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Re: [Qemu-ppc] [Qemu-devel] [PATCH v14 18/19] qapi: Simplify semantics o
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From: |
Markus Armbruster |
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Subject: |
Re: [Qemu-ppc] [Qemu-devel] [PATCH v14 18/19] qapi: Simplify semantics of visit_next_list() |
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Date: |
Fri, 15 Apr 2016 16:09:29 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Eric Blake <address@hidden> writes:
> We have two uses of list visits in the entire code base: one in
> spapr_drc (which completely avoids visit_next_list(), feeding in
> integers from a different source than uint8List), and one in
> qapi-visit.py
Period here, convert the parenthesis to a sentence.
> (that is, all other list visitors are generated
> in qapi-visit.c, and share the same paradigm based on a qapi
> FooList type).
The above reviews existing uses. Next, you show that visit_next_list()
semantics are awkward. Suggest to start with the awkward semantics, and
only then review existing uses.
> What's more, the semantics of the list visit are
> somewhat baroque, with the following pseudocode when FooList is
> used:
>
> start()
> for (prev = head; cur = next(prev); prev = &cur) {
> visit(&cur->value)
> }
>
> Note that these semantics (advance before visit) requires that
> the first call to next() return the list head, while all other
> calls return the next element of the list; that is, every visitor
> implementation is required to track extra state to decide whether
> to return the input as-is, or to advance. It also requires an
> argument of 'GenericList **' to next(), solely because the first
> iteration might need to modify the caller's GenericList head, so
> that all other calls have to do a layer of dereferencing.
>
> We can greatly simplify things by hoisting the special case
> into the start() routine, and flipping the order in the loop
> to visit before advance:
>
> start(head)
> for (tail = *head; tail; tail = next(tail)) {
> visit(&tail->value)
> }
>
> With the simpler semantics, visitors have less state to track,
> the argument to next() is reduced to 'GenericList *', and it
> also becomes obvious whether an input visitor is allocating a
> FooList during visit_start_list() (rather than the old way of
> not knowing if an allocation happened until the first
> visit_next_list()).
Minor drawback: we now allocate both in start_list() and in next_list().
Minor, because the allocation is trivial.
> The signature of visit_start_list() is chosen to match
> visit_start_struct(), with the new parameters after 'name'.
Good idea.
> The spapr_drc case is a virtual visit, done by passing NULL for
> list, similarly to how NULL is passed to visit_start_struct()
> when a qapi type is not used in those visits. It was easy to
> provide these semantics for qmp-output and dealloc visitors,
> and a bit harder for qmp-input (several prerequisite patches
> refactored things to make this patch straightforward). But it
> turned out that the string and opts visitors munge enough other
> state during visit_next_list() to make it easier to just
> document and require a GenericList visit for now; an assertion
> will remind us to adjust things if we need the semantics in the
> future.
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> v14: no change
> v13: documentation wording tweaks
> v12: rebase to earlier changes, drop R-b, improve documentation,
> split out qmp-input cleanups into prereq patches
> [no v10, v11]
> v9: no change
> v8: consistent parameter order, fix qmp_input_get_next_type() to not
> skip list entries
> v7: new patch
> ---
> include/qapi/visitor.h | 47
> +++++++++++++++++++-----------------
> include/qapi/visitor-impl.h | 7 +++---
> scripts/qapi-visit.py | 18 +++++++-------
> include/qapi/opts-visitor.h | 2 +-
> include/qapi/string-input-visitor.h | 3 ++-
> include/qapi/string-output-visitor.h | 3 ++-
> qapi/qapi-visit-core.c | 12 +++++----
> hw/ppc/spapr_drc.c | 2 +-
> qapi/opts-visitor.c | 33 +++++++++++--------------
> qapi/qapi-dealloc-visitor.c | 35 ++++++---------------------
> qapi/qmp-input-visitor.c | 32 ++++++++++++------------
> qapi/qmp-output-visitor.c | 22 ++++-------------
> qapi/string-input-visitor.c | 36 +++++++++++++--------------
> qapi/string-output-visitor.c | 41 +++++++++++--------------------
> docs/qapi-code-gen.txt | 17 +++++++------
> 15 files changed, 133 insertions(+), 177 deletions(-)
>
> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
> index e1213a3..a22a7ce 100644
> --- a/include/qapi/visitor.h
> +++ b/include/qapi/visitor.h
> @@ -165,7 +165,7 @@
> * if (err) {
> * goto outobj;
> * }
> - * visit_start_list(v, "list", &err);
> + * visit_start_list(v, "list", NULL, 0, &err);
> * if (err) {
> * goto outobj;
> * }
> @@ -268,40 +268,43 @@ void visit_end_struct(Visitor *v);
> * @name expresses the relationship of this list to its parent
> * container; see the general description of @name above.
