Re: [RFC][PATCH 6/6] staging: android: ion: Introduce new ioctls for dynamic heaps

[Liviu Dudau <Liviu.Dudau@arm.com>]

On Mon, Jun 06, 2016 at 11:23:33AM -0700, Laura Abbott wrote:
> From: Laura Abbott <labbott@fedoraproject.org>
> 
> 
> The Ion ABI for heaps is limiting to work with for more complex systems.
> Heaps have to be registered at boot time with known ids available to
> userspace. This becomes a tight ABI which is prone to breakage.
> 
> Introduce a new mechanism for registering heap ids dynamically. A base
> set of heap ids are registered at boot time but there is no knowledge
> of fallbacks. Fallback information can be remapped and changed
> dynamically. Information about available heaps can also be queried with
> an ioctl to avoid the need to have heap ids be an ABI with userspace.
> 
> Signed-off-by: Laura Abbott <labbott@redhat.com>
> ---
>  drivers/staging/android/ion/ion-ioctl.c | 109 +++++++++++++++++--
>  drivers/staging/android/ion/ion.c       | 184 ++++++++++++++++++++++++++++++--
>  drivers/staging/android/ion/ion_priv.h  |  15 +++
>  drivers/staging/android/uapi/ion.h      | 135 +++++++++++++++++++++++
>  4 files changed, 426 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/staging/android/ion/ion-ioctl.c b/drivers/staging/android/ion/ion-ioctl.c
> index 45b89e8..169cad8 100644
> --- a/drivers/staging/android/ion/ion-ioctl.c
> +++ b/drivers/staging/android/ion/ion-ioctl.c
> @@ -22,6 +22,49 @@
>  #include "ion_priv.h"
>  #include "compat_ion.h"
>  
> +union ion_ioctl_arg {
> +	struct ion_fd_data fd;
> +	struct ion_allocation_data allocation;
> +	struct ion_handle_data handle;
> +	struct ion_custom_data custom;
> +	struct ion_abi_version abi_version;
> +	struct ion_new_alloc_data allocation2;
> +	struct ion_usage_id_map id_map;
> +	struct ion_usage_cnt usage_cnt;
> +	struct ion_heap_query query;
> +};
> +
> +static int validate_ioctl_arg(unsigned int cmd, union ion_ioctl_arg *arg)
> +{
> +	int ret = 0;
> +
> +	switch (cmd) {
> +	case ION_IOC_ABI_VERSION:
> +		ret =  arg->abi_version.reserved != 0;
> +		break;
> +	case ION_IOC_ALLOC2:
> +		ret = arg->allocation2.reserved0 != 0;
> +		ret |= arg->allocation2.reserved1 != 0;
> +		ret |= arg->allocation2.reserved2 != 0;
> +		break;
> +	case ION_IOC_ID_MAP:
> +		ret = arg->id_map.reserved0 != 0;
> +		ret |= arg->id_map.reserved1 != 0;
> +		break;
> +	case ION_IOC_USAGE_CNT:
> +		ret = arg->usage_cnt.reserved != 0;
> +		break;
> +	case ION_IOC_HEAP_QUERY:
> +		ret = arg->query.reserved0 != 0;
> +		ret |= arg->query.reserved1 != 0;
> +		ret |= arg->query.reserved2 != 0;
> +		break;
> +	default:
> +		break;
> +	}
> +	return ret ? -EINVAL : 0;
> +}
> +
>  /* fix up the cases where the ioctl direction bits are incorrect */
>  static unsigned int ion_ioctl_dir(unsigned int cmd)
>  {
> @@ -42,14 +85,7 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  	struct ion_handle *cleanup_handle = NULL;
>  	int ret = 0;
>  	unsigned int dir;
> -
> -	union {
> -		struct ion_fd_data fd;
> -		struct ion_allocation_data allocation;
> -		struct ion_handle_data handle;
> -		struct ion_custom_data custom;
> -		struct ion_abi_version abi_version;
> -	} data;
> +	union ion_ioctl_arg data;
>  
>  	dir = ion_ioctl_dir(cmd);
>  
> @@ -60,7 +96,12 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		if (copy_from_user(&data, (void __user *)arg, _IOC_SIZE(cmd)))
>  			return -EFAULT;
>  
> +	ret = validate_ioctl_arg(cmd, &data);
> +	if (ret)
> +		return ret;
> +
>  	switch (cmd) {
> +	/* Old ioctl */

I can see the value of this comment, given ION_IOC_ALLOC2, but not for the other cases.

