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This patch introduces three new ioctls. They all should be called on a data endpoint (ie. not ep0). They are: - FUNCTIONFS_DMABUF_ATTACH, which takes the file descriptor of a DMABUF object to attach to the endpoint. - FUNCTIONFS_DMABUF_DETACH, which takes the file descriptor of the DMABUF to detach from the endpoint. Note that closing the endpoint's file descriptor will automatically detach all attached DMABUFs. - FUNCTIONFS_DMABUF_TRANSFER, which requests a data transfer from / to the given DMABUF. Its argument is a structure that packs the DMABUF's file descriptor, the size in bytes to transfer (which should generally be set to the size of the DMABUF), and a 'flags' field which is unused for now. Before this ioctl can be used, the related DMABUF must be attached with FUNCTIONFS_DMABUF_ATTACH. These three ioctls enable the FunctionFS code to transfer data between the USB stack and a DMABUF object, which can be provided by a driver from a completely different subsystem, in a zero-copy fashion. Signed-off-by: Paul Cercueil <paul@crapouillou.net> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Acked-by: Christian König <christian.koenig@amd.com> Link: https://lore.kernel.org/r/20240130122340.54813-4-paul@crapouillou.net Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>