> *
> + * @list must be non-NULL for a real walk, in which case @size
> + * determines how much memory an input visitor will allocate into
> + * address@hidden (at least sizeof(GenericList)). Some visitors also allow
> + * @list to be NULL for a virtual walk, in which case @size is
> + * ignored.
> + *
> * @errp must be NULL-initialized, and is set if an error is detected
> * (such as if a member @name is not present, or is present but not a
> - * list).
> + * list). On error, input visitors set address@hidden to NULL.
I guess you copied this from visit_start_struct(), which only makes
sense. Except the thing is called @list here. More of the same below.
> *
> * After visit_start_list() succeeds, the caller may visit its members
> - * one after the other. A real visit uses visit_next_list() for
> - * traversing the linked list, while a virtual visit uses other means.
> - * For each list element, call the appropriate visit_type_FOO() with
> - * name set to NULL and obj set to the address of the value member of
> - * the list element. Finally, visit_end_list() needs to be called to
> - * clean up, even if intermediate visits fail. See the examples
> - * above.
> + * one after the other. A real visit (where @obj is non-NULL) uses
> + * visit_next_list() for traversing the linked list, while a virtual
> + * visit (where @obj is NULL) uses other means. For each list
> + * element, call the appropriate visit_type_FOO() with name set to
> + * NULL and obj set to the address of the value member of the list
> + * element. Finally, visit_end_list() needs to be called to clean up,
> + * even if intermediate visits fail. See the examples above.
> */
> -void visit_start_list(Visitor *v, const char *name, Error **errp);
> +void visit_start_list(Visitor *v, const char *name, GenericList **list,
> + size_t size, Error **errp);
>
> /*
> - * Iterate over a GenericList during a list visit.
> + * Iterate over a GenericList during a non-virtual list visit.
Is "non-virtual" new in this patch? If not, is this the right patch to
insert it?
> *
> - * @size represents the size of a linked list node.
> + * @size represents the size of a linked list node (at least
> + * sizeof(GenericList)).
Likewise.
> *
> - * @list must not be NULL; on the first call, @list contains the
> - * address of the list head, and on subsequent calls address@hidden must be
> - * the previously returned value. Must be called in a loop until a
> + * @tail must not be NULL; on the first call, @tail is the value of
> + * *list after visit_start_list(), and on subsequent calls @tail must
> + * be the previously returned value. Must be called in a loop until a
> * NULL return or error occurs; for each non-NULL return, the caller
> * must then call the appropriate visit_type_*() for the element type
> * of the list, with that function's name parameter set to NULL and
> - * obj set to the address of (address@hidden)->value.
> - *
> - * FIXME: This interface is awkward; it requires all callbacks to
> - * track whether it is the first or a subsequent call. A better
> - * interface would pass the head of the list through
> - * visit_start_list().
> + * obj set to the address of @tail->value.
> */
> -GenericList *visit_next_list(Visitor *v, GenericList **list, size_t size);
> +GenericList *visit_next_list(Visitor *v, GenericList *tail, size_t size);
>
> /*
> * Complete a list visit started earlier.
> diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
> index d44fcd1..0471465 100644
> --- a/include/qapi/visitor-impl.h
> +++ b/include/qapi/visitor-impl.h
> @@ -45,11 +45,12 @@ struct Visitor
> /* Must be set to visit structs. */
> void (*end_struct)(Visitor *v);
>
> - /* Must be set. */
> - void (*start_list)(Visitor *v, const char *name, Error **errp);
> + /* Must be set; document if @list may not be NULL. */
Too terse, I'm afraid. Suggest something like "implementations may
require @list to be non-null, but must document it."
