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drm: new helper: drm_gem_prime_handle_to_dmabuf()

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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: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Al Viro 2024-08-02 09:56:28 -04:00 committed by Alex Deucher
parent 81f7804ba8
commit b2d4da31a1
2 changed files with 57 additions and 30 deletions
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84
drivers/gpu/drm/drm_prime.c
View file

@ -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;
if (ret) {
dma_buf_put(dmabuf);
dmabuf = ERR_PTR(ret);
}
goto out;
fail_put_dmabuf:
dma_buf_put(dmabuf);
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);

3
include/drm/drm_prime.h
View file

@ -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);