Re: [Qemu-devel] [PATCH v8 18/23] qmp: support out-of-band (oob) execution

["Marc-André Lureau" <marcandre.lureau@gmail.com>]

Hi

On Fri, Mar 23, 2018 at 6:18 AM, Peter Xu <peterx@redhat.com> wrote:
> On Thu, Mar 22, 2018 at 11:22:14AM +0100, Marc-André Lureau wrote:
>> Hi
>>
>> On Fri, Mar 9, 2018 at 10:00 AM, Peter Xu <peterx@redhat.com> wrote:
>> > Having "allow-oob" to true for a command does not mean that this command
>> > will always be run in out-of-band mode.  The out-of-band quick path will
>> > only be executed if we specify the extra "run-oob" flag when sending the
>> > QMP request:
>> >
>> >     { "execute":   "command-that-allows-oob",
>> >       "arguments": { ... },
>> >       "control":   { "run-oob": true } }
>> >
>> > The "control" key is introduced to store this extra flag.  "control"
>> > field is used to store arguments that are shared by all the commands,
>> > rather than command specific arguments.  Let "run-oob" be the first.
>> >
>> > Note that in the patch I exported qmp_dispatch_check_obj() to be used to
>> > check the request earlier, and at the same time allowed "id" field to be
>> > there since actually we always allow that.
>> >
>> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>> > Signed-off-by: Peter Xu <peterx@redhat.com>
>> > ---
>> >  include/qapi/qmp/dispatch.h |  2 ++
>> >  monitor.c                   | 84 ++++++++++++++++++++++++++++++++++++++++-----
>> >  qapi/qmp-dispatch.c         | 33 +++++++++++++++++-
>> >  trace-events                |  2 ++
>> >  4 files changed, 111 insertions(+), 10 deletions(-)
>> >
>> > diff --git a/include/qapi/qmp/dispatch.h b/include/qapi/qmp/dispatch.h
>> > index 26eb13ff41..ffb4652f71 100644
>> > --- a/include/qapi/qmp/dispatch.h
>> > +++ b/include/qapi/qmp/dispatch.h
>> > @@ -48,6 +48,8 @@ bool qmp_command_is_enabled(const QmpCommand *cmd);
>> >  const char *qmp_command_name(const QmpCommand *cmd);
>> >  bool qmp_has_success_response(const QmpCommand *cmd);
>> >  QObject *qmp_build_error_object(Error *err);
>> > +QDict *qmp_dispatch_check_obj(const QObject *request, Error **errp);
>> > +bool qmp_is_oob(QDict *dict);
>> >
>> >  typedef void (*qmp_cmd_callback_fn)(QmpCommand *cmd, void *opaque);
>> >
>> > diff --git a/monitor.c b/monitor.c
>> > index 4d57a8d341..5c8afe9f50 100644
>> > --- a/monitor.c
>> > +++ b/monitor.c
>> > @@ -1110,6 +1110,44 @@ static void qmp_caps_apply(Monitor *mon, QMPCapabilityList *list)
>> >      }
>> >  }
>> >
>> > +/*
>> > + * Return true if check successful, or false otherwise.  When false is
>> > + * returned, detailed error will be in errp if provided.
>> > + */
>> > +static bool qmp_cmd_oob_check(Monitor *mon, QDict *req, Error **errp)
>> > +{
>> > +    const char *command;
>> > +    QmpCommand *cmd;
>> > +
>> > +    command = qdict_get_try_str(req, "execute");
>> > +    if (!command) {
>> > +        error_setg(errp, "Command field 'execute' missing");
>> > +        return false;
>> > +    }
>> > +
>> > +    cmd = qmp_find_command(mon->qmp.commands, command);
>> > +    if (!cmd) {
>> > +        error_set(errp, ERROR_CLASS_COMMAND_NOT_FOUND,
>> > +                  "The command %s has not been found", command);
>> > +        return false;
>> > +    }
>> > +
>> > +    if (qmp_is_oob(req)) {
>> > +        if (!qmp_oob_enabled(mon)) {
>> > +            error_setg(errp, "Please enable Out-Of-Band first "
>> > +                       "for the session during capabilities negociation");
>> > +            return false;
>> > +        }
>> > +        if (!(cmd->options & QCO_ALLOW_OOB)) {
>> > +            error_setg(errp, "The command %s does not support OOB",
>> > +                       command);
>> > +            return false;
>> > +        }
>> > +    }
>> > +
>> > +    return true;
>> > +}
>> > +
>> >  void qmp_qmp_capabilities(bool has_enable, QMPCapabilityList *enable,
>> >                            Error **errp)
>> >  {
>> > @@ -4001,6 +4039,7 @@ static void monitor_qmp_bh_dispatcher(void *data)
>> >      QMPRequest *req_obj = monitor_qmp_requests_pop_one();
>> >
>> >      if (req_obj) {
>> > +        trace_monitor_qmp_cmd_in_band(qobject_get_try_str(req_obj->id) ?: "");
>> >          monitor_qmp_dispatch_one(req_obj);
>> >          /* Reschedule instead of looping so the main loop stays responsive */
>> >          qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
>> > @@ -4024,17 +4063,31 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
>> >          error_setg(&err, QERR_JSON_PARSING);
>> >      }
>> >      if (err) {
>> > -        monitor_qmp_respond(mon, NULL, err, NULL);
>> > -        qobject_decref(req);
>> > -        return;
>> > +        goto err;
>> > +    }
>> > +
>> > +    /* Check against the request in general layout */
>> > +    qdict = qmp_dispatch_check_obj(req, &err);
>> > +    if (!qdict) {
>> > +        goto err;
>> >      }
>> >
>> > -    qdict = qobject_to_qdict(req);
>> > -    if (qdict) {
>> > -        id = qdict_get(qdict, "id");
>> > -        qobject_incref(id);
>> > -        qdict_del(qdict, "id");
>> > -    } /* else will fail qmp_dispatch() */
>> > +    /* Check against OOB specific */
>> > +    if (!qmp_cmd_oob_check(mon, qdict, &err)) {
>> > +        goto err;
>> > +    }
>>
>> This check happens before monitor_qmp_dispatch_one(), where there is
>> now dead code for COMMAND_NOT_FOUND error handling (changing the error
>> description), since it will error here.
>>
>> A solution is to move the error manipulation code to monitor_qmp_respond():
>
> So yes, now it'll be checked earlier now since the allow-oob is bound
> to per command, then we'll need that info earlier here.  While I kept
> the other check untouched since there'll be other places that calls
> qmp_dispatch() too.
>
> I'm just wondering would there be any problem even without below change?

