[PATCH] Introduce a handy list_first_entry macro

[PATCH] Introduce a handy list_first_entry macro

[Pavel Emelianov]

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>

---

diff --git a/fs/dquot.c b/fs/dquot.c
index ac40503..e5cce5a 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -474,7 +474,7 @@ int vfs_quota_sync(struct super_block *s
 		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 aeedc99..1aad34e 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -371,7 +371,7 @@ static void ep_unregister_pollwait(struc
 
 	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);
@@ -602,7 +602,7 @@ void eventpoll_release_file(struct 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);
@@ -943,7 +943,7 @@ static int ep_send_events(struct eventpo
 	 * 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 224fe4d..359f406 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -286,7 +286,7 @@ static void dispose_list(struct list_hea
 	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
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -509,7 +509,7 @@ void inotify_destroy(struct inotify_hand
 			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 213f7ab..4627e1d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -518,7 +518,7 @@ void release_mounts(struct list_head *he
 {
 	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;
@@ -1196,7 +1196,7 @@ static void expire_mount_list(struct lis
 
 	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
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -59,7 +59,7 @@ static int do_make_slave(struct vfsmount
 	} 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 fd59659..71318fc 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -425,6 +425,9 @@ static inline void list_splice_init_rcu(
 #define list_entry(ptr, type, member) \
 	container_of(ptr, type, member)
 
+#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
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -971,7 +971,7 @@ static void check_thread_timers(struct t
 	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 t
 	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 t
 	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 
 	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 
 	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 
 	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_s
 	 */
 	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 2baf189..b990e95 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -627,7 +627,7 @@ static inline void __run_timers(tvec_bas
 			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;
 
@@ -1246,7 +1246,7 @@ static void migrate_timer_list(tvec_base
 	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);

Re: [PATCH] Introduce a handy list_first_entry macro

[Andi Kleen]

Pavel Emelianov <xemul@sw.ru> writes:

> 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)

Thanks. I always wanted that too.

-andi

Re: [PATCH] Introduce a handy list_first_entry macro

[Zach Brown]

On Tue, Apr 17, 2007 at 03:18:56PM +0400, Pavel Emelianov wrote:
> 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)

> -			dquot = list_entry(dirty->next, struct dquot, dq_dirty);
> +			dquot = list_first_entry(dirty, struct dquot, dq_dirty);

I think it's more than just descriptive and neat.  A common sneaky bug
is to accidentally pass &list->next into list_entry() instead of
list->next. This is easy to do because one is used to typing &list in
list_empty(), etc.  So by following ->next in the macro we make the list
argument consistent in list_empty() and list_first_entry() and hopefully
reduce the risk of making that mistake.

I like it.

- z

Re: [PATCH] Introduce a handy list_first_entry macro

[Randy Dunlap]

On Tue, 17 Apr 2007 15:18:56 +0400 Pavel Emelianov wrote:

> 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>
> 
> ---
> diff --git a/include/linux/list.h b/include/linux/list.h
> index fd59659..71318fc 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -425,6 +425,9 @@ static inline void list_splice_init_rcu(
>  #define list_entry(ptr, type, member) \
>  	container_of(ptr, type, member)
>  
> +#define list_first_entry(ptr, type, member) \
> +	list_entry((ptr)->next, type, member)
> +

Please provide kernel-doc for that like the rest of list.h has.

>  /**
>   * list_for_each	-	iterate over a list
>   * @pos:	the &struct list_head to use as a loop cursor.


---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

Re: [PATCH] Introduce a handy list_first_entry macro

[Nikita Danilov]

Pavel Emelianov writes:
 > 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)

Won't list_next_entry() be more descriptive name for that?

Nikita.