Message ID | 1460131992-32278-8-git-send-email-eblake@redhat.com |
---|---|
State | New |
Headers | show |
Eric Blake <eblake@redhat.com> writes: > Refactor the code to advance the QListEntry pointer at the point > where visit_type_FOO() is called, rather than visit_next_list(). > This will allow a future patch to move the visit of the list head > into visit_start_list(), and get rid of the 'first' flag. > > Signed-off-by: Eric Blake <eblake@redhat.com> After having read the patch, I think the change is from this sequence of states start_list next_list type_ELT ... next_list type_ELT end_list entry NULL 1st elt 1st elt last elt last elt gone where type_ELT() returns (entry ? entry : 1st elt) and next_list() steps entry to this one start_list next_list type_ELT ... next_list type_ELT end_list entry 1st elt 1nd elt 2nd elt last elt NULL gone where type_ELT() steps entry and returns the old entry, and next_list() leaves entry alone. Correct? Now have a look at the typical generated visit: void visit_type_FOOList(Visitor *v, const char *name, FOOList **obj, Error **errp) { Error *err = NULL; FOOList *tail; size_t size = sizeof(**obj); visit_start_list(v, name, (GenericList **)obj, size, &err); if (err) { goto out; } for (tail = *obj; tail; tail = (FOOList *)visit_next_list(v, (GenericList *)tail, size)) { visit_type_FOO(v, NULL, &tail->value, &err); if (err) { break; } } if (visit_end_list(v) && err) { qapi_free_FOOList(*obj); *obj = NULL; } out: error_propagate(errp, err); } While the loop variable is still stepped in the for's third expression as it should, the actual stepping below the hood now happens in the loop body. I find this mildly confusing. Perhaps a more natural loop would be void visit_type_FOOList(Visitor *v, const char *name, FOOList **obj, Error **errp) { Error *err = NULL; GenericList *tail; size_t size = sizeof(**obj); visit_start_list(v, name, (GenericList **)obj, size, &err); if (err) { goto out; } while ((tail = visit_next_list(v, tail, size))) { visit_type_FOO(v, NULL, &((FOOList *)tail)->value, &err); if (err) { break; } } if (visit_end_list(v) && err) { qapi_free_FOOList(*obj); *obj = NULL; } out: error_propagate(errp, err); } Might also permit de-duplicating the g_malloc0(size), since we now call next_list() *before* each iteration instead of *between* iterations. > --- > v14: no change > v13: no change > v12: new patch > --- > qapi/qmp-input-visitor.c | 40 +++++++++++++++++++++------------------- > 1 file changed, 21 insertions(+), 19 deletions(-) > > diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c > index cfaf378..1820360 100644 > --- a/qapi/qmp-input-visitor.c > +++ b/qapi/qmp-input-visitor.c > @@ -27,9 +27,10 @@ typedef struct StackObject > { > QObject *obj; /* Object being visited */ > > - /* If obj is list: NULL if list is at head, otherwise tail of list > - * still needing visits */ > + /* If obj is list: tail of list still needing visits */ > const QListEntry *entry; > + /* If obj is list: true if head is not visited yet */ > + bool first; Temporary, PATCH 18 will get rid of it. Good, because the less state, the happier I am :) > > GHashTable *h; /* If obj is dict: remaining keys needing visits */ > } StackObject; > @@ -77,7 +78,12 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv, /* If we are in the middle of a list, then return the next element > * of the list. */ > if (tos->entry) { Before the patch, the condition matches the comment: tos->entry implies this is a list and we're not at its head. After the patch, the condition only implies it's a list, but ... > assert(qobject_type(qobj) == QTYPE_QLIST); > - return qlist_entry_obj(tos->entry); > + assert(!tos->first); ... you assert that "not at its head" can't happen. Why is that the case? > + qobj = qlist_entry_obj(tos->entry); > + if (consume) { > + tos->entry = qlist_next(tos->entry); > + } > + return qobj; The remainder of the hunk adds the qlist_next() call moved from qmp_input_next_list(), as advertized by the commit message. Good. > } > > /* Otherwise, we are at the root of the visit or the start of a > @@ -91,7 +97,8 @@ static void qdict_add_key(const char *key, QObject *obj, void *opaque) > g_hash_table_insert(h, (gpointer) key, NULL); > } > > -static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) > +static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, > + const QListEntry *entry, Error **errp) > { > GHashTable *h; > StackObject *tos = &qiv->stack[qiv->nb_stack]; > @@ -103,7 +110,8 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) > } > > tos->obj = obj; > - tos->entry = NULL; > + tos->entry = entry; > + tos->first = true; > tos->h = NULL; > > if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) { Here, you change the initial state. Not explicitly advertized in the commit message, unlike the change to qlist_next(). I guess that's okay, but perhaps my ramblings give you ideas on improving the commit message. I wonder whether we really need the new argument. Could we do something like if (qobject_type(obj) == QTYPE_QLIST) { tos->entry = qlist_first(qobject_to_qlist(obj)); tos->first = true; } ? > @@ -153,7 +161,7 @@ static void qmp_input_start_struct(Visitor *v, const char *name, void **obj, > return; > } > > - qmp_input_push(qiv, qobj, &err); > + qmp_input_push(qiv, qobj, NULL, &err); Since @qobj is a dictionary, the StackObject's entry will be unused, so pass null. Okay. > if (err) { > error_propagate(errp, err); > return; > @@ -175,6 +183,7 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) > { > QmpInputVisitor *qiv = to_qiv(v); > QObject *qobj = qmp_input_get_object(qiv, name, true); > + const QListEntry *entry; > > if (!qobj || qobject_type(qobj) != QTYPE_QLIST) { > error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null", > @@ -182,7 +191,8 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) > return; > } > > - qmp_input_push(qiv, qobj, errp); > + entry = qlist_first(qobject_to_qlist(qobj)); > + qmp_input_push(qiv, qobj, entry, errp); @qobj is a list, the StackObject's entry must be initialized to its first member, so pass that. > } > > static GenericList *qmp_input_next_list(Visitor *v, GenericList **list, > @@ -191,23 +201,15 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list, > QmpInputVisitor *qiv = to_qiv(v); > GenericList *entry; > StackObject *so = &qiv->stack[qiv->nb_stack - 1]; > - bool first; > > - if (so->entry == NULL) { > - so->entry = qlist_first(qobject_to_qlist(so->obj)); > - first = true; > - } else { > - so->entry = qlist_next(so->entry); > - first = false; > - } > - > - if (so->entry == NULL) { > + if (!so->entry) { > return NULL; > } > > entry = g_malloc0(size); > - if (first) { > + if (so->first) { > *list = entry; > + so->first = false; > } else { > (*list)->next = entry; > } Here, you drop the qlist_next() call. It moves to qmp_input_get_object(). Good. > @@ -382,7 +384,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj) > v->visitor.type_any = qmp_input_type_any; > v->visitor.optional = qmp_input_optional; > > - qmp_input_push(v, obj, NULL); > + qmp_input_push(v, obj, NULL, NULL); @obj is the root of the visit. Can it be a list? If yes, then StackObject's entry is not its first element. Why is that correct? > qobject_incref(obj); > > return v;
On 04/13/2016 11:38 AM, Markus Armbruster wrote: > Eric Blake <eblake@redhat.com> writes: > >> Refactor the code to advance the QListEntry pointer at the point >> where visit_type_FOO() is called, rather than visit_next_list(). >> This will allow a future patch to move the visit of the list head >> into visit_start_list(), and get rid of the 'first' flag. >> >> Signed-off-by: Eric Blake <eblake@redhat.com> > > After having read the patch, I think the change is from this sequence of > states > > start_list next_list type_ELT ... next_list type_ELT end_list > entry NULL 1st elt 1st elt last elt last elt gone > > where type_ELT() returns (entry ? entry : 1st elt) and next_list() steps > entry > > to this one > > start_list next_list type_ELT ... next_list type_ELT end_list > entry 1st elt 1nd elt 2nd elt last elt NULL gone > > where type_ELT() steps entry and returns the old entry, and next_list() > leaves entry alone. Correct? Yes. I think I know what diagram I'll be adding to my commit message :) > > Now have a look at the typical generated visit: Which gets greatly simplified later in 18/19 (ie. this patch is doing some of the refactoring to make 18/19 easier). > > void visit_type_FOOList(Visitor *v, const char *name, FOOList **obj, Error **errp) > { > Error *err = NULL; > FOOList *tail; > size_t size = sizeof(**obj); > > visit_start_list(v, name, (GenericList **)obj, size, &err); > if (err) { > goto out; > } > for (tail = *obj; > tail; > tail = (FOOList *)visit_next_list(v, (GenericList *)tail, size)) { > visit_type_FOO(v, NULL, &tail->value, &err); > if (err) { > break; > } > } > if (visit_end_list(v) && err) { > qapi_free_FOOList(*obj); > *obj = NULL; > } > out: > error_propagate(errp, err); > } > > While the loop variable is still stepped in the for's third expression > as it should, the actual stepping below the hood now happens in the loop > body. I find this mildly confusing. There are TWO lists being stepped. The generated code is stepping through the GenericList *. The under-the-hood code is stepping through QList input. My refactoring here is to advance through the under-the-hood QList at the point where we CONSUME data (similar to how we remove things from QDict at the point where we CONSUME it) - during visit_type_FOO, and doesn't touch the GenericList* visits. Yes, that means the two are slightly out of sync, until 18/19 fixes the GenericList* visit to be sane (none of this magic visit the head of the list twice during visit_next_list). > > Perhaps a more natural loop would be > > void visit_type_FOOList(Visitor *v, const char *name, FOOList **obj, Error **errp) > { > Error *err = NULL; > GenericList *tail; > size_t size = sizeof(**obj); > > visit_start_list(v, name, (GenericList **)obj, size, &err); > if (err) { > goto out; > } > while ((tail = visit_next_list(v, tail, size))) { tail has to be set to something before this while loop will work. > visit_type_FOO(v, NULL, &((FOOList *)tail)->value, &err); > if (err) { > break; > } > } And that's kind of the whole point of 18/19. > if (visit_end_list(v) && err) { > qapi_free_FOOList(*obj); > *obj = NULL; > } > out: > error_propagate(errp, err); > } > > Might also permit de-duplicating the g_malloc0(size), since we now call > next_list() *before* each iteration instead of *between* iterations. One other wrinkle to think about in both this patch and 18/19: We have the annoying difference in representation that an empty GenericList* is the NULL pointer, while an empty QList is an actual object. >> @@ -77,7 +78,12 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv, > /* If we are in the middle of a list, then return the next element >> * of the list. */ >> if (tos->entry) { > > Before the patch, the condition matches the comment: tos->entry implies > this is a list and we're not at its head. > > After the patch, the condition only implies it's a list, but ... > >> assert(qobject_type(qobj) == QTYPE_QLIST); >> - return qlist_entry_obj(tos->entry); >> + assert(!tos->first); > > ... you assert that "not at its head" can't happen. Why is that the > case? Because the only way to consume an element is by calling visit_type_FOO(), but until 18/19 reorders the generated loop, we don't call visit_type_FOO() until AFTER our first visit_next_list(). The only time "at its head" can happen is BEFORE the first visit_next_list(). > >> + qobj = qlist_entry_obj(tos->entry); >> + if (consume) { >> + tos->entry = qlist_next(tos->entry); >> + } >> + return qobj; > > The remainder of the hunk adds the qlist_next() call moved from > qmp_input_next_list(), as advertized by the commit message. Good. > >> } >> >> /* Otherwise, we are at the root of the visit or the start of a >> @@ -91,7 +97,8 @@ static void qdict_add_key(const char *key, QObject *obj, void *opaque) >> g_hash_table_insert(h, (gpointer) key, NULL); >> } >> >> -static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) >> +static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, >> + const QListEntry *entry, Error **errp) >> { >> GHashTable *h; >> StackObject *tos = &qiv->stack[qiv->nb_stack]; >> @@ -103,7 +110,8 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) >> } >> >> tos->obj = obj; >> - tos->entry = NULL; >> + tos->entry = entry; >> + tos->first = true; >> tos->h = NULL; >> >> if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) { > > Here, you change the initial state. Not explicitly advertized in the > commit message, unlike the change to qlist_next(). I guess that's okay, > but perhaps my ramblings give you ideas on improving the commit message. Sure. > > I wonder whether we really need the new argument. Could we do something > like > > if (qobject_type(obj) == QTYPE_QLIST) { > tos->entry = qlist_first(qobject_to_qlist(obj)); > tos->first = true; > } > I'll try it. But I seem to recall the reason I did it this way was because... > ? > >> @@ -153,7 +161,7 @@ static void qmp_input_start_struct(Visitor *v, const char *name, void **obj, >> return; >> } >> >> - qmp_input_push(qiv, qobj, &err); >> + qmp_input_push(qiv, qobj, NULL, &err); > > Since @qobj is a dictionary, the StackObject's entry will be unused, so > pass null. Okay. > >> if (err) { >> error_propagate(errp, err); >> return; >> @@ -175,6 +183,7 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) >> { >> QmpInputVisitor *qiv = to_qiv(v); >> QObject *qobj = qmp_input_get_object(qiv, name, true); >> + const QListEntry *entry; >> >> if (!qobj || qobject_type(qobj) != QTYPE_QLIST) { >> error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null", >> @@ -182,7 +191,8 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) >> return; >> } >> >> - qmp_input_push(qiv, qobj, errp); >> + entry = qlist_first(qobject_to_qlist(qobj)); >> + qmp_input_push(qiv, qobj, entry, errp); > > @qobj is a list, the StackObject's entry must be initialized to its > first member, so pass that. ...in 18/19, the semantics of visit_start_list() change such that we have to know whether we are visiting an empty QList (we set **obj differently for an empty vs. non-empty list) - so it was either grab entry locally and pass it in as a parameter, or let qmp_input_push() populate entry and then read it after the fact. >> @@ -382,7 +384,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj) >> v->visitor.type_any = qmp_input_type_any; >> v->visitor.optional = qmp_input_optional; >> >> - qmp_input_push(v, obj, NULL); >> + qmp_input_push(v, obj, NULL, NULL); > > @obj is the root of the visit. Can it be a list? > > If yes, then StackObject's entry is not its first element. Why is that > correct? Because when the root of the visit is a QList, you STILL have to call visit_start_list() before visiting list element members. It is visit_start_list() that sets up entry in preparation for visit_next_list(). The root of the QMP input visitor is currently a bit odd; we have weird semantics where a dictionary as root behaves differently depending on whether name is NULL or non-NULL. See 17/19, where I clean that up later in the series, at which point I get rid of the qmp_input_push() during visitor initialization.
