Re: [PATCH v3 1/1] util/async-teardown: wire up query-command-line-options

[Thomas Huth <thuth@redhat.com>]

On 24/03/2023 18.45, Claudio Imbrenda wrote:
> The recently introduced -async-teardown commandline option was not
> wired up properly and did not show up in the output of the QMP command
> query-command-line-options. This means that libvirt will have no way to
> discover whether the feature is supported.
> 
> This patch fixes the issue by correctly wiring up the commandline
> option so that it appears in the output of query-command-line-options.
> 
> 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>
> ---
>   os-posix.c            | 14 ++++++++++++++
>   qemu-options.hx       | 35 ++++++++++++++++++++++++-----------
>   util/async-teardown.c | 21 +++++++++++++++++++++
>   3 files changed, 59 insertions(+), 11 deletions(-)
> 
> diff --git a/os-posix.c b/os-posix.c
> index 5adc69f560..48acd7acf5 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);
> @@ -155,6 +159,16 @@ int os_parse_cmd_args(int index, const char *optarg)
>       case QEMU_OPTION_asyncteardown:
>           init_async_teardown();
>           break;
> +    case QEMU_OPTION_teardown:
> +        opts = qemu_opts_parse_noisily(qemu_find_opts("teardown"),
> +                                       optarg, false);
> +        if (!opts) {
> +            return -1;

Maybe it's better to use exit(1) here (like it is done in the -runas part), 
otherwise you get a somewhat weird second error message:

$ ./qemu-system-s390x -teardown aysnc=on
qemu-system-s390x: -teardown aysnc=on: Invalid parameter 'aysnc'
qemu-system-s390x: -teardown aysnc=on: Option not supported in this build

> +        }
> +        if (qemu_opt_get_bool(opts, "async", false)) {
> +            init_async_teardown();
> +        }
> +        break;
>   #endif
>       default:
>           return -1;
> diff --git a/qemu-options.hx b/qemu-options.hx
> index d42f60fb91..8582980b12 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4766,20 +4766,33 @@ DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log, "", QEMU_ARCH_ALL)
>   DEF("async-teardown", 0, QEMU_OPTION_asyncteardown,
>       "-async-teardown enable 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.
> +    Equivalent to -teardown async=on
> +ERST
> +
> +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)
> +SRST
> +``-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

While you're at it, we officially spell QEMU with capital letters, so I'd 
maybe do a s/qemu/QEMU/g here.

> +    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);

  Thomas