[PATCH v5 0/1] util/async-teardown: appear in query-command-line-options

[PATCH v5 0/1] util/async-teardown: appear in query-command-line-options

[Claudio Imbrenda]

Add new -teardown option with an async=on|off parameter. It is visible
in the output of query-command-line-options QMP command, so it can be
discovered and used by libvirt.

The option -async-teardown is now redundant. We'd normally deprecate it
and remove it after a grace period, but it was introduced only in the
previous version and it had no users, since it was not visible in the
query-command-line-options QMP command. Drop it.


v4->v5
* reword commit message [Markus]
* document the removal of the -async-teardown commandline option in
  docs/about/removed-features.rst [Markus]

v3->v4
* completely remove the useless -async-teardown option, since it was
  not wired up properly and it had no users [thomas]
* QEMU should be always uppercase in text and documentation [thomas]
* if the new -teardown option fails to parse, exit immediately instead
  of returning an error [thomas]

v2->v3
* add a new teardown option with an async parameter [Markus]
* reworded documentation of existing -async-teardown option so that it
  points to the new teardown option

v1->v2
* remove the unneeded .implied_opt_name initializer [Thomas]

Claudio Imbrenda (1):
  util/async-teardown: wire up query-command-line-options

 docs/about/removed-features.rst |  5 +++++
 os-posix.c                      | 15 +++++++++++++--
 qemu-options.hx                 | 33 +++++++++++++++++++--------------
 util/async-teardown.c           | 21 +++++++++++++++++++++
 4 files changed, 58 insertions(+), 16 deletions(-)

-- 
2.39.2

[PATCH v5 1/1] util/async-teardown: wire up query-command-line-options

[Claudio Imbrenda]

Add new -teardown option with an async=on|off parameter. It is visible
in the output of query-command-line-options QMP command, so it can be
discovered and used by libvirt.

The option -async-teardown is now redundant. We'd normally deprecate it
and remove it after a grace period, but it was introduced only in the
previous version and it had no users, since it was not visible in the
query-command-line-options QMP command. Drop it.

Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Fixes: c891c24b1a ("os-posix: asynchronous teardown for shutdown on Linux")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 docs/about/removed-features.rst |  5 +++++
 os-posix.c                      | 15 +++++++++++++--
 qemu-options.hx                 | 33 +++++++++++++++++++--------------
 util/async-teardown.c           | 21 +++++++++++++++++++++
 4 files changed, 58 insertions(+), 16 deletions(-)

diff --git a/docs/about/removed-features.rst b/docs/about/removed-features.rst
index 5b258b446b..6d89f69be9 100644
--- a/docs/about/removed-features.rst
+++ b/docs/about/removed-features.rst
@@ -416,6 +416,11 @@ Input parameters that take a size value should only use a size suffix
 the value is hexadecimal.  That is, '0x20M' should be written either as
 '32M' or as '0x2000000'.
 
+``-async-teardown`` (removed in 8.0)
+,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
+
+Use ``-teardown async=on`` instead.
+
 ``-chardev`` backend aliases ``tty`` and ``parport`` (removed in 8.0)
 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
diff --git a/os-posix.c b/os-posix.c
index 5adc69f560..c1ca7b1cb3 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -36,6 +36,8 @@
 #include "qemu/log.h"
 #include "sysemu/runstate.h"
 #include "qemu/cutils.h"
+#include "qemu/config-file.h"
+#include "qemu/option.h"
 
 #ifdef CONFIG_LINUX
 #include <sys/prctl.h>
@@ -132,6 +134,8 @@ static bool os_parse_runas_uid_gid(const char *optarg)
  */
 int os_parse_cmd_args(int index, const char *optarg)
 {
+    QemuOpts *opts;
+
     switch (index) {
     case QEMU_OPTION_runas:
         user_pwd = getpwnam(optarg);
@@ -152,8 +156,15 @@ int os_parse_cmd_args(int index, const char *optarg)
         daemonize = 1;
         break;
 #if defined(CONFIG_LINUX)
-    case QEMU_OPTION_asyncteardown:
-        init_async_teardown();
+    case QEMU_OPTION_teardown:
+        opts = qemu_opts_parse_noisily(qemu_find_opts("teardown"),
+                                       optarg, false);
+        if (!opts) {
+            exit(1);
+        }
+        if (qemu_opt_get_bool(opts, "async", false)) {
+            init_async_teardown();
+        }
         break;
 #endif
     default:
diff --git a/qemu-options.hx b/qemu-options.hx
index d42f60fb91..6a69b84f3c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4763,23 +4763,28 @@ DEF("qtest", HAS_ARG, QEMU_OPTION_qtest, "", QEMU_ARCH_ALL)
 DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log, "", QEMU_ARCH_ALL)
 
