[PATCH 1/2] cdev: simplify loop in cdev_by_device_node

[PATCH 1/2] cdev: simplify loop in cdev_by_device_node

[Ahmad Fatoum]

We don't need to compare the cdev's device node pointer both against NULL
and against the searched for device node on each iteration.

Instead, it's sufficient to just compare the device nodes directly.
To maintain previous behavior, when searching for a NULL device node, we
shouldn't return the first cdev, but return NULL. Do that via an early
exit instead of doing it after iterating over all cdevs.

No functional change.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 fs/devfs-core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index 244f76f62c52..c79b092a112e 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -87,9 +87,10 @@ struct cdev *cdev_by_device_node(struct device_node *node)
 {
 	struct cdev *cdev;
 
+	if (!node)
+		return NULL;
+
 	for_each_cdev(cdev) {
-		if (!cdev->device_node)
-			continue;
 		if (cdev->device_node == node)
 			return cdev_readlink(cdev);
 	}
-- 
2.39.2

[PATCH 2/2] cdev: add cdev_alloc helper for creating cdevs

[Ahmad Fatoum]

We have different helpers for creating cdevs, depending on whether they
are loop devices, partitions or links.

Create a common cdev_alloc function, so it's easier to instrument cdev
creation during debugging.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 fs/devfs-core.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index c79b092a112e..9f5b41761f52 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -324,6 +324,16 @@ int cdev_truncate(struct cdev *cdev, size_t size)
 	return -EPERM;
 }
 
+static struct cdev *cdev_alloc(const char *name)
+{
+	struct cdev *new;
+
+	new = xzalloc(sizeof(*new));
+	new->name = xstrdup(name);
+
+	return new;
+}
+
 int devfs_create(struct cdev *new)
 {
 	struct cdev *cdev;
@@ -358,8 +368,7 @@ int devfs_create_link(struct cdev *cdev, const char *name)
 	 */
 	cdev = cdev_readlink(cdev);
 
-	new = xzalloc(sizeof(*new));
-	new->name = xstrdup(name);
+	new = cdev_alloc(name);
 	new->link = cdev;
 
 	if (cdev->partname) {
@@ -540,8 +549,7 @@ struct cdev *cdevfs_add_partition(struct cdev *cdev,
 		return &mtd->cdev;
 	}
 
-	new = xzalloc(sizeof(*new));
-	new->name = strdup(partinfo->name);
+	new = cdev_alloc(partinfo->name);
 	if (!strncmp(cdev->name, partinfo->name, strlen(cdev->name)))
 		new->partname = xstrdup(partinfo->name + strlen(cdev->name) + 1);
 
@@ -679,6 +687,7 @@ static const struct cdev_operations loop_ops = {
 
 struct cdev *cdev_create_loop(const char *path, ulong flags, loff_t offset)
 {
+	char str[16];
 	struct cdev *new;
 	struct loop_priv *priv;
 	static int loopno;
@@ -692,10 +701,10 @@ struct cdev *cdev_create_loop(const char *path, ulong flags, loff_t offset)
 		return NULL;
 	}
 
-	new = xzalloc(sizeof(*new));
+	snprintf(str, sizeof(str), "loop%u", loopno++);
 
+	new = cdev_alloc(str);
 	new->ops = &loop_ops;
-	new->name = basprintf("loop%u", loopno++);
 	new->priv = priv;
 
 	ofs = lseek(priv->fd, 0, SEEK_END);
-- 
2.39.2

Re: [PATCH 1/2] cdev: simplify loop in cdev_by_device_node

[Sascha Hauer]

On Wed, Jan 03, 2024 at 11:20:34AM +0100, Ahmad Fatoum wrote:
> We don't need to compare the cdev's device node pointer both against NULL
> and against the searched for device node on each iteration.
> 
> Instead, it's sufficient to just compare the device nodes directly.
> To maintain previous behavior, when searching for a NULL device node, we
> shouldn't return the first cdev, but return NULL. Do that via an early
> exit instead of doing it after iterating over all cdevs.
> 
> No functional change.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  fs/devfs-core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/fs/devfs-core.c b/fs/devfs-core.c
> index 244f76f62c52..c79b092a112e 100644
> --- a/fs/devfs-core.c
> +++ b/fs/devfs-core.c
> @@ -87,9 +87,10 @@ struct cdev *cdev_by_device_node(struct device_node *node)
>  {
>  	struct cdev *cdev;
>  
> +	if (!node)
> +		return NULL;
> +
>  	for_each_cdev(cdev) {
> -		if (!cdev->device_node)
> -			continue;
>  		if (cdev->device_node == node)
>  			return cdev_readlink(cdev);
>  	}
> -- 
> 2.39.2
> 
> 
> 

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