[PATCH 2/2] gpiolib: cdev: export the consumer's PID

[Bartosz Golaszewski <brgl@xxxxxxxx>]

It's useful for user-space to be able to know the PIDs of processes
holding GPIO lines in case they have the permissions and need to kill
them.

Extend the gpio_v2_line_info structure with the consumer_pid field
that's set to the PID of the user-space process or 0 if the user lives
in the kernel.

Signed-off-by: Bartosz Golaszewski <brgl@xxxxxxxx>
---
 drivers/gpio/gpiolib-cdev.c |  2 ++
 drivers/gpio/gpiolib.c      | 24 +++++++++++++++++++-----
 drivers/gpio/gpiolib.h      |  2 ++
 include/uapi/linux/gpio.h   |  5 ++++-
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f8041d4898d1..9b6d518680dc 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2120,6 +2120,8 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 	if (desc->label)
 		strscpy(info->consumer, desc->label, sizeof(info->consumer));
 
+	info->consumer_pid = desc->pid;
+
 	/*
 	 * Userspace only need to know that the kernel is using this GPIO so
 	 * it can't use it.
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 6768734b9e15..0c9d1639b04d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -96,6 +96,11 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label)
 	d->label = label;
 }
 
+static inline void desc_set_pid(struct gpio_desc *d, pid_t pid)
+{
+	d->pid = pid;
+}
+
 /**
  * gpio_to_desc - Convert a GPIO number to its descriptor
  * @gpio: global GPIO number
@@ -1892,7 +1897,8 @@ EXPORT_SYMBOL_GPL(gpiochip_remove_pin_ranges);
  * on each other, and help provide better diagnostics in debugfs.
  * They're called even less than the "set direction" calls.
  */
-static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
+static int
+gpiod_request_commit(struct gpio_desc *desc, const char *label, pid_t pid)
 {
 	struct gpio_chip	*gc = desc->gdev->chip;
 	int			ret;
@@ -1913,6 +1919,7 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
 
 	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
 		desc_set_label(desc, label ? : "?");
+		desc_set_pid(desc, pid);
 	} else {
 		ret = -EBUSY;
 		goto out_free_unlock;
@@ -1987,7 +1994,8 @@ static int validate_desc(const struct gpio_desc *desc, const char *func)
 		return; \
 	} while (0)
 
-int gpiod_request(struct gpio_desc *desc, const char *label)
+static int
+gpiod_request_with_pid(struct gpio_desc *desc, const char *label, pid_t pid)
 {
 	int ret = -EPROBE_DEFER;
 	struct gpio_device *gdev;
@@ -1996,7 +2004,7 @@ int gpiod_request(struct gpio_desc *desc, const char *label)
 	gdev = desc->gdev;
 
 	if (try_module_get(gdev->owner)) {
-		ret = gpiod_request_commit(desc, label);
+		ret = gpiod_request_commit(desc, label, pid);
 		if (ret)
 			module_put(gdev->owner);
 		else
@@ -2009,11 +2017,16 @@ int gpiod_request(struct gpio_desc *desc, const char *label)
 	return ret;
 }
 
+int gpiod_request(struct gpio_desc *desc, const char *label)
+{
+	return gpiod_request_with_pid(desc, label, 0);
+}
+
 int gpiod_request_user(struct gpio_desc *desc, const char *label)
 {
 	int ret;
 
-	ret = gpiod_request(desc, label);
+	ret = gpiod_request_with_pid(desc, label, current->pid);
 	if (ret == -EPROBE_DEFER)
 		ret = -ENODEV;
 
@@ -2042,6 +2055,7 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
 		}
 		kfree_const(desc->label);
 		desc_set_label(desc, NULL);
+		desc_set_pid(desc, 0);
 		clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
 		clear_bit(FLAG_REQUESTED, &desc->flags);
 		clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
@@ -2140,7 +2154,7 @@ struct gpio_desc *gpiochip_request_own_desc(struct gpio_chip *gc,
 		return desc;
 	}
 
-	ret = gpiod_request_commit(desc, label);
+	ret = gpiod_request_commit(desc, label, 0);
 	if (ret < 0)
 		return ERR_PTR(ret);
 
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index b35deb08a7f5..d1535677e162 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -165,6 +165,8 @@ struct gpio_desc {
 
 	/* Connection label */
 	const char		*label;
+	/* Consumer's PID (if consumer is in user-space, otherwise 0) */
+	pid_t			pid;
 	/* Name of the GPIO */
 	const char		*name;
 #ifdef CONFIG_OF_DYNAMIC
diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
index cb9966d49a16..37f10021d1aa 100644
--- a/include/uapi/linux/gpio.h
+++ b/include/uapi/linux/gpio.h
@@ -219,6 +219,8 @@ struct gpio_v2_line_request {
  * gpio_v2_line_flag, such as %GPIO_V2_LINE_FLAG_ACTIVE_LOW,
  * %GPIO_V2_LINE_FLAG_OUTPUT etc, added together.
  * @attrs: the configuration attributes associated with the line
+ * @consumer_pid: process ID of the user-space consumer or 0 if the consumer
+ * lives in kernel space
  * @padding: reserved for future use
  */
 struct gpio_v2_line_info {
@@ -228,8 +230,9 @@ struct gpio_v2_line_info {
 	__u32 num_attrs;
 	__aligned_u64 flags;
 	struct gpio_v2_line_attribute attrs[GPIO_V2_LINE_NUM_ATTRS_MAX];
+	__s32 consumer_pid;
 	/* Space reserved for future use. */
-	__u32 padding[4];
+	__u32 padding[3];
 };
 
 /**
-- 
2.34.1