 #ifdef __linux__
-DEF("async-teardown", 0, QEMU_OPTION_asyncteardown,
-    "-async-teardown enable asynchronous teardown\n",
+DEF("teardown", HAS_ARG, QEMU_OPTION_teardown,
+    "-teardown async[=on|off]\n"
+    "                process teardown options\n"
+    "                async=on enables asynchronous teardown\n"
+   ,
     QEMU_ARCH_ALL)
-#endif
 SRST
-``-async-teardown``
-    Enable asynchronous teardown. A new process called "cleanup/<QEMU_PID>"
-    will be created at startup sharing the address space with the main qemu
-    process, using clone. It will wait for the main qemu process to
-    terminate completely, and then exit.
-    This allows qemu to terminate very quickly even if the guest was
-    huge, leaving the teardown of the address space to the cleanup
-    process. Since the cleanup process shares the same cgroups as the
-    main qemu process, accounting is performed correctly. This only
-    works if the cleanup process is not forcefully killed with SIGKILL
-    before the main qemu process has terminated completely.
+``-teardown``
+    Set process teardown options.
+
+    ``async=on`` enables asynchronous teardown. A new process called
+    "cleanup/<QEMU_PID>" will be created at startup sharing the address
+    space with the main QEMU process, using clone. It will wait for the
+    main QEMU process to terminate completely, and then exit. This allows
+    QEMU to terminate very quickly even if the guest was huge, leaving the
+    teardown of the address space to the cleanup process. Since the cleanup
+    process shares the same cgroups as the main QEMU process, accounting is
+    performed correctly. This only works if the cleanup process is not
+    forcefully killed with SIGKILL before the main QEMU process has
+    terminated completely.
 ERST
+#endif
 
 DEF("msg", HAS_ARG, QEMU_OPTION_msg,
     "-msg [timestamp[=on|off]][,guest-name=[on|off]]\n"
diff --git a/util/async-teardown.c b/util/async-teardown.c
index 62cdeb0f20..4a5dbce958 100644
--- a/util/async-teardown.c
+++ b/util/async-teardown.c
@@ -12,6 +12,9 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/config-file.h"
+#include "qemu/option.h"
+#include "qemu/module.h"
 #include <dirent.h>
 #include <sys/prctl.h>
 #include <sched.h>
@@ -144,3 +147,21 @@ void init_async_teardown(void)
     clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL);
     sigprocmask(SIG_SETMASK, &old_signals, NULL);
 }
+
+static QemuOptsList qemu_teardown_opts = {
+    .name = "teardown",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_teardown_opts.head),
+    .desc = {
+        {
+            .name = "async",
+            .type = QEMU_OPT_BOOL,
+        },
+        { /* end of list */ }
+    },
+};
+
+static void register_teardown(void)
+{
+    qemu_add_opts(&qemu_teardown_opts);
+}
+opts_init(register_teardown);
-- 
2.39.2

Re: [PATCH v5 1/1] util/async-teardown: wire up query-command-line-options

[Paolo Bonzini]

[-- Attachment #1: Type: text/plain, Size: 6593 bytes --]

I am honestly not a fan of adding a more complex option,.just because
query-command-line-options only returns the square holes whereas here we
got a round one.

Can we imagine another functionality that would be added to -teardown? If
not, it's not a good design. If it works, I would add a completely dummy
(no suboptions) group "async-teardown" and not modify the parsing at all.