> + void (*start_list)(Visitor *v, const char *name, GenericList **list,
> + size_t size, Error **errp);
>
> /* Must be set. */
> - GenericList *(*next_list)(Visitor *v, GenericList **list, size_t size);
> + GenericList *(*next_list)(Visitor *v, GenericList *tail, size_t size);
>
> /* Must be set. */
> void (*end_list)(Visitor *v);
> diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
> index bfe4a09..69f0133 100644
> --- a/scripts/qapi-visit.py
> +++ b/scripts/qapi-visit.py
> @@ -117,20 +117,20 @@ def gen_visit_list(name, element_type):
> void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj,
> Error **errp)
> {
> Error *err = NULL;
> - GenericList *i, **prev;
> + %(c_name)s *tail;
> + size_t size = sizeof(**obj);
>
> - visit_start_list(v, name, &err);
> + visit_start_list(v, name, (GenericList **)obj, size, &err);
> if (err) {
> goto out;
> }
> -
> - for (prev = (GenericList **)obj;
> - !err && (i = visit_next_list(v, prev, sizeof(**obj))) != NULL;
> - prev = &i) {
> - %(c_name)s *native_i = (%(c_name)s *)i;
> - visit_type_%(c_elt_type)s(v, NULL, &native_i->value, &err);
> + for (tail = *obj; tail;
> + tail = (%(c_name)s *)visit_next_list(v, (GenericList *)tail, size))
> {
> + visit_type_%(c_elt_type)s(v, NULL, &tail->value, &err);
> + if (err) {
> + break;
> + }
> }
> -
Keep the blank lines around the loop?
> visit_end_list(v);
> out:
> error_propagate(errp, err);
> diff --git a/include/qapi/opts-visitor.h b/include/qapi/opts-visitor.h
> index 3fcd327..7c9a7e5 100644
> --- a/include/qapi/opts-visitor.h
> +++ b/include/qapi/opts-visitor.h
> @@ -32,7 +32,7 @@ typedef struct OptsVisitor OptsVisitor;
> *
> * The Opts input visitor does not yet implement support for visiting
> * QAPI alternates, numbers (other than integers), null, or arbitrary
> - * QTypes.
> + * QTypes. It also requires non-NULL list to visit_start_list().
non-null list argument to
> */
> OptsVisitor *opts_visitor_new(const QemuOpts *opts);
> void opts_visitor_cleanup(OptsVisitor *nv);
> diff --git a/include/qapi/string-input-visitor.h
> b/include/qapi/string-input-visitor.h
> index 1a34c52..d26a845 100644
> --- a/include/qapi/string-input-visitor.h
> +++ b/include/qapi/string-input-visitor.h
> @@ -19,7 +19,8 @@ typedef struct StringInputVisitor StringInputVisitor;
>
> /*
> * The string input visitor does not yet implement support for
> - * visiting QAPI structs, alternates, null, or arbitrary QTypes.
> + * visiting QAPI structs, alternates, null, or arbitrary QTypes. It
> + * also requires non-NULL list to visit_start_list().
Likewise.
> */
> StringInputVisitor *string_input_visitor_new(const char *str);
> void string_input_visitor_cleanup(StringInputVisitor *v);
> diff --git a/include/qapi/string-output-visitor.h
> b/include/qapi/string-output-visitor.h
> index 2564833..0a9354c 100644
> --- a/include/qapi/string-output-visitor.h
> +++ b/include/qapi/string-output-visitor.h
> @@ -19,7 +19,8 @@ typedef struct StringOutputVisitor StringOutputVisitor;
>
> /*
> * The string output visitor does not yet implement support for
> - * visiting QAPI structs, alternates, null, or arbitrary QTypes.
> + * visiting QAPI structs, alternates, null, or arbitrary QTypes. It
> + * also requires non-NULL list to visit_start_list().
Likewise.
