drivers/base/dma-buf.c - kernel/msm - Gitiles

 /*
  * Framework for buffer objects that can be shared across devices/subsystems.
  *
  * Copyright(C) 2011 Linaro Limited. All rights reserved.
  * Author: Sumit Semwal <sumit.semwal@ti.com>
  *
  * Many thanks to linaro-mm-sig list, and specially
  * Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
  * Daniel Vetter <daniel@ffwll.ch> for their support in creation and
  * refining of this idea.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published by
  * the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  * more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/dma-buf.h>
 #include <linux/anon_inodes.h>
 #include <linux/export.h>

 static inline int is_dma_buf_file(struct file *);

 static int dma_buf_release(struct inode *inode, struct file *file)
 {
 	struct dma_buf *dmabuf;

 	if (!is_dma_buf_file(file))
 		return -EINVAL;

 	dmabuf = file->private_data;

 	dmabuf->ops->release(dmabuf);
 	kfree(dmabuf);
 	return 0;
 }

 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;

 	if (!is_dma_buf_file(file))
 		return -EINVAL;

 	dmabuf = file->private_data;

 	/* check for overflowing the buffer's size */
 	if (vma->vm_pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;

 	return dmabuf->ops->mmap(dmabuf, vma);
 }

 static const struct file_operations dma_buf_fops = {
 	.release	= dma_buf_release,
 	.mmap		= dma_buf_mmap_internal,
 };

 /*
  * is_dma_buf_file - Check if struct file* is associated with dma_buf
  */
 static inline int is_dma_buf_file(struct file *file)
 {
 	return file->f_op == &dma_buf_fops;
 }

 /**
  * dma_buf_export - Creates a new dma_buf, and associates an anon file
  * with this buffer, so it can be exported.
  * Also connect the allocator specific data and ops to the buffer.
  *
  * @priv:	[in]	Attach private data of allocator to this buffer
  * @ops:	[in]	Attach allocator-defined dma buf ops to the new buffer.
  * @size:	[in]	Size of the buffer
  * @flags:	[in]	mode flags for the file.
  *
  * Returns, on success, a newly created dma_buf object, which wraps the
  * supplied private data and operations for dma_buf_ops. On either missing
  * ops, or error in allocating struct dma_buf, will return negative error.
  *
  */
 struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
 				size_t size, int flags)
 {
 	struct dma_buf *dmabuf;
 	struct file *file;

 	if (WARN_ON(!priv || !ops
 			  || !ops->map_dma_buf
 			  || !ops->unmap_dma_buf
 			  || !ops->release
 			  || !ops->kmap_atomic
 			  || !ops->kmap
 			  || !ops->mmap)) {
 		return ERR_PTR(-EINVAL);
 	}

 	dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
 	if (dmabuf == NULL)
 		return ERR_PTR(-ENOMEM);

 	dmabuf->priv = priv;
 	dmabuf->ops = ops;
 	dmabuf->size = size;

 	file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);

 	dmabuf->file = file;

 	mutex_init(&dmabuf->lock);
 	INIT_LIST_HEAD(&dmabuf->attachments);

 	return dmabuf;
 }
 EXPORT_SYMBOL_GPL(dma_buf_export);


 /**
  * dma_buf_fd - returns a file descriptor for the given dma_buf
  * @dmabuf:	[in]	pointer to dma_buf for which fd is required.
  * @flags:      [in]    flags to give to fd
  *
  * On success, returns an associated 'fd'. Else, returns error.
  */
 int dma_buf_fd(struct dma_buf *dmabuf, int flags)
 {
 	int error, fd;

 	if (!dmabuf || !dmabuf->file)
 		return -EINVAL;

 	error = get_unused_fd_flags(flags);
 	if (error < 0)
 		return error;
 	fd = error;

 	fd_install(fd, dmabuf->file);

 	return fd;
 }
 EXPORT_SYMBOL_GPL(dma_buf_fd);

