Date:   Thu, 6 Jun 2019 12:23:07 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Nick Crews <ncrews@...omium.org>, bleung@...omium.org
Cc:     linux-kernel@...r.kernel.org, dlaurie@...omium.org,
        djkurtz@...omium.org, dtor@...gle.com
Subject: Re: [PATCH v4] platform/chrome: wilco_ec: Add event handling



On 24/5/19 1:06, Nick Crews wrote:
> The Wilco Embedded Controller can create custom events that
> are not handled as standard ACPI objects. These events can
> contain information about changes in EC controlled features,
> such as errors and events in the dock or display. For example,
> an event is triggered if the dock is plugged into a display
> incorrectly. These events are needed for telemetry and
> diagnostics reasons, and for possibly alerting the user.
> 
> These events are triggered by the EC with an ACPI Notify(0x90),
> and then the BIOS reads the event buffer from EC RAM via an
> ACPI method. When the OS receives these events via ACPI,
> it passes them along to this driver. The events are put into
> a queue which can be read by a userspace daemon via a char device
> that implements read() and poll(). The event queue acts as a
> circular buffer of size 64, so if there are no userspace consumers
> the kernel will not run out of memory. The char device will appear at
> /dev/wilco_event{n}, where n is some small non-negative integer,
> starting from 0. Standard ACPI events such as the battery getting
> plugged/unplugged can also come through this path, but they are
> dealt with via other paths, and are ignored here.
> 
> To test, you can tail the binary data with
> $ cat /dev/wilco_event0 | hexdump -ve '1/1 "%x\n"'
> and then create an event by plugging/unplugging the battery.
> 
> Signed-off-by: Nick Crews <ncrews@...omium.org>

applied for 5.3

Thanks,
 Enric


> ---
> v4 changes:
> - Added size limit to queue to kernel would not run out of
>   memory if there were no userspace consumers
> - Change pr_warn() to pr_err() in module_init()
> - Fix two print format specifiers
> - A couple renaming tweaks
> - Removed "v2" from MODULE_LICENSE
> v3 changes:
> - Made commit description more accurate and useful.
> - Added an exclusive lock for opening the char device,
>   so only one userspace process can read events at a time.
> 
>  drivers/platform/chrome/wilco_ec/Kconfig  |   9 +
>  drivers/platform/chrome/wilco_ec/Makefile |   2 +
>  drivers/platform/chrome/wilco_ec/event.c  | 541 ++++++++++++++++++++++
>  3 files changed, 552 insertions(+)
>  create mode 100644 drivers/platform/chrome/wilco_ec/event.c
> 
> diff --git a/drivers/platform/chrome/wilco_ec/Kconfig b/drivers/platform/chrome/wilco_ec/Kconfig
> index e09e4cebe9b4..2c8f6f15f28f 100644
> --- a/drivers/platform/chrome/wilco_ec/Kconfig
> +++ b/drivers/platform/chrome/wilco_ec/Kconfig
> @@ -18,3 +18,12 @@ config WILCO_EC_DEBUGFS
>  	  manipulation and allow for testing arbitrary commands.  This
>  	  interface is intended for debug only and will not be present
>  	  on production devices.
> +
> +config WILCO_EC_EVENTS
> +	tristate "Enable event forwarding from EC to userspace"
> +	depends on WILCO_EC
> +	help
> +	  If you say Y here, you get support for the EC to send events
> +	  (such as power state changes) to userspace. The EC sends the events
> +	  over ACPI, and a driver queues up the events to be read by a
> +	  userspace daemon from /dev/wilco_event using read() and poll().