> */
> StringOutputVisitor *string_output_visitor_new(bool human);
> void string_output_visitor_cleanup(StringOutputVisitor *v);
> diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
> index 76ea690..622b315 100644
> --- a/qapi/qapi-visit-core.c
> +++ b/qapi/qapi-visit-core.c
> @@ -42,15 +42,17 @@ void visit_end_struct(Visitor *v)
> v->end_struct(v);
> }
>
> -void visit_start_list(Visitor *v, const char *name, Error **errp)
> +void visit_start_list(Visitor *v, const char *name, GenericList **list,
> + size_t size, Error **errp)
> {
> - v->start_list(v, name, errp);
> + assert(!list || size >= sizeof(GenericList));
> + v->start_list(v, name, list, size, errp);
> }
>
> -GenericList *visit_next_list(Visitor *v, GenericList **list, size_t size)
> +GenericList *visit_next_list(Visitor *v, GenericList *tail, size_t size)
> {
> - assert(list && size >= sizeof(GenericList));
> - return v->next_list(v, list, size);
> + assert(tail && size >= sizeof(GenericList));
> + return v->next_list(v, tail, size);
> }
>
> void visit_end_list(Visitor *v)
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index 5395c02..dd3c502 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -309,7 +309,7 @@ static void prop_get_fdt(Object *obj, Visitor *v, const
> char *name,
> int i;
> prop = fdt_get_property_by_offset(fdt, fdt_offset, &prop_len);
> name = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
> - visit_start_list(v, name, &err);
> + visit_start_list(v, name, NULL, 0, &err);
> if (err) {
> error_propagate(errp, err);
> return;
> diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
> index a08d5a7..6d572cc 100644
> --- a/qapi/opts-visitor.c
> +++ b/qapi/opts-visitor.c
> @@ -23,9 +23,8 @@
> enum ListMode
> {
> LM_NONE, /* not traversing a list of repeated options */
> - LM_STARTED, /* opts_start_list() succeeded */
>
> - LM_IN_PROGRESS, /* opts_next_list() has been called.
> + LM_IN_PROGRESS, /* opts_next_list() ready to be called.
> *
> * Generating the next list link will consume the
> most
> * recently parsed QemuOpt instance of the repeated
> @@ -214,35 +213,33 @@ lookup_distinct(const OptsVisitor *ov, const char
> *name, Error **errp)
>
>
> static void
> -opts_start_list(Visitor *v, const char *name, Error **errp)
> +opts_start_list(Visitor *v, const char *name, GenericList **list, size_t
> size,
> + Error **errp)
> {
> OptsVisitor *ov = to_ov(v);
>
> /* we can't traverse a list in a list */
> assert(ov->list_mode == LM_NONE);
> + /* we don't support visits without GenericList, yet */
without a list
Do we plan to support them? If not, scratch "yet".
> + assert(list);
> ov->repeated_opts = lookup_distinct(ov, name, errp);
> - if (ov->repeated_opts != NULL) {
> - ov->list_mode = LM_STARTED;
> + if (ov->repeated_opts) {
> + ov->list_mode = LM_IN_PROGRESS;
> + *list = g_malloc0(size);
> + } else {
> + *list = NULL;
> }
> }
>
>
> static GenericList *
> -opts_next_list(Visitor *v, GenericList **list, size_t size)
> +opts_next_list(Visitor *v, GenericList *tail, size_t size)
> {
> OptsVisitor *ov = to_ov(v);
> - GenericList **link;
>
> switch (ov->list_mode) {
> - case LM_STARTED:
> - ov->list_mode = LM_IN_PROGRESS;
> - link = list;
> - break;
> -
> case LM_SIGNED_INTERVAL:
> case LM_UNSIGNED_INTERVAL:
> - link = &(*list)->next;
> -
> if (ov->list_mode == LM_SIGNED_INTERVAL) {
> if (ov->range_next.s < ov->range_limit.s) {
> ++ov->range_next.s;
> @@ -263,7 +260,6 @@ opts_next_list(Visitor *v, GenericList **list, size_t
> size)
> g_hash_table_remove(ov->unprocessed_opts, opt->name);
> return NULL;
> }
> - link = &(*list)->next;
> break;
> }
>
> @@ -271,8 +267,8 @@ opts_next_list(Visitor *v, GenericList **list, size_t
> size)
> abort();
> }
>
> - *link = g_malloc0(size);
> - return *link;
> + tail->next = g_malloc0(size);
> + return tail->next;
> }
>
>
> @@ -281,8 +277,7 @@ opts_end_list(Visitor *v)
> {
> OptsVisitor *ov = to_ov(v);
>
> - assert(ov->list_mode == LM_STARTED ||
> - ov->list_mode == LM_IN_PROGRESS ||
> + assert(ov->list_mode == LM_IN_PROGRESS ||
> ov->list_mode == LM_SIGNED_INTERVAL ||