>  	case ION_IOC_ALLOC:
>  	{
>  		struct ion_handle *handle;
> @@ -77,6 +118,7 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		cleanup_handle = handle;
>  		break;
>  	}
> +	/* Old ioctl */
>  	case ION_IOC_FREE:
>  	{
>  		struct ion_handle *handle;
> @@ -92,6 +134,7 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		mutex_unlock(&client->lock);
>  		break;
>  	}
> +	/* Old ioctl */
>  	case ION_IOC_SHARE:
>  	case ION_IOC_MAP:
>  	{
> @@ -106,6 +149,7 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  			ret = data.fd.fd;
>  		break;
>  	}
> +	/* Old ioctl */
>  	case ION_IOC_IMPORT:
>  	{
>  		struct ion_handle *handle;
> @@ -117,11 +161,13 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  			data.handle.handle = handle->id;
>  		break;
>  	}
> +	/* Old ioctl */
>  	case ION_IOC_SYNC:
>  	{
>  		ret = ion_sync_for_device(client, data.fd.fd);
>  		break;
>  	}
> +	/* Old ioctl */
>  	case ION_IOC_CUSTOM:
>  	{
>  		if (!dev->custom_ioctl)
> @@ -135,6 +181,53 @@ long ion_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		data.abi_version.abi_version = ION_ABI_VERSION;
>  		break;
>  	}
> +	case ION_IOC_ALLOC2:
> +	{
> +		struct ion_handle *handle;
> +
> +		handle = ion_alloc2(client, data.allocation2.len,
> +					data.allocation2.align,
> +					data.allocation2.usage_id,
> +					data.allocation2.flags);
> +		if (IS_ERR(handle))
> +			return PTR_ERR(handle);
> +
> +		if (data.allocation2.flags & ION_FLAG_NO_HANDLE) {
> +			data.allocation2.fd = ion_share_dma_buf_fd(client,
> +								handle);
> +			ion_handle_put(handle);
> +			if (data.allocation2.fd < 0)
> +				ret = data.allocation2.fd;
> +		} else {
> +			data.allocation2.handle = handle->id;
> +
> +			cleanup_handle = handle;
> +		}
> +		break;
> +	}
> +	case ION_IOC_ID_MAP:
> +	{
> +		ret = ion_map_usage_ids(client,
> +				(unsigned int __user *)data.id_map.usage_ids,
> +				data.id_map.cnt);
> +		if (ret > 0)
> +			data.id_map.new_id = ret;
> +		break;
> +	}
> +	case ION_IOC_USAGE_CNT:
> +	{
> +		down_read(&client->dev->lock);
> +		data.usage_cnt.cnt = client->dev->heap_cnt;
> +		up_read(&client->dev->lock);
> +		break;
> +	}
> +	case ION_IOC_HEAP_QUERY:
> +	{
> +		ret = ion_query_heaps(client,
> +				(struct ion_heap_data __user *)data.query.heaps,
> +				data.query.cnt);
> +		break;
> +	}
>  	default:
>  		return -ENOTTY;
>  	}
> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> index 129707f..c096cb9 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -459,6 +459,48 @@ static struct ion_handle *__ion_alloc(struct ion_client *client, size_t len,
>  	return handle;
>  }
>  
> +struct ion_handle *ion_alloc2(struct ion_client *client, size_t len,