> diff --git a/drivers/platform/chrome/wilco_ec/Makefile b/drivers/platform/chrome/wilco_ec/Makefile
> index 72df9b5e1983..4d8a5f068f8b 100644
> --- a/drivers/platform/chrome/wilco_ec/Makefile
> +++ b/drivers/platform/chrome/wilco_ec/Makefile
> @@ -4,3 +4,5 @@ wilco_ec-objs				:= core.o mailbox.o properties.o sysfs.o
>  obj-$(CONFIG_WILCO_EC)			+= wilco_ec.o
>  wilco_ec_debugfs-objs			:= debugfs.o
>  obj-$(CONFIG_WILCO_EC_DEBUGFS)		+= wilco_ec_debugfs.o
> +wilco_ec_events-objs			:= event.o
> +obj-$(CONFIG_WILCO_EC_EVENTS)		+= wilco_ec_events.o
> diff --git a/drivers/platform/chrome/wilco_ec/event.c b/drivers/platform/chrome/wilco_ec/event.c
> new file mode 100644
> index 000000000000..4d2776f77dbd
> --- /dev/null
> +++ b/drivers/platform/chrome/wilco_ec/event.c
> @@ -0,0 +1,541 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ACPI event handling for Wilco Embedded Controller
> + *
> + * Copyright 2019 Google LLC
> + *
> + * The Wilco Embedded Controller can create custom events that
> + * are not handled as standard ACPI objects. These events can
> + * contain information about changes in EC controlled features,
> + * such as errors and events in the dock or display. For example,
> + * an event is triggered if the dock is plugged into a display
> + * incorrectly. These events are needed for telemetry and
> + * diagnostics reasons, and for possibly alerting the user.
> +
> + * These events are triggered by the EC with an ACPI Notify(0x90),
> + * and then the BIOS reads the event buffer from EC RAM via an
> + * ACPI method. When the OS receives these events via ACPI,
> + * it passes them along to this driver. The events are put into
> + * a queue which can be read by a userspace daemon via a char device
> + * that implements read() and poll(). The event queue acts as a
> + * circular buffer of size 64, so if there are no userspace consumers
> + * the kernel will not run out of memory. The char device will appear at
> + * /dev/wilco_event{n}, where n is some small non-negative integer,
> + * starting from 0. Standard ACPI events such as the battery getting
> + * plugged/unplugged can also come through this path, but they are
> + * dealt with via other paths, and are ignored here.
> +
> + * To test, you can tail the binary data with
> + * $ cat /dev/wilco_event0 | hexdump -ve '1/1 "%x\n"'
> + * and then create an event by plugging/unplugging the battery.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/cdev.h>
> +#include <linux/device.h>
> +#include <linux/fs.h>
> +#include <linux/idr.h>
> +#include <linux/io.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/poll.h>
> +#include <linux/uaccess.h>
> +#include <linux/wait.h>
> +
> +/* ACPI Notify event code indicating event data is available. */
> +#define EC_ACPI_NOTIFY_EVENT		0x90
> +/* ACPI Method to execute to retrieve event data buffer from the EC. */
> +#define EC_ACPI_GET_EVENT		"QSET"
> +/* Maximum number of words in event data returned by the EC. */
> +#define EC_ACPI_MAX_EVENT_WORDS		6
> +#define EC_ACPI_MAX_EVENT_SIZE \
> +	(sizeof(struct ec_event) + (EC_ACPI_MAX_EVENT_WORDS) * sizeof(u16))
> +
> +/* Node will appear in /dev/EVENT_DEV_NAME */
> +#define EVENT_DEV_NAME		"wilco_event"
> +#define EVENT_CLASS_NAME	EVENT_DEV_NAME
> +#define DRV_NAME		EVENT_DEV_NAME
> +#define EVENT_DEV_NAME_FMT	(EVENT_DEV_NAME "%d")
> +static struct class event_class = {
> +	.owner	= THIS_MODULE,
> +	.name	= EVENT_CLASS_NAME,
> +};
> +
> +/* Keep track of all the device numbers used. */
> +#define EVENT_MAX_DEV 128
> +static int event_major;
> +static DEFINE_IDA(event_ida);
> +
> +/* Size of circular queue of events. */
> +#define MAX_NUM_EVENTS 64
> +
> +/**
> + * struct event_device_data - Data for a Wilco EC device that responds to ACPI.
> + * @events: Circular queue of EC events to be provided to userspace.
> + * @num_events: Number of events in the queue.
