Message-ID: <7154851c-fc55-e157-5a01-21abdd4a23e6@ti.com>
Date:   Wed, 6 Nov 2019 08:52:09 -0500
From:   "Andrew F. Davis" <afd@...com>
To:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>
CC:     Laura Abbott <labbott@...hat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Sudipto Paul <Sudipto.Paul@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Hillf Danton <hdanton@...a.com>,
        Dave Airlie <airlied@...il.com>,
        <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v15 1/5] dma-buf: Add dma-buf heaps framework

On 11/5/19 11:22 PM, John Stultz wrote:
> From: "Andrew F. Davis" <afd@...com>
> 
> This framework allows a unified userspace interface for dma-buf
> exporters, allowing userland to allocate specific types of memory
> for use in dma-buf sharing.
> 
> Each heap is given its own device node, which a user can allocate
> a dma-buf fd from using the DMA_HEAP_IOC_ALLOC.
> 
> This code is an evoluiton of the Android ION implementation,
> and a big thanks is due to its authors/maintainers over time
> for their effort:
>   Rebecca Schultz Zavin, Colin Cross, Benjamin Gaignard,
>   Laura Abbott, and many other contributors!
> 
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Benjamin Gaignard <benjamin.gaignard@...aro.org>
> Cc: Sumit Semwal <sumit.semwal@...aro.org>
> Cc: Liam Mark <lmark@...eaurora.org>
> Cc: Pratik Patel <pratikp@...eaurora.org>
> Cc: Brian Starkey <Brian.Starkey@....com>
> Cc: Vincent Donnefort <Vincent.Donnefort@....com>
> Cc: Sudipto Paul <Sudipto.Paul@....com>
> Cc: Andrew F. Davis <afd@...com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Chenbo Feng <fengc@...gle.com>
> Cc: Alistair Strachan <astrachan@...gle.com>
> Cc: Hridya Valsaraju <hridya@...gle.com>
> Cc: Sandeep Patil <sspatil@...gle.com>
> Cc: Hillf Danton <hdanton@...a.com>
> Cc: Dave Airlie <airlied@...il.com>
> Cc: dri-devel@...ts.freedesktop.org
> Reviewed-by: Brian Starkey <brian.starkey@....com>
> Acked-by: Sandeep Patil <sspatil@...roid.com>
> Signed-off-by: Andrew F. Davis <afd@...com>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
> v2:
> * Folded down fixes I had previously shared in implementing
>   heaps
> * Make flags a u64 (Suggested by Laura)
> * Add PAGE_ALIGN() fix to the core alloc funciton
> * IOCTL fixups suggested by Brian
> * Added fixes suggested by Benjamin
> * Removed core stats mgmt, as that should be implemented by
>   per-heap code
> * Changed alloc to return a dma-buf fd, rather than a buffer
>   (as it simplifies error handling)
> v3:
> * Removed scare-quotes in MAINTAINERS email address
> * Get rid of .release function as it didn't do anything (from
>   Christoph)
> * Renamed filp to file (suggested by Christoph)
> * Split out ioctl handling to separate function (suggested by
>   Christoph)
> * Add comment documenting PAGE_ALIGN usage (suggested by Brian)
> * Switch from idr to Xarray (suggested by Brian)
> * Fixup cdev creation (suggested by Brian)
> * Avoid EXPORT_SYMBOL until we finalize modules (suggested by
>   Brian)
> * Make struct dma_heap internal only (folded in from Andrew)
> * Small cleanups suggested by GregKH
> * Provide class->devnode callback to get consistent /dev/
>   subdirectory naming (Suggested by Bjorn)
> v4:
> * Folded down dma-heap.h change that was in a following patch
> * Added fd_flags entry to allocation structure and pass it