Paolo

Il lun 27 mar 2023, 15:35 Claudio Imbrenda <imbrenda@linux.ibm.com> ha
scritto:

> Add new -teardown option with an async=on|off parameter. It is visible
> in the output of query-command-line-options QMP command, so it can be
> discovered and used by libvirt.
>
> The option -async-teardown is now redundant. We'd normally deprecate it
> and remove it after a grace period, but it was introduced only in the
> previous version and it had no users, since it was not visible in the
> query-command-line-options QMP command. Drop it.
>
> Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
> Fixes: c891c24b1a ("os-posix: asynchronous teardown for shutdown on Linux")
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>  docs/about/removed-features.rst |  5 +++++
>  os-posix.c                      | 15 +++++++++++++--
>  qemu-options.hx                 | 33 +++++++++++++++++++--------------
>  util/async-teardown.c           | 21 +++++++++++++++++++++
>  4 files changed, 58 insertions(+), 16 deletions(-)
>
> diff --git a/docs/about/removed-features.rst
> b/docs/about/removed-features.rst
> index 5b258b446b..6d89f69be9 100644
> --- a/docs/about/removed-features.rst
> +++ b/docs/about/removed-features.rst
> @@ -416,6 +416,11 @@ Input parameters that take a size value should only
> use a size suffix
>  the value is hexadecimal.  That is, '0x20M' should be written either as
>  '32M' or as '0x2000000'.
>
> +``-async-teardown`` (removed in 8.0)
> +,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
> +
> +Use ``-teardown async=on`` instead.
> +
>  ``-chardev`` backend aliases ``tty`` and ``parport`` (removed in 8.0)
>  '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
>
> diff --git a/os-posix.c b/os-posix.c
> index 5adc69f560..c1ca7b1cb3 100644
> --- a/os-posix.c
> +++ b/os-posix.c
> @@ -36,6 +36,8 @@
>  #include "qemu/log.h"
>  #include "sysemu/runstate.h"
>  #include "qemu/cutils.h"
> +#include "qemu/config-file.h"
> +#include "qemu/option.h"
>
>  #ifdef CONFIG_LINUX
>  #include <sys/prctl.h>
> @@ -132,6 +134,8 @@ static bool os_parse_runas_uid_gid(const char *optarg)
>   */
>  int os_parse_cmd_args(int index, const char *optarg)
>  {
> +    QemuOpts *opts;
> +
>      switch (index) {
>      case QEMU_OPTION_runas:
>          user_pwd = getpwnam(optarg);
> @@ -152,8 +156,15 @@ int os_parse_cmd_args(int index, const char *optarg)
>          daemonize = 1;
>          break;
>  #if defined(CONFIG_LINUX)
> -    case QEMU_OPTION_asyncteardown:
> -        init_async_teardown();
> +    case QEMU_OPTION_teardown:
> +        opts = qemu_opts_parse_noisily(qemu_find_opts("teardown"),
> +                                       optarg, false);
> +        if (!opts) {
> +            exit(1);
> +        }
> +        if (qemu_opt_get_bool(opts, "async", false)) {
> +            init_async_teardown();
> +        }
>          break;
>  #endif
>      default:
> diff --git a/qemu-options.hx b/qemu-options.hx
> index d42f60fb91..6a69b84f3c 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4763,23 +4763,28 @@ DEF("qtest", HAS_ARG, QEMU_OPTION_qtest, "",
> QEMU_ARCH_ALL)
>  DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log, "", QEMU_ARCH_ALL)
>
>  #ifdef __linux__
> -DEF("async-teardown", 0, QEMU_OPTION_asyncteardown,
> -    "-async-teardown enable asynchronous teardown\n",
> +DEF("teardown", HAS_ARG, QEMU_OPTION_teardown,
> +    "-teardown async[=on|off]\n"
> +    "                process teardown options\n"
> +    "                async=on enables asynchronous teardown\n"
> +   ,
>      QEMU_ARCH_ALL)
> -#endif
>  SRST
> -``-async-teardown``
> -    Enable asynchronous teardown. A new process called
> "cleanup/<QEMU_PID>"
> -    will be created at startup sharing the address space with the main
> qemu
> -    process, using clone. It will wait for the main qemu process to
> -    terminate completely, and then exit.
> -    This allows qemu to terminate very quickly even if the guest was
> -    huge, leaving the teardown of the address space to the cleanup
> -    process. Since the cleanup process shares the same cgroups as the
> -    main qemu process, accounting is performed correctly. This only
> -    works if the cleanup process is not forcefully killed with SIGKILL
> -    before the main qemu process has terminated completely.
> +``-teardown``
> +    Set process teardown options.
> +
> +    ``async=on`` enables asynchronous teardown. A new process called
> +    "cleanup/<QEMU_PID>" will be created at startup sharing the address
> +    space with the main QEMU process, using clone. It will wait for the
> +    main QEMU process to terminate completely, and then exit. This allows
> +    QEMU to terminate very quickly even if the guest was huge, leaving the
> +    teardown of the address space to the cleanup process. Since the
> cleanup
> +    process shares the same cgroups as the main QEMU process, accounting
> is
> +    performed correctly. This only works if the cleanup process is not
> +    forcefully killed with SIGKILL before the main QEMU process has
> +    terminated completely.
>  ERST
> +#endif
>
>  DEF("msg", HAS_ARG, QEMU_OPTION_msg,
>      "-msg [timestamp[=on|off]][,guest-name=[on|off]]\n"
> diff --git a/util/async-teardown.c b/util/async-teardown.c
> index 62cdeb0f20..4a5dbce958 100644
> --- a/util/async-teardown.c
> +++ b/util/async-teardown.c
> @@ -12,6 +12,9 @@
>   */
>
>  #include "qemu/osdep.h"
> +#include "qemu/config-file.h"
> +#include "qemu/option.h"
> +#include "qemu/module.h"
>  #include <dirent.h>
>  #include <sys/prctl.h>
>  #include <sched.h>
> @@ -144,3 +147,21 @@ void init_async_teardown(void)
>      clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL);
>      sigprocmask(SIG_SETMASK, &old_signals, NULL);
>  }
> +
> +static QemuOptsList qemu_teardown_opts = {
> +    .name = "teardown",
> +    .head = QTAILQ_HEAD_INITIALIZER(qemu_teardown_opts.head),
> +    .desc = {
> +        {
> +            .name = "async",
> +            .type = QEMU_OPT_BOOL,
> +        },
> +        { /* end of list */ }
> +    },
> +};
> +
> +static void register_teardown(void)
> +{
> +    qemu_add_opts(&qemu_teardown_opts);
> +}
> +opts_init(register_teardown);
> --
> 2.39.2
>
>

