Sometimes, the behaviour of QEMU changes without a change in the QMP
syntax (usually by allowing values or operations that previously
resulted in an error). QMP clients may still need to know whether
they can rely on the changed behavior.
Let's add feature flags to the QAPI schema language, so that we can make
such changes visible with schema introspection.
An example for a schema definition using feature flags looks like this:
{ 'struct': 'TestType',
'data': { 'number': 'int' },
'features': [ 'allow-negative-numbers' ] }
Introspection information then looks like this:
{ "name": "TestType", "meta-type": "object",
"members": [
{ "name": "number", "type": "int" } ],
"features": [ "allow-negative-numbers" ] }
This patch implements feature flags only for struct types. We'll
implement them more widely as needed.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20190606153803.5278-2-armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Making 'allow-oob' optional in SchemaInfoCommand permits omitting it
in the common case. Shrinks query-qmp-schema's output from 122.1KiB
to 118.6KiB for me.
Note that out-of-band execution is still experimental (you have to
configure the monitor with x-oob=on to use it).
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180718090557.17248-1-armbru@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
According to commit 047f7038f5, option --preconfig
[...] allows pausing QEMU in the new RUN_STATE_PRECONFIG state,
allowing the configuration of QEMU from QMP before the machine
jumps into board initialization code of machine_run_board_init()
The intent is to allow management to query machine state and
additionally configure it using previous query results within one
QEMU instance (i.e. eliminate the need to start QEMU twice, 1st to
query board specific parameters and 2nd for actual VM start using
query results for additional parameters).
The implementation is a bit of a hack: it splices in an additional
main loop before machine creation, in special runstate preconfig. New
command exit-preconfig exits that main loop. QEMU continues
initializing, creates the machine, and runs the good old main loop.
The replacement of the main loop is transparent to monitors.
Sadly, some commands expect initialization to be complete. Running
them in --preconfig's main loop violates their preconditions. Since
we don't really know which commands are safe, we use a whitelist.
This drags the concept of run state into the QMP core.
The whitelist is done as a command flag in the QAPI schema (commit
d6fe3d02e9). Drags the concept of run state further into the QAPI
language.
The command flag is exposed in query-qmp-schema (also commit
d6fe3d02e9). This makes it ABI.
I consider the whole thing an offensively ugly hack, but sometimes an
ugly hack is the best we can do to solve a problem people have.
The need described by the commit message quote above is genuine. The
proper solution would be a main loop that permits complete
configuration via QMP. This is out of reach, thus the hack.
However, even though the need is genuine, it isn't urgent: libvirt is
not going to use this anytime soon. Baking a hack into ABI before it
has any users is a bad idea.
This commit reverts the parts of commit d6fe3d02e9 that affect ABI
via query-qmp-schema. The commit did the following:
(1) Add command flag 'allow-preconfig' to the QAPI schema language
(2) Pass it to code generators
(3) Have the commands.py code generator pass it to the command
registry (so commit 047f7038f5 can use it as whitelist)
(4) Add 'allow-preconfig' to SchemaInfoCommand (neglecting to update
qapi-code-gen.txt section "Client JSON Protocol introspection")
(5) Set 'allow-preconfig': true for commands qmp_capabilities,
query-commands, query-command-line-options, query-status
Revert exactly (4), plus a bit of documentation added to
qemu-tech.info in commit 047f7038f5.
Shrinks query-qmp-schema's output from 126.5KiB to 121.8KiB for me.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180705091402.26244-2-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
[Straightforward conflict with commit d626b6c1ae resolved]
New option will be used to allow commands, which are prepared/need
to run, during preconfig state. Other commands that should be able
to run in preconfig state, should be amended to not expect machine
in initialized state or deal with it.
For compatibility reasons, commands that don't use new flag
'allow-preconfig' explicitly are not permitted to run in
preconfig state but allowed in all other states like they used
to be.
