[Qemu-devel] [PATCH 0/2] Let's not chisel --preconfig in stone without a user

[Qemu-devel] [PATCH 0/2] Let's not chisel --preconfig in stone without a user

[Markus Armbruster]

Please refer to PATCH 1 for rationale.

Markus Armbruster (2):
  qapi: Do not expose "allow-preconfig" in query-qmp-schema
  cli qmp: Mark --preconfig, exit-preconfig experimental

 hmp.c                      |  2 +-
 qapi/introspect.json       |  5 +----
 qapi/misc.json             |  6 +++---
 qemu-options.hx            |  9 +++++----
 qemu-tech.texi             | 11 ++++-------
 qmp.c                      |  2 +-
 scripts/qapi/introspect.py |  3 +--
 tests/numa-test.c          |  2 +-
 tests/qmp-test.c           |  6 +++---
 9 files changed, 20 insertions(+), 26 deletions(-)

-- 
2.17.1

[Qemu-devel] [PATCH 1/2] qapi: Do not expose "allow-preconfig" in query-qmp-schema

[Markus Armbruster]

According to commit 047f7038f58, 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
d6fe3d02e9a).  Drags the concept of run state further into the QAPI
language.

The command flag is exposed in query-qmp-schema (also commit
d6fe3d02e9a).  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 d6fe3d02e9a 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 047f7038f58 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 047f7038f58.

Shrinks query-qmp-schema's output from 126.5KiB to 121.8KiB for me.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 qapi/introspect.json       | 5 +----
 qemu-tech.texi             | 3 ---
 scripts/qapi/introspect.py | 3 +--
 3 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/qapi/introspect.json b/qapi/introspect.json
index 80a0a3e656..c7f67b7d78 100644
--- a/qapi/introspect.json
+++ b/qapi/introspect.json
@@ -262,16 +262,13 @@
 # @allow-oob: whether the command allows out-of-band execution.
 #             (Since: 2.12)
 #
-# @allow-preconfig: command can be executed in preconfig runstate,
-#                   default: false (Since 3.0)
-#
 # TODO: @success-response (currently irrelevant, because it's QGA, not QMP)
 #
 # Since: 2.5
 ##
 { 'struct': 'SchemaInfoCommand',
   'data': { 'arg-type': 'str', 'ret-type': 'str',
-            'allow-oob': 'bool', 'allow-preconfig': 'bool' } }
+            'allow-oob': 'bool' } }
 
 ##
 # @SchemaInfoEvent:
diff --git a/qemu-tech.texi b/qemu-tech.texi
index dcecba83cb..f843341ffa 100644
--- a/qemu-tech.texi
+++ b/qemu-tech.texi
@@ -350,9 +350,6 @@ depend on an initialized machine, including but not limited to:
 @item query-status
 @item exit-preconfig
 @end table
-The full list of commands is in QMP schema which could be queried with
-query-qmp-schema, where commands supported at preconfig state have option
-'allow-preconfig' set to true.
 
 @node Bibliography
 @section Bibliography
diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index 6ad198ae5b..802b1949d0 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -175,8 +175,7 @@ const QLitObject %(c_name)s = %(c_string)s;
         self._gen_qlit(name, 'command',
                        {'arg-type': self._use_type(arg_type),
                         'ret-type': self._use_type(ret_type),
-                        'allow-oob': allow_oob,
-                        'allow-preconfig': allow_preconfig})
+                        'allow-oob': allow_oob})
 
     def visit_event(self, name, info, arg_type, boxed):
         arg_type = arg_type or self._schema.the_empty_object_type
-- 
2.17.1

[Qemu-devel] [PATCH 2/2] cli qmp: Mark --preconfig, exit-preconfig experimental

[Markus Armbruster]

Committing to the current --preconfig / exit-preconfig interface
before it has seen any use is premature.  Mark both as experimental,
the former in documentation, the latter by renaming it to
x-exit-preconfig.

See the previous commit for more detailed rationale.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hmp.c             | 2 +-
 qapi/misc.json    | 6 +++---
 qemu-options.hx   | 9 +++++----
 qemu-tech.texi    | 8 ++++----
 qmp.c             | 2 +-
 tests/numa-test.c | 2 +-
 tests/qmp-test.c  | 6 +++---
 7 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/hmp.c b/hmp.c
index fe4477a8fb..3e689dfc6b 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1074,7 +1074,7 @@ void hmp_exit_preconfig(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
 
-    qmp_exit_preconfig(&err);
+    qmp_x_exit_preconfig(&err);
     hmp_handle_error(mon, &err);
 }
 
diff --git a/qapi/misc.json b/qapi/misc.json
index 29da7856e3..2e9902371a 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -1205,7 +1205,7 @@
 { 'command': 'cont' }
 
 ##
-# @exit-preconfig:
+# @x-exit-preconfig:
 #
 # Exit from "preconfig" state
 #
@@ -1221,11 +1221,11 @@
 #
 # Example:
 #
-# -> { "execute": "exit-preconfig" }
+# -> { "execute": "x-exit-preconfig" }
 # <- { "return": {} }
 #
 ##
-{ 'command': 'exit-preconfig', 'allow-preconfig': true }
+{ 'command': 'x-exit-preconfig', 'allow-preconfig': true }
 