[-- Attachment #2: Type: text/html, Size: 8496 bytes --]

Re: [PATCH v5 1/1] util/async-teardown: wire up query-command-line-options

[Markus Armbruster]

Paolo Bonzini <pbonzini@redhat.com> writes:

> I am honestly not a fan of adding a more complex option,.just because
> query-command-line-options only returns the square holes whereas here we
> got a round one.
>
> Can we imagine another functionality that would be added to -teardown? If
> not, it's not a good design. If it works, I would add a completely dummy
> (no suboptions) group "async-teardown" and not modify the parsing at all.

Does v2 implement your suggestion?
Message-Id: <20230320131648.61728-1-imbrenda@linux.ibm.com>

I dislike it, because it makes query-command-line-options claim
-async-teardown has an option argument with unknown keys, which is
plainly wrong, and must be treated as a special case.  Worse, a new kind
of special case.

Can we have a QMP command, so libvirt can use query-qmp-schema?

In case QMP becomes functional too late for the command to actually
work: make it always fail for now.  It can still serve as a witness for
-async-teardown.  If we rework QEMU startup so that QMP can do
everything the CLI can do, we'll make the QMP command work.

Re: [PATCH v5 1/1] util/async-teardown: wire up query-command-line-options

[Thomas Huth]

On 28/03/2023 07.26, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> I am honestly not a fan of adding a more complex option,.just because
>> query-command-line-options only returns the square holes whereas here we
>> got a round one.
>>
>> Can we imagine another functionality that would be added to -teardown? If
>> not, it's not a good design. If it works, I would add a completely dummy
>> (no suboptions) group "async-teardown" and not modify the parsing at all.
> 
> Does v2 implement your suggestion?
> Message-Id: <20230320131648.61728-1-imbrenda@linux.ibm.com>
> 
> I dislike it, because it makes query-command-line-options claim
> -async-teardown has an option argument with unknown keys, which is
> plainly wrong, and must be treated as a special case.  Worse, a new kind
> of special case.