> +				size_t align, unsigned int usage_id,
> +				unsigned int flags)
> +{
> +	struct ion_device *dev = client->dev;
> +	struct ion_heap *heap;
> +	struct ion_handle *handle = ERR_PTR(-ENODEV);
> +
> +	down_read(&dev->lock);
> +	heap = idr_find(&dev->idr, usage_id);
> +	if (!heap) {
> +		handle = ERR_PTR(-EINVAL);
> +		goto out;
> +	}
> +
> +	if (heap->type == ION_USAGE_ID_MAP) {
> +		int i;
> +
> +		for (i = 0; i < heap->fallback_cnt; i++){
> +			heap = idr_find(&dev->idr, heap->fallbacks[i]);
> +			if (!heap)
> +				continue;
> +
> +			/* Don't recurse for now? */
> +			if (heap->type == ION_USAGE_ID_MAP)
> +				continue;
> +
> +			handle =  __ion_alloc(client, len, align, heap, flags);
> +			if (IS_ERR(handle))
> +				continue;
> +			else
> +				break;
> +		}
> +	} else {
> +		handle = __ion_alloc(client, len, align, heap, flags);
> +	}
> +out:
> +	up_read(&dev->lock);
> +	return handle;
> +}
> +EXPORT_SYMBOL(ion_alloc2);
> +
>  struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
>  				size_t align, unsigned int heap_mask,
>  				unsigned int flags)
> @@ -1243,6 +1285,55 @@ int ion_sync_for_device(struct ion_client *client, int fd)
>  	return 0;
>  }
>  
> +struct ion_query_data {
> +	struct ion_heap_data __user *buffer;
> +	int cnt;
> +	int max_cnt;
> +};
> +
> +int __ion_query(int id, void *p, void *data)
> +{
> +	struct ion_heap *heap = p;
> +	struct ion_query_data *query = data;
> +	struct ion_heap_data hdata = {0};
> +
> +	if (query->cnt >= query->max_cnt)
> +		return -ENOSPC;
> +
> +	strncpy(hdata.name, heap->name, 20);
> +	hdata.name[sizeof(hdata.name) - 1] = '\0';
> +	hdata.type = heap->type;
> +	hdata.usage_id = heap->id;
> +
> +	return copy_to_user(&query->buffer[query->cnt++], &hdata, sizeof(hdata));
> +}
> +
> +int ion_query_heaps(struct ion_client *client,
> +		struct ion_heap_data __user *buffer,
> +		int cnt)
> +{
> +	struct ion_device *dev = client->dev;
> +	struct ion_query_data data;
> +	int ret;
> +
> +	data.buffer = buffer;
> +	data.cnt = 0;
> +	data.max_cnt = cnt;
> +
> +	down_read(&dev->lock);
> +	if (data.max_cnt < 0 || data.max_cnt > dev->heap_cnt) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +	ret = idr_for_each(&dev->idr, __ion_query, &data);
> +out:
> +	up_read(&dev->lock);
> +
> +	return ret;
> +}
> +
> +
> +
>  static int ion_release(struct inode *inode, struct file *file)
>  {
>  	struct ion_client *client = file->private_data;
> @@ -1407,13 +1498,69 @@ static int debug_shrink_get(void *data, u64 *val)
>  DEFINE_SIMPLE_ATTRIBUTE(debug_shrink_fops, debug_shrink_get,
>  			debug_shrink_set, "%llu\n");
>  
> +int ion_map_usage_ids(struct ion_client *client,
