On 01/07/2018 06:23 AM, Richard Palethorpe wrote: > Add QAPI wrapper functions for the existing snapshot functionality. These > functions behave the same way as the HMP savevm, loadvm and delvm > commands. This will allow applications, such as OpenQA, to programmatically > revert the VM to a previous state with no dependence on HMP or qemu-img.
That's already possible; libvirt uses QMP's human-monitor-command to access these HMP commands programmatically. We've had discussions in the past about what it would take to have specific QMP commands for these operations; the biggest problem is that these commands promote the use of internal snapshots, and there are enough performance and other issues with internal snapshots that we are not yet ready to commit to a long-term interface for making their use easier. At this point, our recommendation is to prefer external snapshots. https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg02427.html is an example thread that has tried to tackle the QMP-ification of these HMP commands in the past; here we are two years later, and I'm still not sure we are ready. I'm worried that taking this commands as-is will bake in an interface that we don't want to support in the long term. In particular, the qemu-img counterpart of taking an internal snapshot of an offline guest is different from QMP context where the guest is running and would always include a snapshot of CPU state in addition to disk state; I'm also worried that the command is too broad, compared to doing a transaction built on lower-level building blocks (take an internal snapshot of disk storage, coupled with take an internal snapshot of cpu state to be placed into a particular BDS); the HMP command is a bit hard to use because the internal snapshot of CPU state has no user control over which BDS will actually hold the state (other than which disk was installed/hot-plugged first), whereas at the lower level, we probably do want to allow management more fine-grained control over where the internal snapshot lands. Also, when sending a two-patch series, be sure to include a 0/2 cover letter. More patch submission hints at https://wiki.qemu.org/Contribute/SubmitAPatch > > I used the term snapshot instead of VM because I think it is less ambiguous > and matches the internal function names. > > Signed-off-by: Richard Palethorpe <richi...@f-m.fm> > --- > migration/savevm.c | 27 ++++++++++++++++++++++ > qapi-schema.json | 66 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 93 insertions(+) > > +++ b/qapi-schema.json > @@ -1125,6 +1125,72 @@ > { 'command': 'pmemsave', > 'data': {'val': 'int', 'size': 'int', 'filename': 'str'} } > > +## > +# @save-snapshot: > +# > +# Save a snapshot of the entire Virtual Machine > +# > +# @name: A string identifying the snapshot. This can later be used with > +# @load-snapshot or @delete-snapshot > +# > +# Since: 2.12.0 > +# > +# Returns: If successful, nothing > +# > +# Notes: The equivalent HMP command is savevm. This stores all of the virtual I don't see why we have to document HMP commands in the QMP document. > +# machine's current state within the virtual machine's > +# image(s)/storage. If the VM is currently running, this includes the > +# state of the CPU and RAM. Later the VM can be reverted to this > state. How would the VM _not_ be currently running at the point where QMP can be executed? > +# > +# qemu-img can also be used to manipulate snapshots. > +# > +# Examples: > +# > +# -> { "execute": "save-snapshot", "arguments": { "name": "lastgood" } } > +# <- { "return": {} } > +## > +{ 'command': 'save-snapshot', > + 'data': {'name': 'str'} } > + > +## > +# @load-snapshot: > +# > +# Load a snapshot of the entire Virtual Machine, completely reverting it to > +# that state > +# > +# Since: 2.12.0 > +# > +# Returns: If successful, nothing > +# > +# Notes: The equivalent HMP command is loadvm. See the @save-snapshot notes. > +# > +# Examples: > +# > +# -> { "execute": "load-snapshot", "arguments": { "name": "lastgood" } } > +# <- { "return": {} } > +## > +{ 'command': 'load-snapshot', > + 'data': {'name': 'str'} } > + > +## > +# @delete-snapshot: > +# > +# Delete a VM snapshot > +# > +# Since: 2.12.0 > +# > +# Returns: If successful, nothing > +# > +# Notes: The equivalent HMP command is delvm. See the @save-snapshot notes. > +# > +# Examples: > +# > +# -> { "execute": "delete-snapshot", "arguments": { "name": "lastgood" } } > +# <- { "return": {} } > +## > +{ 'command': 'delete-snapshot', > + 'data': {'name': 'str'} } > + > ## > # @cont: > # > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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