I agree with Markus, it sounds like a bad idea to create a new special case 
for this.

Paolo, what do you think of my "-run-with" suggestion here:

 
https://lore.kernel.org/qemu-devel/3237c289-b8c2-6ea2-8bfb-7eeed637efc7@redhat.com/

I still think that this is a good idea, even if it is a "grab-bag" as Markus 
said, it would give us a place where we could wire future similar options, 
too, without running into this problem here again and again.

> Can we have a QMP command, so libvirt can use query-qmp-schema?

Question is whether this could be toggled during runtime...? Or did you mean 
a command that just queries the setting of the option, e.g. 
"query-async-teardown" which then reports whether it is enabled or not?

> In case QMP becomes functional too late for the command to actually
> work: make it always fail for now.  It can still serve as a witness for
> -async-teardown.  If we rework QEMU startup so that QMP can do
> everything the CLI can do, we'll make the QMP command work.

Adding non-working functions sounds ugly... Anyway, we're slowly running out 
of time for QEMU 8.0 ... if we can't find an easy solution, I think we 
should rather postpone this to the next cycle instead of rushing unfinished 
stuff now.

  Thomas

Re: [PATCH v5 1/1] util/async-teardown: wire up query-command-line-options

[Markus Armbruster]

Thomas Huth <thuth@redhat.com> writes:

> On 28/03/2023 07.26, Markus Armbruster wrote:
>> Paolo Bonzini <pbonzini@redhat.com> writes:
>> 
>>> I am honestly not a fan of adding a more complex option,.just because
>>> query-command-line-options only returns the square holes whereas here we
>>> got a round one.
>>>
>>> Can we imagine another functionality that would be added to -teardown? If
>>> not, it's not a good design. If it works, I would add a completely dummy
>>> (no suboptions) group "async-teardown" and not modify the parsing at all.
>>
>> Does v2 implement your suggestion?
>> Message-Id: <20230320131648.61728-1-imbrenda@linux.ibm.com>
>>
>> I dislike it, because it makes query-command-line-options claim
>> -async-teardown has an option argument with unknown keys, which is
>> plainly wrong, and must be treated as a special case.  Worse, a new kind
>> of special case.
>
> I agree with Markus, it sounds like a bad idea to create a new special case for this.
>
> Paolo, what do you think of my "-run-with" suggestion here:
>
>
> https://lore.kernel.org/qemu-devel/3237c289-b8c2-6ea2-8bfb-7eeed637efc7@redhat.com/
>
> I still think that this is a good idea, even if it is a "grab-bag" as Markus said, it would give us a place where we could wire future similar options, too, without running into this problem here again and again.
>
>> Can we have a QMP command, so libvirt can use query-qmp-schema?
>
> Question is whether this could be toggled during runtime...? Or did you mean a command that just queries the setting of the option, e.g. "query-async-teardown" which then reports whether it is enabled or not?

Mildly ugly, as the command is pretty much useless except as a witness
for the CLI option.  We've done this before.

>> In case QMP becomes functional too late for the command to actually
>> work: make it always fail for now.  It can still serve as a witness for
>> -async-teardown.  If we rework QEMU startup so that QMP can do
>> everything the CLI can do, we'll make the QMP command work.
>
> Adding non-working functions sounds ugly...

Non-working functions that could totally work with QEMU startup reworked
are only mildly ugly, I think.

> Anyway, we're slowly running out of time for QEMU 8.0 ... if we can't find an easy solution, I think we should rather postpone this to the next cycle instead of rushing unfinished stuff now.

Yes.

I think we can still do it if we agree quickly on which kind of ugly we
hate the least.

Adding -async-teardown as a stable interface was premature.  We should
have marked it unstable when no libvirt patch was ready when we cut QEMU
7.2.

Adding new external interfaces is still not hard enough :)