Commit b2d4da31 authored by Al Viro's avatar Al Viro Committed by Alex Deucher
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drm: new helper: drm_gem_prime_handle_to_dmabuf() 



Once something had been put into descriptor table, the only thing you
can do with it is returning descriptor to userland - you can't withdraw
it on subsequent failure exit, etc.  You certainly can't count upon
it staying in the same slot of descriptor table - another thread
could've played with close(2)/dup2(2)/whatnot.

drm_gem_prime_handle_to_fd() creates a dmabuf, allocates a descriptor
and attaches dmabuf's file to it (the last two steps are done
in dma_buf_fd()).  That's nice when all you are going to do is
passing a descriptor to userland.  If you just need to work with the
resulting object or have something else to be done that might fail,
drm_gem_prime_handle_to_fd() is racy.

The problem is analogous to one with anon_inode_getfd(), and solution
is similar to what anon_inode_getfile() provides.

Add drm_gem_prime_handle_to_dmabuf() - the "set dmabuf up" parts of
drm_gem_prime_handle_to_fd() without the descriptor-related ones.
Instead of inserting into descriptor table and returning the file
descriptor it just returns the struct file.

drm_gem_prime_handle_to_fd() becomes a wrapper for it.  Other users
will be introduced in the next commit.

Acked-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
parent 81f7804b

drivers/gpu/drm/drm_prime.c

+54 −30
Original line number Diff line number Diff line
@@ -410,22 +410,30 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev, 
}



/**

 * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers

 * drm_gem_prime_handle_to_dmabuf - PRIME export function for GEM drivers

 * @dev: dev to export the buffer from

 * @file_priv: drm file-private structure

 * @handle: buffer handle to export

 * @flags: flags like DRM_CLOEXEC

 * @prime_fd: pointer to storage for the fd id of the create dma-buf

 *

 * This is the PRIME export function which must be used mandatorily by GEM

 * drivers to ensure correct lifetime management of the underlying GEM object.

 * The actual exporting from GEM object to a dma-buf is done through the

 * &drm_gem_object_funcs.export callback.

 *

 * Unlike drm_gem_prime_handle_to_fd(), it returns the struct dma_buf it

 * has created, without attaching it to any file descriptors.  The difference

 * between those two is similar to that between anon_inode_getfile() and

 * anon_inode_getfd(); insertion into descriptor table is something you

 * can not revert if any cleanup is needed, so the descriptor-returning

 * variants should only be used when you are past the last failure exit

 * and the only thing left is passing the new file descriptor to userland.

 * When all you need is the object itself or when you need to do something

 * else that might fail, use that one instead.

 */

int drm_gem_prime_handle_to_fd(struct drm_device *dev,

struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,

			       struct drm_file *file_priv, uint32_t handle,

			       uint32_t flags,

			       int *prime_fd)

			       uint32_t flags)

{

	struct drm_gem_object *obj;

	int ret = 0;
@@ -434,14 +442,14 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev, 
	mutex_lock(&file_priv->prime.lock);

	obj = drm_gem_object_lookup(file_priv, handle);

	if (!obj)  {

		ret = -ENOENT;

		dmabuf = ERR_PTR(-ENOENT);

		goto out_unlock;

	}



	dmabuf = drm_prime_lookup_buf_by_handle(&file_priv->prime, handle);

	if (dmabuf) {

		get_dma_buf(dmabuf);

		goto out_have_handle;

		goto out;

	}



	mutex_lock(&dev->object_name_lock);
@@ -463,7 +471,6 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev, 
		/* normally the created dma-buf takes ownership of the ref,

		 * but if that fails then drop the ref

		 */

		ret = PTR_ERR(dmabuf);

		mutex_unlock(&dev->object_name_lock);

		goto out;

	}
@@ -478,34 +485,51 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev, 
	ret = drm_prime_add_buf_handle(&file_priv->prime,

				       dmabuf, handle);

	mutex_unlock(&dev->object_name_lock);

	if (ret)

		goto fail_put_dmabuf;



out_have_handle:

	ret = dma_buf_fd(dmabuf, flags);

	/*

	 * We must _not_ remove the buffer from the handle cache since the newly

	 * created dma buf is already linked in the global obj->dma_buf pointer,

	 * and that is invariant as long as a userspace gem handle exists.

	 * Closing the handle will clean out the cache anyway, so we don't leak.

	 */

	if (ret < 0) {

		goto fail_put_dmabuf;

	} else {

		*prime_fd = ret;

		ret = 0;

	}



	goto out;



fail_put_dmabuf:

	if (ret) {

		dma_buf_put(dmabuf);

		dmabuf = ERR_PTR(ret);

	}

out:

	drm_gem_object_put(obj);

out_unlock:

	mutex_unlock(&file_priv->prime.lock);

	return dmabuf;

}

EXPORT_SYMBOL(drm_gem_prime_handle_to_dmabuf);



	return ret;

/**

 * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers

 * @dev: dev to export the buffer from

 * @file_priv: drm file-private structure

 * @handle: buffer handle to export

 * @flags: flags like DRM_CLOEXEC

 * @prime_fd: pointer to storage for the fd id of the create dma-buf

 *

 * This is the PRIME export function which must be used mandatorily by GEM

 * drivers to ensure correct lifetime management of the underlying GEM object.

 * The actual exporting from GEM object to a dma-buf is done through the

 * &drm_gem_object_funcs.export callback.

 */

int drm_gem_prime_handle_to_fd(struct drm_device *dev,

			       struct drm_file *file_priv, uint32_t handle,

			       uint32_t flags,

			       int *prime_fd)

{

	struct dma_buf *dmabuf;

	int fd = get_unused_fd_flags(flags);



	if (fd < 0)

		return fd;



	dmabuf = drm_gem_prime_handle_to_dmabuf(dev, file_priv, handle, flags);

	if (IS_ERR(dmabuf)) {

		put_unused_fd(fd);

		return PTR_ERR(dmabuf);

	}



	fd_install(fd, dmabuf->file);

	*prime_fd = fd;

	return 0;

}

EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);

include/drm/drm_prime.h

+3 −0
Original line number Diff line number Diff line
@@ -69,6 +69,9 @@ void drm_gem_dmabuf_release(struct dma_buf *dma_buf); 


int drm_gem_prime_fd_to_handle(struct drm_device *dev,

			       struct drm_file *file_priv, int prime_fd, uint32_t *handle);

struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev,

			       struct drm_file *file_priv, uint32_t handle,

			       uint32_t flags);

int drm_gem_prime_handle_to_fd(struct drm_device *dev,

			       struct drm_file *file_priv, uint32_t handle, uint32_t flags,

			       int *prime_fd);