> + * @lock: Mutex to guard the queue.
> + * @wq: Wait queue to notify processes when events or available or the
> + *	device has been removed.
> + * @cdev: Char dev that userspace reads() and polls() from.
> + * @dev: Device associated with the %cdev.
> + * @exist: Has the device been not been removed? Once a device has been removed,
> + *	   writes, reads, and new opens will fail.
> + * @available: Guarantee only one client can open() file and read from queue.
> + *
> + * There will be one of these structs for each ACPI device registered. This data
> + * is the queue of events received from ACPI that still need to be read from
> + * userspace (plus a supporting lock and wait queue), as well as the device and
> + * char device that userspace is using, plus a flag on whether the ACPI device
> + * has been removed.
> + */
> +struct event_device_data {
> +	struct list_head events;
> +	size_t num_events;
> +	struct mutex lock;
> +	wait_queue_head_t wq;
> +	struct device dev;
> +	struct cdev cdev;
> +	bool exist;
> +	atomic_t available;
> +};
> +
> +/**
> + * struct ec_event - Extended event returned by the EC.
> + * @size: Number of words in structure after the size word.
> + * @type: Extended event type from &enum ec_event_type.
> + * @event: Event data words.  Max count is %EC_ACPI_MAX_EVENT_WORDS.
> + */
> +struct ec_event {
> +	u16 size;
> +	u16 type;
> +	u16 event[0];
> +} __packed;
> +
> +/**
> + * struct ec_event_entry - Event queue entry.
> + * @list: List node.
> + * @size: Number of bytes in event structure.
> + * @event: Extended event returned by the EC.  This should be the last
> + *         element because &struct ec_event includes a zero length array.
> + */
> +struct ec_event_entry {
> +	struct list_head list;
> +	size_t size;
> +	struct ec_event event;
> +};
> +
> +/**
> + * enqueue_events() - Place EC events in queue to be read by userspace.
> + * @adev: Device the events came from.
> + * @buf: Buffer of event data.
> + * @length: Length of event data buffer.
> + *
> + * %buf contains a number of ec_event's, packed one after the other.
> + * Each ec_event is of variable length. Start with the first event, copy it
> + * into a containing ev_event_entry, store that entry in a list, move on
> + * to the next ec_event in buf, and repeat.
> + *
> + * Return: 0 on success or negative error code on failure.
> + */
> +static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
> +{
> +	struct event_device_data *dev_data = adev->driver_data;
> +	struct ec_event *event;
> +	struct ec_event_entry *entry, *oldest_entry;
> +	size_t event_size, num_words, word_size;
> +	u32 offset = 0;
> +
> +	while (offset < length) {
> +		event = (struct ec_event *)(buf + offset);
> +		if (!event)
> +			return -EINVAL;
> +
> +		/* Number of 16bit event data words is size - 1 */
> +		num_words = event->size - 1;
> +		word_size = num_words * sizeof(u16);
> +		event_size = sizeof(*event) + word_size;
> +		if (num_words > EC_ACPI_MAX_EVENT_WORDS) {
> +			dev_err(&adev->dev, "Too many event words: %zu > %d\n",
> +				num_words, EC_ACPI_MAX_EVENT_WORDS);
> +			return -EOVERFLOW;
> +		};
> +
> +		/* Ensure event does not overflow the available buffer */
> +		if ((offset + event_size) > length) {
> +			dev_err(&adev->dev, "Event exceeds buffer: %zu > %d\n",
> +				offset + event_size, length);
> +			return -EOVERFLOW;
> +		}
> +
> +		/* Point to the next event in the buffer */
> +		offset += event_size;
> +
> +		/* Create event entry for the queue */
> +		entry = kzalloc(sizeof(struct ec_event_entry) + word_size,
> +				GFP_KERNEL);
> +		if (!entry)
> +			return -ENOMEM;
> +		entry->size = event_size;
> +		memcpy(&entry->event, event, entry->size);
> +
> +		mutex_lock(&dev_data->lock);
> +
> +		/* If the queue is full, delete the oldest event */
> +		if (dev_data->num_events >= MAX_NUM_EVENTS) {
> +			oldest_entry = list_first_entry(&dev_data->events,
> +						      struct ec_event_entry,
> +						      list);
> +			list_del(&oldest_entry->list);
> +			kfree(oldest_entry);
> +			dev_data->num_events--;
> +		}
> +
> +		/* Add this event to the queue */
> +		list_add_tail(&entry->list, &dev_data->events);
> +		dev_data->num_events++;
> +
> +		mutex_unlock(&dev_data->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * event_device_notify() - Callback when EC generates an event over ACPI.