> ov->list_mode == LM_UNSIGNED_INTERVAL);
> ov->repeated_opts = NULL;
> diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
> index 9005bad..cd68b55 100644
> --- a/qapi/qapi-dealloc-visitor.c
> +++ b/qapi/qapi-dealloc-visitor.c
> @@ -22,7 +22,6 @@
> typedef struct StackEntry
> {
> void *value;
> - bool is_list_head;
> QTAILQ_ENTRY(StackEntry) node;
> } StackEntry;
>
> @@ -43,10 +42,6 @@ static void qapi_dealloc_push(QapiDeallocVisitor *qov,
> void *value)
>
> e->value = value;
>
> - /* see if we're just pushing a list head tracker */
> - if (value == NULL) {
> - e->is_list_head = true;
> - }
> QTAILQ_INSERT_HEAD(&qov->stack, e, node);
> }
>
> @@ -93,38 +88,22 @@ static void qapi_dealloc_end_alternate(Visitor *v)
> }
> }
>
> -static void qapi_dealloc_start_list(Visitor *v, const char *name, Error
> **errp)
> +static void qapi_dealloc_start_list(Visitor *v, const char *name,
> + GenericList **list, size_t size,
> + Error **errp)
> {
> - QapiDeallocVisitor *qov = to_qov(v);
> - qapi_dealloc_push(qov, NULL);
> }
>
> -static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp,
> +static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList *tail,
> size_t size)
> {
> - GenericList *list = *listp;
> - QapiDeallocVisitor *qov = to_qov(v);
> - StackEntry *e = QTAILQ_FIRST(&qov->stack);
> -
> - if (e && e->is_list_head) {
> - e->is_list_head = false;
> - return list;
> - }
> -
> - if (list) {
> - list = list->next;
> - g_free(*listp);
> - return list;
> - }
> -
> - return NULL;
> + GenericList *next = tail->next;
> + g_free(tail);
> + return next;
> }
>
> static void qapi_dealloc_end_list(Visitor *v)
> {
> - QapiDeallocVisitor *qov = to_qov(v);
> - void *obj = qapi_dealloc_pop(qov);
> - assert(obj == NULL); /* should've been list head tracker with no payload
> */
> }
>
One step closer to killing the stack.
> static void qapi_dealloc_type_str(Visitor *v, const char *name, char **obj,
> diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
> index 16f2f5a..5360744 100644
> --- a/qapi/qmp-input-visitor.c
> +++ b/qapi/qmp-input-visitor.c
> @@ -29,8 +29,6 @@ typedef struct StackObject
>
> /* 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;
> @@ -87,7 +85,6 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
> assert(!name);
>
> if (tos->entry) {
> - assert(!tos->first);
> qobj = qlist_entry_obj(tos->entry);
> if (consume) {
> tos->entry = qlist_next(tos->entry);
> @@ -117,7 +114,6 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject
> *obj,
>
> tos->obj = obj;
> tos->entry = entry;
> - tos->first = true;
> tos->h = NULL;
>
> if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) {
> @@ -194,13 +190,17 @@ static void qmp_input_start_struct(Visitor *v, const
> char *name, void **obj,
> }
>
>
> -static void qmp_input_start_list(Visitor *v, const char *name, Error **errp)
> +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);
> const QListEntry *entry;
>
> if (!qobj || qobject_type(qobj) != QTYPE_QLIST) {
> + if (list) {
> + *list = NULL;
> + }
> error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
> "list");
> return;
> @@ -208,28 +208,26 @@ static void qmp_input_start_list(Visitor *v, const char
> *name, Error **errp)
>
> entry = qlist_first(qobject_to_qlist(qobj));
> qmp_input_push(qiv, qobj, entry, errp);
> + if (list) {
> + if (entry) {
> + *list = g_malloc0(size);
> + } else {
> + *list = NULL;
> + }
> + }
> }
>
> -static GenericList *qmp_input_next_list(Visitor *v, GenericList **list,
> +static GenericList *qmp_input_next_list(Visitor *v, GenericList *tail,
> size_t size)
> {
> QmpInputVisitor *qiv = to_qiv(v);
> - GenericList *entry;
> StackObject *so = &qiv->stack[qiv->nb_stack - 1];
>
> if (!so->entry) {
> return NULL;
> }
> -
> - entry = g_malloc0(size);
> - if (so->first) {
> - *list = entry;
> - so->first = false;
> - } else {
> - (*list)->next = entry;
> - }
> -
> - return entry;
> + tail->next = g_malloc0(size);
> + return tail->next;
> }
>
>
> diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
> index ecb2005..40657be 100644
> --- a/qapi/qmp-output-visitor.c
> +++ b/qapi/qmp-output-visitor.c
