[PATCH 3/5] qemu/queue.h: add QLIST_SAFE_REMOVE()

[Stefan Hajnoczi <stefanha@redhat.com>]

QLIST_REMOVE() assumes the element is in a list.  It also leaves the
element's linked list pointers dangling.

Introduce a safe version of QLIST_REMOVE() and convert open-coded
instances of this pattern.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block.c              |  5 +----
 chardev/spice.c      |  4 +---
 include/qemu/queue.h | 14 ++++++++++++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/block.c b/block.c
index 9c810534d6..484e01d042 100644
--- a/block.c
+++ b/block.c
@@ -2499,10 +2499,7 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
 
 static void bdrv_detach_child(BdrvChild *child)
 {
-    if (child->next.le_prev) {
-        QLIST_REMOVE(child, next);
-        child->next.le_prev = NULL;
-    }
+    QLIST_SAFE_REMOVE(child, next);
 
     bdrv_replace_child(child, NULL);
 
diff --git a/chardev/spice.c b/chardev/spice.c
index 241e2b7770..bf7ea1e294 100644
--- a/chardev/spice.c
+++ b/chardev/spice.c
@@ -216,9 +216,7 @@ static void char_spice_finalize(Object *obj)
 
     vmc_unregister_interface(s);
 
-    if (s->next.le_prev) {
-        QLIST_REMOVE(s, next);
-    }
+    QLIST_SAFE_REMOVE(s, next);
 
     g_free((char *)s->sin.subtype);
     g_free((char *)s->sin.portname);
diff --git a/include/qemu/queue.h b/include/qemu/queue.h
index 19425f973f..a276363372 100644
--- a/include/qemu/queue.h
+++ b/include/qemu/queue.h
@@ -144,6 +144,20 @@ struct {                                                                \
         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 } while (/*CONSTCOND*/0)
 
+/*
+ * Like QLIST_REMOVE() but safe to call when elm is not in a list
+ */
+#define QLIST_SAFE_REMOVE(elm, field) do {                              \
+        if ((elm)->field.le_prev != NULL) {                             \
+                if ((elm)->field.le_next != NULL)                       \
+                        (elm)->field.le_next->field.le_prev =           \
+                            (elm)->field.le_prev;                       \
+                *(elm)->field.le_prev = (elm)->field.le_next;           \
+                (elm)->field.le_next = NULL;                            \
+                (elm)->field.le_prev = NULL;                            \
+        }                                                               \
+} while (/*CONSTCOND*/0)
+
 #define QLIST_FOREACH(var, head, field)                                 \
         for ((var) = ((head)->lh_first);                                \
                 (var);                                                  \
-- 
2.24.1