>   through to heap code for use on dma-buf fd creation (suggested
>   by Benjamin)
> v5:
> * Minor cleanups
> v6:
> * Improved error path handling, minor whitespace fixes, both
>   suggested by Brian
> v7:
> * Longer Kconfig description to quiet checkpatch warnings
> * Re-add compat_ioctl bits (Hridya noticed 32bit userland wasn't
>   working)
> v8:
> * Make struct dma_heap_ops consts (Suggested by Christoph)
> * Checkpatch whitespace fixups
> v9:
> * Minor cleanups suggested by Brian Starkey
> * Rename dma_heap_get_data->dma_heap_get_drvdata suggested
>   by Hilf Danton
> v11:
> * Kconfig text improvements suggested by Randy Dunlap
> v12:
> * Add logic to prevent duplicately named heaps being added
> * Add symbol exports for heaps as modules
> v13:
> * Re-remove symbol exports per discussion w/ Brian. Will
>   resubmit in a separte patch for review
> v14:
> * Reworked ioctl handler to zero fill any difference in
>   structure size, similar to what the DRM core does, as
>   suggested by Dave Airlie
> * Removed now unnecessary reserved bits in allocate_data
> * Added get_features ioctl as suggested by Dave Airlie
> * Removed pr_warn_once messages as requested by Dave
>   Airlie
> v15:
> * Dropped the get_features ioctl as suggested by Brian
>   Starkey and Daniel Vetter
> * Add listhead comment suggested by Sandeep Patil
> * Dropped minor value in struct dma_heap as suggested by
>   Sandeep Patil
> * Fix grammar typo from Brian Starkey
> ---
>  MAINTAINERS                   |  18 +++
>  drivers/dma-buf/Kconfig       |   9 ++
>  drivers/dma-buf/Makefile      |   1 +
>  drivers/dma-buf/dma-heap.c    | 297 ++++++++++++++++++++++++++++++++++
>  include/linux/dma-heap.h      |  59 +++++++
>  include/uapi/linux/dma-heap.h |  53 ++++++
>  6 files changed, 437 insertions(+)
>  create mode 100644 drivers/dma-buf/dma-heap.c
>  create mode 100644 include/linux/dma-heap.h
>  create mode 100644 include/uapi/linux/dma-heap.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index cba1095547fd..568f94172905 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4940,6 +4940,24 @@ F:	include/linux/*fence.h
>  F:	Documentation/driver-api/dma-buf.rst
>  T:	git git://anongit.freedesktop.org/drm/drm-misc
>  
> +DMA-BUF HEAPS FRAMEWORK
> +M:	Sumit Semwal <sumit.semwal@...aro.org>
> +R:	Andrew F. Davis <afd@...com>
> +R:	Benjamin Gaignard <benjamin.gaignard@...aro.org>
> +R:	Liam Mark <lmark@...eaurora.org>
> +R:	Laura Abbott <labbott@...hat.com>
> +R:	Brian Starkey <Brian.Starkey@....com>
> +R:	John Stultz <john.stultz@...aro.org>
> +S:	Maintained
> +L:	linux-media@...r.kernel.org
> +L:	dri-devel@...ts.freedesktop.org
> +L:	linaro-mm-sig@...ts.linaro.org (moderated for non-subscribers)
> +F:	include/uapi/linux/dma-heap.h
> +F:	include/linux/dma-heap.h
> +F:	drivers/dma-buf/dma-heap.c
> +F:	drivers/dma-buf/heaps/*
> +T:	git git://anongit.freedesktop.org/drm/drm-misc
> +
>  DMA GENERIC OFFLOAD ENGINE SUBSYSTEM
>  M:	Vinod Koul <vkoul@...nel.org>
>  L:	dmaengine@...r.kernel.org
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index a23b6752d11a..bffa58fc3e6e 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -44,4 +44,13 @@ config DMABUF_SELFTESTS
>  	default n
>  	depends on DMA_SHARED_BUFFER
>  
> +menuconfig DMABUF_HEAPS
> +	bool "DMA-BUF Userland Memory Heaps"
> +	select DMA_SHARED_BUFFER
> +	help
> +	  Choose this option to enable the DMA-BUF userland memory heaps.
