[patch] gettimeofday.2: Expand on the historic historical meaning of tz_dsttime.

["Carlos O'Donell" <carlos-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Given that the NOTES in question are willing to discuss
hitory, I have clarified the use of tz_dsttime for non-Linux
and Linux to allow the reader to contrast that with the older
system usage.

On a non-Linux glibc the meaning of tz_dsttime is exactly
that of daylight for the current zone. It has been this way
since the beginning of glibc:

^28f540f (Roland McGrath 1995-02-18 01:27:10 +0000 52)
       tz->tz_dsttime = __daylight;

On a Linux glibc the field has never been used.

Clarify the meaning of tz_dsttime for gettimeofday,
and for settimeofday distinctly for non-Linux and Linux
glibc cases (for historical completeness).

Signed-off-by: Carlos O'Donell <carlos-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
Cheers,
Carlos.

diff --git a/man2/gettimeofday.2 b/man2/gettimeofday.2
index 8006797..5df82e6 100644
--- a/man2/gettimeofday.2
+++ b/man2/gettimeofday.2
@@ -190,15 +190,30 @@ Traditionally, the fields of
 were of type
 .IR long .
 
-The
+On a non-Linux kernel, with glibc, the
+.I tz_dsttime
+field of
+.I struct timezone
+will be set to a non-zero value by
+.BR gettimeofday ()
+if the current timezone has ever had or will have a daylight saving
+rule applied. In this sense it exactly mirrors the meaning of
+.BR daylight (3)
+for the current zone.
+On Linux, with glibc, the setting of the
 .I tz_dsttime
-field has never been used under Linux.
+field of
+.I struct timezone
+has never been used by
+.BR settimeofday ()
+or
+.BR gettimeofday ().
 .\" it has not
 .\" been and will not be supported by libc or glibc.
 .\" Each and every occurrence of this field in the kernel source
 .\" (other than the declaration) is a bug.
 Thus, the following
-is purely of historic interest.
+is purely of historical interest.
 
 On old systems, the field
 .I tz_dsttime
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