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.
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Eric Blake c615c14246 virsh: Add snapshot-list --topological
For snapshots, virsh already has a (shockingly naive [1]) client-side
topological sorter with the --tree option. But as a series of REDEFINE
calls must be presented in topological order, it's worth letting the
server do the work for us, especially since the server can give us a
topological sorting with less effort than our naive client
reconstruction.

[1] The XXX comment in virshSnapshotListCollect() about --tree being
O(n^3) is telling; https://en.wikipedia.org/wiki/Topological_sorting
is an interesting resource describing Kahn's algorithm and other
approaches for O(n) topological sorting for anyone motivated to use a
more elegant algorithm than brute force - but that doesn't affect this
patch.

For now, I am purposefully NOT implementing virsh fallback code to
provide a topological sort when the flag was rejected as unsupported;
we can worry about that down the road if users actually demonstrate
that they use new virsh but old libvirt to even need the fallback.
(The code we use for --tree could be repurposed to be such a fallback,
whether or not we keep it naive or improve it to be faster - but
again, no one should spend time on a fallback without evidence that we
need it.)

The test driver makes it easy to test:
$ virsh -c test:///default '
snapshot-create-as test a
snapshot-create-as test c
snapshot-create-as test b
snapshot-list test
snapshot-list test --topological
snapshot-list test --descendants a
snapshot-list test --descendants a --topological
snapshot-list test --tree
snapshot-list test --tree --topological
'

Without any flags, virsh does client-side sorting alphabetically, and
lists 'b' before 'c' (even though 'c' is the parent of 'b'); with the
flag, virsh skips sorting, and you can now see that the server handed
back data in a correct ordering. As shown here with a simple linear
chain, there isn't any other possible ordering, so --tree mode doesn't
seem to care whether --topological is used.  But it is possible to
compose more complicated DAGs with multiple children to a parent
(representing reverting back to a snapshot then creating more
snapshots along those divergent execution timelines), where it is then
possible (but not guaranteed) that adding the --topological flag
changes the --tree output (the client-side --tree algorithm breaks
ties based on alphabetical sorting between two nodes that share the
same parent, while the --topological sort skips the client-side
alphabetical sort and ends up exposing the server's internal order for
siblings, whether that be historical creation order or dependent on a
random hash seed).  But even if the results differ, they will still be
topologically correct.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
2019-03-12 20:46:09 -05:00
.gnulib@8089c00979 maint: update gnulib for syntax-check on BSD 2019-01-07 13:54:07 -06:00
build-aux Fix header ifdef check for config-post.h in VPATH build 2018-12-14 14:08:51 +00:00
docs conf: Introduce firmware attribute to <os/> 2019-03-12 15:29:44 +01:00
examples Drop some useless comparisons and checks 2019-03-07 09:22:47 +01:00
gnulib maint: Fix VPATH build 2019-01-07 21:56:16 -06:00
include/libvirt snapshots: Add flag to guarantee topological sort 2019-03-12 20:38:53 -05:00
m4 tools: Drop support for pre-2.4.0 wireshark 2019-02-12 09:22:59 +01:00
po po: refresh translations from zanata 2019-01-14 18:10:21 +00:00
src qemu: Support topological visits 2019-03-12 20:46:09 -05:00
tests qemu: Enable firmware autoselection 2019-03-12 16:09:55 +01:00
tools virsh: Add snapshot-list --topological 2019-03-12 20:46:09 -05:00
.color_coded.in Add color_coded support 2017-05-09 09:51:11 +02:00
.ctags ctags: Generate tags for headers, i.e. function prototypes 2018-09-18 14:21:33 +02:00
.dir-locals.el
.gitignore tools: Keep wireshark plugin registration code in git 2019-02-12 09:22:59 +01:00
.gitmodules gnulib: switch to use https:// instead of git:// protocol 2018-03-19 16:32:34 +00:00
.gitpublish git: add config file telling git-publish how to send patches 2018-04-23 11:36:09 +01:00
.mailmap AUTHORS: Add Katerina Koukiou 2018-07-17 17:01:19 +02:00
.travis.yml travis: Switch from Docker Hub to quay.io 2018-11-13 13:46:38 +01:00
.ycm_extra_conf.py.in Add YouCompleteMe support 2017-05-09 09:51:11 +02:00
ABOUT-NLS po: provide custom make rules for po file management 2018-04-19 10:35:58 +01:00
AUTHORS.in AUTHORS: Add Katerina Koukiou 2018-07-17 17:01:19 +02:00
autogen.sh po: provide custom make rules for po file management 2018-04-19 10:35:58 +01:00
bootstrap maint: update gnulib for syntax-check on BSD 2019-01-07 13:54:07 -06:00
bootstrap.conf bootstrap.conf: Fix LGPL information 2019-01-25 14:04:19 +01:00
cfg.mk syntax-check: require intialization for new VIR_AUTO macros 2019-03-04 13:04:20 +01:00
ChangeLog-old
config-post.h config-post: Remove duplicated 'undef WITH_CAPNG' 2019-01-21 14:44:47 +01:00
configure.ac maint: Post-release version bump to 5.1.0 2019-03-04 12:42:24 +01:00
COPYING
COPYING.LESSER maint: Remove control characters from LGPL license file 2015-09-25 09:16:24 +02:00
libvirt-admin.pc.in Add libvirt-admin library 2015-06-16 13:46:20 +02:00
libvirt-lxc.pc.in
libvirt-qemu.pc.in
libvirt.pc.in
libvirt.spec.in rpm: add dep on xfsprogs-devel for reflink support 2019-03-07 11:46:16 +00:00
Makefile.am Forget last daemon/ dir artefacts 2018-07-27 15:44:38 +02:00
Makefile.nonreentrant Remove backslash alignment attempts 2017-11-03 13:24:12 +01:00
mingw-libvirt.spec.in docs: Add schema for storage pool capabilities 2019-03-06 11:12:48 -05:00
README Provide a useful README file 2017-05-22 17:01:37 +01:00
README-hacking docs: update all GIT repo examples to use https:// protocol 2018-03-21 14:48:01 +00:00
README.md Add CII best practices badge 2017-10-13 16:08:01 +01:00
run.in run: Fix LIBVIRTD_PATH 2018-07-24 12:10:21 -04:00

Build Status CII Best Practices

Libvirt API for virtualization

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.

For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.

Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.

Further information about the libvirt project can be found on the website:

https://libvirt.org

License

The libvirt C API is distributed under the terms of GNU Lesser General Public License, version 2.1 (or later). Some parts of the code that are not part of the C library may have the more restrictive GNU General Public License, version 2.1 (or later). See the files COPYING.LESSER and COPYING for full license terms & conditions.

Installation

Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands. For example, to build in a manner that is suitable for installing as root, use:

$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install

While to build & install as an unprivileged user

$ ./configure --prefix=$HOME/usr
$ make
$ make install

The libvirt code relies on a large number of 3rd party libraries. These will be detected during execution of the configure script and a summary printed which lists any missing (optional) dependencies.

Contributing

The libvirt project welcomes contributions in many ways. For most components the best way to contribute is to send patches to the primary development mailing list. Further guidance on this can be found on the website:

https://libvirt.org/contribute.html

Contact

The libvirt project has two primary mailing lists:

Further details on contacting the project are available on the website:

https://libvirt.org/contact.html