Not a problem, just less descriptive error. And we should remove the dead code.

It's best imho to apply the below change. I will send a patch.

> Thanks,
>
>>
>>
>> diff --git a/monitor.c b/monitor.c
>> index 52b4c77ac3..df09a1657d 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -3997,6 +3997,18 @@ static void monitor_qmp_respond(Monitor *mon,
>> QObject *rsp,
>>              qdict_put_obj(qobject_to(QDict, rsp), "id", id);
>>          }
>>
>> +        if (mon->qmp.commands == &qmp_cap_negotiation_commands) {
>> +            qdict = qdict_get_qdict(qobject_to(QDict, rsp), "error");
>> +            if (qdict
>> +                && !g_strcmp0(qdict_get_try_str(qdict, "class"),
>> +
>> QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
>> +                /* Provide a more useful error message */
>> +                qdict_del(qdict, "desc");
>> +                qdict_put_str(qdict, "desc", "Expecting capabilities
>> negotiation"
>> +                              " with 'qmp_capabilities'");
>> +            }
>> +        }
>> +
>>          monitor_json_emitter(mon, rsp);
>>      }
>>
>> @@ -4022,7 +4034,6 @@ static void monitor_qmp_dispatch_one(QMPRequest
>> *req_obj, bool oob_cmd)
>>  {
>>      Monitor *mon, *old_mon;
>>      QObject *req, *rsp = NULL, *id;
>> -    QDict *qdict = NULL;
>>      bool need_resume;
>>
>>      req = req_obj->req;
>> @@ -4045,18 +4056,6 @@ static void monitor_qmp_dispatch_one(QMPRequest
>> *req_obj, bool oob_cmd)
>>
>>      cur_mon = old_mon;
>>
>> -    if (mon->qmp.commands == &qmp_cap_negotiation_commands) {
>> -        qdict = qdict_get_qdict(qobject_to(QDict, rsp), "error");
>> -        if (qdict
>> -            && !g_strcmp0(qdict_get_try_str(qdict, "class"),
>> -                    QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
>> -            /* Provide a more useful error message */
>> -            qdict_del(qdict, "desc");
>> -            qdict_put_str(qdict, "desc", "Expecting capabilities negotiation"
>> -                          " with 'qmp_capabilities'");
>> -        }
>> -    }
>> -
>>      /* Respond if necessary */
>>      monitor_qmp_respond(mon, rsp, NULL, id);
>>
>>
>> > +
>> > +    id = qdict_get(qdict, "id");
>> > +
>> > +    /* When OOB is enabled, the "id" field is mandatory. */
>> > +    if (qmp_oob_enabled(mon) && !id) {
>> > +        error_setg(&err, "Out-Of-Band capability requires that "
>> > +                   "every command contains an 'id' field");
>> > +        goto err;
>> > +    }
>> > +
>> > +    qobject_incref(id);
>> > +    qdict_del(qdict, "id");
>> >
>> >      req_obj = g_new0(QMPRequest, 1);
>> >      req_obj->mon = mon;
>> > @@ -4042,6 +4095,14 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
>> >      req_obj->req = req;
>> >      req_obj->need_resume = false;
>> >
>> > +    if (qmp_is_oob(qdict)) {
>> > +        /* Out-Of-Band (OOB) requests are executed directly in parser. */
>> > +        trace_monitor_qmp_cmd_out_of_band(qobject_get_try_str(req_obj->id)
>> > +                                          ?: "");
>> > +        monitor_qmp_dispatch_one(req_obj);
>> > +        return;
>> > +    }
>> > +
>> >      /* Protect qmp_requests and fetching its length. */
>> >      qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
>> >
