tailq.3: Add remaining details to complete the page

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/tailq.3

@@ -55,6 +55,7 @@ TAILQ_NEXT,
 TAILQ_PREV,
 TAILQ_REMOVE
 .\"TAILQ_SWAP
+\- implementation of a doubly-linked tail queue
 .SH SYNOPSIS
 .nf
 .B #include sys/queue.h
@@ -110,6 +111,7 @@ TAILQ_REMOVE
 .\" .PP
 .\" .BI "void TAILQ_SWAP(TAILQ_HEAD *" head1 ", TAILQ_HEAD *" head2 ", TYPE, TAILQ_ENTRY " NAME ");"
 .SH DESCRIPTION
+These macros define and operate on doubly-linked tail queues.
 .PP
 In the macro definitions,
 .I TYPE
@@ -336,11 +338,44 @@ from the tail queue.
 .\" and
 .\" .IR head2 .
 .SH RETURN VALUE
+.BR TAILQ_EMPTY ()
+returns nonzero if the queue is empty,
+and zero if the queue contains at least one entry.
+.PP
+.BR TAILQ_FIRST (),
+.BR TAILQ_LAST (),
+.BR TAILQ_NEXT (),
+and
+.BR TAILQ_PREV ()
+return a pointer to the first, last, next or previous
+.I TYPE
+structure, respectively.
+.PP
+.BR TAILQ_HEAD_INITIALIZER ()
+returns an initializer that can be assigned to the queue
+.IR head .
 .SH CONFORMING TO
 Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008.
 Present on the BSDs.
 (TAILQ functions first appeared in 4.4BSD).
 .SH BUGS
+The macros
+.BR TAILQ_FOREACH ()
+and
+.BR TAILQ_FOREACH_REVERSE ()
+don't allow
+.I var
+to be removed or freed within the loop,
+as it would interfere with the traversal.
+The macros
+.BR TAILQ_FOREACH_SAFE ()
+and
+.BR TAILQ_FOREACH_REVERSE_SAFE (),
+which are present on the BSDs but are not present in glibc,
+fix this limitation by allowing
+.I var
+to safely be removed from the list and freed from within the loop
+without interfering with the traversal.
 .SH EXAMPLES
 .EX
 #include <stddef.h>
@@ -398,3 +433,5 @@ main(void)
 }
 .EE
 .SH SEE ALSO
+.BR insque (3),
+.BR queue (3)