tweaks + update async-signal-safe function to that given in POSIX.1-2004

man7/signal.7

@@ -353,7 +353,8 @@ If a signal interrupts the execution of an unsafe function, and
 .I handler
 calls an unsafe function, then the behavior of the program is undefined.
 
-POSIX.1-2003 requires an implementation to guarantee that the following
+POSIX.1-2004 (also known as POSIX.1-2001 Technical Corrigendum 2)
+requires an implementation to guarantee that the following
 functions can be safely called inside a signal handler:
 .\" FIXME . SUSv4 adds functions to this list, and removes a few.
 
@@ -452,6 +453,7 @@ sigset()
 sigsuspend()
 sleep()
 socket()
+sockatmark()
 socketpair()
 stat()
 symlink()
@@ -488,7 +490,8 @@ and whether or not the signal handler was established using the
 .BR SA_RESTART
 flag (see
 .BR sigaction (2)).
-The details vary across Unix systems.
+The details vary across Unix systems;
+below, are the details for Linux.
 
 For the following interfaces,
 if the
@@ -518,7 +521,7 @@ then the call will return a success status
 (normally, the number of bytes transferred).
 .IP *
 .BR open (2),
-if it can block (e.g., for a FIFO; see
+if it can block (e.g., when opening a FIFO; see
 .BR fifo (7)).
 .IP *
 .BR wait (2),