Re: [Qemu-devel] [PATCH v4 6/6] trace: Add QAPI/QMP interfaces to query and control per-vCPU tracing state

[Markus Armbruster <armbru@redhat.com>]

Lluís Vilanova <vilanova@ac.upc.edu> writes:

> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  monitor.c       |    4 +-
>  qapi/trace.json |   20 ++++++--
>  qmp-commands.hx |   17 ++++++-
>  trace/qmp.c     |  143 ++++++++++++++++++++++++++++++++++++++++++++-----------
>  4 files changed, 147 insertions(+), 37 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index a27e115..bb89877 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -910,7 +910,7 @@ static void hmp_trace_event(Monitor *mon, const QDict *qdict)
>      bool new_state = qdict_get_bool(qdict, "option");
>      Error *local_err = NULL;
>  
> -    qmp_trace_event_set_state(tp_name, new_state, true, true, &local_err);
> +    qmp_trace_event_set_state(tp_name, new_state, true, true, false, 0, &local_err);
>      if (local_err) {
>          error_report_err(local_err);
>      }
> @@ -1069,7 +1069,7 @@ static void hmp_info_cpustats(Monitor *mon, const QDict *qdict)
>  
>  static void hmp_info_trace_events(Monitor *mon, const QDict *qdict)
>  {
> -    TraceEventInfoList *events = qmp_trace_event_get_state("*", NULL);
> +    TraceEventInfoList *events = qmp_trace_event_get_state("*", false, 0, NULL);
>      TraceEventInfoList *elem;
>  
>      for (elem = events; elem != NULL; elem = elem->next) {

The new feature remains inaccessible in HMP.  Any plans to extend HMP?
Any reasons not to?

> diff --git a/qapi/trace.json b/qapi/trace.json
> index 01b0a52..25d8095 100644
> --- a/qapi/trace.json
> +++ b/qapi/trace.json
> @@ -1,6 +1,6 @@
>  # -*- mode: python -*-
>  #
> -# Copyright (C) 2011-2014 Lluís Vilanova <vilanova@ac.upc.edu>
> +# Copyright (C) 2011-2016 Lluís Vilanova <vilanova@ac.upc.edu>
>  #
>  # This work is licensed under the terms of the GNU GPL, version 2 or later.
>  # See the COPYING file in the top-level directory.
> @@ -29,11 +29,12 @@
>  #
>  # @name: Event name.
>  # @state: Tracing state.
> +# @vcpu: Whether this is a per-vCPU event (since 2.7).
>  #
>  # Since 2.2
>  ##
>  { 'struct': 'TraceEventInfo',
> -  'data': {'name': 'str', 'state': 'TraceEventState'} }
> +  'data': {'name': 'str', 'state': 'TraceEventState', 'vcpu': 'bool'} }
>  
>  ##
>  # @trace-event-get-state:
> @@ -41,13 +42,18 @@
>  # Query the state of events.
>  #
>  # @name: Event name pattern (case-sensitive glob).
> +# @vcpu: #optional The vCPU to check (any by default; since 2.7).
>  #
>  # Returns: a list of @TraceEventInfo for the matching events
>  #
> +# For any event without the "vcpu" property:

All events have the vcpu property, but for some of them the property's
value is false.

> +# - If @name is a pattern and @vcpu is set, events are ignored.

I figure "ignored" means they're not included in the return value.
Correct?

> +# - If @name is not a pattern and @vcpu is set, an error is raised.

Perhaps we could clarify as follows:

# Returns: a list of @TraceEventInfo for the matching events
#
# An event matches if
# - its name matches the @name pattern, and
# - if @vcpu is given, its vCPU equals @vcpu.
# It follows that with @vcpu given, the query can match only per-vCPU
# events.  Special case: if the name is an exact match, you get an error
# instead of an empty list.

> +#
>  # Since 2.2
>  ##
>  { 'command': 'trace-event-get-state',
> -  'data': {'name': 'str'},
> +  'data': {'name': 'str', '*vcpu': 'int'},
>    'returns': ['TraceEventInfo'] }
>  
>  ##
> @@ -58,8 +64,14 @@
>  # @name: Event name pattern (case-sensitive glob).
>  # @enable: Whether to enable tracing.
>  # @ignore-unavailable: #optional Do not match unavailable events with @name.
> +# @vcpu: #optional The vCPU to act upon (all by default; since 2.7).
> +#
> +# For any event without the "vcpu" property:
> +# - If @name is a pattern and @vcpu is set, events are ignored.
> +# - If @name is not a pattern and @vcpu is set, an error is raised.

Likewise.

