recv.2: Equivalence to read

Describe the recv(2)-read(2) and the recvfrom(2)-recv(2)
equivalences for zero-valued arguments.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/recv.2

@@ -68,6 +68,26 @@ to receive data on both connectionless and connection-oriented sockets.
 This page first describes common features of all three system calls,
 and then describes the differences between the calls.
 .PP
+The only difference between
+.BR recv ()
+and
+.BR read (2)
+is the presence of
+.IR flags .
+With a zero
+.I flags
+argument,
+.BR recv ()
+is equivalent to
+.BR read (2).
+Also, the following call
+
+    recv(sockfd, buf, len, flags);
+
+is equivalent to
+
+    recvfrom(sockfd, buf, len, flags, NULL, NULL);
+.PP
 All three calls return the length of the message on successful
 completion.
 If a message is too long to fit in the supplied buffer, excess