Hi
Am 23.08.24 um 03:57 schrieb Al Viro:
Do you have any problems with the variant below? The only changes are
in commit message and added comment for new helper...
commit 8c291056e3e88153ef4b6316d5247547da200757
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Fri Aug 2 09:56:28 2024 -0400
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.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Thank you so much.
Best regards
Thomas
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 03bd3c7bd0dc..0e3f8adf162f 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -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);
diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
index 2a1d01e5b56b..fa085c44d4ca 100644
--- a/include/drm/drm_prime.h
+++ b/include/drm/drm_prime.h
@@ -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);
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
