[src/trunk]: src openlog(3): add LOG_PTRIM and LOG_NLOG log options.

[roy <roy%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/98d185b3c4fd
branches:  trunk
changeset: 822489:98d185b3c4fd
user:      roy <roy%NetBSD.org@localhost>
date:      Wed Mar 22 17:52:36 2017 +0000

description:
openlog(3): add LOG_PTRIM and LOG_NLOG log options.

syslog(3) is the one stop method of logging system events and diagnostics.
When debugging a daemon in the foreground on a terminal, each line is
prefixed with tag[pid]: which is very repetative and can take up valuable
screen estate.
LOG_PTRIM solves this by removing this prefix from stderr output.

There is also the case where the debugging could involve a dry-run and
syslog(3) calls would pollute the system log with incorrect data.
LOG_NLOG solves this by not writing the the system log, but allowing
LOG_PERROR to operate as before.

Initially discussed here:
https://mail-index.netbsd.org/tech-userlevel/2016/10/06/msg010330.html

diffstat:

 lib/libc/gen/syslog.3  |  11 +++++++++--
 lib/libc/gen/xsyslog.c |  20 +++++++++++++++++---
 sys/sys/syslog.h       |   4 +++-
 3 files changed, 29 insertions(+), 6 deletions(-)

diffs (109 lines):

diff -r 0e097be16545 -r 98d185b3c4fd lib/libc/gen/syslog.3
--- a/lib/libc/gen/syslog.3     Wed Mar 22 16:07:12 2017 +0000
+++ b/lib/libc/gen/syslog.3     Wed Mar 22 17:52:36 2017 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: syslog.3,v 1.30 2017/02/21 18:22:15 abhinav Exp $
+.\"    $NetBSD: syslog.3,v 1.31 2017/03/22 17:52:36 roy Exp $
 .\"    $OpenBSD: syslog.3,v 1.25 2005/07/22 03:16:58 jaredy Exp $
 .\"
 .\" Copyright (c) 1985, 1991, 1993
@@ -30,7 +30,7 @@
 .\"
 .\"     @(#)syslog.3   8.1 (Berkeley) 6/4/93
 .\"
-.Dd May 3, 2010
+.Dd March 22, 2017
 .Dt SYSLOG 3
 .Os
 .Sh NAME
@@ -295,6 +295,10 @@
 Normally the open is delayed until the first message is logged.
 Useful for programs that need to manage the order in which file
 descriptors are allocated.
+.It Dv LOG_NLOG
+Stops syslog from writing to the system log.
+Only useful with
+.Dv LOG_PERROR .
 .It Dv LOG_PERROR
 Write the message to standard error output as well to the system log.
 .It Dv LOG_PID
@@ -302,6 +306,9 @@
 instantiations of daemons.
 (This PID is placed within brackets
 between the ident and the message.)
+.It Dv LOG_PTRIM
+Trim anything syslog added to the message before writing to 
+standard error output.
 .El
 .Pp
 The
diff -r 0e097be16545 -r 98d185b3c4fd lib/libc/gen/xsyslog.c
--- a/lib/libc/gen/xsyslog.c    Wed Mar 22 16:07:12 2017 +0000
+++ b/lib/libc/gen/xsyslog.c    Wed Mar 22 17:52:36 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: xsyslog.c,v 1.2 2017/01/12 01:58:39 christos Exp $     */
+/*     $NetBSD: xsyslog.c,v 1.3 2017/03/22 17:52:36 roy Exp $  */
 
 /*
  * Copyright (c) 1983, 1988, 1993
@@ -34,7 +34,7 @@
 #if 0
 static char sccsid[] = "@(#)syslog.c   8.5 (Berkeley) 4/29/95";
 #else
-__RCSID("$NetBSD: xsyslog.c,v 1.2 2017/01/12 01:58:39 christos Exp $");
+__RCSID("$NetBSD: xsyslog.c,v 1.3 2017/03/22 17:52:36 roy Exp $");
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -301,11 +301,24 @@
 
        /* Output to stderr if requested. */
        if (data->log_stat & LOG_PERROR) {
+               struct iovec *piov;
+               int piovcnt;
+
                iov[iovcnt].iov_base = __UNCONST(CRLF + 1);
                iov[iovcnt].iov_len = 1;
-               (void)writev(STDERR_FILENO, iov, iovcnt + 1);
+               if (data->log_stat & LOG_PTRIM) {
+                       piov = &iov[iovcnt - 1];
+                       piovcnt = 2;
+               } else {
+                       piov = iov;
+                       piovcnt = iovcnt + 1;
+               }
+               (void)writev(STDERR_FILENO, piov, piovcnt);
        }
 
+       if (data->log_stat & LOG_NLOG)
+               goto out;
+
        /* Get connected, output the message to the local logger. */
        (*fun->lock)(data);
        opened = !data->log_opened;
@@ -345,6 +358,7 @@
                (void)close(fd);
        }
 
+out:
        if (!(*fun->unlock)(data) && opened)
                _closelog_unlocked_r(data);
 }
diff -r 0e097be16545 -r 98d185b3c4fd sys/sys/syslog.h
--- a/sys/sys/syslog.h  Wed Mar 22 16:07:12 2017 +0000
+++ b/sys/sys/syslog.h  Wed Mar 22 17:52:36 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: syslog.h,v 1.40 2017/03/21 11:54:46 roy Exp $  */
+/*     $NetBSD: syslog.h,v 1.41 2017/03/22 17:52:36 roy Exp $  */
 
 /*
  * Copyright (c) 1982, 1986, 1988, 1993
@@ -168,6 +168,8 @@
 #define        LOG_NDELAY      0x08    /* don't delay open */
 #define        LOG_NOWAIT      0x10    /* don't wait for console forks: DEPRECATED */
 #define        LOG_PERROR      0x20    /* log to stderr as well */
+#define LOG_PTRIM      0x40    /* trim tag and pid from messages to stderr */
+#define LOG_NLOG       0x80    /* don't write to the system log */
 
 #ifndef _KERNEL