Hi Ben,
Please refer to comments below.
On 02/22/2012 08:29 PM, Ben Widawsky wrote:
dma-buf export implementation. Heavily influenced by Dave Airlie's proof
of concept work.
Cc: Daniel Vetter<daniel.vet...@ffwll.ch>
Cc: Dave Airlie<airl...@redhat.com>
Signed-off-by: Ben Widawsky<b...@bwidawsk.net>
---
drivers/gpu/drm/vgem/Makefile | 2 +-
drivers/gpu/drm/vgem/vgem_dma_buf.c | 128 +++++++++++++++++++++++++++++++++++
drivers/gpu/drm/vgem/vgem_drv.c | 6 ++
drivers/gpu/drm/vgem/vgem_drv.h | 7 ++
4 files changed, 142 insertions(+), 1 deletions(-)
create mode 100644 drivers/gpu/drm/vgem/vgem_dma_buf.c
[snip]
+
+int vgem_prime_to_fd(struct drm_device *dev, struct drm_file *file,
+ uint32_t handle, int *prime_fd)
+{
+ struct drm_vgem_file_private *file_priv = file->driver_priv;
+ struct drm_vgem_gem_object *obj;
+ int ret;
+
+ DRM_DEBUG_PRIME("Request fd for handle %d\n", handle);
+
+ obj = to_vgem_bo(drm_gem_object_lookup(dev, file, handle));
+ if (!obj)
+ return -EBADF;
+
+ /* This means a user has already called get_fd on this */
+ if (obj->base.prime_fd != -1) {
+ DRM_DEBUG_PRIME("User requested a previously exported buffer "
+ "%d %d\n", handle, obj->base.prime_fd);
+ drm_gem_object_unreference(&obj->base);
+ goto out_fd;
IMO, it is not safe to cache a number of file descriptor. This number
may unexpectedly become invalid introducing a bug. Please refer to the
scenario:
- application possess a GEM buffer called A
- call DRM_IOCTL_PRIME_HANDLE_TO_FD on A to obtain a file descriptor fd_A
- application calls fd_B = dup(fd_A). Now both fd_A and fd_B point to
the same DMABUF instance.
- application calls close(fd_A), now fd_A is no longer a valid file
descriptor
- application tries to export the buffer again and calls ioctl
DRM_IOCTL_PRIME_HANDLE_TO_FD on GEM buffer. The field obj->base.prime_fd
is already set to fd_A so value fd_A is returned to userspace. Notice
that this is a bug because fd_A is no longer valid.
I think that field prime_fd should be removed because it is too
unreliable. The driver should call dma_buf_fd every time when the buffer
is exported.
+ }
+
+ /* Make a dma buf out of our vgem object */
+ obj->base.export_dma_buf = dma_buf_export(obj,&vgem_dmabuf_ops,
+ obj->base.size,
+ VGEM_FD_PERMS);
+ if (IS_ERR(obj->base.export_dma_buf)) {
+ DRM_DEBUG_PRIME("export fail\n");
+ return PTR_ERR(obj->base.export_dma_buf);
+ } else
+ obj->base.prime_fd = dma_buf_fd(obj->base.export_dma_buf);
+
+ mutex_lock(&dev->prime_mutex);
+ ret = drm_prime_insert_fd_handle_mapping(&file_priv->prime,
+ obj->base.export_dma_buf,
+ handle);
+ WARN_ON(ret);
+ ret = drm_prime_add_dma_buf(dev,&obj->base);
+ mutex_unlock(&dev->prime_mutex);
+ if (ret)
+ return ret;
+
+out_fd:
+ *prime_fd = obj->base.prime_fd;
+
+ return 0;
+}
+
Regards,
Tomasz Stanislawski
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