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[linuxjm/LDP_man-pages.git] / original / man2 / intro.2

diff --git a/original/man2/intro.2 b/original/man2/intro.2
index c828737..246eca2 100644 (file)
--- a/original/man2/intro.2
+++ b/original/man2/intro.2
@@ -26,7 +26,7 @@
 .\"     new _syscall(2) page, and substantially enhanced and rewrote
 .\"     the remaining material on this page.
 .\"
-.TH INTRO 2 2010-11-11 "Linux" "Linux Programmer's Manual"
+.TH INTRO 2 2014-02-20 "Linux" "Linux Programmer's Manual"
 .SH NAME
 intro \- introduction to system calls
 .SH DESCRIPTION
@@ -40,6 +40,29 @@ the system call.
 Thus, making a system call looks the same as invoking a normal
 library function.
 
+In many cases, the C library wrapper function does nothing more than:
+.IP * 3
+copying arguments and the unique system call number to the
+registers where the kernel expects them;
+.IP *
+trapping to kernel mode,
+at which point the kernel does the real work of the system call; and
+.IP *
+setting
+.I errno
+if the system call returns an error number when the kernel returns the
+CPU to user mode.
+.LP
+However, in a few cases, a wrapper function may do rather more than this,
+for example, performing some preprocessing
+of the arguments of arguments before trapping to kernel mode,
+or postprocessing of values returned by the system call.
+Where this is the case, the manual pages in Section 2 generally
+try to note the details of both the (usually GNU) C library API
+interface and the raw system call.
+Most commonly, the main DESCRIPTION will focus on the C library interface,
+and differences for the system call are covered in the NOTES section.
+
 For a list of the Linux system calls, see
 .BR syscalls (2).
 .SH RETURN VALUE
@@ -109,3 +132,12 @@ Note that these can be different from page to page!
 .BR svipc (7),
 .BR symlink (7),
 .BR time (7)
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.