> + * @adev: The device that the event is coming from.
> + * @value: Value passed to Notify() in ACPI.
> + *
> + * This function will read the events from the device and enqueue them.
> + */
> +static void event_device_notify(struct acpi_device *adev, u32 value)
> +{
> +	struct acpi_buffer event_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> +	struct event_device_data *dev_data = adev->driver_data;
> +	union acpi_object *obj;
> +	acpi_status status;
> +
> +	if (value != EC_ACPI_NOTIFY_EVENT) {
> +		dev_err(&adev->dev, "Invalid event: 0x%08x\n", value);
> +		return;
> +	}
> +
> +	/* Execute ACPI method to get event data buffer. */
> +	status = acpi_evaluate_object(adev->handle, EC_ACPI_GET_EVENT,
> +				      NULL, &event_buffer);
> +	if (ACPI_FAILURE(status)) {
> +		dev_err(&adev->dev, "Error executing ACPI method %s()\n",
> +			EC_ACPI_GET_EVENT);
> +		return;
> +	}
> +
> +	obj = (union acpi_object *)event_buffer.pointer;
> +	if (!obj) {
> +		dev_err(&adev->dev, "Nothing returned from %s()\n",
> +			EC_ACPI_GET_EVENT);
> +		return;
> +	}
> +	if (obj->type != ACPI_TYPE_BUFFER) {
> +		dev_err(&adev->dev, "Invalid object returned from %s()\n",
> +			EC_ACPI_GET_EVENT);
> +		kfree(obj);
> +		return;
> +	}
> +	if (obj->buffer.length < sizeof(struct ec_event)) {
> +		dev_err(&adev->dev, "Invalid buffer length %d from %s()\n",
> +			obj->buffer.length, EC_ACPI_GET_EVENT);
> +		kfree(obj);
> +		return;
> +	}
> +
> +	enqueue_events(adev, obj->buffer.pointer, obj->buffer.length);
> +	kfree(obj);
> +
> +	if (dev_data->num_events)
> +		wake_up_interruptible(&dev_data->wq);
> +}
> +
> +static int event_open(struct inode *inode, struct file *filp)
> +{
> +	struct event_device_data *dev_data;
> +
> +	dev_data = container_of(inode->i_cdev, struct event_device_data, cdev);
> +	if (!dev_data->exist)
> +		return -ENODEV;
> +
> +	if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
> +		return -EBUSY;
> +
> +	/* Increase refcount on device so dev_data is not freed */
> +	get_device(&dev_data->dev);
> +	nonseekable_open(inode, filp);
> +	filp->private_data = dev_data;
> +
> +	return 0;
> +}
> +
> +static __poll_t event_poll(struct file *filp, poll_table *wait)
> +{
> +	struct event_device_data *dev_data = filp->private_data;
> +	__poll_t mask = 0;
> +
> +	poll_wait(filp, &dev_data->wq, wait);
> +	if (!dev_data->exist)
> +		return EPOLLHUP;
> +	if (dev_data->num_events)
> +		mask |= EPOLLIN | EPOLLRDNORM | EPOLLPRI;
> +	return mask;
> +}
> +
> +/**
> + * event_read() - Callback for passing event data to userspace via read().
> + * @filp: The file we are reading from.
> + * @buf: Pointer to userspace buffer to fill with one event.
> + * @count: Number of bytes requested. Must be at least EC_ACPI_MAX_EVENT_SIZE.
