Eric Blake <ebl...@redhat.com> writes:
> As mentioned in previous patches, we want to call visit_end_struct()
> functions unconditionally, so that visitors can release resources
> tied up since the matching visit_start_struct() without also having
> to worry about error priority if more than one error occurs.
>
> Even though error_propagate() can be safely used to ignore a second
> error during cleanup caused by a first error, it is simpler if the
> cleanup cannot set an error, and we instead split the task of
> checking that an input visitor has no unvisited input as a new
> function visit_check_struct(), called only if all prior steps are
> successful.
>
> Generated code has diffs resembling:
>
> |@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
> | goto out_obj;
> | }
> | visit_type_ACPIOSTInfo_fields(v, obj, &err);
> |+ if (err) {
> |+ goto out_obj;
> |+ }
> |+ visit_check_struct(v, &err);
> | out_obj:
> |- error_propagate(errp, err);
> |- err = NULL;
> |- visit_end_struct(v, &err);
> |+ visit_end_struct(v);
> | out:
Basically, split visit_end_struct() into a part that runs only when
there have been no errors and a part that runs as before, i.e. when
visit_start_struct() succeeded, even when there have been errors since.
This second part cannot fail, which simplifies error handling a bit.
To review: skipping the first part when there have been errors is safe.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
>
> ---
> v9: rebase to earlier changes, drop Marc-Andre's R-b
> v8: rebase to 'name' motion
> v7: rebase to earlier changes
> v6: new patch, revised version of RFC based on discussion of v5 7/46
> ---
> hmp.c | 7 ++++---
> hw/ppc/spapr_drc.c | 3 ++-
> hw/virtio/virtio-balloon.c | 12 ++++++------
> include/qapi/visitor-impl.h | 4 +++-
> include/qapi/visitor.h | 13 ++++++++++---
> qapi/opts-visitor.c | 17 +++++++++++++++--
> qapi/qapi-dealloc-visitor.c | 2 +-
> qapi/qapi-visit-core.c | 11 +++++++++--
> qapi/qmp-input-visitor.c | 34 +++++++++++++++++++---------------
> qapi/qmp-output-visitor.c | 2 +-
> qom/object.c | 5 ++---
> scripts/qapi-event.py | 3 ++-
> scripts/qapi-visit.py | 9 ++++-----
> tests/test-qmp-input-visitor.c | 3 ++-
> vl.c | 11 +++++------
> 15 files changed, 85 insertions(+), 51 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index a4b74df..245617d 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -1687,13 +1687,14 @@ void hmp_object_add(Monitor *mon, const QDict *qdict)
> }
>
> object_add(type, id, pdict, v, &err);
> -
> -out_end:
> - visit_end_struct(v, &err_end);
> + visit_check_struct(v, &err_end);
> if (!err && err_end) {
> qmp_object_del(id, NULL);
> }
> error_propagate(&err, err_end);
> +
> +out_end:
> + visit_end_struct(v);
> out_clean:
> opts_visitor_cleanup(ov);
>
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index 831ce23..3b27caa 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -287,11 +287,12 @@ static void prop_get_fdt(Object *obj, Visitor *v, const
> char *name,
> case FDT_END_NODE:
> /* shouldn't ever see an FDT_END_NODE before FDT_BEGIN_NODE */
> g_assert(fdt_depth > 0);
> - visit_end_struct(v, &err);
> + visit_check_struct(v, &err);
> if (err) {
> error_propagate(errp, err);
> return;
> }
> + visit_end_struct(v);
> fdt_depth--;
> break;
> case FDT_PROP: {
No longer calls visit_end_struct() when visit_end_struct() fails.
Contradicts the rule to always call it after visit_start_struct()
succeded.
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 24ecd87..cefd43f 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -136,15 +136,15 @@ static void balloon_stats_get_all(Object *obj, Visitor
> *v, const char *name,
> goto out_nested;
> }
> }
> + visit_check_struct(v, &err);
> out_nested:
> - error_propagate(errp, err);
> - err = NULL;
> - visit_end_struct(v, &err);
> + visit_end_struct(v);
>
> + if (!err) {
> + visit_check_struct(v, &err);
> + }
> out_end:
> - error_propagate(errp, err);
> - err = NULL;
> - visit_end_struct(v, &err);
> + visit_end_struct(v);
> out:
> error_propagate(errp, err);
> }
> diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
> index 3b68b7b..248b1e5 100644
> --- a/include/qapi/visitor-impl.h
> +++ b/include/qapi/visitor-impl.h
> @@ -28,8 +28,10 @@ struct Visitor
> * currently visit structs). */
> void (*start_struct)(Visitor *v, const char *name, void **obj,
> size_t size, Error **errp);
> + /* May be NULL; most useful for input visitors. */
> + void (*check_struct)(Visitor *v, Error **errp);
Well, "most useful" is certainly correct since other visitors have had
no use for it so far :)
"intended for input visitors"?