 /**
  * dma_buf_get - returns the dma_buf structure related to an fd
  * @fd:	[in]	fd associated with the dma_buf to be returned
  *
  * On success, returns the dma_buf structure associated with an fd; uses
  * file's refcounting done by fget to increase refcount. returns ERR_PTR
  * otherwise.
  */
 struct dma_buf *dma_buf_get(int fd)
 {
 	struct file *file;

 	file = fget(fd);

 	if (!file)
 		return ERR_PTR(-EBADF);

 	if (!is_dma_buf_file(file)) {
 		fput(file);
 		return ERR_PTR(-EINVAL);
 	}

 	return file->private_data;
 }
 EXPORT_SYMBOL_GPL(dma_buf_get);

 /**
  * dma_buf_put - decreases refcount of the buffer
  * @dmabuf:	[in]	buffer to reduce refcount of
  *
  * Uses file's refcounting done implicitly by fput()
  */
 void dma_buf_put(struct dma_buf *dmabuf)
 {
 	if (WARN_ON(!dmabuf || !dmabuf->file))
 		return;

 	fput(dmabuf->file);
 }
 EXPORT_SYMBOL_GPL(dma_buf_put);

 /**
  * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
  * calls attach() of dma_buf_ops to allow device-specific attach functionality
  * @dmabuf:	[in]	buffer to attach device to.
  * @dev:	[in]	device to be attached.
  *
  * Returns struct dma_buf_attachment * for this attachment; may return negative
  * error codes.
  *
  */
 struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
 					  struct device *dev)
 {
 	struct dma_buf_attachment *attach;
 	int ret;

 	if (WARN_ON(!dmabuf || !dev))
 		return ERR_PTR(-EINVAL);

 	attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
 	if (attach == NULL)
 		return ERR_PTR(-ENOMEM);

 	attach->dev = dev;
 	attach->dmabuf = dmabuf;

 	mutex_lock(&dmabuf->lock);

 	if (dmabuf->ops->attach) {
 		ret = dmabuf->ops->attach(dmabuf, dev, attach);
 		if (ret)
 			goto err_attach;
 	}
 	list_add(&attach->node, &dmabuf->attachments);

 	mutex_unlock(&dmabuf->lock);
 	return attach;

 err_attach:
 	kfree(attach);
 	mutex_unlock(&dmabuf->lock);
 	return ERR_PTR(ret);
 }
 EXPORT_SYMBOL_GPL(dma_buf_attach);

 /**
  * dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
  * optionally calls detach() of dma_buf_ops for device-specific detach
  * @dmabuf:	[in]	buffer to detach from.
  * @attach:	[in]	attachment to be detached; is free'd after this call.
  *
  */
 void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
 {
 	if (WARN_ON(!dmabuf || !attach))
 		return;

 	mutex_lock(&dmabuf->lock);
 	list_del(&attach->node);
 	if (dmabuf->ops->detach)
 		dmabuf->ops->detach(dmabuf, attach);

 	mutex_unlock(&dmabuf->lock);
 	kfree(attach);
 }
 EXPORT_SYMBOL_GPL(dma_buf_detach);

 /**
  * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
  * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
  * dma_buf_ops.
  * @attach:	[in]	attachment whose scatterlist is to be returned
  * @direction:	[in]	direction of DMA transfer
  *
  * Returns sg_table containing the scatterlist to be returned; may return NULL
  * or ERR_PTR.
  *
  */
 struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
 					enum dma_data_direction direction)
 {
 	struct sg_table *sg_table = ERR_PTR(-EINVAL);

 	might_sleep();

 	if (WARN_ON(!attach || !attach->dmabuf))
 		return ERR_PTR(-EINVAL);

 	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);

 	return sg_table;
 }
 EXPORT_SYMBOL_GPL(dma_buf_map_attachment);