> +	  This options creates per heap chardevs in /dev/dma_heap/ which
> +	  allows userspace to allocate dma-bufs that can be shared
> +	  between drivers.
> +
>  endmenu
> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> index 03479da06422..caee5eb3d351 100644
> --- a/drivers/dma-buf/Makefile
> +++ b/drivers/dma-buf/Makefile
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
>  	 dma-resv.o seqno-fence.o
> +obj-$(CONFIG_DMABUF_HEAPS)	+= dma-heap.o
>  obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
>  obj-$(CONFIG_SW_SYNC)		+= sw_sync.o sync_debug.o
>  obj-$(CONFIG_UDMABUF)		+= udmabuf.o
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> new file mode 100644
> index 000000000000..4f04d104ae61
> --- /dev/null
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -0,0 +1,297 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Framework for userspace DMA-BUF allocations
> + *
> + * Copyright (C) 2011 Google, Inc.
> + * Copyright (C) 2019 Linaro Ltd.
> + */
> +
> +#include <linux/cdev.h>
> +#include <linux/debugfs.h>
> +#include <linux/device.h>
> +#include <linux/dma-buf.h>
> +#include <linux/err.h>
> +#include <linux/xarray.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/syscalls.h>
> +#include <linux/dma-heap.h>
> +#include <uapi/linux/dma-heap.h>
> +
> +#define DEVNAME "dma_heap"
> +
> +#define NUM_HEAP_MINORS 128
> +
> +/**
> + * struct dma_heap - represents a dmabuf heap in the system
> + * @name:		used for debugging/device-node name
> + * @ops:		ops struct for this heap
> + * @heap_devt		heap device node
> + * @list		list head connecting to list of heaps
> + * @heap_cdev		heap char device
> + *
> + * Represents a heap of memory from which buffers can be made.
> + */
> +struct dma_heap {
> +	const char *name;
> +	const struct dma_heap_ops *ops;
> +	void *priv;
> +	dev_t heap_devt;
> +	struct list_head list;
> +	struct cdev heap_cdev;
> +};
> +
> +static LIST_HEAD(heap_list);
> +static DEFINE_MUTEX(heap_list_lock);
> +static dev_t dma_heap_devt;
> +static struct class *dma_heap_class;
> +static DEFINE_XARRAY_ALLOC(dma_heap_minors);
> +
> +static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
> +				 unsigned int fd_flags,
> +				 unsigned int heap_flags)
> +{
> +	/*
> +	 * Allocations from all heaps have to begin
> +	 * and end on page boundaries.
> +	 */
> +	len = PAGE_ALIGN(len);
> +	if (!len)
> +		return -EINVAL;
> +
> +	return heap->ops->allocate(heap, len, fd_flags, heap_flags);
> +}
> +
> +static int dma_heap_open(struct inode *inode, struct file *file)
> +{
> +	struct dma_heap *heap;
> +
> +	heap = xa_load(&dma_heap_minors, iminor(inode));
> +	if (!heap) {
> +		pr_err("dma_heap: minor %d unknown.\n", iminor(inode));
> +		return -ENODEV;
> +	}
> +
> +	/* instance data as context */
> +	file->private_data = heap;
> +	nonseekable_open(inode, file);
> +
> +	return 0;
> +}
> +
> +static long dma_heap_ioctl_allocate(struct file *file, void *data)
> +{
> +	struct dma_heap_allocation_data *heap_allocation = data;
