On Tue, Mar 11, 2014 at 10:04:56AM +0100, Markus Armbruster wrote:
Eric Blake <eblake@redhat.com> writes:
On 03/07/2014 02:54 AM, Markus Armbruster wrote:
Eric Blake <eblake@redhat.com> writes:
On 03/05/2014 07:36 PM, Amos Kong wrote:
vm_config_groups[] only contains part of the options which have argument, and all options which have no argument aren't added to vm_config_groups[]. Current query-command-line-options only checks options from vm_config_groups[], so some options will be lost.
Example: -device takes unspecified parameters. -cdrom doesn't take parameters, it takes a file name. Yet, the command reports the same for both: "parameters": [], "argument": true.
Looks like we need a tri-state: option takes no argument, QemuOpts argument, or other argument.
I don't buy that. '-cdrom filename' could easily be re-written [in a future qemu version] to use QemuOpts with an implied parameter name (we've done that elsewhere, such as for '-machine'). In other words, I think we could make it become shorthand for '-cdrom file=filename', at which point the QemuOpts spelling is available and would now show up as "parameters":[{"name":"file"...}]. Thus, in converting -cdrom to QemuOpts, we can still maintain command-line back-compat, while making the query-command-line-options output more featureful. In other words, _for now_ it takes unspecified parameters, and the fact that it is only a single parameter in the form 'filename' rather than a more typical parameter 'file=filename' is not a show-stopper.
Incompatible change for funny filenames: -cdrom you,break=me.
Besides breaking funny filenames, we'd also buy ourselves some stupid -readconfig / -writeconfig trouble. Let me explain.
-cdrom F is effectively sugar for "-drive media=cdrom,index=2,file=FF", where FF is F with comma doubled.
-writeconfig writes out desugared QemuOpts. Therefore, "-cdrom r7.iso" gets written as
[drive] media = "cdrom" index = "2" file = "r7.iso"
which -readconfig can read.
If we convert -cdrom to QemuOpts, it gets written out like this:
[cdrom] file = "r7.iso"
If we continue to desugar it, it'll *also* get written out as before. Either we *delete* the sugared QemuOpts to avoid duplication, or we *stop* desugaring. The latter breaks -readconfig of existing configuration files, and complicates the code reading configuration from QemuOpts.
I don't think any of the old non-QemuOpts options that have become sugar for newer, more flexible QemuOpts options should be converted to QemuOpts.
So your idea of a tri-state (QemuOpts, no argument, or other argument) doesn't add anything - any option that takes "other argument" could be converted to take QemuOpts, and from the command line, we can't tell the difference from whether something was implemented by QemuOpts, only by whether we have introspection on what the argument consists of.
I doubt we can convert all existing options to QemuOpts without breaking backward compatibility and complicating the code.
Meanwhile, it DOES point out that our use of implicit argument in QemuOpts ought to be exposed to the introspection mechanism, for introspection to be fully descriptive. That is, maybe we should modify our introspection to add a new 'implied-name':
## # @CommandLineParameterInfo: # ... # @implied-name: #optional, if present and true, the parameter can be # specified as '-option value' instead of the preferred # spelling of '-option name=value' (since 2.0) # Since 1.5 { 'type': 'CommandLineParameterInfo', 'data': { 'name': 'str', 'type': 'CommandLineParameterType', '*help': 'str', '*implied-name': 'bool' } }
How can we get this information? it's not good to rely on the help message. And the parameters [] only have content when the option have a non-NULL desc table, so we always just return a NULL parameters list, the 'implied-name' information will be lost. I thinks Markus's suggestion is fine, we can use tri-state (no-arg, unsuecified-para-arg, no-para-arg). Thanks, Amos
The only use for implied-name I can think of is interpreting a user's command line. Is that a real use case?
parameters is [] unless it's a QemuOpts argument. Then it lists the recognized parameters.
This part is still true. When parameters[] is non-empty, it is a QemuOpts and we know all recognized parameters (well, more precisely, the subset of QemuOpts that were explicitly called out - given your point 2 about the mess of -drive); when it is empty, then all we know is whether the argument is a boolean or takes unspecified arguments (where the conversion of those unknown arguments to QemuOpts will be what finally lets us introspect the format of those unknown arguments).
