Document sun change.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/process.c b/src/process.c
index d056e1111bf..f383c95511a 100644
--- a/src/process.c
+++ b/src/process.c
@@ -1843,7 +1843,13 @@ wait_reading_process_input (time_limit, microsecs, read_kbd, do_display)
         }
 #if defined(sun) && !defined(USG5_4)
       else if (nfds > 0 && FD_ISSET (0, &Available) && interrupt_input)
-        /* System sometimes fails to deliver SIGIO.  */
+        /* System sometimes fails to deliver SIGIO.
+
+           David J. Mackenzie says that Emacs doesn't compile under
+           Solaris if this code is enabled, thus the USG5_4 in the CPP
+           conditional.  "I haven't noticed any ill effects so far.
+           If you find a Solaris expert somewhere, they might know
+           better." */
         kill (getpid (), SIGIO);
 #endif