> /* Must be provided if start_struct is present. */
> - void (*end_struct)(Visitor *v, Error **errp);
> + void (*end_struct)(Visitor *v);
>
> /* May be NULL; most useful for input visitors. */
> void (*start_implicit_struct)(Visitor *v, void **obj, size_t size,
> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
> index d7a0110..e5dcde4 100644
> --- a/include/qapi/visitor.h
> +++ b/include/qapi/visitor.h
> @@ -68,12 +68,19 @@ typedef struct GenericList
> void visit_start_struct(Visitor *v, const char *name, void **obj,
> size_t size, Error **errp);
> /**
> + * Prepare for completing a struct visit.
> + * Should be called prior to visit_end_struct() if all other intermediate
> + * visit steps were successful, to allow the caller one last chance to
> + * report errors such as remaining data that was not consumed by the visit.
> + */
> +void visit_check_struct(Visitor *v, Error **errp);
> +/**
> * Complete a struct visit started earlier.
> * Must be called after any successful use of visit_start_struct(),
> * even if intermediate processing was skipped due to errors, to allow
> * the backend to release any resources.
> */
> -void visit_end_struct(Visitor *v, Error **errp);
> +void visit_end_struct(Visitor *v);
>
> /**
> * Prepare to visit an implicit struct.
> @@ -96,8 +103,8 @@ void visit_start_implicit_struct(Visitor *v, void **obj,
> size_t size,
> * Must be called after any successful use of visit_start_implicit_struct(),
> * even if intermediate processing was skipped due to errors, to allow
> * the backend to release any resources. Unlike visit_end_struct(), this
> - * does not need to check for errors (detection of unused keys is only
> - * possible for the overall struct, not a subset).
> + * does not need a counterpart function to check for errors (detection of
> + * unused keys is only possible for the overall struct, not a subset).
> */
> void visit_end_implicit_struct(Visitor *v);
>
> diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
> index df312e6..b469573 100644
> --- a/qapi/opts-visitor.c
> +++ b/qapi/opts-visitor.c
> @@ -157,13 +157,13 @@ opts_start_struct(Visitor *v, const char *name, void
> **obj,
>
>
> static void
> -opts_end_struct(Visitor *v, Error **errp)
> +opts_check_struct(Visitor *v, Error **errp)
> {
> OptsVisitor *ov = to_ov(v);
> GHashTableIter iter;
> GQueue *any;
>
> - if (--ov->depth > 0) {
> + if (ov->depth > 0) {
> return;
> }
>
Not fully visible in this diff: this function's only possible side
effect is setting an error. Therefore, skipping this when there have
been errors is safe.
