Date: Tue, 24 Oct 2006 23:59:01 -0400 (EDT) From: "Brian A. Seklecki" <lavalamp@spiritual-machines.org> To: freebsd-questions@freebsd.org Subject: Reading /dev/klog / log(9) Message-ID: <20061024235219.I63561@arbitor.digitalfreaks.org>
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/dev/klog seems to be special in that, even in O_NONBLOCk, it:
*) