Re: [Qemu-devel] [PATCH v2 02/11] monitor: Split monitor_init in HMP and QMP function

[Markus Armbruster <armbru@redhat.com>]

Kevin Wolf <kwolf@redhat.com> writes:

> Instead of mixing HMP and QMP monitors in the same function, separate
> the monitor creation function for both.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  monitor.c | 86 +++++++++++++++++++++++++++++++------------------------
>  1 file changed, 49 insertions(+), 37 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 70ce9e8a77..bb23cc0450 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -702,7 +702,7 @@ static void handle_hmp_command(Monitor *mon, const char *cmdline);
>  
>  static void monitor_iothread_init(void);
>  
> -static void monitor_data_init(Monitor *mon, bool skip_flush,
> +static void monitor_data_init(Monitor *mon, int flags, bool skip_flush,
>                                bool use_io_thread)
>  {
>      if (use_io_thread && !mon_iothread) {
> @@ -717,6 +717,7 @@ static void monitor_data_init(Monitor *mon, bool skip_flush,
>      mon->skip_flush = skip_flush;
>      mon->use_io_thread = use_io_thread;
>      mon->qmp.qmp_requests = g_queue_new();
> +    mon->flags = flags;
>  }
>  
>  static void monitor_data_destroy(Monitor *mon)
> @@ -740,7 +741,7 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
>      char *output = NULL;
>      Monitor *old_mon, hmp;
>  
> -    monitor_data_init(&hmp, true, false);
> +    monitor_data_init(&hmp, 0, true, false);
>  
>      old_mon = cur_mon;
>      cur_mon = &hmp;

Explicit initialization replaced implicit zero-initialization.  Okay.

> @@ -4603,19 +4604,48 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
>      monitor_list_append(mon);
>  }
>  
> -void monitor_init(Chardev *chr, int flags)
> +static void monitor_init_qmp(Chardev *chr, int flags)
>  {
>      Monitor *mon = g_malloc(sizeof(*mon));
> -    bool use_readline = flags & MONITOR_USE_READLINE;
>  
>      /* Note: we run QMP monitor in I/O thread when @chr supports that */
> -    monitor_data_init(mon, false,
> -                      (flags & MONITOR_USE_CONTROL)
> -                      && qemu_chr_has_feature(chr,
> -                                              QEMU_CHAR_FEATURE_GCONTEXT));
> +    monitor_data_init(mon, flags, false,
> +                      qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT));
>  
>      qemu_chr_fe_init(&mon->chr, chr, &error_abort);
> -    mon->flags = flags;
> +    qemu_chr_fe_set_echo(&mon->chr, true);
> +
> +    json_message_parser_init(&mon->qmp.parser, handle_qmp_command, mon, NULL);
> +    if (mon->use_io_thread) {
> +        /*
> +         * Make sure the old iowatch is gone.  It's possible when
> +         * e.g. the chardev is in client mode, with wait=on.
> +         */
> +        remove_fd_in_watch(chr);
> +        /*
> +         * We can't call qemu_chr_fe_set_handlers() directly here
> +         * since chardev might be running in the monitor I/O
> +         * thread.  Schedule a bottom half.
> +         */
> +        aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
> +                                monitor_qmp_setup_handlers_bh, mon);
> +        /* The bottom half will add @mon to @mon_list */
> +    } else {
> +        qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read,
> +                                 monitor_qmp_read, monitor_qmp_event,
> +                                 NULL, mon, NULL, true);
> +        monitor_list_append(mon);
> +    }
> +}
> +
> +static void monitor_init_hmp(Chardev *chr, int flags)
> +{
> +    Monitor *mon = g_malloc(sizeof(*mon));
> +    bool use_readline = flags & MONITOR_USE_READLINE;
> +
> +    monitor_data_init(mon, flags, false, false);
> +    qemu_chr_fe_init(&mon->chr, chr, &error_abort);
> +
>      if (use_readline) {
>          mon->rs = readline_init(monitor_readline_printf,
>                                  monitor_readline_flush,
> @@ -4624,36 +4654,18 @@ void monitor_init(Chardev *chr, int flags)
>          monitor_read_command(mon, 0);
>      }
>  
> -    if (monitor_is_qmp(mon)) {
> -        qemu_chr_fe_set_echo(&mon->chr, true);
> -        json_message_parser_init(&mon->qmp.parser, handle_qmp_command,
> -                                 mon, NULL);
> -        if (mon->use_io_thread) {
> -            /*
> -             * Make sure the old iowatch is gone.  It's possible when
> -             * e.g. the chardev is in client mode, with wait=on.
> -             */
> -            remove_fd_in_watch(chr);
> -            /*
> -             * We can't call qemu_chr_fe_set_handlers() directly here
> -             * since chardev might be running in the monitor I/O
> -             * thread.  Schedule a bottom half.
> -             */
> -            aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
> -                                    monitor_qmp_setup_handlers_bh, mon);
> -            /* The bottom half will add @mon to @mon_list */
> -            return;
> -        } else {
> -            qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read,
> -                                     monitor_qmp_read, monitor_qmp_event,
> -                                     NULL, mon, NULL, true);
> -        }
> +    qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_read,
> +                             monitor_event, NULL, mon, NULL, true);
> +    monitor_list_append(mon);
> +}
> +
> +void monitor_init(Chardev *chr, int flags)
> +{
> +    if (flags & MONITOR_USE_CONTROL) {
> +        monitor_init_qmp(chr, flags);
>      } else {
> -        qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_read,
> -                                 monitor_event, NULL, mon, NULL, true);
> +        monitor_init_hmp(chr, flags);
>      }
> -
> -    monitor_list_append(mon);
>  }
>  
>  void monitor_cleanup(void)