>  #
>  # Since 2.2
>  ##
>  { 'command': 'trace-event-set-state',
> -  'data': {'name': 'str', 'enable': 'bool', '*ignore-unavailable': 'bool'} }
> +  'data': {'name': 'str', 'enable': 'bool', '*ignore-unavailable': 'bool',
> +           '*vcpu': 'int'} }
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 28801a2..c9eb25c 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -4676,7 +4676,7 @@ EQMP
>  
>      {
>          .name       = "trace-event-get-state",
> -        .args_type  = "name:s",
> +        .args_type  = "name:s,vcpu:i?",
>          .mhandler.cmd_new = qmp_marshal_trace_event_get_state,
>      },
>  
> @@ -4686,6 +4686,11 @@ trace-event-get-state
>  
>  Query the state of events.
>  
> +Arguments:
> +
> +- "name": Event name pattern (json-string).
> +- "vcpu": Specific vCPU to query, any vCPU by default (json-int, optional).
> +

Less information than you give in the schema.  Easy enough to fix.

>  Example:
>  
>  -> { "execute": "trace-event-get-state", "arguments": { "name": "qemu_memalign" } }
> @@ -4694,7 +4699,7 @@ EQMP
>  
>      {
>          .name       = "trace-event-set-state",
> -        .args_type  = "name:s,enable:b,ignore-unavailable:b?",
> +        .args_type  = "name:s,enable:b,ignore-unavailable:b?,vcpu:i?",
>          .mhandler.cmd_new = qmp_marshal_trace_event_set_state,
>      },
>  
> @@ -4704,6 +4709,14 @@ trace-event-set-state
>  
>  Set the state of events.
>  
> +Arguments:
> +
> +- "name": Event name pattern (json-string).
> +- "enable": Whether to enable or disable the event (json-bool).
> +- "ignore-unavailable": Whether to ignore errors for events that cannot be
> +  changed (json-bool, optional).
> +- "vcpu": Specific vCPU to set, all vCPUs by default (json-int, optional).
> +

Likewise.

>  Example:
>  
>  -> { "execute": "trace-event-set-state", "arguments": { "name": "qemu_memalign", "enable": "true" } }
> diff --git a/trace/qmp.c b/trace/qmp.c
> index 8aa2660..c18e750 100644
> --- a/trace/qmp.c
> +++ b/trace/qmp.c
> @@ -1,7 +1,7 @@
>  /*
>   * QMP commands for tracing events.
>   *
> - * Copyright (C) 2014 Lluís Vilanova <vilanova@ac.upc.edu>
> + * Copyright (C) 2014-2016 Lluís Vilanova <vilanova@ac.upc.edu>
>   *
>   * This work is licensed under the terms of the GNU GPL, version 2 or later.
>   * See the COPYING file in the top-level directory.
> @@ -12,63 +12,148 @@
>  #include "trace/control.h"
>  
>  
> -TraceEventInfoList *qmp_trace_event_get_state(const char *name, Error **errp)
> +static bool get_cpu(bool has_vcpu, int vcpu, CPUState **cpu, Error **errp)
> +{
> +    if (has_vcpu) {
> +        *cpu = qemu_get_cpu(vcpu);
> +        if (*cpu == NULL) {
> +            error_setg(errp, "invalid vCPU index %u", vcpu);
> +            return false;
> +        }
> +    } else {
> +        *cpu = NULL;
> +    }
> +    return true;
> +}

This returns three things: a bool (via return value), a CPUState *
(via @cpu) and an Error (via customary @errp).  Possible combinations:

* Success with has_vcpu: true, non-null CPU *, no error
* Failure with has_vcpu: false, null CPU *, error set
* Success without has_vcpu: true, null CPU *, no error

Usage:

    if (!get_cpu(has_vcpu, vcpu, &cpu, errp)) {
        error out...
    }

If you dispense with the bool and return the pointer instead, you'd get:

    Error *err = NULL;

    cpu = get_cpu(has_vcpu, vcpu, &err);
    if (err) {
        error_propagate(errp, err);
        error out...
    }

This is more in line with how we use Error elsewhere.  Needs more code,
though.  Since it's just a local helper function, the choice is yours.