> @@ -175,6 +175,18 @@ opts_end_struct(Visitor *v, Error **errp)
> first = g_queue_peek_head(any);
> error_setg(errp, QERR_INVALID_PARAMETER, first->name);
> }
> +}
> +
> +
> +static void
> +opts_end_struct(Visitor *v)
> +{
> + OptsVisitor *ov = DO_UPCAST(OptsVisitor, visitor, v);
> +
> + if (--ov->depth > 0) {
> + return;
> + }
> +
> g_hash_table_destroy(ov->unprocessed_opts);
> ov->unprocessed_opts = NULL;
> if (ov->fake_id_opt) {
> @@ -506,6 +518,7 @@ opts_visitor_new(const QemuOpts *opts)
> ov = g_malloc0(sizeof *ov);
>
> ov->visitor.start_struct = &opts_start_struct;
> + ov->visitor.check_struct = &opts_check_struct;
> ov->visitor.end_struct = &opts_end_struct;
>
> ov->visitor.start_list = &opts_start_list;
> diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
> index 1a54864..a89e6d1 100644
> --- a/qapi/qapi-dealloc-visitor.c
> +++ b/qapi/qapi-dealloc-visitor.c
> @@ -65,7 +65,7 @@ static void qapi_dealloc_start_struct(Visitor *v, const
> char *name, void **obj,
> qapi_dealloc_push(qov, obj);
> }
>
> -static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
> +static void qapi_dealloc_end_struct(Visitor *v)
> {
> QapiDeallocVisitor *qov = to_qov(v);
> void **obj = qapi_dealloc_pop(qov);
> diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
> index 3360cdf..9506a02 100644
> --- a/qapi/qapi-visit-core.c
> +++ b/qapi/qapi-visit-core.c
> @@ -36,9 +36,16 @@ void visit_start_struct(Visitor *v, const char *name, void
> **obj,
> v->start_struct(v, name, obj, size, errp);
> }
>
> -void visit_end_struct(Visitor *v, Error **errp)
> +void visit_check_struct(Visitor *v, Error **errp)
> {
> - v->end_struct(v, errp);
> + if (v->check_struct) {
> + v->check_struct(v, errp);
> + }
> +}
> +
> +void visit_end_struct(Visitor *v)
> +{
> + v->end_struct(v);
> }
>
> void visit_start_implicit_struct(Visitor *v, void **obj, size_t size,
> diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
> index 91ef945..f256d9e 100644
> --- a/qapi/qmp-input-visitor.c
> +++ b/qapi/qmp-input-visitor.c
> @@ -89,8 +89,10 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject
> *obj, Error **errp)
> }
>
>
> -static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
> +static void qmp_input_check_struct(Visitor *v, Error **errp)
> {
> + QmpInputVisitor *qiv = to_qiv(v);
> +
> assert(qiv->nb_stack > 0);
>
> if (qiv->strict) {
Same argument as for opts_check_struct().
> @@ -103,6 +105,19 @@ static void qmp_input_pop(QmpInputVisitor *qiv, Error
> **errp)
> if (g_hash_table_iter_next(&iter, (void **)&key, NULL)) {
> error_setg(errp, QERR_QMP_EXTRA_MEMBER, key);
> }
> + }
> + }
> +}
> +
> +static void qmp_input_pop(Visitor *v)
> +{
> + QmpInputVisitor *qiv = to_qiv(v);
> +
> + assert(qiv->nb_stack > 0);
> +
> + if (qiv->strict) {
> + GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
> + if (top_ht) {
> g_hash_table_unref(top_ht);
> }
> }
> @@ -134,12 +149,6 @@ static void qmp_input_start_struct(Visitor *v, const
> char *name, void **obj,
> }
> }
>
> -static void qmp_input_end_struct(Visitor *v, Error **errp)
> -{
> - QmpInputVisitor *qiv = to_qiv(v);
> -
> - qmp_input_pop(qiv, errp);
> -}
Order is now funny: the end_struct() method preceeds the start_struct()
method. I guess that's okay.
>
> static void qmp_input_start_implicit_struct(Visitor *v, void **obj,
> size_t size, Error **errp)
> @@ -193,12 +202,6 @@ static GenericList *qmp_input_next_list(Visitor *v,
> GenericList **list,
> return entry;
> }
>
> -static void qmp_input_end_list(Visitor *v)
> -{
> - QmpInputVisitor *qiv = to_qiv(v);
> -
> - qmp_input_pop(qiv, &error_abort);
> -}
Likewise.
