linux-kernel - [PATCH 6/7] [media] tm6000: drop unnecessary list

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Message-Id: <1595761112-11003-7-git-send-email-Julia.Lawall@inria.fr>
Date:   Sun, 26 Jul 2020 12:58:31 +0200
From:   Julia Lawall <Julia.Lawall@...ia.fr>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     kernel-janitors@...r.kernel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 6/7] [media] tm6000: drop unnecessary list_empty

list_for_each_entry is able to handle an empty list.
The only effect of avoiding the loop is not initializing the
index variable.
Drop list_empty tests in cases where these variables are not
used.

Note that list_for_each_entry is defined in terms of list_first_entry,
which indicates that it should not be used on an empty list.  But in
list_for_each_entry, the element obtained by list_first_entry is not
really accessed, only the address of its list_head field is compared
to the address of the list head, so the list_first_entry is safe.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@
expression x,e;
iterator name list_for_each_entry;
statement S;
identifier i;
@@

-if (!(list_empty(x))) {
   list_for_each_entry(i,x,...) S
- }
 ... when != i
? i = e
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@...ia.fr>

---
 drivers/media/usb/tm6000/tm6000-core.c |   24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/drivers/media/usb/tm6000/tm6000-core.c b/drivers/media/usb/tm6000/tm6000-core.c
index 2c72370..5c8cbc5 100644
--- a/drivers/media/usb/tm6000/tm6000-core.c
+++ b/drivers/media/usb/tm6000/tm6000-core.c
@@ -853,11 +853,9 @@ int tm6000_call_fillbuf(struct tm6000_core *dev, enum tm6000_ops_type type,
 
 	/* FIXME: tm6000_extension_devlist_lock should be a spinlock */
 
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->fillbuf && ops->type == type)
-				ops->fillbuf(dev, buf, size);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->fillbuf && ops->type == type)
+			ops->fillbuf(dev, buf, size);
 	}
 
 	return 0;
@@ -898,11 +896,9 @@ void tm6000_init_extension(struct tm6000_core *dev)
 	struct tm6000_ops *ops = NULL;
 
 	mutex_lock(&tm6000_devlist_mutex);
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->init)
-				ops->init(dev);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->init)
+			ops->init(dev);
 	}
 	mutex_unlock(&tm6000_devlist_mutex);
 }
@@ -912,11 +908,9 @@ void tm6000_close_extension(struct tm6000_core *dev)
 	struct tm6000_ops *ops = NULL;
 
 	mutex_lock(&tm6000_devlist_mutex);
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->fini)
-				ops->fini(dev);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->fini)
+			ops->fini(dev);
 	}
 	mutex_unlock(&tm6000_devlist_mutex);
 }