> +	struct dma_heap *heap = file->private_data;
> +	int fd;
> +
> +	if (heap_allocation->fd)
> +		return -EINVAL;
> +
> +	if (heap_allocation->fd_flags & ~DMA_HEAP_VALID_FD_FLAGS)
> +		return -EINVAL;
> +
> +	if (heap_allocation->heap_flags & ~DMA_HEAP_VALID_HEAP_FLAGS)
> +		return -EINVAL;
> +
> +	fd = dma_heap_buffer_alloc(heap, heap_allocation->len,
> +				   heap_allocation->fd_flags,
> +				   heap_allocation->heap_flags);
> +	if (fd < 0)
> +		return fd;
> +
> +	heap_allocation->fd = fd;
> +
> +	return 0;
> +}
> +
> +unsigned int dma_heap_ioctl_cmds[] = {
> +	DMA_HEAP_IOC_ALLOC,
> +};
> +
> +static long dma_heap_ioctl(struct file *file, unsigned int ucmd,
> +			   unsigned long arg)
> +{
> +	char stack_kdata[128];
> +	char *kdata = stack_kdata;
> +	unsigned int kcmd;
> +	unsigned int in_size, out_size, drv_size, ksize;
> +	int nr = _IOC_NR(ucmd);
> +	int ret = 0;
> +
> +	if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
> +		return -EINVAL;
> +
> +	/* Get the kernel ioctl cmd that matches */
> +	kcmd = dma_heap_ioctl_cmds[nr];


Why do we need this indirection here and all the complexity below? I
know DRM ioctl does something like this but it has a massive table,
legacy ioctls, driver defined ioctls, etc..

I don't expect we will ever need complex handling like this, could we
switch back to the more simple handler from v13?

If I'm wrong someday then we can add all this back, but right now this
is a lot for a single simple ioctl.

Andrew


> +
> +	/* Figure out the delta between user cmd size and kernel cmd size */
> +	drv_size = _IOC_SIZE(kcmd);
> +	out_size = _IOC_SIZE(ucmd);
> +	in_size = out_size;
> +	if ((ucmd & kcmd & IOC_IN) == 0)
> +		in_size = 0;
> +	if ((ucmd & kcmd & IOC_OUT) == 0)
> +		out_size = 0;
> +	ksize = max(max(in_size, out_size), drv_size);
> +
> +	/* If necessary, allocate buffer for ioctl argument */
> +	if (ksize > sizeof(stack_kdata)) {
> +		kdata = kmalloc(ksize, GFP_KERNEL);
> +		if (!kdata)
> +			return -ENOMEM;
> +	}
> +
> +	if (copy_from_user(kdata, (void __user *)arg, in_size) != 0) {
> +		ret = -EFAULT;
> +		goto err;
> +	}
> +
> +	/* zero out any difference between the kernel/user structure size */
> +	if (ksize > in_size)
> +		memset(kdata + in_size, 0, ksize - in_size);
> +
> +	switch (kcmd) {
> +	case DMA_HEAP_IOC_ALLOC:
> +		ret = dma_heap_ioctl_allocate(file, kdata);
> +		break;
> +	default:
> +		return -ENOTTY;
> +	}
> +
> +	if (copy_to_user((void __user *)arg, kdata, out_size) != 0)
> +		ret = -EFAULT;
> +err:
> +	if (kdata != stack_kdata)
> +		kfree(kdata);
> +	return ret;
> +}
> +
> +static const struct file_operations dma_heap_fops = {
> +	.owner          = THIS_MODULE,
> +	.open		= dma_heap_open,
> +	.unlocked_ioctl = dma_heap_ioctl,
> +#ifdef CONFIG_COMPAT
> +	.compat_ioctl	= dma_heap_ioctl,
> +#endif
> +};
> +
> +/**
> + * dma_heap_get_drvdata() - get per-subdriver data for the heap
> + * @heap: DMA-Heap to retrieve private data for
> + *
> + * Returns:
> + * The per-subdriver data for the heap.
