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>

9 files changed, 29 insertions, 18 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index dcc5a582e1f1..3a995841de90 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -474,7 +474,7 @@ int vfs_quota_sync(struct super_block *sb, int type)
                 spin_lock(&dq_list_lock);
                 dirty = &dqopt->info[cnt].dqi_dirty_list;
                 while (!list_empty(dirty)) {
-                        dquot = list_entry(dirty->next, struct dquot, dq_dirty);
+                        dquot = list_first_entry(dirty, struct dquot, dq_dirty);
                         /* Dirty and inactive can be only bad dquot... */
                         if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) {
                                 clear_dquot_dirty(dquot);
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index d0b86060cc19..b5c7ca584939 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -453,7 +453,7 @@ void eventpoll_release_file(struct file *file)
         mutex_lock(&epmutex);
 
         while (!list_empty(lsthead)) {
-                epi = list_entry(lsthead->next, struct epitem, fllink);
+                epi = list_first_entry(lsthead, struct epitem, fllink);
 
                 ep = epi->ep;
                 list_del_init(&epi->fllink);
@@ -1143,7 +1143,7 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
 
         if (nwait) {
                 while (!list_empty(lsthead)) {
-                        pwq = list_entry(lsthead->next, struct eppoll_entry, llink);
+                        pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
 
                         list_del_init(&pwq->llink);
                         remove_wait_queue(pwq->whead, &pwq->wait);
@@ -1359,7 +1359,7 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
          * read.
          */
         for (eventcnt = 0; !list_empty(txlist) && eventcnt < maxevents;) {
-                epi = list_entry(txlist->next, struct epitem, rdllink);
+                epi = list_first_entry(txlist, struct epitem, rdllink);
                 prefetch(epi->rdllink.next);
 
                 /*
diff --git a/fs/inode.c b/fs/inode.c
index 81508b0a3a70..410f235c337b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -275,7 +275,7 @@ static void dispose_list(struct list_head *head)
         while (!list_empty(head)) {
                 struct inode *inode;
 
-                inode = list_entry(head->next, struct inode, i_list);
+                inode = list_first_entry(head, struct inode, i_list);
                 list_del(&inode->i_list);
 
                 if (inode->i_data.nrpages)
diff --git a/fs/inotify.c b/fs/inotify.c
index f5099d86fd91..7457501b9565 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -509,7 +509,7 @@ void inotify_destroy(struct inotify_handle *ih)
                         mutex_unlock(&ih->mutex);
                         break;
                 }
-                watch = list_entry(watches->next, struct inotify_watch, h_list);
+                watch = list_first_entry(watches, struct inotify_watch, h_list);
                 get_inotify_watch(watch);
                 mutex_unlock(&ih->mutex);
 
diff --git a/fs/namespace.c b/fs/namespace.c
index c5b88100d914..72bb1062bfe7 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -499,7 +499,7 @@ void release_mounts(struct list_head *head)
 {
         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 @@ static void expire_mount_list(struct list_head *graveyard, struct list_head *mou
 
         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
diff --git a/fs/pnode.c b/fs/pnode.c
index 56aacead8362..89940f243fc2 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -59,7 +59,7 @@ static int do_make_slave(struct vfsmount *mnt)
         } else {
                 struct list_head *p = &mnt->mnt_slave_list;
                 while (!list_empty(p)) {
-                        slave_mnt = list_entry(p->next,
+                        slave_mnt = list_first_entry(p,
                                         struct vfsmount, mnt_slave);
                         list_del_init(&slave_mnt->mnt_slave);
                         slave_mnt->mnt_master = NULL;
diff --git a/include/linux/list.h b/include/linux/list.h
index f9d71eab05ee..9202703be2a4 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -426,6 +426,17 @@ static inline void list_splice_init_rcu(struct list_head *list,
         container_of(ptr, type, member)
 
 /**
+ * list_first_entry - get the first element from a list
+ * @ptr:        the list head to take the element from.
+ * @type:       the type of the struct this is embedded in.
+ * @member:     the name of the list_struct within the struct.
+ *
+ * Note, that list is expected to be not empty.
+ */
+#define list_first_entry(ptr, type, member) \
+        list_entry((ptr)->next, type, member)
+
+/**
  * list_for_each        -       iterate over a list
  * @pos:        the &struct list_head to use as a loop cursor.
  * @head:       the head for your list.
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 657f77697415..1de710e18373 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -971,7 +971,7 @@ static void check_thread_timers(struct task_struct *tsk,
         maxfire = 20;
         tsk->it_prof_expires = cputime_zero;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || cputime_lt(prof_ticks(tsk), t->expires.cpu)) {
@@ -986,7 +986,7 @@ static void check_thread_timers(struct task_struct *tsk,
         maxfire = 20;
         tsk->it_virt_expires = cputime_zero;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || cputime_lt(virt_ticks(tsk), t->expires.cpu)) {
@@ -1001,7 +1001,7 @@ static void check_thread_timers(struct task_struct *tsk,
         maxfire = 20;
         tsk->it_sched_expires = 0;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || tsk->sched_time < t->expires.sched) {
@@ -1057,7 +1057,7 @@ static void check_process_timers(struct task_struct *tsk,
         maxfire = 20;
         prof_expires = cputime_zero;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || cputime_lt(ptime, t->expires.cpu)) {
@@ -1072,7 +1072,7 @@ static void check_process_timers(struct task_struct *tsk,
         maxfire = 20;
         virt_expires = cputime_zero;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || cputime_lt(utime, t->expires.cpu)) {
@@ -1087,7 +1087,7 @@ static void check_process_timers(struct task_struct *tsk,
         maxfire = 20;
         sched_expires = 0;
         while (!list_empty(timers)) {
-                struct cpu_timer_list *t = list_entry(timers->next,
+                struct cpu_timer_list *t = list_first_entry(timers,
                                                       struct cpu_timer_list,
                                                       entry);
                 if (!--maxfire || sched_time < t->expires.sched) {
@@ -1400,7 +1400,7 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
          */
         head = &tsk->signal->cpu_timers[clock_idx];
         if (list_empty(head) ||
-            cputime_ge(list_entry(head->next,
+            cputime_ge(list_first_entry(head,
                                   struct cpu_timer_list, entry)->expires.cpu,
                        *newval)) {
                 /*
diff --git a/kernel/timer.c b/kernel/timer.c
index ba41af2bb6cc..7a6448340f90 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -629,7 +629,7 @@ static inline void __run_timers(tvec_base_t *base)
                         void (*fn)(unsigned long);
                         unsigned long data;
 
-                        timer = list_entry(head->next,struct timer_list,entry);
+                        timer = list_first_entry(head, struct timer_list,entry);
                         fn = timer->function;
                         data = timer->data;
 
@@ -1248,7 +1248,7 @@ static void migrate_timer_list(tvec_base_t *new_base, struct list_head *head)
         struct timer_list *timer;
 
         while (!list_empty(head)) {
-                timer = list_entry(head->next, struct timer_list, entry);
+                timer = list_first_entry(head, struct timer_list, entry);
                 detach_timer(timer, 0);
                 timer_set_base(timer, new_base);
                 internal_add_timer(new_base, timer);