Re: [Qemu-devel] [PATCH 1/3] qapi: return a 'missing parameter' error

[Marc-André Lureau]

Hi

----- Original Message -----
> Marc-André Lureau <address@hidden> writes:
> 
> > The 'old' dispatch code returned a QERR_MISSING_PARAMETER for missing
> > parameters, but the qapi qmp_dispatch() code uses
> > QERR_INVALID_PARAMETER_TYPE.
> >
> > Improve qapi code to return QERR_INVALID_PARAMETER_TYPE where
> > appropriate.
> >
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> >  qapi/qmp-input-visitor.c | 109
> >  +++++++++++++++++++++++++++++++----------------
> >  1 file changed, 73 insertions(+), 36 deletions(-)
> >
> > diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
> > index 64dd392..ea9972d 100644
> > --- a/qapi/qmp-input-visitor.c
> > +++ b/qapi/qmp-input-visitor.c
> > @@ -56,7 +56,7 @@ static QmpInputVisitor *to_qiv(Visitor *v)
> >  
> >  static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
> >                                       const char *name,
> > -                                     bool consume)
> > +                                     bool consume, Error **errp)
> >  {
> >      StackObject *tos;
> >      QObject *qobj;
> > @@ -64,30 +64,34 @@ static QObject *qmp_input_get_object(QmpInputVisitor
> > *qiv,
> >  
> >      if (QSLIST_EMPTY(&qiv->stack)) {
> >          /* Starting at root, name is ignored. */
> > -        return qiv->root;
> > -    }
> 
> First case: not in a container.
> 
> qiv->root cannot be null.
> 
> The old code is relatively clear: it returns this non-null value.
> Callers rely on it being non-null.

I didn't realize that, ok

> 
> The new code muddies the waters: it handles the impossible null value by
> setting an error with a misleading message, then returns null.
> 
> Please go back to the old code and simply return qiv->root.  You may
> assert it's non-null.

ok


> Two more cases:
> 
> * In a QTYPE_QDICT container:
> 
>   If ret = qdict_get(qobject_to_qdict(qobj, name) is null, parameter
>   name is missing, and we want to
>   error_setg(errp, QERR_MISSING_PARAMETER, name).  No ternary, because
>   name can't be null.
> 
> * In a QTYPE_QLIST container:
> 
>   ret = qlist_entry_obj(tos->entry) is the list member, a QObject.  It
>   must not be null because null is not a valid QObject.  If we want to
>   catch this, we should assert, not set an error with a misleading
>   message.
> 
> Note for the rest of the review: we return null excactly when we set an
> error.
> 

ok

> >  
> > @@ -163,13 +167,16 @@ static void qmp_input_start_struct(Visitor *v, const
> > char *name, void **obj,
> >                                     size_t size, Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, true);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> >      Error *err = NULL;
> >  
> >      if (obj) {
> >          *obj = NULL;
> >      }
> > -    if (!qobj || qobject_type(qobj) != QTYPE_QDICT) {
> > +    if (!qobj) {
> > +        return;
> > +    }
> > +    if (qobject_type(qobj) != QTYPE_QDICT) {
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> >                     "QDict");
> >          return;
> 
> Mechanical; the next hunk is the same pattern.
> 
> > @@ -191,10 +198,13 @@ static void qmp_input_start_list(Visitor *v, const
> > char *name,
> >                                   GenericList **list, size_t size, Error
> >                                   **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, true);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> >      const QListEntry *entry;
> >  
> > -    if (!qobj || qobject_type(qobj) != QTYPE_QLIST) {
> > +    if (!qobj) {
> > +        return;
> > +    }
> > +    if (qobject_type(qobj) != QTYPE_QLIST) {
> >          if (list) {
> >              *list = NULL;
> >          }
> > @@ -232,11 +242,12 @@ static void qmp_input_start_alternate(Visitor *v,
> > const char *name,
> >                                        bool promote_int, Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, false);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, false, errp);
> >  
> > -    if (!qobj) {
> > +    if (obj) {
> >          *obj = NULL;
> > -        error_setg(errp, QERR_MISSING_PARAMETER, name ? name : "null");
> > +    }
> > +    if (!qobj) {
> >          return;
> >      }
> >      *obj = g_malloc0(size);
> 
> Why are you deviating from the mechanical change here?

Because there is already a QERR_MISSING_PARAMETER return.