 /**
  * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
  * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
  * dma_buf_ops.
  * @attach:	[in]	attachment to unmap buffer from
  * @sg_table:	[in]	scatterlist info of the buffer to unmap
  * @direction:  [in]    direction of DMA transfer
  *
  */
 void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 				struct sg_table *sg_table,
 				enum dma_data_direction direction)
 {
 	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
 		return;

 	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
 						direction);
 }
 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);


 /**
  * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
  * cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
  * preparations. Coherency is only guaranteed in the specified range for the
  * specified access direction.
  * @dma_buf:	[in]	buffer to prepare cpu access for.
  * @start:	[in]	start of range for cpu access.
  * @len:	[in]	length of range for cpu access.
  * @direction:	[in]	length of range for cpu access.
  *
  * Can return negative error values, returns 0 on success.
  */
 int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
 			     enum dma_data_direction direction)
 {
 	int ret = 0;

 	if (WARN_ON(!dmabuf))
 		return -EINVAL;

 	if (dmabuf->ops->begin_cpu_access)
 		ret = dmabuf->ops->begin_cpu_access(dmabuf, start, len, direction);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);

 /**
  * dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
  * cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
  * actions. Coherency is only guaranteed in the specified range for the
  * specified access direction.
  * @dma_buf:	[in]	buffer to complete cpu access for.
  * @start:	[in]	start of range for cpu access.
  * @len:	[in]	length of range for cpu access.
  * @direction:	[in]	length of range for cpu access.
  *
  * This call must always succeed.
  */
 void dma_buf_end_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
 			    enum dma_data_direction direction)
 {
 	WARN_ON(!dmabuf);

 	if (dmabuf->ops->end_cpu_access)
 		dmabuf->ops->end_cpu_access(dmabuf, start, len, direction);
 }
 EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);

 /**
  * dma_buf_kmap_atomic - Map a page of the buffer object into kernel address
  * space. The same restrictions as for kmap_atomic and friends apply.
  * @dma_buf:	[in]	buffer to map page from.
  * @page_num:	[in]	page in PAGE_SIZE units to map.
  *
  * This call must always succeed, any necessary preparations that might fail
  * need to be done in begin_cpu_access.
  */
 void *dma_buf_kmap_atomic(struct dma_buf *dmabuf, unsigned long page_num)
 {
 	WARN_ON(!dmabuf);

 	return dmabuf->ops->kmap_atomic(dmabuf, page_num);
 }
 EXPORT_SYMBOL_GPL(dma_buf_kmap_atomic);

 /**
  * dma_buf_kunmap_atomic - Unmap a page obtained by dma_buf_kmap_atomic.
  * @dma_buf:	[in]	buffer to unmap page from.
  * @page_num:	[in]	page in PAGE_SIZE units to unmap.
  * @vaddr:	[in]	kernel space pointer obtained from dma_buf_kmap_atomic.
  *
  * This call must always succeed.
  */
 void dma_buf_kunmap_atomic(struct dma_buf *dmabuf, unsigned long page_num,
 			   void *vaddr)
 {
 	WARN_ON(!dmabuf);

 	if (dmabuf->ops->kunmap_atomic)
 		dmabuf->ops->kunmap_atomic(dmabuf, page_num, vaddr);
 }
 EXPORT_SYMBOL_GPL(dma_buf_kunmap_atomic);

 /**
  * dma_buf_kmap - Map a page of the buffer object into kernel address space. The
  * same restrictions as for kmap and friends apply.
  * @dma_buf:	[in]	buffer to map page from.
  * @page_num:	[in]	page in PAGE_SIZE units to map.
  *
  * This call must always succeed, any necessary preparations that might fail
  * need to be done in begin_cpu_access.
  */
 void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long page_num)
 {
 	WARN_ON(!dmabuf);

 	return dmabuf->ops->kmap(dmabuf, page_num);
 }
 EXPORT_SYMBOL_GPL(dma_buf_kmap);