> + * @pos: File position pointer, irrelevant since we don't support seeking.
> + *
> + * Fills the passed buffer with the data from the first event in the queue,
> + * removes that event from the queue. On error, the event remains in the queue.
> + *
> + * If there are no events in the the queue, then one of two things happens,
> + * depending on if the file was opened in nonblocking mode: If in nonblocking
> + * mode, then return -EAGAIN to say there's no data. If in blocking mode, then
> + * block until an event is available.
> + *
> + * Return: Number of bytes placed in buffer, negative error code on failure.
> + */
> +static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
> +			  loff_t *pos)
> +{
> +	struct event_device_data *dev_data = filp->private_data;
> +	struct ec_event_entry *entry;
> +	ssize_t n_bytes_written = 0;
> +	int err;
> +
> +	/* We only will give them the entire event at once */
> +	if (count != 0 && count < EC_ACPI_MAX_EVENT_SIZE)
> +		return -EINVAL;
> +
> +	mutex_lock(&dev_data->lock);
> +
> +	while (dev_data->num_events == 0) {
> +		if (filp->f_flags & O_NONBLOCK) {
> +			mutex_unlock(&dev_data->lock);
> +			return -EAGAIN;
> +		}
> +		/* Need to unlock so that data can actually get added to the
> +		 * queue, and since we recheck before use and it's just
> +		 * comparing pointers, this is safe unlocked.
> +		 */
> +		mutex_unlock(&dev_data->lock);
> +		err = wait_event_interruptible(dev_data->wq,
> +					       dev_data->num_events);
> +		if (err)
> +			return err;
> +
> +		/* Device was removed as we waited? */
> +		if (!dev_data->exist)
> +			return -ENODEV;
> +		mutex_lock(&dev_data->lock);
> +	}
> +
> +	entry = list_first_entry(&dev_data->events,
> +				 struct ec_event_entry, list);
> +	n_bytes_written = entry->size;
> +	if (copy_to_user(buf, &entry->event, n_bytes_written))
> +		return -EFAULT;
> +	list_del(&entry->list);
> +	kfree(entry);
> +	dev_data->num_events--;
> +
> +	mutex_unlock(&dev_data->lock);
> +
> +	return n_bytes_written;
> +}
> +
> +static int event_release(struct inode *inode, struct file *filp)
> +{
> +	struct event_device_data *dev_data = filp->private_data;
> +
> +	atomic_set(&dev_data->available, 1);
> +	put_device(&dev_data->dev);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations event_fops = {
> +	.open = event_open,
> +	.poll  = event_poll,
> +	.read = event_read,
> +	.release = event_release,
> +	.llseek = no_llseek,
> +	.owner = THIS_MODULE,
> +};
> +
> +/**
> + * free_device_data() - Callback to free the event_device_data structure.
> + * @d: The device embedded in our device data, which we have been ref counting.
> + *
> + * This is called only after event_device_remove() has been called and all
> + * userspace programs have called event_release() on all the open file
> + * descriptors.
> + */
> +static void free_device_data(struct device *d)
> +{
> +	struct event_device_data *dev_data;
> +
> +	dev_data = container_of(d, struct event_device_data, dev);
> +	kfree(dev_data);
> +}
> +
> +static void hangup_device(struct event_device_data *dev_data)
> +{
> +	mutex_lock(&dev_data->lock);
> +	dev_data->exist = false;
> +	mutex_unlock(&dev_data->lock);
> +
> +	/* Wake up the waiting processes so they can close. */
> +	wake_up_interruptible(&dev_data->wq);
> +	put_device(&dev_data->dev);
> +}
> +
> +/**
> + * event_device_add() - Callback when creating a new device.
> + * @adev: ACPI device that we will be receiving events from.
> + *
> + * This finds a free minor number for the device, allocates and initializes
> + * some device data, and creates a new device and char dev node.
