forward to the wrapped type. * A QAPISchemaEntity's .module becomes valid at .check(). This is because computing it needs info and schema.fname, and because array types get it from their element type instead. Make it a property just like .ifcond. Additionally, have QAPISchemaEntity.check() assert it gets called at most once, so the design invariant will stick this time. Neglecting that was entirely my fault. Signed-off-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20190914153506.2151-19-armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> [Commit message tidied up]
=========== 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: .. code-block:: shell 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. .. code-block:: shell 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 CODING_STYLE.rst file. 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. .. code-block:: shell 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: .. code-block:: shell $ 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: .. code-block:: shell $ 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 * `<mailto: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>`_