Add GST_FD_MEMORY_FLAG_DONT_CLOSE to avoid closing the fd when the
memory is freed. When you can guarantee the lifetime of the fd is
longer than the memory, this can save a dup() call.
All those where super straight forward from the warnings gtkdoc prints. It kind
of makes sense to apply them before the list of warnings is >100 and people
complain that gtkdoc is noisy.
Make a base class that can help with allocating fd-backed memory.
Make dmabuf extend from the base class.
We can now make methods to check if memory has an fd and get the fd for
all the different types of fd-backed memory.
Make a separate file for the code to handle the fd backed memory.
This would make it possible later to add other allocators also using
fd backed memory.
