[PATCH v2] gpiolib: Refactor gpio_export

[PATCH v2] gpiolib: Refactor gpio_export

[Ryan Mallon]

The gpio_export function uses nested if statements and the status
variable to handle the failure cases. This makes the function logic
difficult to follow. Refactor the code to abort immediately on failure
using goto. This makes the code slightly longer, but significantly
reduces the nesting and number of split lines and makes the code easier
to read.

Signed-off-by: Ryan Mallon
---

Changes since v1:

 - Return immediately if no unwinding needed
 - Added pr_debug to immediate returns
 - Changed unavailable (!requested || exported) to -EPERM

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 5d6c71e..d5f9742 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -702,8 +702,9 @@ int gpio_export(unsigned gpio, bool direction_may_change)
 {
 	unsigned long		flags;
 	struct gpio_desc	*desc;
-	int			status = -EINVAL;
+	int			status;
 	const char		*ioname = NULL;
+	struct device		*dev;
 
 	/* can't export until sysfs is available ... */
 	if (!gpio_class.p) {
@@ -711,59 +712,65 @@ int gpio_export(unsigned gpio, bool direction_may_change)
 		return -ENOENT;
 	}
 
-	if (!gpio_is_valid(gpio))
-		goto done;
+	if (!gpio_is_valid(gpio)) {
+		pr_debug("%s: gpio %d is not valid\n", __func__, gpio);
+		return -EINVAL;
+	}
 
 	mutex_lock(&sysfs_lock);
 
 	spin_lock_irqsave(&gpio_lock, flags);
 	desc = &gpio_desc[gpio];
-	if (test_bit(FLAG_REQUESTED, &desc->flags)
-			&& !test_bit(FLAG_EXPORT, &desc->flags)) {
-		status = 0;
-		if (!desc->chip->direction_input
-				|| !desc->chip->direction_output)
-			direction_may_change = false;
+	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
+	     test_bit(FLAG_EXPORT, &desc->flags)) {
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		pr_debug("%s: gpio %d unavailable (requested=%d, exported=%d)\n",
+				__func__, gpio,
+				test_bit(FLAG_REQUESTED, &desc->flags),
+				test_bit(FLAG_EXPORT, &desc->flags));
+		return -EPERM;
 	}
+
+	if (!desc->chip->direction_input || !desc->chip->direction_output)
+		direction_may_change = false;
 	spin_unlock_irqrestore(&gpio_lock, flags);
 
 	if (desc->chip->names && desc->chip->names[gpio - desc->chip->base])
 		ioname = desc->chip->names[gpio - desc->chip->base];
 
-	if (status == 0) {
-		struct device	*dev;
-
-		dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
-				desc, ioname ? ioname : "gpio%u", gpio);
-		if (!IS_ERR(dev)) {
-			status = sysfs_create_group(&dev->kobj,
-						&gpio_attr_group);
-
-			if (!status && direction_may_change)
-				status = device_create_file(dev,
-						&dev_attr_direction);
-
-			if (!status && gpio_to_irq(gpio) >= 0
-					&& (direction_may_change
-						|| !test_bit(FLAG_IS_OUT,
-							&desc->flags)))
-				status = device_create_file(dev,
-						&dev_attr_edge);
-
-			if (status != 0)
-				device_unregister(dev);
-		} else
-			status = PTR_ERR(dev);
-		if (status == 0)
-			set_bit(FLAG_EXPORT, &desc->flags);
+	dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
+			    desc, ioname ? ioname : "gpio%u", gpio);
+	if (IS_ERR(dev)) {
+		status = PTR_ERR(dev);
+		goto fail_unlock;
 	}
 
-	mutex_unlock(&sysfs_lock);
-
-done:
+	status = sysfs_create_group(&dev->kobj, &gpio_attr_group);
 	if (status)
-		pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
+		goto fail_unregister_device;
+
+	if (direction_may_change) {
+		status = device_create_file(dev, &dev_attr_direction);
+		if (status)
+			goto fail_unregister_device;
+	}
 
+	if (gpio_to_irq(gpio) >= 0 && (direction_may_change ||
+				       !test_bit(FLAG_IS_OUT, &desc->flags))) {
+		status = device_create_file(dev, &dev_attr_edge);
+		if (status)
+			goto fail_unregister_device;
+	}
+
+	set_bit(FLAG_EXPORT, &desc->flags);
+	mutex_unlock(&sysfs_lock);
+	return 0;
+
+fail_unregister_device:
+	device_unregister(dev);
+fail_unlock:
+	mutex_unlock(&sysfs_lock);
+	pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
 	return status;
 }
 EXPORT_SYMBOL_GPL(gpio_export);

Re: [PATCH v2] gpiolib: Refactor gpio_export

[Linus Walleij]

On Mon, Oct 22, 2012 at 2:39 AM, Ryan Mallon <rmallon@gmail.com> wrote:

> The gpio_export function uses nested if statements and the status
> variable to handle the failure cases. This makes the function logic
> difficult to follow. Refactor the code to abort immediately on failure
> using goto. This makes the code slightly longer, but significantly
> reduces the nesting and number of split lines and makes the code easier
> to read.

Splendid, patch applied!

> Signed-off-by: Ryan Mallon

Interesting that you sign off without an email address, I just added it
thinking it was a mistake.

Yours,
Linus Walleij

Re: [PATCH v2] gpiolib: Refactor gpio_export

[Ryan Mallon]

On 23/10/12 09:13, Linus Walleij wrote:
> On Mon, Oct 22, 2012 at 2:39 AM, Ryan Mallon <rmallon@gmail.com> wrote:
> 
>> The gpio_export function uses nested if statements and the status
>> variable to handle the failure cases. This makes the function logic
>> difficult to follow. Refactor the code to abort immediately on failure
>> using goto. This makes the code slightly longer, but significantly
>> reduces the nesting and number of split lines and makes the code easier
>> to read.
> 
> Splendid, patch applied!

Thanks.

>> Signed-off-by: Ryan Mallon
> 
> Interesting that you sign off without an email address, I just added it
> thinking it was a mistake.

Whoops. Yeah, should be:

  Signed-off-by: Ryan Mallon <rmallon@gmail.com>

Thanks,
~Ryan