[Qemu-devel] [PATCH v4 21/28] qstring: Add qstring_wrap_str()

[Eric Blake <eblake@redhat.com>]

Several spots in the code malloc a string, then wrap it in a
QString, which has to duplicate the input.  Adding a new
constructor with transfer semantics makes this pattern more
efficient, comparable to the just-added transfer semantics to
go from QString back to raw string.  Use the new
qstring_wrap_str() where it makes sense.

The new test still passes under valgrind.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v4: new patch
---
 include/qapi/qmp/qstring.h |  1 +
 block.c                    |  3 ++-
 block/archipelago.c        |  6 ++----
 blockdev.c                 |  3 +--
 qobject/qstring.c          | 25 +++++++++++++++++++++++++
 tests/check-qstring.c      | 24 ++++++++++++++++++++++++
 6 files changed, 55 insertions(+), 7 deletions(-)

diff --git a/include/qapi/qmp/qstring.h b/include/qapi/qmp/qstring.h
index 2d55c87..97cf776 100644
--- a/include/qapi/qmp/qstring.h
+++ b/include/qapi/qmp/qstring.h
@@ -25,6 +25,7 @@ typedef struct QString {
 QString *qstring_new(void);
 QString *qstring_from_str(const char *str);
 QString *qstring_from_substr(const char *str, int start, int end);
+QString *qstring_wrap_str(char *str);
 size_t qstring_get_length(const QString *qstring);
 const char *qstring_get_str(const QString *qstring);
 char *qstring_consume_str(QString *qstring);
diff --git a/block.c b/block.c
index 551832f..32d06b5 100644
--- a/block.c
+++ b/block.c
@@ -1448,7 +1448,8 @@ static int bdrv_append_temp_snapshot(BlockDriverState *bs, int flags,
     qdict_put(snapshot_options, "file.driver",
               qstring_from_str("file"));
     qdict_put(snapshot_options, "file.filename",
-              qstring_from_str(tmp_filename));
+              qstring_wrap_str(tmp_filename));
+    tmp_filename = NULL;
     qdict_put(snapshot_options, "driver",
               qstring_from_str("qcow2"));

diff --git a/block/archipelago.c b/block/archipelago.c
index 104f2f9..bfdc14c 100644
--- a/block/archipelago.c
+++ b/block/archipelago.c
@@ -426,13 +426,11 @@ static void archipelago_parse_filename(const char *filename, QDict *options,
     parse_filename_opts(filename, errp, &volume, &segment_name, &mport, &vport);

     if (volume) {
-        qdict_put(options, ARCHIPELAGO_OPT_VOLUME, qstring_from_str(volume));
-        g_free(volume);
+        qdict_put(options, ARCHIPELAGO_OPT_VOLUME, qstring_wrap_str(volume));
     }
     if (segment_name) {
         qdict_put(options, ARCHIPELAGO_OPT_SEGMENT,
-                  qstring_from_str(segment_name));
-        g_free(segment_name);
+                  qstring_wrap_str(segment_name));
     }
     if (mport != NoPort) {
         qdict_put(options, ARCHIPELAGO_OPT_MPORT, qint_from_int(mport));
diff --git a/blockdev.c b/blockdev.c
index adc5058..f293cb3 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1089,8 +1089,7 @@ DriveInfo *drive_new(QemuOpts *all_opts, BlockInterfaceType block_default_type)
             new_id = g_strdup_printf("%s%s%i", if_name[type],
                                      mediastr, unit_id);
         }
-        qdict_put(bs_opts, "id", qstring_from_str(new_id));
-        g_free(new_id);
+        qdict_put(bs_opts, "id", qstring_wrap_str(new_id));
     }

     /* Add virtio block device */
diff --git a/qobject/qstring.c b/qobject/qstring.c
index 7a438e9..2af1914 100644
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -66,6 +66,31 @@ QString *qstring_from_str(const char *str)
     return qstring_from_substr(str, 0, strlen(str) - 1);
 }

+/**
+ * qstring_wrap_str(): Create a new QString around a malloc'd C string
+ *
+ * Returns a strong reference, and caller must not use @str any more.
+ * @str may be NULL, in which case the QString will be "".
+ */
+QString *qstring_wrap_str(char *str)
+{
+    QString *qstring;
+
+    qstring = g_malloc(sizeof(*qstring));
+    qobject_init(QOBJECT(qstring), QTYPE_QSTRING);
+
+    if (str) {
+        qstring->string = str;
+        qstring->length = strlen(str);
+    } else {
+        qstring->string = g_strdup("");
+        qstring->length = 0;
+    }
+    qstring->capacity = qstring->length;
+
+    return qstring;
+}
+
 static void capacity_increase(QString *qstring, size_t len)
 {
     if (qstring->capacity < (qstring->length + len)) {
diff --git a/tests/check-qstring.c b/tests/check-qstring.c
index e6f58e0..0e2e9bd 100644
--- a/tests/check-qstring.c
+++ b/tests/check-qstring.c
@@ -35,6 +35,29 @@ static void qstring_from_str_test(void)
     QDECREF(qstring);
 }

+static void qstring_wrap_str_test(void)
+{
+    QString *qstring;
+    char *str = g_strdup("QEMU");
+
+    qstring = qstring_wrap_str(str);
+    g_assert(qstring != NULL);
+    g_assert(qstring->base.refcnt == 1);
+    g_assert(strcmp("QEMU", qstring->string) == 0);
+    g_assert(qobject_type(QOBJECT(qstring)) == QTYPE_QSTRING);
+
+    QDECREF(qstring);
+
+    str = NULL;
+    qstring = qstring_wrap_str(str);
+    g_assert(qstring != NULL);
+    g_assert(qstring->base.refcnt == 1);
+    g_assert(strcmp("", qstring->string) == 0);
+    g_assert(qobject_type(QOBJECT(qstring)) == QTYPE_QSTRING);
+
+    QDECREF(qstring);
+}
+
 static void qstring_destroy_test(void)
 {
     QString *qstring = qstring_from_str("destroy test");
@@ -120,6 +143,7 @@ int main(int argc, char **argv)
     g_test_init(&argc, &argv, NULL);

     g_test_add_func("/public/from_str", qstring_from_str_test);
+    g_test_add_func("/public/wrap_str", qstring_wrap_str_test);
     g_test_add_func("/public/destroy", qstring_destroy_test);
     g_test_add_func("/public/get_str", qstring_get_str_test);
     g_test_add_func("/public/append_chr", qstring_append_chr_test);
-- 
2.5.5