Note more clearly that fd_set args can be NULL; various other minor edits and ffixes

diff --git a/man2/select.2 b/man2/select.2
index be7abe1ad0bf4ea22739b5d93fa84b642d6beca6..6901260b490044019d4909c52dfbb9dd1f38c9bd 100644 (file)
--- a/man2/select.2
+++ b/man2/select.2
@@ -105,7 +105,8 @@ argument, and behaves as
 called with NULL
 .IR sigmask .
 .PP
-Three independent sets of descriptors are watched.  Those listed in
+Three independent sets of file descriptors are watched.  
+Those listed in
 .I readfds
 will be watched to see if characters become
 available for reading (more precisely, to see if a read will not
@@ -116,7 +117,10 @@ will be watched to see if a write will not block, and
 those in
 .I exceptfds
 will be watched for exceptions.  On exit, the sets are modified in place
-to indicate which descriptors actually changed status.
+to indicate which file descriptors actually changed status.
+Each of the three file descriptor sets may be specified as NULL
+if no file descriptors are to be watched for the corresponding class 
+of events.
 .PP
 Four macros are provided to manipulate the sets.
 .BR FD_ZERO ()
@@ -124,14 +128,15 @@ clears a set.
 .BR FD_SET ()
 and
 .BR FD_CLR ()
-respectively add and remove a given descriptor from a set.
+respectively add and remove a given file descriptor from a set.
 .BR FD_ISSET ()
-tests to see if a descriptor is part of the set; this is useful after
+tests to see if a file descriptor is part of the set; 
+this is useful after
 .BR select ()
 returns.
 .PP
 .I n
-is the highest-numbered descriptor in any of the three sets, plus 1.
+is the highest-numbered file descriptor in any of the three sets, plus 1.
 .PP
 .I timeout
 is an upper bound on the amount of time elapsed before
@@ -226,7 +231,7 @@ Some code calls
 .BR select ()
 with all three sets empty,
 .I n
-zero, and a non-null
+zero, and a non-NULL
 .I timeout
 as a fairly portable way to sleep with subsecond precision.
 .PP
@@ -256,8 +261,8 @@ On success,
 .BR select ()
 and
 .BR pselect ()
-return the number of descriptors contained in the three returned
-descriptor sets (that is, the total number of one bits in
+return the number of file descriptors contained in the three returned
+descriptor sets (that is, the total number of bits that are set in
 .IR readfds ,
 .IR writefds ,
 .IR exceptfds )
@@ -331,7 +336,14 @@ sets the timeout variable before exit, but the BSD variant does not.
 is defined in IEEE Std 1003.1g-2000 (POSIX.1g), and in
 POSIX 1003.1-2001.
 .SH NOTES
-An fd_set is a fixed size buffer. Executing FD_CLR or FD_SET with a value of
+An 
+.I fd_set 
+is a fixed size buffer. 
+Executing 
+.BR FD_CLR ()
+or 
+.BR FD_SET ()
+with a value of
 .I fd
 that is negative or is equal to or larger than FD_SETSIZE will result
 in undefined behavior. Moreover, POSIX requires
@@ -339,8 +351,10 @@ in undefined behavior. Moreover, POSIX requires
 to be a valid file descriptor.
 
 Concerning the types involved, the classical situation is that
-the two fields of a struct timeval are longs (as shown above),
-and the struct is defined in
+the two fields of a
+.I timeval 
+structure are longs (as shown above),
+and the structure is defined in
 .IR <sys/time.h> .
 The POSIX 1003.1-2001 situation is
 
@@ -353,9 +367,13 @@ struct timeval {
 .fi
 .RE
 
-where the struct is defined in
+where the structure is defined in
 .I <sys/select.h>
-and the data types time_t and suseconds_t are defined in
+and the data types i
+.I time_t 
+and 
+.I suseconds_t 
+are defined in
 .IR <sys/types.h> .
 .LP
 Concerning prototypes, the classical situation is that one should