 /**
  * dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
  * @dma_buf:	[in]	buffer to unmap page from.
  * @page_num:	[in]	page in PAGE_SIZE units to unmap.
  * @vaddr:	[in]	kernel space pointer obtained from dma_buf_kmap.
  *
  * This call must always succeed.
  */
 void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
 		    void *vaddr)
 {
 	WARN_ON(!dmabuf);

 	if (dmabuf->ops->kunmap)
 		dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
 }
 EXPORT_SYMBOL_GPL(dma_buf_kunmap);


 /**
  * dma_buf_mmap - Setup up a userspace mmap with the given vma
  * @dma_buf:	[in]	buffer that should back the vma
  * @vma:	[in]	vma for the mmap
  * @pgoff:	[in]	offset in pages where this mmap should start within the
  * 			dma-buf buffer.
  *
  * This function adjusts the passed in vma so that it points at the file of the
  * dma_buf operation. It alsog adjusts the starting pgoff and does bounds
  * checking on the size of the vma. Then it calls the exporters mmap function to
  * set up the mapping.
  *
  * Can return negative error values, returns 0 on success.
  */
 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		 unsigned long pgoff)
 {
 	if (WARN_ON(!dmabuf || !vma))
 		return -EINVAL;

 	/* check for offset overflow */
 	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < pgoff)
 		return -EOVERFLOW;

 	/* check for overflowing the buffer's size */
 	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;

 	/* readjust the vma */
 	if (vma->vm_file)
 		fput(vma->vm_file);

 	vma->vm_file = dmabuf->file;
 	get_file(vma->vm_file);

 	vma->vm_pgoff = pgoff;

 	return dmabuf->ops->mmap(dmabuf, vma);
 }
 EXPORT_SYMBOL_GPL(dma_buf_mmap);
	/*
	* Framework for buffer objects that can be shared across devices/subsystems.
	*
	* Copyright(C) 2011 Linaro Limited. All rights reserved.
	* Author: Sumit Semwal <sumit.semwal@ti.com>
	*
	* Many thanks to linaro-mm-sig list, and specially
	* Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
	* Daniel Vetter <daniel@ffwll.ch> for their support in creation and
	* refining of this idea.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 as published by
	* the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	* more details.
	*
	* You should have received a copy of the GNU General Public License along with
	* this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#include <linux/fs.h>
	#include <linux/slab.h>
	#include <linux/dma-buf.h>
	#include <linux/anon_inodes.h>
	#include <linux/export.h>

	static inline int is_dma_buf_file(struct file *);

	static int dma_buf_release(struct inode inode, struct file file)
	{
	struct dma_buf *dmabuf;

	if (!is_dma_buf_file(file))
	return -EINVAL;

	dmabuf = file->private_data;

	dmabuf->ops->release(dmabuf);
	kfree(dmabuf);
	return 0;
	}

	static int dma_buf_mmap_internal(struct file file, struct vm_area_struct vma)
	{
	struct dma_buf *dmabuf;

	if (!is_dma_buf_file(file))
	return -EINVAL;

	dmabuf = file->private_data;

	/* check for overflowing the buffer's size */
	if (vma->vm_pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
	dmabuf->size >> PAGE_SHIFT)
	return -EINVAL;

	return dmabuf->ops->mmap(dmabuf, vma);
	}

	static const struct file_operations dma_buf_fops = {
	.release = dma_buf_release,
	.mmap = dma_buf_mmap_internal,
	};

	/*
	* is_dma_buf_file - Check if struct file* is associated with dma_buf
	*/
	static inline int is_dma_buf_file(struct file *file)
	{
	return file->f_op == &dma_buf_fops;
	}