This part of the diff is hard to read.  I'm inserting a no-op patch just
for review: make two identical copies of monitor_init() called
monitor_init_qmp() and monitor_init_hmp(), have monitor_init() call them
depending on MONITOR_USE_CONTROL.  Rebasing this patch on top of that
yields a more readable git-diff -w (readable for me, YMMV):

| @@ -4606,28 +4607,15 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
|  static void monitor_init_qmp(Chardev *chr, int flags)
|  {
|      Monitor *mon = g_malloc(sizeof(*mon));
| -    bool use_readline = flags & MONITOR_USE_READLINE;

See below.

|  
|      /* Note: we run QMP monitor in I/O thread when @chr supports that */
| -    monitor_data_init(mon, false,
| -                      (flags & MONITOR_USE_CONTROL)
| -                      && qemu_chr_has_feature(chr,
| -                                              QEMU_CHAR_FEATURE_GCONTEXT));
| +    monitor_data_init(mon, flags, false,
| +                      qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT));

Partially evaluated: flags & MONITOR_USE_CONTROL is true.  Good.

|  
|      qemu_chr_fe_init(&mon->chr, chr, &error_abort);
| -    mon->flags = flags;

Moved into monitor_data_init().  Good.

| -    if (use_readline) {
| -        mon->rs = readline_init(monitor_readline_printf,
| -                                monitor_readline_flush,
| -                                mon,
| -                                monitor_find_completion);
| -        monitor_read_command(mon, 0);
| -    }

Deleting readline support here is not a regression, because nothing ever
passes MONITOR_USE_READLINE along with MONITOR_USE_CONTROL.  We use only
three of the four cases:

* Neither flag: gdbstub.c (I have no idea why and how this uses the
  monitor code, and why it doesn't use readline)

* Just MONITOR_USE_READLINE:

  - vl.c on behalf of -mon mode=readline,... and its various sugared
    forms

  - chardev/char.c for implicit mux monitor (you don't want to know)

* Just MONITOR_USE_CONTROL:

  - vl.c on behalf of -mon mode=control,... and its various sugared
    forms

QMP with readline could perhaps be convenient for testing.  I use
socat's READLINE address type myself.

Speaking of odd flag combinations: MONITOR_USE_PRETTY is silently
ignored unless MONITOR_USE_CONTROL.

