Date:   Thu, 12 Dec 2019 11:52:04 -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: [RESEND][PATCH v16 1/5] dma-buf: Add dma-buf heaps framework

On 12/3/19 12:26 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
> v16:
> * Typo fix suggested by Hridya Valsaraju <hridya@...gle.com>
> ---
>  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 8608724835dd..44b7cbc0ec29 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4971,6 +4971,24 @@ 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];
> +
> +	/* 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..73e7f66c1cae
> --- /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 provides 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)
> +


<subsytem>_IOC_

Seems more common for the internal numberings and such, what the user
calls is more often (espesially in DRM and DMA_BUF):

<subsytem>_IOCTL_<function>

This is really just another naming nit but becouse this one really *is*
ABI then getting our prefrence right is a must, up to you here.

Andrew


> +#endif /* _UAPI_LINUX_DMABUF_POOL_H */
> 

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