	/**
	* dma_buf_export - Creates a new dma_buf, and associates an anon file
	* with this buffer, so it can be exported.
	* Also connect the allocator specific data and ops to the buffer.
	*
	* @priv: [in] Attach private data of allocator to this buffer
	* @ops: [in] Attach allocator-defined dma buf ops to the new buffer.
	* @size: [in] Size of the buffer
	* @flags: [in] mode flags for the file.
	*
	* Returns, on success, a newly created dma_buf object, which wraps the
	* supplied private data and operations for dma_buf_ops. On either missing
	* ops, or error in allocating struct dma_buf, will return negative error.
	*
	*/
	struct dma_buf dma_buf_export(void priv, const struct dma_buf_ops *ops,
	size_t size, int flags)
	{
	struct dma_buf *dmabuf;
	struct file *file;

	if (WARN_ON(!priv \|\| !ops
	\|\| !ops->map_dma_buf
	\|\| !ops->unmap_dma_buf
	\|\| !ops->release
	\|\| !ops->kmap_atomic
	\|\| !ops->kmap
	\|\| !ops->mmap)) {
	return ERR_PTR(-EINVAL);
	}

	dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
	if (dmabuf == NULL)
	return ERR_PTR(-ENOMEM);

	dmabuf->priv = priv;
	dmabuf->ops = ops;
	dmabuf->size = size;

	file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);

	dmabuf->file = file;

	mutex_init(&dmabuf->lock);
	INIT_LIST_HEAD(&dmabuf->attachments);

	return dmabuf;
	}
	EXPORT_SYMBOL_GPL(dma_buf_export);


	/**
	* dma_buf_fd - returns a file descriptor for the given dma_buf
	* @dmabuf: [in] pointer to dma_buf for which fd is required.
	* @flags: [in] flags to give to fd
	*
	* On success, returns an associated 'fd'. Else, returns error.
	*/
	int dma_buf_fd(struct dma_buf *dmabuf, int flags)
	{
	int error, fd;

	if (!dmabuf \|\| !dmabuf->file)
	return -EINVAL;

	error = get_unused_fd_flags(flags);
	if (error < 0)
	return error;
	fd = error;

	fd_install(fd, dmabuf->file);

	return fd;
	}
	EXPORT_SYMBOL_GPL(dma_buf_fd);

	/**
	* dma_buf_get - returns the dma_buf structure related to an fd
	* @fd: [in] fd associated with the dma_buf to be returned
	*
	* On success, returns the dma_buf structure associated with an fd; uses
	* file's refcounting done by fget to increase refcount. returns ERR_PTR
	* otherwise.
	*/
	struct dma_buf *dma_buf_get(int fd)
	{
	struct file *file;

	file = fget(fd);

	if (!file)
	return ERR_PTR(-EBADF);

	if (!is_dma_buf_file(file)) {
	fput(file);
	return ERR_PTR(-EINVAL);
	}

	return file->private_data;
	}
	EXPORT_SYMBOL_GPL(dma_buf_get);

	/**
	* dma_buf_put - decreases refcount of the buffer
	* @dmabuf: [in] buffer to reduce refcount of
	*
	* Uses file's refcounting done implicitly by fput()
	*/
	void dma_buf_put(struct dma_buf *dmabuf)
	{
	if (WARN_ON(!dmabuf \|\| !dmabuf->file))
	return;

	fput(dmabuf->file);
	}
	EXPORT_SYMBOL_GPL(dma_buf_put);

	/**
	* dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
	* calls attach() of dma_buf_ops to allow device-specific attach functionality
	* @dmabuf: [in] buffer to attach device to.
	* @dev: [in] device to be attached.
	*
	* Returns struct dma_buf_attachment * for this attachment; may return negative
	* error codes.
	*
	*/
	struct dma_buf_attachment dma_buf_attach(struct dma_buf dmabuf,
	struct device *dev)
	{
	struct dma_buf_attachment *attach;
	int ret;

	if (WARN_ON(!dmabuf \|\| !dev))
	return ERR_PTR(-EINVAL);

	attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
	if (attach == NULL)
	return ERR_PTR(-ENOMEM);

	attach->dev = dev;
	attach->dmabuf = dmabuf;

	mutex_lock(&dmabuf->lock);

	if (dmabuf->ops->attach) {
	ret = dmabuf->ops->attach(dmabuf, dev, attach);
	if (ret)
	goto err_attach;
	}
	list_add(&attach->node, &dmabuf->attachments);

	mutex_unlock(&dmabuf->lock);
	return attach;

	err_attach:
	kfree(attach);
	mutex_unlock(&dmabuf->lock);
	return ERR_PTR(ret);
	}
	EXPORT_SYMBOL_GPL(dma_buf_attach);

