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/dquot.c b/fs/dquot.c
index dcc5a58..3a99584 100644 (file)
--- 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 d0b8606..b5c7ca5 100644 (file)
--- 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 81508b0..410f235 100644 (file)
--- 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 f5099d8..7457501 100644 (file)
--- 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 c5b8810..72bb106 100644 (file)
--- 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 56aacea..89940f2 100644 (file)
--- 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 f9d71ea..9202703 100644 (file)
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -425,6 +425,17 @@ static inline void list_splice_init_rcu(struct list_head *list,
 #define list_entry(ptr, type, member) \
        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.

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 657f776..1de710e 100644 (file)
--- 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 ba41af2..7a64483 100644 (file)
--- 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);