Re: [Qemu-devel] [PATCH v8 10/20] replay: introduce info hmp/qmp command

[Markus Armbruster <armbru@redhat.com>]

Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> writes:

> This patch introduces 'info replay' monitor command and
> corresponding qmp request.
> These commands request the current record/replay mode, replay log file name,
> and the execution step (number or recorded/replayed instructions).
> User may use step number for replay_seek/replay_break commands and
> for controlling the execution of replay.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> --
>
> v2:
>  - renamed info_replay qmp into query-replay (suggested by Eric Blake)
> v7:
>  - added empty line (suggested by Markus Armbruster)
> ---
>  hmp-commands-info.hx      |   14 ++++++++++++++
>  hmp.h                     |    1 +
>  qapi/misc.json            |   35 +++++++++++++++++++++++++++++++++++
>  replay/Makefile.objs      |    3 ++-
>  replay/replay-debugging.c |   42 ++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 94 insertions(+), 1 deletion(-)
>  create mode 100644 replay/replay-debugging.c
>
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index cbee8b9..9f2f35e 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -918,6 +918,20 @@ STEXI
>  Show SEV information.
>  ETEXI
>  
> +    {
> +        .name       = "replay",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "show parameters of the record/replay",
> +        .cmd        = hmp_info_replay,
> +    },
> +
> +STEXI
> +@item info replay
> +@findex info replay
> +Display the current record/replay mode and the currently executing step.
> +ETEXI
> +
>  STEXI
>  @end table
>  ETEXI
> diff --git a/hmp.h b/hmp.h
> index 5f1addc..d792149 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -148,5 +148,6 @@ void hmp_hotpluggable_cpus(Monitor *mon, const QDict *qdict);
>  void hmp_info_vm_generation_id(Monitor *mon, const QDict *qdict);
>  void hmp_info_memory_size_summary(Monitor *mon, const QDict *qdict);
>  void hmp_info_sev(Monitor *mon, const QDict *qdict);
> +void hmp_info_replay(Monitor *mon, const QDict *qdict);
>  
>  #endif
> diff --git a/qapi/misc.json b/qapi/misc.json
> index 8325e0d..e47aea6 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -3113,6 +3113,41 @@
>    'data': [ 'none', 'record', 'play' ] }
>  
>  ##
> +# @ReplayInfo:
> +#
> +# Status of the record/replay mode.
> +#
> +# @mode: current mode.
> +#
> +# @filename: name of the record/replay log file.
> +#
> +# @step: current step number.
> +#
> +# Since: 4.0
> +#
> +##
> +{ 'struct': 'ReplayInfo',
> +  'data': { 'mode': 'ReplayMode', '*filename': 'str', 'step': 'int' } }

@filename is optional.  For each ReplayMode: is @filename always absent,
always present, or can it be either?

> +
> +##
> +# @query-replay:
> +#
> +# Retrieves the status of the execution record/replay.
> +#
> +# Returns: structure with the properties of the record/replay.

You've used "parameters of the record/replay" (in HMP help info),
"status of the record/replay mode" (QMP ReplayInfo doc), "the status of
the execution record/replay" (QMP query-replay doc), and "structure with
the properties of the record/replay".  Please pick one.  I think I'd
pick "record/replay information".

In my (superficial) review of v6, I asked what a client would do with
@step.  You gave two use cases:

 1. Control current step to be sure that replay is not stalled due to the bug.
 2. Requesting the step for some moment of execution to use it as a parameter
    of replay_seek/replay_break operations. I.e., for returning to the same
    point later.

The first one is a bit vague.  The second one sounds plausible enough to
me at least for stopped VMs (for running VMs, it feels too imprecise to
be useful, but what do I know).  replay-break is in PATCH 11,
replay-seek in PATCH 12.  Would it make sense add a suitable reference
to ReplayInfo's documentation then?

> +#
> +# Since: 4.0
> +#
> +# Example:
> +#
> +# -> { "execute": "query-replay" }
> +# <- { "return": { "mode": "play", "filename": "log.rr", "step": 220414 } }
> +#
> +##
> +{ 'command': 'query-replay',
> +  'returns': 'ReplayInfo' }
> +
> +##
>  # @xen-load-devices-state:
>  #
>  # Load the state of all devices from file. The RAM and the block devices

At the end of this series, record/replay takes almost 100 non-blank
lines in misc.json.  Let's create a separate QAPI schema module
qapi/replay.json, so we can have MAINTAINERS cover this stuff properly.

> diff --git a/replay/Makefile.objs b/replay/Makefile.objs
> index cee6539..6694e3e 100644
> --- a/replay/Makefile.objs
> +++ b/replay/Makefile.objs
> @@ -6,4 +6,5 @@ common-obj-y += replay-input.o
>  common-obj-y += replay-char.o
>  common-obj-y += replay-snapshot.o
>  common-obj-y += replay-net.o
> -common-obj-y += replay-audio.o
> \ No newline at end of file
> +common-obj-y += replay-audio.o
> +common-obj-y += replay-debugging.o
> diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
> new file mode 100644
> index 0000000..1d7e75d
> --- /dev/null
> +++ b/replay/replay-debugging.c
> @@ -0,0 +1,42 @@
> +/*
> + * replay-debugging.c
> + *
> + * Copyright (c) 2010-2018 Institute for System Programming
> + *                         of the Russian Academy of Sciences.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "sysemu/replay.h"
> +#include "replay-internal.h"
> +#include "hmp.h"
> +#include "monitor/monitor.h"
> +#include "qapi/qapi-commands-misc.h"
> +
> +void hmp_info_replay(Monitor *mon, const QDict *qdict)
> +{
> +    if (replay_mode == REPLAY_MODE_NONE) {
> +        monitor_printf(mon, "No record/replay\n");
> +    } else {
> +        monitor_printf(mon, "%s execution '%s': current step = %"PRId64"\n",
> +            replay_mode == REPLAY_MODE_RECORD ? "Recording" : "Replaying",
> +            replay_get_filename(), replay_get_current_step());
> +    }
> +}
> +
> +ReplayInfo *qmp_query_replay(Error **errp)
> +{
> +    ReplayInfo *retval = g_new0(ReplayInfo, 1);
> +
> +    retval->mode = replay_mode;
> +    if (replay_get_filename()) {
> +        retval->filename = g_strdup(replay_get_filename());
> +        retval->has_filename = true;
> +    }
> +    retval->step = replay_get_current_step();
> +    return retval;
> +}