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It's useful to know how much space can be occupied by qcow2 persistent bitmaps, even though such metadata is unrelated to the guest-visible data. Report this value as an additional QMP field, present when measuring an existing image and output format that both support bitmaps. Update iotest 178 and 190 to updated output, as well as new coverage in 190 demonstrating non-zero values made possible with the recently-added qemu-img bitmap command (see 3b51ab4b). The new 'bitmaps size:' field is displayed automatically as part of 'qemu-img measure' any time it is present in QMP (that is, any time both the source image being measured and destination format support bitmaps, even if the measurement is 0 because there are no bitmaps present). If the field is absent, it means that no bitmaps can be copied (source, destination, or both lack bitmaps, including when measuring based on size rather than on a source image). This behavior is compatible with an upcoming patch adding 'qemu-img convert --bitmaps': that command will fail in the same situations where this patch omits the field. The addition of a new field demonstrates why we should always zero-initialize qapi C structs; while the qcow2 driver still fully populates all fields, the raw and crypto drivers had to be tweaked to avoid uninitialized data. Consideration was also given towards having a 'qemu-img measure --bitmaps' which errors out when bitmaps are not possible, and otherwise sums the bitmaps into the existing allocation totals rather than displaying as a separate field, as a potential convenience factor. But this was ultimately decided to be more complexity than necessary when the QMP interface was sufficient enough with bitmaps remaining a separate field. See also: https://bugzilla.redhat.com/1779904 Reported-by: Nir Soffer <nsoffer@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20200521192137.1120211-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.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: .. 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>`_