I see no reason why this XXX should not be solved.

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 63d146be15c..e39c4ff6986 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -57,9 +57,6 @@
 #include <sys/tracepoint.h>
 #include <uvm/uvm_extern.h>
 
-/* XXX Should really be in buf.h, but for uvm_constraint_range.. */
-int	buf_realloc_pages(struct buf *, struct uvm_constraint_range *, int);
-
 struct uvm_constraint_range high_constraint;
 int fliphigh;
 
diff --git a/sys/sys/buf.h b/sys/sys/buf.h
index 5c08b91e6ef..51b99e0f16c 100644
--- a/sys/sys/buf.h
+++ b/sys/sys/buf.h
@@ -284,6 +284,7 @@ int	buf_dealloc_mem(struct buf *);
 void	buf_fix_mapping(struct buf *, vsize_t);
 void	buf_alloc_pages(struct buf *, vsize_t);
 void	buf_free_pages(struct buf *);
+int	buf_realloc_pages(struct buf *, struct uvm_constraint_range *, int);
 
 void	minphys(struct buf *bp);
 int	physio(void (*strategy)(struct buf *), dev_t dev, int flags,