vss: Add documentation of MAP_POPULATE.

It should be clear why the vss should ask the kernel to prefault the
page tables for the mapping, but it's less clear why we might need
to define the preprocessor symbol.

diff --git a/vss.c b/vss.c
index f6ec83934d971d3f6de50c363e9c15bb7c94866c..73c7231128b94152268b1bc8ea02d1f524b25b6a 100644 (file)
--- a/vss.c
+++ b/vss.c
@@ -941,6 +941,7 @@ static int recv_afs_msg(int afs_socket, int *fd, uint32_t *code, uint32_t *data)
 }
 
 #ifndef MAP_POPULATE
+/** As of 2018, neither FreeBSD-11.2 nor NetBSD-8.0 have MAP_POPULATE. */
 #define MAP_POPULATE 0
 #endif