drivers/dma-buf/dma-buf.c

/*
 * 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/fence.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/reservation.h>

static inline int is_dma_buf_file(struct file *);

struct dma_buf_list {
	struct list_head head;
	struct mutex lock;
};

static struct dma_buf_list db_list;

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;

	BUG_ON(dmabuf->vmapping_counter);

	/*
	 * Any fences that a dma-buf poll can wait on should be signaled
	 * before releasing dma-buf. This is the responsibility of each
	 * driver that uses the reservation objects.
	 *
	 * If you hit this BUG() it means someone dropped their ref to the
	 * dma-buf while still having pending operation to the buffer.
	 */
	BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);

	dmabuf->ops->release(dmabuf);

	mutex_lock(&db_list.lock);
	list_del(&dmabuf->list_node);
	mutex_unlock(&db_list.lock);

	if (dmabuf->resv == (struct reservation_object *)&dmabuf[1])
		reservation_object_fini(dmabuf->resv);

	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 loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
{
	struct dma_buf *dmabuf;
	loff_t base;

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

	dmabuf = file->private_data;

	/* only support discovering the end of the buffer,
	   but also allow SEEK_SET to maintain the idiomatic
	   SEEK_END(0), SEEK_CUR(0) pattern */
	if (whence == SEEK_END)
		base = dmabuf->size;
	else if (whence == SEEK_SET)
		base = 0;
	else
		return -EINVAL;

	if (offset != 0)
		return -EINVAL;

	return base + offset;
}

static void dma_buf_poll_cb(struct fence *fence, struct fence_cb *cb)
{
	struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
	unsigned long flags;

	spin_lock_irqsave(&dcb->poll->lock, flags);
	wake_up_locked_poll(dcb->poll, dcb->active);
	dcb->active = 0;
	spin_unlock_irqrestore(&dcb->poll->lock, flags);
}

static unsigned int dma_buf_poll(struct file *file, poll_table *poll)
{
	struct dma_buf *dmabuf;
	struct reservation_object *resv;
	unsigned long events;

	dmabuf = file->private_data;
	if (!dmabuf || !dmabuf->resv)
		return POLLERR;

	resv = dmabuf->resv;

	poll_wait(file, &dmabuf->poll, poll);

	events = poll_requested_events(poll) & (POLLIN | POLLOUT);
	if (!events)
		return 0;

	ww_mutex_lock(&resv->lock, NULL);

	if (resv->fence_excl && (!(events & POLLOUT) ||
				 resv->fence_shared_count == 0)) {
		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
		unsigned long pevents = POLLIN;

		if (resv->fence_shared_count == 0)
			pevents |= POLLOUT;

		spin_lock_irq(&dmabuf->poll.lock);
		if (dcb->active) {
			dcb->active |= pevents;
			events &= ~pevents;
		} else
			dcb->active = pevents;
		spin_unlock_irq(&dmabuf->poll.lock);

		if (events & pevents) {
			if (!fence_add_callback(resv->fence_excl,
						&dcb->cb, dma_buf_poll_cb))
				events &= ~pevents;
			else
				/*
				 * No callback queued, wake up any additional
				 * waiters.
				 */
				dma_buf_poll_cb(NULL, &dcb->cb);
		}
	}

	if ((events & POLLOUT) && resv->fence_shared_count > 0) {
		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
		int i;

		/* Only queue a new callback if no event has fired yet */
		spin_lock_irq(&dmabuf->poll.lock);
		if (dcb->active)
			events &= ~POLLOUT;
		else
			dcb->active = POLLOUT;
		spin_unlock_irq(&dmabuf->poll.lock);

		if (!(events & POLLOUT))
			goto out;

		for (i = 0; i < resv->fence_shared_count; ++i)
			if (!fence_add_callback(resv->fence_shared[i],
						&dcb->cb, dma_buf_poll_cb)) {
				events &= ~POLLOUT;
				break;
			}

		/* No callback queued, wake up any additional waiters. */
		if (i == resv->fence_shared_count)
			dma_buf_poll_cb(NULL, &dcb->cb);
	}

out:
	ww_mutex_unlock(&resv->lock);
	return events;
}

static const struct file_operations dma_buf_fops = {
	.release	= dma_buf_release,
	.mmap		= dma_buf_mmap_internal,
	.llseek		= dma_buf_llseek,
	.poll		= dma_buf_poll,
};

