Import a simple queue implementation from NetBSD

Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-queue.h

-/*      $NetBSD: queue.h,v 1.45.14.1 2007/07/18 20:13:24 liamjfoy Exp $ */
+/*      $NetBSD: queue.h,v 1.52 2009/04/20 09:56:08 mschuett Exp $ */
 
 /*
  * Qemu version: Copy from netbsd, removed debug code, removed some of
- * the implementations.  Left in lists, tail queues and circular queues.
+ * the implementations.  Left in lists, simple queues, tail queues and
+ * circular queues.
  */
 
 /*
@@ -40,8 +41,8 @@
 #define QEMU_SYS_QUEUE_H_
 
 /*
- * This file defines three types of data structures:
- * lists, tail queues, and circular queues.
+ * This file defines four types of data structures:
+ * lists, simple queues, tail queues, and circular queues.
  *
  * A list is headed by a single forward pointer (or an array of forward
  * pointers for a hash table header). The elements are doubly linked
@@ -50,6 +51,13 @@
  * or after an existing element or at the head of the list. A list
  * may only be traversed in the forward direction.
  *
+ * A simple queue is headed by a pair of pointers, one the head of the
+ * list and the other to the tail of the list. The elements are singly
+ * linked to save space, so elements can only be removed from the
+ * head of the list. New elements can be added to the list after
+ * an existing element, at the head of the list, or at the end of the
+ * list. A simple queue may only be traversed in the forward direction.
+ *
  * A tail queue is headed by a pair of pointers, one to the head of the
  * list and the other to the tail of the list. The elements are doubly
  * linked so that an arbitrary element can be removed without a need to
@@ -139,6 +147,99 @@ struct {                                                                \
 #define QLIST_NEXT(elm, field)           ((elm)->field.le_next)
 
 
+/*
+ * Simple queue definitions.
+ */
+#define QSIMPLEQ_HEAD(name, type)                                       \
+struct name {                                                           \
+    struct type *sqh_first;    /* first element */                      \
+    struct type **sqh_last;    /* addr of last next element */          \
+}
+
+#define QSIMPLEQ_HEAD_INITIALIZER(head)                                 \
+    { NULL, &(head).sqh_first }
+
+#define QSIMPLEQ_ENTRY(type)                                            \
+struct {                                                                \
+    struct type *sqe_next;    /* next element */                        \
+}
+
+/*
+ * Simple queue functions.
+ */
+#define QSIMPLEQ_INIT(head) do {                                        \
+    (head)->sqh_first = NULL;                                           \
+    (head)->sqh_last = &(head)->sqh_first;                              \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_INSERT_HEAD(head, elm, field) do {                     \
+    if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)            \
+        (head)->sqh_last = &(elm)->field.sqe_next;                      \
+    (head)->sqh_first = (elm);                                          \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_INSERT_TAIL(head, elm, field) do {                     \
+    (elm)->field.sqe_next = NULL;                                       \
+    *(head)->sqh_last = (elm);                                          \
+    (head)->sqh_last = &(elm)->field.sqe_next;                          \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {           \
+    if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)    \
+        (head)->sqh_last = &(elm)->field.sqe_next;                      \
+    (listelm)->field.sqe_next = (elm);                                  \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_REMOVE_HEAD(head, field) do {                          \
+    if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL)\
+        (head)->sqh_last = &(head)->sqh_first;                          \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_REMOVE(head, elm, type, field) do {                    \
+    if ((head)->sqh_first == (elm)) {                                   \
+        QSIMPLEQ_REMOVE_HEAD((head), field);                            \
+    } else {                                                            \
+        struct type *curelm = (head)->sqh_first;                        \
+        while (curelm->field.sqe_next != (elm))                         \
+            curelm = curelm->field.sqe_next;                            \
+        if ((curelm->field.sqe_next =                                   \
+            curelm->field.sqe_next->field.sqe_next) == NULL)            \
+                (head)->sqh_last = &(curelm)->field.sqe_next;           \
+    }                                                                   \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_FOREACH(var, head, field)                              \
+    for ((var) = ((head)->sqh_first);                                   \
+        (var);                                                          \
+        (var) = ((var)->field.sqe_next))
+
+#define QSIMPLEQ_FOREACH_SAFE(var, head, field, next)                   \
+    for ((var) = ((head)->sqh_first);                                   \
+        (var) && ((next = ((var)->field.sqe_next)), 1);                 \
+        (var) = (next))
+
+#define QSIMPLEQ_CONCAT(head1, head2) do {                              \
+    if (!QSIMPLEQ_EMPTY((head2))) {                                     \
+        *(head1)->sqh_last = (head2)->sqh_first;                        \
+        (head1)->sqh_last = (head2)->sqh_last;                          \
+        QSIMPLEQ_INIT((head2));                                         \
+    }                                                                   \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_LAST(head, type, field)                                \
+    (QSIMPLEQ_EMPTY((head)) ?                                           \
+        NULL :                                                          \
+            ((struct type *)(void *)                                    \
+        ((char *)((head)->sqh_last) - offsetof(struct type, field))))
+
+/*
+ * Simple queue access methods.
+ */
+#define QSIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
+#define QSIMPLEQ_FIRST(head)        ((head)->sqh_first)
+#define QSIMPLEQ_NEXT(elm, field)   ((elm)->field.sqe_next)
+
+
 /*
  * Tail queue definitions.
  */