> 
> Note that obj can't be null here, by function contract.  If called via
> visit_start_alternate() as it should be, the contract is enforced there.

ok

> 
> > @@ -250,8 +261,12 @@ static void qmp_input_type_int64(Visitor *v, const
> > char *name, int64_t *obj,
> >                                   Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QInt *qint = qobject_to_qint(qmp_input_get_object(qiv, name, true));
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> > +    QInt *qint = qobject_to_qint(qobj);
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> 
> I'd call qobject_to_qint() here, not least for consistency with
> qmp_input_type_number().  Of course, your code works, and if you feel
> strongly about it, we can do it your way here.

ok

> 
> >      if (!qint) {
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> >                     "integer");
> 
> Mechanical; the next few hunks are the same pattern.
> 
> > @@ -266,8 +281,12 @@ static void qmp_input_type_uint64(Visitor *v, const
> > char *name, uint64_t *obj,
> >  {
> >      /* FIXME: qobject_to_qint mishandles values over INT64_MAX */
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QInt *qint = qobject_to_qint(qmp_input_get_object(qiv, name, true));
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> > +    QInt *qint = qobject_to_qint(qobj);
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> >      if (!qint) {
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> >                     "integer");
> > @@ -281,8 +300,12 @@ static void qmp_input_type_bool(Visitor *v, const char
> > *name, bool *obj,
> >                                  Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QBool *qbool = qobject_to_qbool(qmp_input_get_object(qiv, name,
> > true));
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> > +    QBool *qbool = qobject_to_qbool(qobj);
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> >      if (!qbool) {
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> >                     "boolean");
> > @@ -296,8 +319,12 @@ static void qmp_input_type_str(Visitor *v, const char
> > *name, char **obj,
> >                                 Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QString *qstr = qobject_to_qstring(qmp_input_get_object(qiv, name,
> > true));
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> > +    QString *qstr = qobject_to_qstring(qobj);
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> >      if (!qstr) {
> >          *obj = NULL;
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> > @@ -312,10 +339,13 @@ static void qmp_input_type_number(Visitor *v, const
> > char *name, double *obj,
> >                                    Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, true);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> >      QInt *qint;
> >      QFloat *qfloat;
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> >      qint = qobject_to_qint(qobj);
> >      if (qint) {
> >          *obj = qint_get_int(qobject_to_qint(qobj));
> > @@ -336,7 +366,11 @@ static void qmp_input_type_any(Visitor *v, const char
> > *name, QObject **obj,
> >                                 Error **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, true);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> > +
> > +    if (!qobj) {
> > +        return;
> > +    }
> >  
> >      qobject_incref(qobj);
> >      *obj = qobj;
> 
> Aha, we got a different bug fix!  The old code fails to fail when the
> parameter doesn't exist.  Instead, it sets *obj = NULL, which seems very
> likely to crash QEMU.  Let me try... yup:
> 
>     { "execute": "object-add",
>       "arguments": { "qom-type": "memory-backend-file", "id": "foo" } }
> 
> Kills QEMU with "qemu/qom/object_interfaces.c:115: user_creatable_add_type:
> Assertion `qdict' failed."
> 
> Either fix this in a separate patch before this one, or cover it in this
> one's commit message.  Your choice.

ok, I'll make a seperate patch

> 
> A separate patch might be usable for qemu-stable.
> 
> > @@ -345,8 +379,11 @@ static void qmp_input_type_any(Visitor *v, const char
> > *name, QObject **obj,
> >  static void qmp_input_type_null(Visitor *v, const char *name, Error
> >  **errp)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, true);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, true, errp);
> >  
> > +    if (!qobj) {
> > +        return;
> > +    }
> >      if (qobject_type(qobj) != QTYPE_QNULL) {
> >          error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name :
> >          "null",
> >                     "null");
> 
> Same bug, I think, but I don't have a reproducer handy.

let's include it in the same patch

> 
> > @@ -356,7 +393,7 @@ static void qmp_input_type_null(Visitor *v, const char
> > *name, Error **errp)
> >  static void qmp_input_optional(Visitor *v, const char *name, bool
> >  *present)
> >  {
> >      QmpInputVisitor *qiv = to_qiv(v);
> > -    QObject *qobj = qmp_input_get_object(qiv, name, false);
> > +    QObject *qobj = qmp_input_get_object(qiv, name, false, NULL);
> >  
> >      if (!qobj) {
> >          *present = false;
> 
> Thanks for following my suggestion to move the "Parameter FOO is
> missing" error into qmp_input_get_object()!  You fixed two crash bugs
> that way :)
>