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c index cfaf378..1820360 100644 --- a/qapi/qmp-input-visitor.c +++ b/qapi/qmp-input-visitor.c @@ -27,9 +27,10 @@ typedef struct StackObject { QObject *obj; /* Object being visited */ - /* If obj is list: NULL if list is at head, otherwise tail of list - * still needing visits */ + /* If obj is list: tail of list still needing visits */ const QListEntry *entry; + /* If obj is list: true if head is not visited yet */ + bool first; GHashTable *h; /* If obj is dict: remaining keys needing visits */ } StackObject; @@ -77,7 +78,12 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv, * of the list. */ if (tos->entry) { assert(qobject_type(qobj) == QTYPE_QLIST); - return qlist_entry_obj(tos->entry); + assert(!tos->first); + qobj = qlist_entry_obj(tos->entry); + if (consume) { + tos->entry = qlist_next(tos->entry); + } + return qobj; } /* Otherwise, we are at the root of the visit or the start of a @@ -91,7 +97,8 @@ static void qdict_add_key(const char *key, QObject *obj, void *opaque) g_hash_table_insert(h, (gpointer) key, NULL); } -static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) +static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, + const QListEntry *entry, Error **errp) { GHashTable *h; StackObject *tos = &qiv->stack[qiv->nb_stack]; @@ -103,7 +110,8 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp) } tos->obj = obj; - tos->entry = NULL; + tos->entry = entry; + tos->first = true; tos->h = NULL; if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) { @@ -153,7 +161,7 @@ static void qmp_input_start_struct(Visitor *v, const char *name, void **obj, return; } - qmp_input_push(qiv, qobj, &err); + qmp_input_push(qiv, qobj, NULL, &err); if (err) { error_propagate(errp, err); return; @@ -175,6 +183,7 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) { QmpInputVisitor *qiv = to_qiv(v); QObject *qobj = qmp_input_get_object(qiv, name, true); + const QListEntry *entry; if (!qobj || qobject_type(qobj) != QTYPE_QLIST) { error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null", @@ -182,7 +191,8 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) return; } - qmp_input_push(qiv, qobj, errp); + entry = qlist_first(qobject_to_qlist(qobj)); + qmp_input_push(qiv, qobj, entry, errp); } static GenericList *qmp_input_next_list(Visitor *v, GenericList **list, @@ -191,23 +201,15 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list, QmpInputVisitor *qiv = to_qiv(v); GenericList *entry; StackObject *so = &qiv->stack[qiv->nb_stack - 1]; - bool first; - if (so->entry == NULL) { - so->entry = qlist_first(qobject_to_qlist(so->obj)); - first = true; - } else { - so->entry = qlist_next(so->entry); - first = false; - } - - if (so->entry == NULL) { + if (!so->entry) { return NULL; } entry = g_malloc0(size); - if (first) { + if (so->first) { *list = entry; + so->first = false; } else { (*list)->next = entry; } @@ -382,7 +384,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj) v->visitor.type_any = qmp_input_type_any; v->visitor.optional = qmp_input_optional; - qmp_input_push(v, obj, NULL); + qmp_input_push(v, obj, NULL, NULL); qobject_incref(obj); return v;
Refactor the code to advance the QListEntry pointer at the point where visit_type_FOO() is called, rather than visit_next_list(). This will allow a future patch to move the visit of the list head into visit_start_list(), and get rid of the 'first' flag. Signed-off-by: Eric Blake <eblake@redhat.com> --- v14: no change v13: no change v12: new patch --- qapi/qmp-input-visitor.c | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-)