> @@ -22,7 +22,6 @@
> typedef struct QStackEntry
> {
> QObject *value;
> - bool is_list_head;
> QTAILQ_ENTRY(QStackEntry) node;
> } QStackEntry;
>
> @@ -52,9 +51,6 @@ static void qmp_output_push_obj(QmpOutputVisitor *qov,
> QObject *value)
> assert(qov->root);
> assert(value);
> e->value = value;
> - if (qobject_type(e->value) == QTYPE_QLIST) {
> - e->is_list_head = true;
> - }
> QTAILQ_INSERT_HEAD(&qov->stack, e, node);
> }
>
> @@ -120,7 +116,9 @@ static void qmp_output_end_struct(Visitor *v)
> assert(qobject_type(value) == QTYPE_QDICT);
> }
>
> -static void qmp_output_start_list(Visitor *v, const char *name, Error **errp)
> +static void qmp_output_start_list(Visitor *v, const char *name,
> + GenericList **listp, size_t size,
> + Error **errp)
> {
> QmpOutputVisitor *qov = to_qov(v);
> QList *list = qlist_new();
> @@ -129,20 +127,10 @@ static void qmp_output_start_list(Visitor *v, const
> char *name, Error **errp)
> qmp_output_push(qov, list);
> }
>
> -static GenericList *qmp_output_next_list(Visitor *v, GenericList **listp,
> +static GenericList *qmp_output_next_list(Visitor *v, GenericList *tail,
> size_t size)
> {
> - GenericList *list = *listp;
> - QmpOutputVisitor *qov = to_qov(v);
> - QStackEntry *e = QTAILQ_FIRST(&qov->stack);
> -
> - assert(e);
> - if (e->is_list_head) {
> - e->is_list_head = false;
> - return list;
> - }
> -
> - return list ? list->next : NULL;
> + return tail->next;
> }
>
> static void qmp_output_end_list(Visitor *v)
> diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c
> index 797973a..77dd1a7 100644
> --- a/qapi/string-input-visitor.c
> +++ b/qapi/string-input-visitor.c
> @@ -25,8 +25,6 @@ struct StringInputVisitor
> {
> Visitor visitor;
>
> - bool head;
> -
> GList *ranges;
> GList *cur_range;
> int64_t cur;
> @@ -125,11 +123,21 @@ error:
> }
>
> static void
> -start_list(Visitor *v, const char *name, Error **errp)
> +start_list(Visitor *v, const char *name, GenericList **list, size_t size,
> + Error **errp)
> {
> StringInputVisitor *siv = to_siv(v);
> + Error *err = NULL;
>
> - parse_str(siv, errp);
> + /* We don't support visits without a GenericList, yet */
without a list
Do we plan to support them? If not, scratch "yet".
> + assert(list);
> +
> + parse_str(siv, &err);
> + if (err) {
> + *list = NULL;
> + error_propagate(errp, err);
> + return;
> + }
>
> siv->cur_range = g_list_first(siv->ranges);
> if (siv->cur_range) {
> @@ -137,13 +145,15 @@ start_list(Visitor *v, const char *name, Error **errp)
> if (r) {
> siv->cur = r->begin;
> }
> + *list = g_malloc0(size);
> + } else {
> + *list = NULL;
> }
> }
>
> -static GenericList *next_list(Visitor *v, GenericList **list, size_t size)
> +static GenericList *next_list(Visitor *v, GenericList *tail, size_t size)
> {
> StringInputVisitor *siv = to_siv(v);
> - GenericList **link;
> Range *r;
>
> if (!siv->ranges || !siv->cur_range) {
> @@ -167,21 +177,12 @@ static GenericList *next_list(Visitor *v, GenericList
> **list, size_t size)
> siv->cur = r->begin;
> }
>
> - if (siv->head) {
> - link = list;
> - siv->head = false;
> - } else {
> - link = &(*list)->next;
> - }
> -
> - *link = g_malloc0(size);
> - return *link;
> + tail->next = g_malloc0(size);
> + return tail->next;
> }
>
> static void end_list(Visitor *v)
> {
> - StringInputVisitor *siv = to_siv(v);
> - siv->head = true;
> }
>
> static void parse_type_int64(Visitor *v, const char *name, int64_t *obj,
> @@ -362,6 +363,5 @@ StringInputVisitor *string_input_visitor_new(const char
> *str)
> v->visitor.optional = parse_optional;
>
> v->string = str;
> - v->head = true;
> return v;
> }
> diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
> index 0d44d7e..e27e2df 100644
> --- a/qapi/string-output-visitor.c
> +++ b/qapi/string-output-visitor.c
> @@ -20,7 +20,7 @@
>
> enum ListMode {
> LM_NONE, /* not traversing a list of repeated options */
> - LM_STARTED, /* start_list() succeeded */
> + LM_STARTED, /* start_list() succeeded with multiple elements */
In opts-visitor.c, the comment says "opts_next_list() ready to be
called". Any reason for the difference?
