This uses the same passing protocol as UVERBS_ATTR_FD (eg len = 0 data_s64
= fd), except that the FD is not required to be a uverbs object and the
core code does not covert the FD to an object handle automatically.
Access to the int fd is provided by uverbs_get_raw_fd().
Link: https://lore.kernel.org/r/2-v1-bd147097458e+ede-umem_dmabuf_jgg@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
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