The radix-tree is not used in userspace code. In kernel it's for
tracking unpersisted and in-memory structures and has been replaced by
the xarray.
Signed-off-by: David Sterba <dsterba@suse.com>
Let libbtrfs use own copy of the exported header files to avoid
potential breakage when syncing with kernel headers and also to remove
declarations that are not used by userspace. The send.h is frozen to
support protocol v1.
Signed-off-by: David Sterba <dsterba@suse.com>