mmap2.2: Clarify that this system call should not be invoked directly

See https://bugzilla.kernel.org/show_bug.cgi?id=42892

Reported-by: Kevin O'Gorman <kevinogorman4@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/mmap2.2

@@ -26,7 +26,7 @@
 .\"	Added description of mmap2
 .\" Modified, 2004-11-25, mtk -- removed stray #endif in prototype
 .\"
-.TH MMAP2 2 2008-04-22 "Linux" "Linux Programmer's Manual"
+.TH MMAP2 2 2012-04-16 "Linux" "Linux Programmer's Manual"
 .SH NAME
 mmap2 \- map files or devices into memory
 .SH SYNOPSIS
@@ -37,9 +37,13 @@ mmap2 \- map files or devices into memory
 .BI "             int " flags ", int " fd ", off_t " pgoffset );
 .fi
 .SH DESCRIPTION
+This is probably not the system call you are interested; instead, see
+.BR mmap (2),
+which describes the glibc wrapper function that invokes this system call.
+
 The
 .BR mmap2 ()
-system call operates in exactly the same way as
+system call provides the same interface as
 .BR mmap (2),
 except that the final argument specifies the offset into the
 file in 4096-byte units (instead of bytes, as is done by
@@ -65,7 +69,7 @@ Problem with getting the data from userspace.
 is not a multiple of the system page size.
 .PP
 .BR mmap2 ()
-can return any of the same errors as
+can also return any of the errors described in
 .BR mmap (2).
 .SH VERSIONS
 .BR mmap2 ()