qemu-devel.nongnu.org archive mirror
 help / color / mirror / Atom feed
From: Markus Armbruster <armbru@redhat.com>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [PULL 14/23] qapi: Add visit_type_null() visitor
Date: Thu, 12 May 2016 09:59:01 +0200	[thread overview]
Message-ID: <1463039950-4021-15-git-send-email-armbru@redhat.com> (raw)
In-Reply-To: <1463039950-4021-1-git-send-email-armbru@redhat.com>

From: Eric Blake <eblake@redhat.com>

Right now, qmp-output-visitor happens to produce a QNull result
if nothing is actually visited between the creation of the visitor
and the request for the resulting QObject.  A stronger protocol
would require that a QMP output visit MUST visit something.  But
to still be able to produce a JSON 'null' output, we need a new
visitor function that states our intentions.  Yes, we could say
that such a visit must go through visit_type_any(), but that
feels clunky.

So this patch introduces the new visit_type_null() interface and
its no-op interface in the dealloc visitor, and stubs in the
qmp visitors (the next patch will finish the implementation).
For the visitors that will not implement the callback, document
the situation. The code in qapi-visit-core unconditionally
dereferences the callback pointer, so that a segfault will inform
a developer if they need to implement the callback for their
choice of visitor.

Note that JSON has a primitive null type, with the single value
null; likewise with the QNull type for QObject; but for QAPI,
we just have the 'null' value without a null type.  We may
eventually want to add more support in QAPI for null (most likely,
we'd use it via an alternate type that permits 'null' or an
object); but we'll create that usage when we need it.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-15-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 include/qapi/opts-visitor.h          |  3 ++-
 include/qapi/string-input-visitor.h  |  2 +-
 include/qapi/string-output-visitor.h |  2 +-
 include/qapi/visitor-impl.h          |  3 +++
 include/qapi/visitor.h               | 12 ++++++++++++
 qapi/qapi-dealloc-visitor.c          |  5 +++++
 qapi/qapi-visit-core.c               |  5 +++++
 qapi/qmp-input-visitor.c             |  6 ++++++
 qapi/qmp-output-visitor.c            |  6 ++++++
 9 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/include/qapi/opts-visitor.h b/include/qapi/opts-visitor.h
index 633aa71..fe37ed9 100644
--- a/include/qapi/opts-visitor.h
+++ b/include/qapi/opts-visitor.h
@@ -31,7 +31,8 @@ typedef struct OptsVisitor OptsVisitor;
  * - values above INT64_MAX or LLONG_MAX are rejected.
  *
  * The Opts input visitor does not implement support for visiting QAPI
- * alternates, numbers (other than integers), or arbitrary QTypes.
+ * alternates, numbers (other than integers), null, or arbitrary
+ * QTypes.
  */
 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 fdf33ae..a8d8f67 100644
--- a/include/qapi/string-input-visitor.h
+++ b/include/qapi/string-input-visitor.h
@@ -19,7 +19,7 @@ typedef struct StringInputVisitor StringInputVisitor;
 
 /*
  * The string input visitor does not implement support for visiting
- * QAPI structs, alternates, or arbitrary QTypes.
+ * QAPI structs, alternates, null, or arbitrary QTypes.
  */
 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 3bb09af..89b7e4b 100644
--- a/include/qapi/string-output-visitor.h
+++ b/include/qapi/string-output-visitor.h
@@ -19,7 +19,7 @@ typedef struct StringOutputVisitor StringOutputVisitor;
 
 /*
  * The string output visitor does not implement support for visiting
- * QAPI structs, alternates, or arbitrary QTypes.
+ * QAPI structs, alternates, null, or arbitrary QTypes.
  */
 StringOutputVisitor *string_output_visitor_new(bool human);
 void string_output_visitor_cleanup(StringOutputVisitor *v);
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 796d180..88d27d5 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -90,6 +90,9 @@ struct Visitor
     void (*type_any)(Visitor *v, const char *name, QObject **obj,
                      Error **errp);
 
+    /* Must be set to visit explicit null values.  */
+    void (*type_null)(Visitor *v, const char *name, Error **errp);
+
     /* Must be set for input visitors, optional otherwise.  The core
      * takes care of the return type in the public interface. */
     void (*optional)(Visitor *v, const char *name, bool *present);
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 2211637..709cca0 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -522,4 +522,16 @@ void visit_type_number(Visitor *v, const char *name, double *obj,
  */
 void visit_type_any(Visitor *v, const char *name, QObject **obj, Error **errp);
 
+/*
+ * Visit a JSON null value.
+ *
+ * @name expresses the relationship of the null value to its parent
+ * container; see the general description of @name above.
+ *
+ * Unlike all other visit_type_* functions, no obj parameter is
+ * needed; rather, this is a witness that an explicit null value is
+ * expected rather than any other type.
+ */
+void visit_type_null(Visitor *v, const char *name, Error **errp);
+
 #endif
diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
index c19a459..413d525 100644
--- a/qapi/qapi-dealloc-visitor.c
+++ b/qapi/qapi-dealloc-visitor.c
@@ -163,6 +163,10 @@ static void qapi_dealloc_type_anything(Visitor *v, const char *name,
     }
 }
 