 ##
 # @system_wakeup:
diff --git a/qemu-options.hx b/qemu-options.hx
index 16208f63f2..1d04613a17 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3291,16 +3291,17 @@ Run the emulation in single step mode.
 ETEXI
 
 DEF("preconfig", 0, QEMU_OPTION_preconfig, \
-    "--preconfig     pause QEMU before machine is initialized\n",
+    "--preconfig     pause QEMU before machine is initialized (experimental)\n",
     QEMU_ARCH_ALL)
 STEXI
 @item --preconfig
 @findex --preconfig
 Pause QEMU for interactive configuration before the machine is created,
 which allows querying and configuring properties that will affect
-machine initialization. Use the QMP command 'exit-preconfig' to exit
-the preconfig state and move to the next state (ie. run guest if -S
-isn't used or pause the second time if -S is used).
+machine initialization.  Use QMP command 'x-exit-preconfig' to exit
+the preconfig state and move to the next state (i.e. run guest if -S
+isn't used or pause the second time if -S is used).  This option is
+experimental.
 ETEXI
 
 DEF("S", 0, QEMU_OPTION_S, \
diff --git a/qemu-tech.texi b/qemu-tech.texi
index f843341ffa..7c3d1f05e1 100644
--- a/qemu-tech.texi
+++ b/qemu-tech.texi
@@ -336,9 +336,9 @@ additionally configure the machine (by hotplugging devices) in runtime before
 allowing VM code to run.
 
 However, at the -S pause point, it's impossible to configure options that affect
-initial VM creation (like: -smp/-m/-numa ...) or cold plug devices. That's
-when the --preconfig command line option should be used. It allows pausing QEMU
-before the initial VM creation, in a new preconfig state, where additional
+initial VM creation (like: -smp/-m/-numa ...) or cold plug devices. The
+experimental --preconfig command line option  allows pausing QEMU
+before the initial VM creation, in a ``preconfig'' state, where additional
 queries and configuration can be performed via QMP before moving on to
 the resulting configuration startup. In the preconfig state, QEMU only allows
 a limited set of commands over the QMP monitor, where the commands do not
@@ -348,7 +348,7 @@ depend on an initialized machine, including but not limited to:
 @item query-qmp-schema
 @item query-commands
 @item query-status
-@item exit-preconfig
+@item x-exit-preconfig
 @end table
 
 @node Bibliography
diff --git a/qmp.c b/qmp.c
index 73e46d795f..411e3210bb 100644
--- a/qmp.c
+++ b/qmp.c
@@ -161,7 +161,7 @@ SpiceInfo *qmp_query_spice(Error **errp)
 };
 #endif
 
-void qmp_exit_preconfig(Error **errp)
+void qmp_x_exit_preconfig(Error **errp)
 {
     if (!runstate_check(RUN_STATE_PRECONFIG)) {
         error_setg(errp, "The command is permitted only in '%s' state",
diff --git a/tests/numa-test.c b/tests/numa-test.c
index b7a6ef8815..893f826acb 100644
--- a/tests/numa-test.c
+++ b/tests/numa-test.c
@@ -285,7 +285,7 @@ static void pc_dynamic_cpu_cfg(const void *data)
         " 'arguments': { 'type': 'cpu', 'node-id': 1, 'socket-id': 0 } }")));
 
     /* let machine initialization to complete and run */
-    g_assert(!qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'exit-preconfig' }")));
+    g_assert(!qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'x-exit-preconfig' }")));
     qtest_qmp_eventwait(qs, "RESUME");
 
     /* check that CPUs are mapped as expected */
diff --git a/tests/qmp-test.c b/tests/qmp-test.c
index a49cbc6fde..ca8c599526 100644
--- a/tests/qmp-test.c
+++ b/tests/qmp-test.c
@@ -412,7 +412,7 @@ static void test_qmp_preconfig(void)
     qobject_unref(rsp);
 
     /* exit preconfig state */
-    g_assert(!qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'exit-preconfig' }")));
+    g_assert(!qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'x-exit-preconfig' }")));
     qtest_qmp_eventwait(qs, "RESUME");
 
     /* check that query-status returns running state */
@@ -422,8 +422,8 @@ static void test_qmp_preconfig(void)
     g_assert_cmpstr(qdict_get_try_str(ret, "status"), ==, "running");
     qobject_unref(rsp);
 
-    /* check that exit-preconfig returns error after exiting preconfig */
-    g_assert(qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'exit-preconfig' }")));
+    /* check that x-exit-preconfig returns error after exiting preconfig */
+    g_assert(qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'x-exit-preconfig' }")));
 
     /* enabled commands, no error expected  */
     g_assert(!qmp_rsp_is_err(qtest_qmp(qs, "{ 'execute': 'query-cpus' }")));
-- 
2.17.1

Re: [Qemu-devel] [PATCH 1/2] qapi: Do not expose "allow-preconfig" in query-qmp-schema

[Eric Blake]

On 07/05/2018 04:14 AM, Markus Armbruster wrote:
> According to commit 047f7038f58, 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 command flag is exposed in query-qmp-schema (also commit
> d6fe3d02e9a).  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.
> 

> Revert exactly (4), plus a bit of documentation added to
> qemu-tech.info in commit 047f7038f58.
> 
> Shrinks query-qmp-schema's output from 126.5KiB to 121.8KiB for me.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>   qapi/introspect.json       | 5 +----
>   qemu-tech.texi             | 3 ---
>   scripts/qapi/introspect.py | 3 +--
>   3 files changed, 2 insertions(+), 9 deletions(-)

Good reasons for not baking it into the ABI just yet (similar to how we 
did not bake OOB into the 2.12 ABI).