Within this patch allow following commands in preconfig state:
qmp_capabilities
query-qmp-schema
query-commands
query-command-line-options
query-status
exit-preconfig
to allow qmp connection, basic introspection and moving to the next
state.
PS:
set-numa-node and query-hotpluggable-cpus will be enabled later in
a separate patches.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1526057503-39287-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[ehabkost: Changed "since 2.13" to "since 3.0"]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Here "oob" stands for "Out-Of-Band". When "allow-oob" is set, it means
the command allows out-of-band execution.
The "oob" idea is proposed by Markus Armbruster in following thread:
https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg02057.html
This new "allow-oob" boolean will be exposed by "query-qmp-schema" as
well for command entries, so that QMP clients can know which commands
can be used in out-of-band calls. For example the command "migrate"
originally looks like:
{"name": "migrate", "ret-type": "17", "meta-type": "command",
"arg-type": "86"}
And it'll be changed into:
{"name": "migrate", "ret-type": "17", "allow-oob": false,
"meta-type": "command", "arg-type": "86"}
This patch only provides the QMP interface level changes. It does not
contain the real out-of-band execution implementation yet.
Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-18-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: rebase on introspection done by qlit]
Signed-off-by: Eric Blake <eblake@redhat.com>
Bug: introspection documentation is in section "Tracing commands".
Cause: sub-schema qapi/introspect.json lacks a section header, and
therefore goes into whatever section precedes its include.
Fix: add a section header.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1503602048-12268-3-git-send-email-armbru@redhat.com>
With the move of some docs to docs/interop on ac06724a71,
a couple of references were not updated.
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
We traditionally mark optional members #optional in the doc comment.
Before commit 3313b61, this was entirely manual.
Commit 3313b61 added some automation because its qapi2texi.py relied
on #optional to determine whether a member is optional. This is no
longer the case since the previous commit: the only thing qapi2texi.py
still does with #optional is stripping it out. We still reject bogus
qapi-schema.json and six places for qga/qapi-schema.json.
Thus, you can't actually rely on #optional to see whether something is
optional. Yet we still make people add it manually. That's just
busy-work.
Drop the code to check, fix up and strip out #optional, along with all
instances of #optional. To keep it out, add code to reject it, to be
dropped again once the dust settles.
No change to generated documentation.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1489582656-31133-18-git-send-email-armbru@redhat.com>
The doc generator we're going to add expects a fairly rigid doc
comment structure. Reorder / rephrase some doc comments to please it.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170113144135.5150-8-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message rewritten]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Consistently put a colon after TODO. This will make the TODOs stand
out in the documentation we're going to generate.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170113144135.5150-4-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message rewritten]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
The documentation parser we are going to add expects a section name to
end with ':', otherwise the comment is treated as free-form text body.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20161117155504.21843-9-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Now that the generator supports it, we might as well use an
anonymous base rather than breaking out a single-use Base
structure, for all three of our current QMP flat unions.
Oddly enough, this change does not affect the resulting
introspection output (because we already inline the members of
a base type into an object, and had no independent use of the
base type reachable from a command).
The case_whitelist now has to list the name of an implicit
type; which is not too bad (consider it a feature if it makes
it harder for developers to make the whitelist grow :)
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1458254921-17042-16-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
We are not ready (and might never be ready) to declare
introspection stable between releases. Clients written to
control multiple versions of qemu, and desiring to know
whether a particular member is supported for a given
command, must be prepared to locate that member in spite
of qapi changes that may affect the member's location or
type within the overall object, even though such changes
did not break QMP wire back-compatibility.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1447264202-19554-1-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
To eliminate the temptation for clients to look up types by name
(which are not ABI), replace all type names by meaningless strings.
Reduces output of query-schema by 13 out of 85KiB.
As a debugging aid, provide option -u to suppress the hiding.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1442401589-24189-27-git-send-email-armbru@redhat.com>
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