QemuOpts argument with only unspecified parameters is not the same as non-QemuOpts argument. I don't think conflating the two is useful.
2. Our dear friend -drive is more complicated than you might think
We special-case it to report the union of drive_config_groups[], which contains qemu_legacy_drive_opts, qemu_common_drive_opts and qemu_drive_opts. The latter accepts unspecified parameters.
I believe qemu_drive_opts is actually not used by the (complex!) code parsing the argument of -drive.
Nevertheless, said code accepts more than just qemu_legacy_drive_opts and qemu_common_drive_opts, namely driver-specific parameters.
Until we define those properly in a schema, I guess the best we can do is add one more case: option takes QemuOpts argument, but parameters is not exhaustive.
We already know 'query-command-line-options' is not a full introspection yet. So far, libvirt has managed to get by on partial information (in fact, the whole hack for special-casing -drive to merge multiple lists together was precisely to avoid a regression with at least providing the partial information that libvirt was actually using). Documenting that QemuOpts information may be incomplete may be nice, but shouldn't hold up the initial purpose of this patch which is to document non-QemuOpts options. And knowing that an option takes unspecified arguments is still better than not knowing about the option at all.
If all we want is a quick fix for "I can't see whether -frobnicate is supported", then let's add a command to dump qemu_options[], and leave query-command-line-options broken as designed.
But if we want proper command line introspection, then let's do it properly: no quick hacks, no half-truths.
I can't get contents right and do backward compatibility acrobatics at the same time. I need to come up with the data to convey first, and a way to shoehorn it into the existing command second. *If* we choose to shoehorn rather than deprecate & replace.
This patch also fixes options to match their actual command-line spelling rather than an alternate name associated with the option table in use by the command.
Should we independently patch hw/acpi/core.c to rename qemu_acpi_opts from "acpi" to "acpitable" to match the command line option? Same for vl.c and qemu_boot_opts from "boot-opts" to "boot"? Same for vl.c and qemu_smp_opts from "smp-opts" to "smp"? Those were the obvious mismatches I found where the command line was spelled differently than the vm_config_groups entry.
Without such a change, the command lies, because it fails to connect the option to its QemuOptsList. Example:
{"parameters": [], "option": "acpitable", "argument": true},
However, the vm_config_groups[].name values are ABI: they're the section names recognized by -readconfig and produced by -writeconfig. Thus, this is an incompatible change. It's also an improvement of sorts: things become more consistent.
Ouch. I did not realize they were ABI. 'query-command-line-options' should expose the command line spelling, but maybe that argues that we need to enhance our QAPI introspection to make it easier to document the special cases:
## # @CommandLineOptionInfo: ... # @config-name: #optional if present, the command line spelling differs # from the name used by -readconfig (since 2.0) # Since 1.5 ## { 'type': 'CommandLineOptionInfo', 'data': { 'option': 'str', '*config-name':'str', 'parameters': ['CommandLineParameterInfo'] } }
and where we would expose:
{"parameters": [], "option": "acpitable", "config-name": "acpi", "argument": true},
or even combining my above suggestions:
{"option":"M", "parameters":[], "config-name":"machine", "argument": true}, {"option":"machine", "parameters":[ {"name": "firmware", "help": "firmware image", "type": "string"}, {"name": "type", "implied-name": true, "help": "emulated machine", "type": "string"}, ...]},
to make it a bit more obvious that '-M str' and '-machine str' are both shorthands for the preferred '-machine type=str', and that the same effect is reached via a config file that has a [machine] section.
Use case for the introspection into the desugaring of -M?
Can't cover less trivial desugarings, like -cdrom.
We got more sugar than a jelly doughnut with radioactive pink frosting!
We could avoid it with a suitable mapping from option name to option group name. Simplest way to do that is store only the exceptions from the rule "the names are the same".
Yes. We've identified at least 3 exceptions now (acpitable, boot, smp), and exposing those exceptions in the introspection is a good idea, to make us quit adding new ones.
It'll make us quit adding new ones only if we can come up with a test that breaks when we add new ones :)
Do we care?
This is a bug fix patch, so let's shoot to get it into 2.0.
Yes.
How much work are we able to do before hard freeze? How much work are we willing to accept as bug fix after hard freeze?
I don't know.
Is better command line introspection in 2.0 worth the risk that comes with softening up the hard freeze?
-- Amos.