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drm: document DRM_IOCTL_GEM_CLOSE

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This is a bit tricky, because of the ref'counting considerations.
See also [1] for more discussion about this topic. Since this is
kernel docs, I've decided to elaborate a bit less on the user-space
details.

[1]: https://gitlab.freedesktop.org/mesa/drm/-/merge_requests/110

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Daniel Stone <daniel@fooishbar.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216130934.156541-2-contact@emersion.fr
This commit is contained in:
Simon Ser 2023-02-16 13:09:45 +00:00
parent 9a87e28da1
commit 158350aae1
1 changed files with 13 additions and 0 deletions
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13
include/uapi/drm/drm.h
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@ -972,6 +972,19 @@ extern "C" {
#define DRM_IOCTL_GET_STATS DRM_IOR( 0x06, struct drm_stats)
#define DRM_IOCTL_SET_VERSION DRM_IOWR(0x07, struct drm_set_version)
#define DRM_IOCTL_MODESET_CTL DRM_IOW(0x08, struct drm_modeset_ctl)
/**
* DRM_IOCTL_GEM_CLOSE - Close a GEM handle.
*
* GEM handles are not reference-counted by the kernel. User-space is
* responsible for managing their lifetime. For example, if user-space imports
* the same memory object twice on the same DRM file description, the same GEM
* handle is returned by both imports, and user-space needs to ensure
* &DRM_IOCTL_GEM_CLOSE is performed once only. The same situation can happen
* when a memory object is allocated, then exported and imported again on the
* same DRM file description. The &DRM_IOCTL_MODE_GETFB2 IOCTL is an exception
* and always returns fresh new GEM handles even if an existing GEM handle
* already refers to the same memory object before the IOCTL is performed.
*/
#define DRM_IOCTL_GEM_CLOSE DRM_IOW (0x09, struct drm_gem_close)
#define DRM_IOCTL_GEM_FLINK DRM_IOWR(0x0a, struct drm_gem_flink)
#define DRM_IOCTL_GEM_OPEN DRM_IOWR(0x0b, struct drm_gem_open)