> +			unsigned int __user *usage_ids,
> +			int cnt)
> +{
> +	struct ion_heap *heap = kzalloc(sizeof(*heap), GFP_KERNEL);
> +	unsigned int *fallbacks;
> +	int i;
> +	int ret;
> +
> +	if (!heap)
> +		return -ENOMEM;
> +
> +	fallbacks = kzalloc(sizeof(unsigned int)*cnt, GFP_KERNEL);
> +	if (!fallbacks) {
> +		ret = -ENOMEM;
> +		goto out1;
> +	}
> +
> +	ret = copy_from_user(fallbacks, usage_ids, sizeof(unsigned int)*cnt);
> +	if (ret)
> +		goto out2;
> +
> +	down_read(&client->dev->lock);
> +	for (i = 0; i < cnt; i++) {
> +		if (idr_find(&client->dev->idr, fallbacks[i]) == NULL) {
> +			ret = -EINVAL;
> +			goto out3;
> +		}
> +	}
> +	up_read(&client->dev->lock);
> +
> +	/*
> +	 * This is a racy check since the lock is dropped before the heap
> +	 * is actually added. It's okay though because ids are never actually
> +	 * deleted. Worst case some user gets an error back and an indication
> +	 * to fix races in their code.
> +	 */
> +
> +	heap->fallbacks = fallbacks;
> +	heap->fallback_cnt = cnt;
> +	heap->type = ION_USAGE_ID_MAP;
> +	heap->id = ION_DYNAMIC_HEAP_ASSIGN;
> +	ion_device_add_heap(client->dev, heap);
> +	return heap->id;
> +out3:
> +	up_read(&client->dev->lock);
> +out2:
> +	kfree(fallbacks);
> +out1:
> +	kfree(heap);
> +	return ret;
> +}
> +
>  int ion_device_add_heap(struct ion_device *dev, struct ion_heap *heap)
>  {
>  	struct dentry *debug_file;
>  	int ret;
>  
> -	if (!heap->ops->allocate || !heap->ops->free || !heap->ops->map_dma ||
> -	    !heap->ops->unmap_dma) {
> +	if (heap->type != ION_USAGE_ID_MAP &&
> +	   (!heap->ops->allocate ||
> +	    !heap->ops->free ||
> +	    !heap->ops->map_dma ||
> +	    !heap->ops->unmap_dma)) {
>  		pr_err("%s: can not add heap with invalid ops struct.\n",
>  		       __func__);
>  		return -EINVAL;
> @@ -1425,18 +1572,36 @@ int ion_device_add_heap(struct ion_device *dev, struct ion_heap *heap)
>  	if (heap->flags & ION_HEAP_FLAG_DEFER_FREE)
>  		ion_heap_init_deferred_free(heap);
>  
> -	if ((heap->flags & ION_HEAP_FLAG_DEFER_FREE) || heap->ops->shrink)
> +	if ((heap->flags & ION_HEAP_FLAG_DEFER_FREE) || (heap->ops && heap->ops->shrink))
>  		ion_heap_init_shrinker(heap);
>  
>  	heap->dev = dev;
>  	down_write(&dev->lock);
>  
> -	ret = idr_alloc(&dev->idr, heap, heap->id, heap->id + 1, GFP_KERNEL);
> -	if (ret < 0 || ret != heap->id) {
> -		pr_info("%s: Failed to add heap id, expected %d got %d\n",
> -			__func__, heap->id, ret);
> -		up_write(&dev->lock);
> -		return ret < 0 ? ret : -EINVAL;
> +	if (heap->id == ION_DYNAMIC_HEAP_ASSIGN) {
> +		ret = idr_alloc(&dev->idr, heap,
> +				ION_DYNAMIC_HEAP_ASSIGN + 1, 0, GFP_KERNEL);