>
> LM_IN_PROGRESS, /* next_list() has been called.
> *
> @@ -48,7 +48,7 @@ enum ListMode {
>
> LM_UNSIGNED_INTERVAL,/* Same as above, only for an unsigned interval. */
>
> - LM_END
> + LM_END, /* next_list() called, about to see last element. */
> };
>
> typedef enum ListMode ListMode;
> @@ -58,7 +58,6 @@ struct StringOutputVisitor
> Visitor visitor;
> bool human;
> GString *string;
> - bool head;
> ListMode list_mode;
> union {
> int64_t s;
> @@ -266,39 +265,29 @@ static void print_type_number(Visitor *v, const char
> *name, double *obj,
> }
>
> static void
> -start_list(Visitor *v, const char *name, Error **errp)
> +start_list(Visitor *v, const char *name, GenericList **list, size_t size,
> + Error **errp)
> {
> StringOutputVisitor *sov = to_sov(v);
>
> /* we can't traverse a list in a list */
> assert(sov->list_mode == LM_NONE);
> - sov->list_mode = LM_STARTED;
> - sov->head = true;
> + /* We don't support visits without a GenericList, yet */
without a list
Do we plan to support them? If not, scratch "yet".
> + assert(list);
> + /* List handling is only needed if there are at least two elements */
> + if (*list && (*list)->next) {
> + sov->list_mode = LM_STARTED;
> + }
> }
>
> -static GenericList *next_list(Visitor *v, GenericList **list, size_t size)
> +static GenericList *next_list(Visitor *v, GenericList *tail, size_t size)
> {
> StringOutputVisitor *sov = to_sov(v);
> - GenericList *ret = NULL;
> - if (*list) {
> - if (sov->head) {
> - ret = *list;
> - } else {
> - ret = (*list)->next;
> - }
> + GenericList *ret = tail->next;
>
> - if (sov->head) {
> - if (ret && ret->next == NULL) {
> - sov->list_mode = LM_NONE;
> - }
> - sov->head = false;
> - } else {
> - if (ret && ret->next == NULL) {
> - sov->list_mode = LM_END;
> - }
> - }
> + if (ret && !ret->next) {
> + sov->list_mode = LM_END;
> }
> -
> return ret;
> }
>
> @@ -311,8 +300,6 @@ static void end_list(Visitor *v)
> sov->list_mode == LM_NONE ||
> sov->list_mode == LM_IN_PROGRESS);
> sov->list_mode = LM_NONE;
> - sov->head = true;
> -
> }
>
> char *string_output_get_string(StringOutputVisitor *sov)
> diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
> index 3b2422f..99080db 100644
> --- a/docs/qapi-code-gen.txt
> +++ b/docs/qapi-code-gen.txt
> @@ -912,18 +912,19 @@ Example:
> void visit_type_UserDefOneList(Visitor *v, const char *name,
> UserDefOneList **obj, Error **errp)
> {
> Error *err = NULL;
> - GenericList *i, **prev;
> + UserDefOneList *tail;
> + size_t size = sizeof(**obj);
>
> - visit_start_list(v, name, &err);
> + visit_start_list(v, name, (GenericList **)obj, size, &err);
> if (err) {
> goto out;
> }
> -
> - for (prev = (GenericList **)obj;
> - !err && (i = visit_next_list(v, prev, sizeof(**obj))) != NULL;
> - prev = &i) {
> - UserDefOneList *native_i = (UserDefOneList *)i;
> - visit_type_UserDefOne(v, NULL, &native_i->value, &err);
> + for (tail = *obj; tail;
> + tail = (UserDefOneList *)visit_next_list(v, (GenericList
> *)tail, size)) {
> + visit_type_UserDefOne(v, NULL, &tail->value, &err);
> + if (err) {
> + break;
> + }
> }
>
> visit_end_list(v);