> + *
> + * The device data is freed in free_device_data(), which is called when
> + * %dev_data->dev is release()ed. This happens after all references to
> + * %dev_data->dev are dropped, which happens once both event_device_remove()
> + * has been called and every open()ed file descriptor has been release()ed.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +static int event_device_add(struct acpi_device *adev)
> +{
> +	struct event_device_data *dev_data;
> +	int error, minor;
> +
> +	minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
> +	if (minor < 0) {
> +		error = minor;
> +		dev_err(&adev->dev, "Failed to find minor number: %d", error);
> +		return error;
> +	}
> +
> +	dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
> +	if (!dev_data) {
> +		error = -ENOMEM;
> +		goto free_minor;
> +	}
> +
> +	/* Initialize the device data. */
> +	adev->driver_data = dev_data;
> +	INIT_LIST_HEAD(&dev_data->events);
> +	mutex_init(&dev_data->lock);
> +	init_waitqueue_head(&dev_data->wq);
> +	dev_data->exist = true;
> +	atomic_set(&dev_data->available, 1);
> +
> +	/* Initialize the device. */
> +	dev_data->dev.devt = MKDEV(event_major, minor);
> +	dev_data->dev.class = &event_class;
> +	dev_data->dev.release = free_device_data;
> +	dev_set_name(&dev_data->dev, EVENT_DEV_NAME_FMT, minor);
> +	device_initialize(&dev_data->dev);
> +
> +	/* Initialize the character device, and add it to userspace. */
> +	cdev_init(&dev_data->cdev, &event_fops);
> +	error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
> +	if (error)
> +		goto free_dev_data;
> +
> +	return 0;
> +
> +free_dev_data:
> +	hangup_device(dev_data);
> +free_minor:
> +	ida_simple_remove(&event_ida, minor);
> +	return error;
> +}
> +
> +static int event_device_remove(struct acpi_device *adev)
> +{
> +	struct event_device_data *dev_data = adev->driver_data;
> +
> +	cdev_device_del(&dev_data->cdev, &dev_data->dev);
> +	ida_simple_remove(&event_ida, MINOR(dev_data->dev.devt));
> +	hangup_device(dev_data);
> +
> +	return 0;
> +}
> +
> +static const struct acpi_device_id event_acpi_ids[] = {
> +	{ "GOOG000D", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(acpi, event_acpi_ids);
> +
> +static struct acpi_driver event_driver = {
> +	.name = DRV_NAME,
> +	.class = DRV_NAME,
> +	.ids = event_acpi_ids,
> +	.ops = {
> +		.add = event_device_add,
> +		.notify = event_device_notify,
> +		.remove = event_device_remove,
> +	},
> +	.owner = THIS_MODULE,
> +};
> +
> +static int __init event_module_init(void)
> +{
> +	dev_t dev_num = 0;
> +	int ret;
> +
> +	ret = class_register(&event_class);
> +	if (ret) {
> +		pr_err(DRV_NAME ": Failed registering class: %d", ret);
> +		return ret;
> +	}
> +
> +	/* Request device numbers, starting with minor=0. Save the major num. */
> +	ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
> +	if (ret) {
> +		pr_err(DRV_NAME ": Failed allocating dev numbers: %d", ret);
> +		goto destroy_class;
> +	}
> +	event_major = MAJOR(dev_num);
> +
> +	ret = acpi_bus_register_driver(&event_driver);
> +	if (ret < 0) {
> +		pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
> +		goto unregister_region;
> +	}
> +
> +	return 0;
> +
> +unregister_region:
> +	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
> +destroy_class:
> +	class_unregister(&event_class);
> +	ida_destroy(&event_ida);
> +	return ret;
> +}
> +
> +static void __exit event_module_exit(void)
> +{
> +	acpi_bus_unregister_driver(&event_driver);
> +	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
> +	class_unregister(&event_class);
> +	ida_destroy(&event_ida);
> +}
> +
> +module_init(event_module_init);
> +module_exit(event_module_exit);
> +
> +MODULE_AUTHOR("Nick Crews <ncrews@...omium.org>");
> +MODULE_DESCRIPTION("Wilco EC ACPI event driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:" DRV_NAME);
> 

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