/*
 * 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_named - 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.
 * Additionally, provide a name string for exporter; useful in debugging.
 *
 * @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.
 * @exp_name:	[in]	name of the exporting module - useful for debugging.
 * @resv:	[in]	reservation-object, NULL to allocate default one.
 *
 * 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_named(void *priv, const struct dma_buf_ops *ops,
				size_t size, int flags, const char *exp_name,
				struct reservation_object *resv)
{
	struct dma_buf *dmabuf;
	struct file *file;
	size_t alloc_size = sizeof(struct dma_buf);
	if (!resv)
		alloc_size += sizeof(struct reservation_object);
	else
		/* prevent &dma_buf[1] == dma_buf->resv */
		alloc_size += 1;

	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(alloc_size, GFP_KERNEL);
	if (dmabuf == NULL)
		return ERR_PTR(-ENOMEM);

	dmabuf->priv = priv;
	dmabuf->ops = ops;
	dmabuf->size = size;
	dmabuf->exp_name = exp_name;
	init_waitqueue_head(&dmabuf->poll);
	dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
	dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;

	if (!resv) {
		resv = (struct reservation_object *)&dmabuf[1];
		reservation_object_init(resv);
	}
	dmabuf->resv = resv;

	file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);
	if (IS_ERR(file)) {
		kfree(dmabuf);
		return ERR_CAST(file);
	}

	file->f_mode |= FMODE_LSEEK;
	dmabuf->file = file;

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

	mutex_lock(&db_list.lock);
	list_add(&dmabuf->list_node, &db_list.head);
	mutex_unlock(&db_list.lock);

	return dmabuf;
}
EXPORT_SYMBOL_GPL(dma_buf_export_named);


/**
 * 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 fd;

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

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

	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; returns ERR_PTR on
 * error.
 */
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; returns ERR_PTR
 * on error.
 */
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);
	if (!sg_table)
		sg_table = ERR_PTR(-ENOMEM);

	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)
{
	might_sleep();

	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.
 * @dmabuf:	[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.
 * @dmabuf:	[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.
 * @dmabuf:	[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.
 * @dmabuf:	[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.
 * @dmabuf:	[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.
 * @dmabuf:	[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
 * @dmabuf:	[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 also 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)
{
	struct file *oldfile;
	int ret;

	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 */
	get_file(dmabuf->file);
	oldfile = vma->vm_file;
	vma->vm_file = dmabuf->file;
	vma->vm_pgoff = pgoff;

	ret = dmabuf->ops->mmap(dmabuf, vma);
	if (ret) {
		/* restore old parameters on failure */
		vma->vm_file = oldfile;
		fput(dmabuf->file);
	} else {
		if (oldfile)
			fput(oldfile);
	}
	return ret;

}
EXPORT_SYMBOL_GPL(dma_buf_mmap);

/**
 * dma_buf_vmap - Create virtual mapping for the buffer object into kernel
 * address space. Same restrictions as for vmap and friends apply.
 * @dmabuf:	[in]	buffer to vmap
 *
 * This call may fail due to lack of virtual mapping address space.
 * These calls are optional in drivers. The intended use for them
 * is for mapping objects linear in kernel space for high use objects.
 * Please attempt to use kmap/kunmap before thinking about these interfaces.
 *
 * Returns NULL on error.
 */
void *dma_buf_vmap(struct dma_buf *dmabuf)
{
	void *ptr;

	if (WARN_ON(!dmabuf))
		return NULL;

	if (!dmabuf->ops->vmap)
		return NULL;

	mutex_lock(&dmabuf->lock);
	if (dmabuf->vmapping_counter) {
		dmabuf->vmapping_counter++;
		BUG_ON(!dmabuf->vmap_ptr);
		ptr = dmabuf->vmap_ptr;
		goto out_unlock;
	}

	BUG_ON(dmabuf->vmap_ptr);

	ptr = dmabuf->ops->vmap(dmabuf);
	if (WARN_ON_ONCE(IS_ERR(ptr)))
		ptr = NULL;
	if (!ptr)
		goto out_unlock;

	dmabuf->vmap_ptr = ptr;
	dmabuf->vmapping_counter = 1;

out_unlock:
	mutex_unlock(&dmabuf->lock);
	return ptr;
}
EXPORT_SYMBOL_GPL(dma_buf_vmap);

