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Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
ece6debbb0
https://bugzilla.redhat.com/show_bug.cgi?id=1199182 documents that
after a series of disk snapshots into existing destination images,
followed by active commits of the top image, it is possible for
qemu 2.2 and earlier to end up tracking a different name for the
image than what it would have had when opening the chain afresh.
That is, when starting with the chain 'a <- b <- c', the name
associated with 'b' is how it was spelled in the metadata of 'c',
but when starting with 'a', taking two snapshots into 'a <- b <- c',
then committing 'c' back into 'b', the name associated with 'b' is
now the name used when taking the first snapshot.
Sadly, older qemu doesn't know how to treat different spellings of
the same filename as identical files (it uses strcmp() instead of
checking for the same inode), which means libvirt's attempt to
commit an image using solely the names learned from qcow2 metadata
fails with a cryptic:
error: internal error: unable to execute QEMU command 'block-commit': Top image file /tmp/images/c/../b/b not found
even though the file exists. Trying to teach libvirt the rules on
which name qemu will expect is not worth the effort (besides, we'd
have to remember it across libvirtd restarts, and track whether a
file was opened via metadata or via snapshot creation for a given
qemu process); it is easier to just always directly ask qemu what
string it expects to see in the first place.
As a safety valve, we validate that any name returned by qemu
still maps to the same local file as we have tracked it, so that
a compromised qemu cannot accidentally cause us to act on an
incorrect file.
* src/qemu/qemu_monitor.h (qemuMonitorDiskNameLookup): New
prototype.
* src/qemu/qemu_monitor_json.h (qemuMonitorJSONDiskNameLookup):
Likewise.
* src/qemu/qemu_monitor.c (qemuMonitorDiskNameLookup): New function.
* src/qemu/qemu_monitor_json.c (qemuMonitorJSONDiskNameLookup)
(qemuMonitorJSONDiskNameLookupOne): Likewise.
* src/qemu/qemu_driver.c (qemuDomainBlockCommit)
(qemuDomainBlockJobImpl): Use it.
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit
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| build-aux | ||
| daemon | ||
| docs | ||
| examples | ||
| gnulib | ||
| include | ||
| m4 | ||
| po | ||
| src | ||
| tests | ||
| tools | ||
| .ctags | ||
| .dir-locals.el | ||
| .gitignore | ||
| .gitmodules | ||
| .mailmap | ||
| AUTHORS.in | ||
| autobuild.sh | ||
| autogen.sh | ||
| bootstrap | ||
| bootstrap.conf | ||
| cfg.mk | ||
| ChangeLog-old | ||
| config-post.h | ||
| configure.ac | ||
| COPYING | ||
| COPYING.LESSER | ||
| HACKING | ||
| libvirt-lxc.pc.in | ||
| libvirt-qemu.pc.in | ||
| libvirt.pc.in | ||
| libvirt.spec.in | ||
| Makefile.am | ||
| Makefile.nonreentrant | ||
| mingw-libvirt.spec.in | ||
| README | ||
| README-hacking | ||
| run.in | ||
| TODO | ||
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>