On Mon, Oct 03, 2016 at 16:04:42 -0300, Eduardo Habkost wrote:
Hi,
When adding new QMP commands that are implemented by arch-specific code, we have been adding stubs that report QERR_UNSUPPORTED (see stubs/arch-query-cpu-model-expansion.c for an example).
But we are using GenericError for that, and this prevents clients from reliably checking if the command is really implemented by the QEMU binary.
What should be the right solution for this? Some of the options I have considered are:
1) Using CommandNotFound as the error class in the stubs. This sounds wrong because the command exists (it is present in query-commands and in the QAPI schema). 2) Creating a CommandNotImplemented error class. Simple to do, but it would require clients to make two separate checks, before concluding that the command is available (checking query-commands or query-qmp-schema, and then checking for CommandNotImplemented errors).
Both options require an extra step to check whether a particular command is implemented or not. It would be highly appreciated if we didn't have to go this way since it would seriously complicate the probing process. We'd need to run each command with some artificial, but sane enough arguments to bypass arguments checking code: (QEMU) query-cpu-model-expansion type=full {"error": {"class": "GenericError", "desc": "Invalid parameter type for 'model', expected: QDict"}} (QEMU) query-cpu-model-expansion type=full model={'name':'host'} {"error": {"class": "GenericError", "desc": "this feature or command is not currently supported"}} (QEMU) query-cpu-model-expansion type=full model={'name':'Penryn'} {"error": {"class": "GenericError", "desc": "this feature or command is not currently supported"}}
3.1) Removing the command from query-commands and from the QAPI schema on binaries that don't implement the command. Needlessly complex? 3.2) Removing the unimplemented command from query-commands only (by calling qmp_disable_command()), but keeping it on the QAPI schema. I am not sure it's OK to do that. If it is, this sounds like the simplest solution.
From my POV (which is quite ignorant to QEMU internals in this area),
These options are both acceptable to libvirt. So it really depends what is acceptable to QEMU... there are a few other options: - implementing a new QMP command to list unsupported commands (e.g., query-unsupported-commands) - adding a flag to qmp-schema which would indicate whether a command is supported or not - even a new stupid command that would take another command as an argument and return whether it's supported or not would be better than having to run each command individually with special arguments I'm not saying these options are clean or doable, I'm just brainstorming here. Jirka