> + */
> +void *dma_heap_get_drvdata(struct dma_heap *heap)
> +{
> +	return heap->priv;
> +}
> +
> +struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
> +{
> +	struct dma_heap *heap, *h, *err_ret;
> +	struct device *dev_ret;
> +	unsigned int minor;
> +	int ret;
> +
> +	if (!exp_info->name || !strcmp(exp_info->name, "")) {
> +		pr_err("dma_heap: Cannot add heap without a name\n");
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	if (!exp_info->ops || !exp_info->ops->allocate) {
> +		pr_err("dma_heap: Cannot add heap with invalid ops struct\n");
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	/* check the name is unique */
> +	mutex_lock(&heap_list_lock);
> +	list_for_each_entry(h, &heap_list, list) {
> +		if (!strcmp(h->name, exp_info->name)) {
> +			mutex_unlock(&heap_list_lock);
> +			pr_err("dma_heap: Already registered heap named %s\n",
> +			       exp_info->name);
> +			return ERR_PTR(-EINVAL);
> +		}
> +	}
> +	mutex_unlock(&heap_list_lock);
> +
> +	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
> +	if (!heap)
> +		return ERR_PTR(-ENOMEM);
> +
> +	heap->name = exp_info->name;
> +	heap->ops = exp_info->ops;
> +	heap->priv = exp_info->priv;
> +
> +	/* Find unused minor number */
> +	ret = xa_alloc(&dma_heap_minors, &minor, heap,
> +		       XA_LIMIT(0, NUM_HEAP_MINORS - 1), GFP_KERNEL);
> +	if (ret < 0) {
> +		pr_err("dma_heap: Unable to get minor number for heap\n");
> +		err_ret = ERR_PTR(ret);
> +		goto err0;
> +	}
> +
> +	/* Create device */
> +	heap->heap_devt = MKDEV(MAJOR(dma_heap_devt), minor);
> +
> +	cdev_init(&heap->heap_cdev, &dma_heap_fops);
> +	ret = cdev_add(&heap->heap_cdev, heap->heap_devt, 1);
> +	if (ret < 0) {
> +		pr_err("dma_heap: Unable to add char device\n");
> +		err_ret = ERR_PTR(ret);
> +		goto err1;
> +	}
> +
> +	dev_ret = device_create(dma_heap_class,
> +				NULL,
> +				heap->heap_devt,
> +				NULL,
> +				heap->name);
> +	if (IS_ERR(dev_ret)) {
> +		pr_err("dma_heap: Unable to create device\n");
> +		err_ret = ERR_CAST(dev_ret);
> +		goto err2;
> +	}
> +	/* Add heap to the list */
> +	mutex_lock(&heap_list_lock);
> +	list_add(&heap->list, &heap_list);
> +	mutex_unlock(&heap_list_lock);
> +
> +	return heap;
> +
> +err2:
> +	cdev_del(&heap->heap_cdev);
> +err1:
> +	xa_erase(&dma_heap_minors, minor);
> +err0:
> +	kfree(heap);
> +	return err_ret;
> +}
> +
> +static char *dma_heap_devnode(struct device *dev, umode_t *mode)
> +{
> +	return kasprintf(GFP_KERNEL, "dma_heap/%s", dev_name(dev));
> +}
> +
> +static int dma_heap_init(void)
> +{
> +	int ret;
> +
> +	ret = alloc_chrdev_region(&dma_heap_devt, 0, NUM_HEAP_MINORS, DEVNAME);
> +	if (ret)
> +		return ret;
> +
> +	dma_heap_class = class_create(THIS_MODULE, DEVNAME);
> +	if (IS_ERR(dma_heap_class)) {
> +		unregister_chrdev_region(dma_heap_devt, NUM_HEAP_MINORS);
> +		return PTR_ERR(dma_heap_class);
> +	}
> +	dma_heap_class->devnode = dma_heap_devnode;
> +
> +	return 0;
> +}
> +subsys_initcall(dma_heap_init);
> diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
> new file mode 100644
> index 000000000000..454e354d1ffb
> --- /dev/null
> +++ b/include/linux/dma-heap.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * DMABUF Heaps Allocation Infrastructure
> + *
> + * Copyright (C) 2011 Google, Inc.
