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intro.2: Describe policy on documenting differences between syscall and glibc API 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2014-02-19 12:28:12 +01:00
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@ -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