+static void qapi_dealloc_type_null(Visitor *v, const char *name, Error **errp)
+{
+}
+
 Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v)
 {
     return &v->visitor;
@@ -193,6 +197,7 @@ QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
     v->visitor.type_str = qapi_dealloc_type_str;
     v->visitor.type_number = qapi_dealloc_type_number;
     v->visitor.type_any = qapi_dealloc_type_anything;
+    v->visitor.type_null = qapi_dealloc_type_null;
 
     QTAILQ_INIT(&v->stack);
 
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 0f59a1d..fe6afe8 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -244,6 +244,11 @@ void visit_type_any(Visitor *v, const char *name, QObject **obj, Error **errp)
     error_propagate(errp, err);
 }
 
+void visit_type_null(Visitor *v, const char *name, Error **errp)
+{
+    v->type_null(v, name, errp);
+}
+
 static void output_type_enum(Visitor *v, const char *name, int *obj,
                              const char *const strings[], Error **errp)
 {
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 5159833..fa460a3 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -340,6 +340,11 @@ static void qmp_input_type_any(Visitor *v, const char *name, QObject **obj,
     *obj = qobj;
 }
 
+static void qmp_input_type_null(Visitor *v, const char *name, Error **errp)
+{
+    abort();
+}
+
 static void qmp_input_optional(Visitor *v, const char *name, bool *present)
 {
     QmpInputVisitor *qiv = to_qiv(v);
@@ -383,6 +388,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj, bool strict)
     v->visitor.type_str = qmp_input_type_str;
     v->visitor.type_number = qmp_input_type_number;
     v->visitor.type_any = qmp_input_type_any;
+    v->visitor.type_null = qmp_input_type_null;
     v->visitor.optional = qmp_input_optional;
     v->strict = strict;
 
diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
index 1f2a7ba..adf7731 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -196,6 +196,11 @@ static void qmp_output_type_any(Visitor *v, const char *name, QObject **obj,
     qmp_output_add_obj(qov, name, *obj);
 }
 
+static void qmp_output_type_null(Visitor *v, const char *name, Error **errp)
+{
+    abort();
+}
+
 /* Finish building, and return the root object. Will not be NULL. */
 QObject *qmp_output_get_qobject(QmpOutputVisitor *qov)
 {
@@ -246,6 +251,7 @@ QmpOutputVisitor *qmp_output_visitor_new(void)
     v->visitor.type_str = qmp_output_type_str;
     v->visitor.type_number = qmp_output_type_number;
     v->visitor.type_any = qmp_output_type_any;
+    v->visitor.type_null = qmp_output_type_null;
 
     QTAILQ_INIT(&v->stack);
 
-- 
2.5.5

  parent reply	other threads:[~2016-05-12  7:59 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-12  7:58 [Qemu-devel] [PULL 00/23] QAPI patches for 2016-05-12 Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 01/23] qapi-visit: Add visitor.type classification Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 02/23] qapi: Guarantee NULL obj on input visitor callback error Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 03/23] qmp: Drop dead command->type Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 04/23] qmp-input: Clean up stack handling Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 05/23] qapi: Consolidate QMP input visitor creation Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 06/23] qapi: Use strict QMP input visitor in more places Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 07/23] qmp-input: Don't consume input when checking has_member Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 08/23] qapi-commands: Wrap argument visit in visit_start_struct Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 09/23] qom: Wrap prop " Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 10/23] qmp-input: Require struct push to visit members of top dict Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 11/23] qmp-input: Refactor when list is advanced Markus Armbruster
2016-05-12  7:58 ` [Qemu-devel] [PULL 12/23] qapi: Document visitor interfaces, add assertions Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 13/23] tests: Add check-qnull Markus Armbruster
2016-05-12  7:59 ` Markus Armbruster [this message]
2016-05-12  7:59 ` [Qemu-devel] [PULL 15/23] qmp: Support explicit null during visits Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 16/23] spapr_drc: Expose 'null' in qom-get when there is no fdt Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 17/23] qmp: Don't reuse qmp visitor after grabbing output Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 18/23] qmp: Tighten output visitor rules Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 19/23] qapi: Split visit_end_struct() into pieces Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 20/23] tests/string-input-visitor: Add negative integer tests Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 21/23] qapi: Fix string input visitor handling of invalid list Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 22/23] qapi: Simplify semantics of visit_next_list() Markus Armbruster
2016-05-12  7:59 ` [Qemu-devel] [PULL 23/23] qapi: Change visit_type_FOO() to no longer return partial objects Markus Armbruster
2016-05-12 14:55 ` [Qemu-devel] [PULL 00/23] QAPI patches for 2016-05-12 Peter Maydell

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1463039950-4021-15-git-send-email-armbru@redhat.com \
    --to=armbru@redhat.com \
    --cc=qemu-devel@nongnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).