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH 2/2] cli qmp: Mark --preconfig, exit-preconfig experimental

[Eric Blake]

On 07/05/2018 04:14 AM, Markus Armbruster wrote:
> Committing to the current --preconfig / exit-preconfig interface
> before it has seen any use is premature.  Mark both as experimental,
> the former in documentation, the latter by renaming it to
> x-exit-preconfig.
> 
> See the previous commit for more detailed rationale.

Should the CLI be spelled --x-preconfig?

> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---

Other than the potential for a spelling change,
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH 0/2] Let's not chisel --preconfig in stone without a user

[Eduardo Habkost]

On Thu, Jul 05, 2018 at 11:14:00AM +0200, Markus Armbruster wrote:
> Please refer to PATCH 1 for rationale.

Justification is good.  We're far from having machine
initialization code (i.e. everything between the two main_loop()
calls) safe to run with an active QMP monitor.

Acked-by: Eduardo Habkost <ehabkost@redhat.com>

> 
> Markus Armbruster (2):
>   qapi: Do not expose "allow-preconfig" in query-qmp-schema
>   cli qmp: Mark --preconfig, exit-preconfig experimental
> 
>  hmp.c                      |  2 +-
>  qapi/introspect.json       |  5 +----
>  qapi/misc.json             |  6 +++---
>  qemu-options.hx            |  9 +++++----
>  qemu-tech.texi             | 11 ++++-------
>  qmp.c                      |  2 +-
>  scripts/qapi/introspect.py |  3 +--
>  tests/numa-test.c          |  2 +-
>  tests/qmp-test.c           |  6 +++---
>  9 files changed, 20 insertions(+), 26 deletions(-)
> 
> -- 
> 2.17.1
> 

-- 
Eduardo

Re: [Qemu-devel] [PATCH 2/2] cli qmp: Mark --preconfig, exit-preconfig experimental

[Eric Blake]

On 07/05/2018 04:14 AM, Markus Armbruster wrote:
> Committing to the current --preconfig / exit-preconfig interface
> before it has seen any use is premature.  Mark both as experimental,
> the former in documentation, the latter by renaming it to
> x-exit-preconfig.
> 
> See the previous commit for more detailed rationale.

One additional point - the fact that 'x-exit-preconfig' vs. 
'exit-preconfig' is introspectable means that even if we decide to 
cement the ABI at a time when libvirt is taught to use it, libvirt will 
know that 3.0's version is not the final form of the feature (ideally, 
of course, we'll be able to fix qemu to avoid the need for the 
--preconfig hack in the first place...)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH 2/2] cli qmp: Mark --preconfig, exit-preconfig experimental

[Markus Armbruster]

Eric Blake <eblake@redhat.com> writes:

> On 07/05/2018 04:14 AM, Markus Armbruster wrote:
>> Committing to the current --preconfig / exit-preconfig interface
>> before it has seen any use is premature.  Mark both as experimental,
>> the former in documentation, the latter by renaming it to
>> x-exit-preconfig.
>>
>> See the previous commit for more detailed rationale.
>
> Should the CLI be spelled --x-preconfig?

Would be the first use of x- with option names.

Since you have to pair --preconfig with x-exit-preconfig, I figure
slapping x- onto the latter suffices.  But I'm not opposed to slapping
it onto the former as well.

>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>
> Other than the potential for a spelling change,
> Reviewed-by: Eric Blake <eblake@redhat.com>

Thanks!

Re: [Qemu-devel] [PATCH 0/2] Let's not chisel --preconfig in stone without a user

[Igor Mammedov]

On Thu,  5 Jul 2018 11:14:00 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Please refer to PATCH 1 for rationale.
> 
> Markus Armbruster (2):
>   qapi: Do not expose "allow-preconfig" in query-qmp-schema
>   cli qmp: Mark --preconfig, exit-preconfig experimental
> 
>  hmp.c                      |  2 +-
>  qapi/introspect.json       |  5 +----
>  qapi/misc.json             |  6 +++---
>  qemu-options.hx            |  9 +++++----
>  qemu-tech.texi             | 11 ++++-------
>  qmp.c                      |  2 +-
>  scripts/qapi/introspect.py |  3 +--
>  tests/numa-test.c          |  2 +-
>  tests/qmp-test.c           |  6 +++---
>  9 files changed, 20 insertions(+), 26 deletions(-)
> 

Acked-by: Igor Mammedov <imammedo@redhat.com>