/**
 * dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
 * @dmabuf:	[in]	buffer to vunmap
 * @vaddr:	[in]	vmap to vunmap
 */
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
{
	if (WARN_ON(!dmabuf))
		return;

	BUG_ON(!dmabuf->vmap_ptr);
	BUG_ON(dmabuf->vmapping_counter == 0);
	BUG_ON(dmabuf->vmap_ptr != vaddr);

	mutex_lock(&dmabuf->lock);
	if (--dmabuf->vmapping_counter == 0) {
		if (dmabuf->ops->vunmap)
			dmabuf->ops->vunmap(dmabuf, vaddr);
		dmabuf->vmap_ptr = NULL;
	}
	mutex_unlock(&dmabuf->lock);
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);

#ifdef CONFIG_DEBUG_FS
static int dma_buf_describe(struct seq_file *s)
{
	int ret;
	struct dma_buf *buf_obj;
	struct dma_buf_attachment *attach_obj;
	int count = 0, attach_count;
	size_t size = 0;

	ret = mutex_lock_interruptible(&db_list.lock);

	if (ret)
		return ret;

	seq_puts(s, "\nDma-buf Objects:\n");
	seq_puts(s, "size\tflags\tmode\tcount\texp_name\n");

	list_for_each_entry(buf_obj, &db_list.head, list_node) {
		ret = mutex_lock_interruptible(&buf_obj->lock);

		if (ret) {
			seq_puts(s,
				 "\tERROR locking buffer object: skipping\n");
			continue;
		}

		seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\n",
				buf_obj->size,
				buf_obj->file->f_flags, buf_obj->file->f_mode,
				(long)(buf_obj->file->f_count.counter),
				buf_obj->exp_name);

		seq_puts(s, "\tAttached Devices:\n");
		attach_count = 0;

		list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
			seq_puts(s, "\t");

			seq_printf(s, "%s\n", dev_name(attach_obj->dev));
			attach_count++;
		}

		seq_printf(s, "Total %d devices attached\n\n",
				attach_count);

		count++;
		size += buf_obj->size;
		mutex_unlock(&buf_obj->lock);
	}

	seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);

	mutex_unlock(&db_list.lock);
	return 0;
}

static int dma_buf_show(struct seq_file *s, void *unused)
{
	void (*func)(struct seq_file *) = s->private;
	func(s);
	return 0;
}

static int dma_buf_debug_open(struct inode *inode, struct file *file)
{
	return single_open(file, dma_buf_show, inode->i_private);
}

static const struct file_operations dma_buf_debug_fops = {
	.open           = dma_buf_debug_open,
	.read           = seq_read,
	.llseek         = seq_lseek,
	.release        = single_release,
};

static struct dentry *dma_buf_debugfs_dir;

static int dma_buf_init_debugfs(void)
{
	int err = 0;
	dma_buf_debugfs_dir = debugfs_create_dir("dma_buf", NULL);
	if (IS_ERR(dma_buf_debugfs_dir)) {
		err = PTR_ERR(dma_buf_debugfs_dir);
		dma_buf_debugfs_dir = NULL;
		return err;
	}

	err = dma_buf_debugfs_create_file("bufinfo", dma_buf_describe);

	if (err)
		pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");

	return err;
}

static void dma_buf_uninit_debugfs(void)
{
	if (dma_buf_debugfs_dir)
		debugfs_remove_recursive(dma_buf_debugfs_dir);
}

int dma_buf_debugfs_create_file(const char *name,
				int (*write)(struct seq_file *))
{
	struct dentry *d;

	d = debugfs_create_file(name, S_IRUGO, dma_buf_debugfs_dir,
			write, &dma_buf_debug_fops);

	return PTR_ERR_OR_ZERO(d);
}
#else
static inline int dma_buf_init_debugfs(void)
{
	return 0;
}
static inline void dma_buf_uninit_debugfs(void)
{
}
#endif

static int __init dma_buf_init(void)
{
	mutex_init(&db_list.lock);
	INIT_LIST_HEAD(&db_list.head);
	dma_buf_init_debugfs();
	return 0;
}
subsys_initcall(dma_buf_init);

static void __exit dma_buf_deinit(void)
{
	dma_buf_uninit_debugfs();
}
__exitcall(dma_buf_deinit);