start = ION_DYNAMIC_HEAP_ASSIGN + 1, end = 0 (aka max) ? Why not end = ION_DYNAMIC_HEAP_ASSIGN + head->fallback_cnt + 1?

At least some comment is warranted explaining the choices here.

> +		if (ret < 0)
> +			goto out_unlock;
> +
> +		heap->id = ret;
> +	} else {
> +		ret = idr_alloc(&dev->idr, heap, heap->id, heap->id + 1,
> +				GFP_KERNEL);
> +		if (ret < 0 || ret != heap->id) {
> +			pr_info("%s: Failed to add heap id, expected %d got %d\n",
> +				__func__, heap->id, ret);
> +			ret = ret < 0 ? ret : -EINVAL;
> +			goto out_unlock;
> +		}
> +	}
> +
> +	if (!heap->name) {
> +		heap->name = kasprintf(GFP_KERNEL, "heap%d", heap->id);
> +		if (!heap->name) {
> +			ret = -ENOMEM;
> +			goto out_unlock;
> +		}
>  	}
>  
>  	debug_file = debugfs_create_file(heap->name, 0664,
> @@ -1467,6 +1632,7 @@ int ion_device_add_heap(struct ion_device *dev, struct ion_heap *heap)
>  		}
>  	}
>  	dev->heap_cnt++;
> +out_unlock:
>  	up_write(&dev->lock);
>  	return 0;
>  }
> diff --git a/drivers/staging/android/ion/ion_priv.h b/drivers/staging/android/ion/ion_priv.h
> index b09d751..e03e940 100644
> --- a/drivers/staging/android/ion/ion_priv.h
> +++ b/drivers/staging/android/ion/ion_priv.h
> @@ -255,6 +255,9 @@ struct ion_heap {
>  	wait_queue_head_t waitqueue;
>  	struct task_struct *task;
>  
> +	unsigned int *fallbacks;
> +	int fallback_cnt;
> +
>  	int (*debug_show)(struct ion_heap *heap, struct seq_file *, void *);
>  };
>  
> @@ -381,6 +384,10 @@ size_t ion_heap_freelist_shrink(struct ion_heap *heap,
>  size_t ion_heap_freelist_size(struct ion_heap *heap);
>  
>  
> +int ion_map_usage_ids(struct ion_client *client,
> +			unsigned int __user *usage_ids,
> +			int cnt);
> +
>  /**
>   * functions for creating and destroying the built in ion heaps.
>   * architectures can add their own custom architecture specific
> @@ -495,4 +502,12 @@ struct ion_handle *ion_handle_get_by_id(struct ion_client *client,
>  
>  int ion_handle_put(struct ion_handle *handle);
>  
> +struct ion_handle *ion_alloc2(struct ion_client *client, size_t len,
> +				size_t align, unsigned int usage_id,
> +				unsigned int flags);
> +
> +int ion_query_heaps(struct ion_client *client,
> +		struct ion_heap_data __user *buffer,
> +		int cnt);
> +
>  #endif /* _ION_PRIV_H */
> diff --git a/drivers/staging/android/uapi/ion.h b/drivers/staging/android/uapi/ion.h
> index 145005f..d36b4e4 100644
> --- a/drivers/staging/android/uapi/ion.h
> +++ b/drivers/staging/android/uapi/ion.h
> @@ -45,10 +45,17 @@ enum ion_heap_type {
>  			       * must be last so device specific heaps always
>  			       * are at the end of this enum
>  			       */
> +	ION_USAGE_ID_MAP,
>  };
>  
>  #define ION_NUM_HEAP_IDS		(sizeof(unsigned int) * 8)
>  
> +/*
> + * This isn't completely random. The old Ion heap ID namespace goes up to
> + * 32 bits so take the first one after that to use as a dynamic setting
> + */
> +#define ION_DYNAMIC_HEAP_ASSIGN		33

Also worth adding that no higher IDs should be defined after this because it's going
to break the code.

