Introduce a handy list_first_entry macro

There are many places in the kernel where the construction like

   foo = list_entry(head->next, struct foo_struct, list);

are used.
The code might look more descriptive and neat if using the macro

   list_first_entry(head, type, member) \
             list_entry((head)->next, type, member)

Here is the macro itself and the examples of its usage in the generic code.
 If it will turn out to be useful, I can prepare the set of patches to
inject in into arch-specific code, drivers, networking, etc.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: John McCutchan <ttb@tentacle.dhs.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/namespace.c b/fs/namespace.c
index c5b8810..72bb106 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -499,7 +499,7 @@
 {
 	struct vfsmount *mnt;
 	while (!list_empty(head)) {
-		mnt = list_entry(head->next, struct vfsmount, mnt_hash);
+		mnt = list_first_entry(head, struct vfsmount, mnt_hash);
 		list_del_init(&mnt->mnt_hash);
 		if (mnt->mnt_parent != mnt) {
 			struct dentry *dentry;
@@ -1177,7 +1177,7 @@
 
 	while (!list_empty(graveyard)) {
 		LIST_HEAD(umounts);
-		mnt = list_entry(graveyard->next, struct vfsmount, mnt_expire);
+		mnt = list_first_entry(graveyard, struct vfsmount, mnt_expire);
 		list_del_init(&mnt->mnt_expire);
 
 		/* don't do anything if the namespace is dead - all the