[PATCH 5/5] ipc: cleanup do_msgrcv() aroung MSG_COPY feature

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

MSG_COPY feature was developed for Checkpoint/Restart In User space project
and thus wrapped in CONFIG_CHECKPOINT_RESTORE macro. But code look a bit ugly.
So this patch is an attempt to cleanup do_msgrcv() a bit and make it looks
better.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
 ipc/msg.c |   79 +++++++++++++++++++++++++++++++++++++------------------------
 1 files changed, 48 insertions(+), 31 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 91873df..d20ffc7 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -769,6 +769,45 @@ static long do_msg_fill(void __user *dest, struct msg_msg *msg, size_t bufsz)
 	return msgsz;
 }
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static inline struct msg_msg *fill_copy(unsigned long copy_nr,
+					unsigned long msg_nr,
+					struct msg_msg *msg,
+					struct msg_msg *copy)
+{
+	if (copy_nr == msg_nr)
+		return copy_msg(msg, copy);
+	return NULL;
+}
+
+static inline struct msg_msg *prepare_copy(void __user *buf, size_t bufsz,
+					   int msgflg, long *msgtyp,
+					   unsigned long *copy_number)
+{
+	struct msg_msg *copy;
+
+	*copy_number = *msgtyp;
+	*msgtyp = 0;
+	/*
+	 * Create dummy message to copy real message to.
+	 */
+	copy = load_msg(buf, bufsz);
+	if (!IS_ERR(copy))
+		copy->m_ts = bufsz;
+	return copy;
+}
+
+static inline void free_copy(int msgflg, struct msg_msg *copy)
+{
+	if (msgflg & MSG_COPY)
+		free_msg(copy);
+}
+#else
+#define free_copy(msgflg, copy)				do {} while (0)
+#define prepare_copy(buf, sz, msgflg, msgtyp, copy_nr)	ERR_PTR(-ENOSYS)
+#define fill_copy(copy_nr, msg_nr, msg, copy)		NULL
+#endif
+
 long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
 	       int msgflg,
 	       long (*msg_handler)(void __user *, struct msg_msg *, size_t))
@@ -777,38 +816,22 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
 	struct msg_msg *msg;
 	int mode;
 	struct ipc_namespace *ns;
-#ifdef CONFIG_CHECKPOINT_RESTORE
-	struct msg_msg *copy = NULL;
-	unsigned long copy_number = 0;
-#endif
+	struct msg_msg *copy;
+	unsigned long __maybe_unused copy_number;
 
 	if (msqid < 0 || (long) bufsz < 0)
 		return -EINVAL;
 	if (msgflg & MSG_COPY) {
-#ifdef CONFIG_CHECKPOINT_RESTORE
-		copy_number = msgtyp;
-		msgtyp = 0;
-
-		/*
-		 * Create dummy message to copy real message to.
-		 */
-		copy = load_msg(buf, bufsz);
+		copy = prepare_copy(buf, bufsz, msgflg, &msgtyp, &copy_number);
 		if (IS_ERR(copy))
 			return PTR_ERR(copy);
-		copy->m_ts = bufsz;
-#else
-		return -ENOSYS;
-#endif
 	}
 	mode = convert_mode(&msgtyp, msgflg);
 	ns = current->nsproxy->ipc_ns;
 
 	msq = msg_lock_check(ns, msqid);
 	if (IS_ERR(msq)) {
-#ifdef CONFIG_CHECKPOINT_RESTORE
-		if (msgflg & MSG_COPY)
-			free_msg(copy);
-#endif
+		free_copy(msgflg, copy);
 		return PTR_ERR(msq);
 	}
 
@@ -835,13 +858,12 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
 				if (mode == SEARCH_LESSEQUAL &&
 						walk_msg->m_type != 1) {
 					msgtyp = walk_msg->m_type - 1;
-#ifdef CONFIG_CHECKPOINT_RESTORE
 				} else if (msgflg & MSG_COPY) {
-					if (copy_number == msg_counter) {
-						msg = copy_msg(walk_msg, copy);
+					msg = fill_copy(copy_number,
+							msg_counter,
+							walk_msg, copy);
+					if (msg)
 						break;
-					}
-#endif
 				} else
 					break;
 				msg_counter++;
@@ -857,10 +879,8 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
 				msg = ERR_PTR(-E2BIG);
 				goto out_unlock;
 			}
-#ifdef CONFIG_CHECKPOINT_RESTORE
 			if (msgflg & MSG_COPY)
 				goto out_unlock;
-#endif
 			list_del(&msg->m_list);
 			msq->q_qnum--;
 			msq->q_rtime = get_seconds();
@@ -945,10 +965,7 @@ out_unlock:
 		}
 	}
 	if (IS_ERR(msg)) {
-#ifdef CONFIG_CHECKPOINT_RESTORE
-		if (msgflg & MSG_COPY)
-			free_msg(copy);
-#endif
+		free_copy(msgflg, copy);
 		return PTR_ERR(msg);
 	}