>
> static void qmp_input_get_next_type(Visitor *v, const char *name, QType
> *type,
> bool promote_int, Error **errp)
> @@ -355,11 +358,12 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj)
> v = g_malloc0(sizeof(*v));
>
> v->visitor.start_struct = qmp_input_start_struct;
> - v->visitor.end_struct = qmp_input_end_struct;
> + v->visitor.check_struct = qmp_input_check_struct;
> + v->visitor.end_struct = qmp_input_pop;
> v->visitor.start_implicit_struct = qmp_input_start_implicit_struct;
> v->visitor.start_list = qmp_input_start_list;
> v->visitor.next_list = qmp_input_next_list;
> - v->visitor.end_list = qmp_input_end_list;
> + v->visitor.end_list = qmp_input_pop;
> v->visitor.type_enum = input_type_enum;
> v->visitor.type_int64 = qmp_input_type_int64;
> v->visitor.type_uint64 = qmp_input_type_uint64;
> diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
> index 2eb200d..5376948 100644
> --- a/qapi/qmp-output-visitor.c
> +++ b/qapi/qmp-output-visitor.c
> @@ -116,7 +116,7 @@ static void qmp_output_start_struct(Visitor *v, const
> char *name, void **obj,
> qmp_output_push(qov, dict);
> }
>
> -static void qmp_output_end_struct(Visitor *v, Error **errp)
> +static void qmp_output_end_struct(Visitor *v)
> {
> QmpOutputVisitor *qov = to_qov(v);
> qmp_output_pop(qov, QTYPE_QDICT);
> diff --git a/qom/object.c b/qom/object.c
> index e5b0566..4644cbd 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -2034,10 +2034,9 @@ static void property_get_tm(Object *obj, Visitor *v,
> const char *name,
> if (err) {
> goto out_end;
> }
> + visit_check_struct(v, &err);
> out_end:
> - error_propagate(errp, err);
> - err = NULL;
> - visit_end_struct(v, errp);
> + visit_end_struct(v);
> out:
> error_propagate(errp, err);
>
> diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
> index cc55de7..dea45c4 100644
> --- a/scripts/qapi-event.py
> +++ b/scripts/qapi-event.py
> @@ -71,8 +71,9 @@ def gen_event_send(name, arg_type):
> ret += gen_visit_fields(arg_type.members, need_cast=True,
> label='out_obj')
> ret += mcgen('''
> + visit_check_struct(v, &err);
> out_obj:
> - visit_end_struct(v, &err);
> + visit_end_struct(v);
> if (err) {
> goto out;
> }
> diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
> index 7a44c13..8039b97 100644
> --- a/scripts/qapi-visit.py
> +++ b/scripts/qapi-visit.py
> @@ -255,8 +255,7 @@ void visit_type_%(c_name)s(Visitor *v, const char *name,
> %(c_name)s **obj, Error
> visit_type_%(c_name)s_fields(v, %(cast)sobj, &err);
> ''',
> c_name=type_name, cast=cast)
> - if variants:
> - ret += gen_err_check(label='out_obj')
> + ret += gen_err_check(label='out_obj')
Can't immediately see why we need this change. Care to explain?
>
> if variants:
> ret += mcgen('''
> @@ -293,12 +292,12 @@ void visit_type_%(c_name)s(Visitor *v, const char
> *name, %(c_name)s **obj, Error
> abort();
> }
> ''')
> + ret += gen_err_check(label='out_obj')
Yes, because we need to skip...
>
> ret += mcgen('''
> + visit_check_struct(v, &err);
... this one.
> out_obj:
> - error_propagate(errp, err);
> - err = NULL;
> - visit_end_struct(v, &err);
> + visit_end_struct(v);
> out:
> error_propagate(errp, err);
> }
> diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
> index 6489e4a..cd5e765 100644
> --- a/tests/test-qmp-input-visitor.c
> +++ b/tests/test-qmp-input-visitor.c
> @@ -290,7 +290,8 @@ static void test_visitor_in_null(TestInputVisitorData
> *data,
> v = visitor_input_test_init(data, "{ 'a': null }");
> visit_start_struct(v, NULL, NULL, 0, &error_abort);
> visit_type_null(v, "a", &error_abort);
> - visit_end_struct(v, &error_abort);
> + visit_check_struct(v, &error_abort);
> + visit_end_struct(v);
>
> /* Check that qnull reference counting is sane:
> * 1 for global use, 1 for our qnull() use, and 1 still owned by 'v'
> diff --git a/vl.c b/vl.c
> index 22062b5..00c92b8 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2842,11 +2842,10 @@ static int object_create(void *opaque, QemuOpts
> *opts, Error **errp)
> qdict_del(pdict, "qom-type");
> visit_type_str(v, "qom-type", &type, &err);
> if (err) {
> - goto out;
> + goto out_end;
Before: visit_end_struct() not called.
After: visit_end_struct() called.
Shouldn't this be fixed in PATCH 05?
> }
> if (!type_predicate(type)) {
> - visit_end_struct(v, NULL);
> - goto out;
> + goto out_end;
> }
>
> qdict_del(pdict, "id");
> @@ -2856,14 +2855,14 @@ static int object_create(void *opaque, QemuOpts
> *opts, Error **errp)
> }
>
> object_add(type, id, pdict, v, &err);
> -
> -out_end:
> - visit_end_struct(v, &err_end);
> + visit_check_struct(v, &err_end);
> if (!err && err_end) {
> qmp_object_del(id, NULL);
> }
> error_propagate(&err, err_end);
>
> +out_end:
> + visit_end_struct(v);
> out:
> opts_visitor_cleanup(ov);