> + * Copyright (C) 2019 Linaro Ltd.
> + */
> +
> +#ifndef _DMA_HEAPS_H
> +#define _DMA_HEAPS_H
> +
> +#include <linux/cdev.h>
> +#include <linux/types.h>
> +
> +struct dma_heap;
> +
> +/**
> + * struct dma_heap_ops - ops to operate on a given heap
> + * @allocate:		allocate dmabuf and return fd
> + *
> + * allocate returns dmabuf fd  on success, -errno on error.
> + */
> +struct dma_heap_ops {
> +	int (*allocate)(struct dma_heap *heap,
> +			unsigned long len,
> +			unsigned long fd_flags,
> +			unsigned long heap_flags);
> +};
> +
> +/**
> + * struct dma_heap_export_info - information needed to export a new dmabuf heap
> + * @name:	used for debugging/device-node name
> + * @ops:	ops struct for this heap
> + * @priv:	heap exporter private data
> + *
> + * Information needed to export a new dmabuf heap.
> + */
> +struct dma_heap_export_info {
> +	const char *name;
> +	const struct dma_heap_ops *ops;
> +	void *priv;
> +};
> +
> +/**
> + * dma_heap_get_drvdata() - get per-heap driver data
> + * @heap: DMA-Heap to retrieve private data for
> + *
> + * Returns:
> + * The per-heap data for the heap.
> + */
> +void *dma_heap_get_drvdata(struct dma_heap *heap);
> +
> +/**
> + * dma_heap_add - adds a heap to dmabuf heaps
> + * @exp_info:		information needed to register this heap
> + */
> +struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info);
> +
> +#endif /* _DMA_HEAPS_H */
> diff --git a/include/uapi/linux/dma-heap.h b/include/uapi/linux/dma-heap.h
> new file mode 100644
> index 000000000000..0dcb95b85886
> --- /dev/null
> +++ b/include/uapi/linux/dma-heap.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * DMABUF Heaps Userspace API
> + *
> + * Copyright (C) 2011 Google, Inc.
> + * Copyright (C) 2019 Linaro Ltd.
> + */
> +#ifndef _UAPI_LINUX_DMABUF_POOL_H
> +#define _UAPI_LINUX_DMABUF_POOL_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +/**
> + * DOC: DMABUF Heaps Userspace API
> + */
> +
> +/* Valid FD_FLAGS are O_CLOEXEC, O_RDONLY, O_WRONLY, O_RDWR */
> +#define DMA_HEAP_VALID_FD_FLAGS (O_CLOEXEC | O_ACCMODE)
> +
> +/* Currently no heap flags */
> +#define DMA_HEAP_VALID_HEAP_FLAGS (0)
> +
> +/**
> + * struct dma_heap_allocation_data - metadata passed from userspace for
> + *                                      allocations
> + * @len:		size of the allocation
> + * @fd:			will be populated with a fd which provdes the
> + *			handle to the allocated dma-buf
> + * @fd_flags:		file descriptor flags used when allocating
> + * @heap_flags:		flags passed to heap
> + *
> + * Provided by userspace as an argument to the ioctl
> + */
> +struct dma_heap_allocation_data {
> +	__u64 len;
> +	__u32 fd;
> +	__u32 fd_flags;
> +	__u64 heap_flags;
> +};
> +
> +#define DMA_HEAP_IOC_MAGIC		'H'
> +
> +/**
> + * DOC: DMA_HEAP_IOC_ALLOC - allocate memory from pool
> + *
> + * Takes a dma_heap_allocation_data struct and returns it with the fd field
> + * populated with the dmabuf handle of the allocation.
> + */
> +#define DMA_HEAP_IOC_ALLOC	_IOWR(DMA_HEAP_IOC_MAGIC, 0x0,\
> +				      struct dma_heap_allocation_data)
> +
> +#endif /* _UAPI_LINUX_DMABUF_POOL_H */
> 

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