	/**
	* dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
	* optionally calls detach() of dma_buf_ops for device-specific detach
	* @dmabuf: [in] buffer to detach from.
	* @attach: [in] attachment to be detached; is free'd after this call.
	*
	*/
	void dma_buf_detach(struct dma_buf dmabuf, struct dma_buf_attachment attach)
	{
	if (WARN_ON(!dmabuf \|\| !attach))
	return;

	mutex_lock(&dmabuf->lock);
	list_del(&attach->node);
	if (dmabuf->ops->detach)
	dmabuf->ops->detach(dmabuf, attach);

	mutex_unlock(&dmabuf->lock);
	kfree(attach);
	}
	EXPORT_SYMBOL_GPL(dma_buf_detach);

	/**
	* dma_buf_map_attachment - Returns the scatterlist table of the attachment;
	* mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
	* dma_buf_ops.
	* @attach: [in] attachment whose scatterlist is to be returned
	* @direction: [in] direction of DMA transfer
	*
	* Returns sg_table containing the scatterlist to be returned; may return NULL
	* or ERR_PTR.
	*
	*/
	struct sg_table dma_buf_map_attachment(struct dma_buf_attachment attach,
	enum dma_data_direction direction)
	{
	struct sg_table *sg_table = ERR_PTR(-EINVAL);

	might_sleep();

	if (WARN_ON(!attach \|\| !attach->dmabuf))
	return ERR_PTR(-EINVAL);

	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);

	return sg_table;
	}
	EXPORT_SYMBOL_GPL(dma_buf_map_attachment);

	/**
	* dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
	* deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
	* dma_buf_ops.
	* @attach: [in] attachment to unmap buffer from
	* @sg_table: [in] scatterlist info of the buffer to unmap
	* @direction: [in] direction of DMA transfer
	*
	*/
	void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
	struct sg_table *sg_table,
	enum dma_data_direction direction)
	{
	if (WARN_ON(!attach \|\| !attach->dmabuf \|\| !sg_table))
	return;

	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
	direction);
	}
	EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);


	/**
	* dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
	* cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
	* preparations. Coherency is only guaranteed in the specified range for the
	* specified access direction.
	* @dma_buf: [in] buffer to prepare cpu access for.
	* @start: [in] start of range for cpu access.
	* @len: [in] length of range for cpu access.
	* @direction: [in] length of range for cpu access.
	*
	* Can return negative error values, returns 0 on success.
	*/
	int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
	enum dma_data_direction direction)
	{
	int ret = 0;

	if (WARN_ON(!dmabuf))
	return -EINVAL;

	if (dmabuf->ops->begin_cpu_access)
	ret = dmabuf->ops->begin_cpu_access(dmabuf, start, len, direction);

	return ret;
	}
	EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);

	/**
	* dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
	* cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
	* actions. Coherency is only guaranteed in the specified range for the
	* specified access direction.
	* @dma_buf: [in] buffer to complete cpu access for.
	* @start: [in] start of range for cpu access.
	* @len: [in] length of range for cpu access.
	* @direction: [in] length of range for cpu access.
	*
	* This call must always succeed.
	*/
	void dma_buf_end_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
	enum dma_data_direction direction)
	{
	WARN_ON(!dmabuf);

	if (dmabuf->ops->end_cpu_access)
	dmabuf->ops->end_cpu_access(dmabuf, start, len, direction);
	}
	EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);