> +
>  /**
>   * allocation flags - the lower 16 bits are used by core ion, the upper 16
>   * bits are reserved for use by the heaps themselves.
> @@ -65,6 +72,11 @@ enum ion_heap_type {
>  					 * caches must be managed
>  					 * manually
>  					 */
> +#define ION_FLAG_NO_HANDLE 3		/*
> +					 * Return only an fd associated with
> +					 * this buffer and not a handle
> +					 */
> +
>  
>  /**
>   * DOC: Ion Userspace API
> @@ -142,6 +154,96 @@ struct ion_abi_version {
>  	__u32 reserved;
>  };
>  
> +/**
> + * struct ion_new_alloc_data - metadata to/from usersapce allocation v2
> + * @len:		size of the allocation
> + * @align:		required alignment of the allocation
> + * @usage_id:		mapping to heap id to allocate. Will try fallbacks
> + *			if specified in the heap mapping
> + * @flags:		flags passed to heap
> + * @handle:		pointer that will be populated with a cookie to use to
> + *			refer to this allocation
> + * @fd:			optionally, may return just an fd with no handle
> + *			reference
> + */
> +struct ion_new_alloc_data {
> +	__u64 len;
> +	__u64 align;
> +	__u32 usage_id;
> +	__u32 flags;
> +	/*
> +	 * I'd like to add a flag to just return the fd instead of just
> +	 * a handle for those who want to skip the next step.
> +	 */
> +	union {
> +		__u32 fd;
> +		__u32 handle;
> +	};
> +	/*
> +	 * Allocation has a definite problem of 'creep' so give more than
> +	 * enough extra bits for expansion
> +	 */
> +	__u32 reserved0;
> +	__u32 reserved1;
> +	__u32 reserved2;
> +};
> +
> +/**
> + * struct ion_usage_id_map - metadata to create a new usage map
> + * @usage_id - userspace allocated array of existing usage ids
> + * @cnt - number of ids to be mapped
> + * @new_id - will be populated with the new usage id
> + */
> +struct ion_usage_id_map {
> +	/* Array of usage ids provided by user */
> +	__u64 usage_ids;
> +	__u32 cnt;
> +
> +	/* Returned on success */
> +	__u32 new_id;
> +	/* Fields for future growth */
> +	__u32 reserved0;
> +	__u32 reserved1;
> +};
> +
> +/**
> + * struct ion_usage_cnt - meta data for the count of heaps
> + * @cnt - returned count of number of heaps present
> + */
> +struct ion_usage_cnt {
> +	__u32 cnt; /* cnt returned */
> +	__u32 reserved;
> +};
> +
> +/**
> + * struct ion_heap_data - data about a heap
> + * @name - first 32 characters of the heap name
> + * @type - heap type
> + * @usage_id - usage id for the heap
> + */
> +struct ion_heap_data {
> +	char name[32];
> +	__u32 type;
> +	__u32 usage_id;
> +	__u32 reserved0;
> +	__u32 reserved1;
> +	__u32 reserved2;
> +};
> +
> +/**
> + * struct ion_heap_query - collection of data about all heaps
> + * @cnt - total number of heaps to be copied
> + * @heaps - buffer to copy heap data
> + */
> +struct ion_heap_query {
> +	__u32 cnt; /* Total number of heaps to be copied */
> +	__u64 heaps; /* buffer to be populated */
> +	__u32 reserved0;
> +	__u32 reserved1;
> +	__u32 reserved2;
> +};
> +
> +
>  #define ION_IOC_MAGIC		'I'
>  
>  /**
> @@ -216,5 +318,38 @@ struct ion_abi_version {
>  #define ION_IOC_ABI_VERSION    _IOR(ION_IOC_MAGIC, 8, \
>  					struct ion_abi_version)
>  
> +/**
> + * DOC: ION_IOC_ALLOC2 - allocate memory via new API
> + *
> + * Same concept as ION_IOC_ALLOC except with updated ABI. Can return an fd
> + * directly in addition to a handle
> + */
> +#define ION_IOC_ALLOC2           _IOWR(ION_IOC_MAGIC, 9, \
> +					struct ion_new_alloc_data)
> +
> +/**
> + * DOC: ION_IOC_ID_MAP - remap an array of heap IDs
> + *
> + * Takes an ion_usage_id_map structure populated with information about
> + * fallback information. Returns a new usage id for use in allocation.
> + */
> +#define ION_IOC_ID_MAP         _IOWR(ION_IOC_MAGIC, 10, \
> +					struct ion_usage_id_map)
> +/**
> + * DOC: ION_IOC_USAGE_CNT - returns a count of the number of usage ids
> + *
> + * Takes an ion_usage_cnt structure and returns the total number of usage
> + * ids available.
> + */
> +#define ION_IOC_USAGE_CNT      _IOR(ION_IOC_MAGIC, 11, \
> +					struct ion_usage_cnt)
> +/**
> + * DOC: ION_IOC_HEAP_QUERY - information about available heaps
> + *
> + * Takes an ion_heap_query structure and populates information about
> + * availble Ion heaps.
> + */
> +#define ION_IOC_HEAP_QUERY     _IOWR(ION_IOC_MAGIC, 12, \
> +					struct ion_heap_query)
>  
>  #endif /* _UAPI_LINUX_ION_H */
> -- 
> 2.5.5
> 

I know that ION doesn't have any kernel documentation or examples in terms of what userspace
should do, but after this patchset I feel like adding some text describing how the dynamic
heap mapping might work on an ideal device that you target is useful.

Best regards,
Liviu

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