Deleting the unused (and untried) code to use QMP with readline is fine
with me, but please document MONITOR_USE_READLINE is silently ignored
with MONITOR_USE_CONTROL, or replace all the flags by an enumeration of
the actual cases: HMP without readline, HMP with readline, QMP, pretty
QMP.

| -
| -    if (monitor_is_qmp(mon)) {
|      qemu_chr_fe_set_echo(&mon->chr, true);
| -        json_message_parser_init(&mon->qmp.parser, handle_qmp_command,
| -                                 mon, NULL);
| +
| +    json_message_parser_init(&mon->qmp.parser, handle_qmp_command, mon, NULL);

Partially evaluated: monitor_is_qmp(mon) is true.  Good.

Keep the line break, please.

|      if (mon->use_io_thread) {
|          /*
|           * Make sure the old iowatch is gone.  It's possible when
| @@ -4642,33 +4630,22 @@ static void monitor_init_qmp(Chardev *chr, int flags)
|          aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
|                                  monitor_qmp_setup_handlers_bh, mon);
|          /* The bottom half will add @mon to @mon_list */
| -            return;
|      } else {
|          qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read,
|                                   monitor_qmp_read, monitor_qmp_event,
|                                   NULL, mon, NULL, true);
| -        }
| -    } else {

This else belongs to if (!monitor_is_qmp(mon)).  Good.

| -        qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_read,
| -                                 monitor_event, NULL, mon, NULL, true);
| -    }
| -
|          monitor_list_append(mon);
|      }
| +}

You simplified

       if (mon->use_io_thread) {
           ...
           /* The bottom half will add @mon to @mon_list */
           return;
       } else {
           ...
       }

       monitor_list_append(mon);

to
           
       if (mon->use_io_thread) {
           ...
           /* The bottom half will add @mon to @mon_list */
       } else {
           ...
           monitor_list_append(mon);
       }

Good.

|  
|  static void monitor_init_hmp(Chardev *chr, int flags)
|  {
|      Monitor *mon = g_malloc(sizeof(*mon));
|      bool use_readline = flags & MONITOR_USE_READLINE;
|  
| -    /* Note: we run QMP monitor in I/O thread when @chr supports that */
| -    monitor_data_init(mon, false,
| -                      (flags & MONITOR_USE_CONTROL)
| -                      && qemu_chr_has_feature(chr,
| -                                              QEMU_CHAR_FEATURE_GCONTEXT));
| -
| +    monitor_data_init(mon, flags, false, false);

Partially evaluated: flags & MONITOR_USE_CONTROL is false.  Good.

|      qemu_chr_fe_init(&mon->chr, chr, &error_abort);
| -    mon->flags = flags;
| +

Moved into monitor_data_init().  Good.

|      if (use_readline) {
|          mon->rs = readline_init(monitor_readline_printf,
|                                  monitor_readline_flush,
| @@ -4677,35 +4654,8 @@ static void monitor_init_hmp(Chardev *chr, int flags)
|          monitor_read_command(mon, 0);
|      }
|  
| -    if (monitor_is_qmp(mon)) {
| -        qemu_chr_fe_set_echo(&mon->chr, true);
| -        json_message_parser_init(&mon->qmp.parser, handle_qmp_command,
| -                                 mon, NULL);
| -        if (mon->use_io_thread) {
| -            /*
| -             * Make sure the old iowatch is gone.  It's possible when
| -             * e.g. the chardev is in client mode, with wait=on.
| -             */
| -            remove_fd_in_watch(chr);
| -            /*
| -             * We can't call qemu_chr_fe_set_handlers() directly here
| -             * since chardev might be running in the monitor I/O
| -             * thread.  Schedule a bottom half.
| -             */
| -            aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
| -                                    monitor_qmp_setup_handlers_bh, mon);
| -            /* The bottom half will add @mon to @mon_list */
| -            return;
| -        } else {
| -            qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read,
| -                                     monitor_qmp_read, monitor_qmp_event,
| -                                     NULL, mon, NULL, true);
| -        }
| -    } else {
|      qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_read,
|                               monitor_event, NULL, mon, NULL, true);
| -    }
| -

Partially evaluated: monitor_is_qmp(mon) is false.  Good.

|      monitor_list_append(mon);
|  }
|  

Duplicates qemu_chr_fe_init(&mon->chr, chr, &error_abort).  Quite
tolerable.

Much clearer overall.