> +
> +static bool check_events(bool has_vcpu, bool ignore_unavailable, bool is_pattern,
> +                         const char *name, Error **errp)
> +{
> +    if (!is_pattern) {
> +        TraceEvent *ev = trace_event_name(name);
> +
> +        /* error for non-existing event */
> +        if (ev == NULL) {
> +            error_setg(errp, "unknown event \"%s\"", name);
> +            return false;
> +        }
> +
> +        /* error for non-vcpu event */
> +        if (has_vcpu && trace_event_is_vcpu(ev)) {
> +            error_setg(errp, "event \"%s\" is not vCPU-specific", name);
> +            return false;
> +        }
> +
> +        /* error for unavailable event */
> +        if (!ignore_unavailable && !trace_event_get_state_static(ev)) {
> +            error_setg(errp, "event \"%s\" is disabled", name);
> +            return false;
> +        }
> +
> +        return true;
> +    } else {
> +        /* error for unavailable events */
> +        TraceEvent *ev = NULL;
> +        while ((ev = trace_event_pattern(name, ev)) != NULL) {
> +            if (!ignore_unavailable && !trace_event_get_state_static(ev)) {
> +                error_setg(errp, "event \"%s\" is disabled", trace_event_get_name(ev));
> +                return false;
> +            }
> +        }
> +        return true;
> +    }
> +}
> +
> +TraceEventInfoList *qmp_trace_event_get_state(const char *name,
> +                                              bool has_vcpu, int64_t vcpu,
> +                                              Error **errp)
>  {
>      TraceEventInfoList *events = NULL;
> -    bool found = false;
>      TraceEvent *ev;
> +    bool is_pattern = trace_event_is_pattern(name);
> +    CPUState *cpu;
>  
> +    /* Check provided vcpu */
> +    if (!get_cpu(has_vcpu, vcpu, &cpu, errp)) {
> +        return NULL;
> +    }
> +
> +    /* Check events */
> +    if (!check_events(has_vcpu, true, is_pattern, name, errp)) {
> +        return NULL;
> +    }
> +
> +    /* Get states (all errors checked above) */
>      ev = NULL;
>      while ((ev = trace_event_pattern(name, ev)) != NULL) {
> -        TraceEventInfoList *elem = g_new(TraceEventInfoList, 1);
> +        TraceEventInfoList *elem;
> +        bool is_vcpu = trace_event_is_vcpu(ev);
> +        if (has_vcpu && !is_vcpu) {
> +            continue;
> +        }
> +
> +        elem = g_new(TraceEventInfoList, 1);
>          elem->value = g_new(TraceEventInfo, 1);
> +        elem->value->vcpu = is_vcpu;
>          elem->value->name = g_strdup(trace_event_get_name(ev));
> +
>          if (!trace_event_get_state_static(ev)) {
>              elem->value->state = TRACE_EVENT_STATE_UNAVAILABLE;
> -        } else if (!trace_event_get_state_dynamic(ev)) {
> -            elem->value->state = TRACE_EVENT_STATE_DISABLED;
>          } else {
> -            elem->value->state = TRACE_EVENT_STATE_ENABLED;
> +            if (has_vcpu) {
> +                if (is_vcpu) {
> +                    if (trace_event_get_vcpu_state_dynamic(cpu, ev)) {
> +                        elem->value->state = TRACE_EVENT_STATE_ENABLED;
> +                    } else {
> +                        elem->value->state = TRACE_EVENT_STATE_DISABLED;
> +                    }
> +                }
> +                /* else: already skipped above */
> +            } else {
> +                if (trace_event_get_state_dynamic(ev)) {
> +                    elem->value->state = TRACE_EVENT_STATE_ENABLED;
> +                } else {
> +                    elem->value->state = TRACE_EVENT_STATE_DISABLED;
> +                }
> +            }
>          }
>          elem->next = events;
>          events = elem;
> -        found = true;
> -    }
> -
> -    if (!found && !trace_event_is_pattern(name)) {
> -        error_setg(errp, "unknown event \"%s\"", name);
>      }
>  
>      return events;
>  }
>  
>  void qmp_trace_event_set_state(const char *name, bool enable,
> -                               bool has_ignore_unavailable,
> -                               bool ignore_unavailable, Error **errp)
> +                               bool has_ignore_unavailable, bool ignore_unavailable,
> +                               bool has_vcpu, int64_t vcpu,
> +                               Error **errp)
>  {
> -    bool found = false;
>      TraceEvent *ev;
> +    bool is_pattern = trace_event_is_pattern(name);
> +    CPUState *cpu;
>  
> -    /* Check all selected events are dynamic */
> -    ev = NULL;
> -    while ((ev = trace_event_pattern(name, ev)) != NULL) {
> -        found = true;
> -        if (!(has_ignore_unavailable && ignore_unavailable) &&
> -            !trace_event_get_state_static(ev)) {
> -            error_setg(errp, "cannot set dynamic tracing state for \"%s\"",
> -                       trace_event_get_name(ev));
> -            return;
> -        }
> +    /* Check provided vcpu */
> +    if (!get_cpu(has_vcpu, vcpu, &cpu, errp)) {
> +        return;
>      }
> -    if (!found && !trace_event_is_pattern(name)) {
> -        error_setg(errp, "unknown event \"%s\"", name);
> +
> +    /* Check events */
> +    if (!check_events(has_vcpu, has_ignore_unavailable && ignore_unavailable,
> +                      is_pattern, name, errp)) {
>          return;
>      }
>  
> -    /* Apply changes */
> +    /* Apply changes (all errors checked above) */
>      ev = NULL;
>      while ((ev = trace_event_pattern(name, ev)) != NULL) {
> -        if (trace_event_get_state_static(ev)) {
> +        if (!trace_event_get_state_static(ev) ||
> +            (has_vcpu && trace_event_is_vcpu(ev))) {
> +            continue;
> +        }
> +        if (has_vcpu) {
> +            trace_event_set_vcpu_state_dynamic(cpu, ev, enable);
> +        } else {
>              trace_event_set_state_dynamic(ev, enable);
>          }
>      }

Looks okay.