>> > @@ -4078,6 +4139,11 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
>> >
>> >      /* Kick the dispatcher routine */
>> >      qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
>> > +    return;
>> > +
>> > +err:
>> > +    monitor_qmp_respond(mon, NULL, err, NULL);
>> > +    qobject_decref(req);
>> >  }
>> >
>> >  static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)
>> > diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
>> > index e31ac4be1f..9a2e18c768 100644
>> > --- a/qapi/qmp-dispatch.c
>> > +++ b/qapi/qmp-dispatch.c
>> > @@ -17,8 +17,9 @@
>> >  #include "qapi/qmp/json-parser.h"
>> >  #include "qapi/qmp/qdict.h"
>> >  #include "qapi/qmp/qjson.h"
>> > +#include "qapi/qmp/qbool.h"
>> >
>> > -static QDict *qmp_dispatch_check_obj(const QObject *request, Error **errp)
>> > +QDict *qmp_dispatch_check_obj(const QObject *request, Error **errp)
>> >  {
>> >      const QDictEntry *ent;
>> >      const char *arg_name;
>> > @@ -50,6 +51,14 @@ static QDict *qmp_dispatch_check_obj(const QObject *request, Error **errp)
>> >                             "QMP input member 'arguments' must be an object");
>> >                  return NULL;
>> >              }
>> > +        } else if (!strcmp(arg_name, "id")) {
>> > +            continue;
>> > +        } else if (!strcmp(arg_name, "control")) {
>> > +            if (qobject_type(arg_obj) != QTYPE_QDICT) {
>> > +                error_setg(errp,
>> > +                           "QMP input member 'control' must be a dict");
>> > +                return NULL;
>> > +            }
>> >          } else {
>> >              error_setg(errp, "QMP input member '%s' is unexpected",
>> >                         arg_name);
>> > @@ -120,6 +129,28 @@ QObject *qmp_build_error_object(Error *err)
>> >                                error_get_pretty(err));
>> >  }
>> >
>> > +/*
>> > + * Detect whether a request should be run out-of-band, by quickly
>> > + * peeking at whether we have: { "control": { "run-oob": True } }. By
>> > + * default commands are run in-band.
>> > + */
>> > +bool qmp_is_oob(QDict *dict)
>> > +{
>> > +    QBool *bool_obj;
>> > +
>> > +    dict = qdict_get_qdict(dict, "control");
>> > +    if (!dict) {
>> > +        return false;
>> > +    }
>> > +
>> > +    bool_obj = qobject_to_qbool(qdict_get(dict, "run-oob"));
>> > +    if (!bool_obj) {
>> > +        return false;
>> > +    }
>> > +
>> > +    return qbool_get_bool(bool_obj);
>> > +}
>> > +
>> >  QObject *qmp_dispatch(QmpCommandList *cmds, QObject *request)
>> >  {
>> >      Error *err = NULL;
>> > diff --git a/trace-events b/trace-events
>> > index fe10c3b487..bd036da278 100644
>> > --- a/trace-events
>> > +++ b/trace-events
>> > @@ -48,6 +48,8 @@ monitor_protocol_event_queue(uint32_t event, void *qdict, uint64_t rate) "event=
>> >  handle_hmp_command(void *mon, const char *cmdline) "mon %p cmdline: %s"
>> >  handle_qmp_command(void *mon, const char *req) "mon %p req: %s"
>> >  monitor_suspend(void *ptr, int cnt) "mon %p: %d"
>> > +monitor_qmp_cmd_in_band(const char *id) "%s"
>> > +monitor_qmp_cmd_out_of_band(const char *id) "%s"
>> >
>> >  # dma-helpers.c
>> >  dma_blk_io(void *dbs, void *bs, int64_t offset, bool to_dev) "dbs=%p bs=%p offset=%" PRId64 " to_dev=%d"
>> > --
>> > 2.14.3
>> >
>> >
>>
>>
>>
>> --
>> Marc-André Lureau
>
> --
> Peter Xu



-- 
Marc-André Lureau