	/**
	* dma_buf_kmap_atomic - Map a page of the buffer object into kernel address
	* space. The same restrictions as for kmap_atomic and friends apply.
	* @dma_buf: [in] buffer to map page from.
	* @page_num: [in] page in PAGE_SIZE units to map.
	*
	* This call must always succeed, any necessary preparations that might fail
	* need to be done in begin_cpu_access.
	*/
	void dma_buf_kmap_atomic(struct dma_buf dmabuf, unsigned long page_num)
	{
	WARN_ON(!dmabuf);

	return dmabuf->ops->kmap_atomic(dmabuf, page_num);
	}
	EXPORT_SYMBOL_GPL(dma_buf_kmap_atomic);

	/**
	* dma_buf_kunmap_atomic - Unmap a page obtained by dma_buf_kmap_atomic.
	* @dma_buf: [in] buffer to unmap page from.
	* @page_num: [in] page in PAGE_SIZE units to unmap.
	* @vaddr: [in] kernel space pointer obtained from dma_buf_kmap_atomic.
	*
	* This call must always succeed.
	*/
	void dma_buf_kunmap_atomic(struct dma_buf *dmabuf, unsigned long page_num,
	void *vaddr)
	{
	WARN_ON(!dmabuf);

	if (dmabuf->ops->kunmap_atomic)
	dmabuf->ops->kunmap_atomic(dmabuf, page_num, vaddr);
	}
	EXPORT_SYMBOL_GPL(dma_buf_kunmap_atomic);

	/**
	* dma_buf_kmap - Map a page of the buffer object into kernel address space. The
	* same restrictions as for kmap and friends apply.
	* @dma_buf: [in] buffer to map page from.
	* @page_num: [in] page in PAGE_SIZE units to map.
	*
	* This call must always succeed, any necessary preparations that might fail
	* need to be done in begin_cpu_access.
	*/
	void dma_buf_kmap(struct dma_buf dmabuf, unsigned long page_num)
	{
	WARN_ON(!dmabuf);

	return dmabuf->ops->kmap(dmabuf, page_num);
	}
	EXPORT_SYMBOL_GPL(dma_buf_kmap);

	/**
	* dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
	* @dma_buf: [in] buffer to unmap page from.
	* @page_num: [in] page in PAGE_SIZE units to unmap.
	* @vaddr: [in] kernel space pointer obtained from dma_buf_kmap.
	*
	* This call must always succeed.
	*/
	void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
	void *vaddr)
	{
	WARN_ON(!dmabuf);

	if (dmabuf->ops->kunmap)
	dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
	}
	EXPORT_SYMBOL_GPL(dma_buf_kunmap);


	/**
	* dma_buf_mmap - Setup up a userspace mmap with the given vma
	* @dma_buf: [in] buffer that should back the vma
	* @vma: [in] vma for the mmap
	* @pgoff: [in] offset in pages where this mmap should start within the
	* dma-buf buffer.
	*
	* This function adjusts the passed in vma so that it points at the file of the
	* dma_buf operation. It alsog adjusts the starting pgoff and does bounds
	* checking on the size of the vma. Then it calls the exporters mmap function to
	* set up the mapping.
	*
	* Can return negative error values, returns 0 on success.
	*/
	int dma_buf_mmap(struct dma_buf dmabuf, struct vm_area_struct vma,
	unsigned long pgoff)
	{
	if (WARN_ON(!dmabuf \|\| !vma))
	return -EINVAL;

	/* check for offset overflow */
	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < pgoff)
	return -EOVERFLOW;

	/* check for overflowing the buffer's size */
	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
	dmabuf->size >> PAGE_SHIFT)
	return -EINVAL;

	/* readjust the vma */
	if (vma->vm_file)
	fput(vma->vm_file);

	vma->vm_file = dmabuf->file;
	get_file(vma->vm_file);

	vma->vm_pgoff = pgoff;

	return dmabuf->ops->mmap(dmabuf, vma);
	}
	EXPORT_SYMBOL_GPL(dma_buf_mmap);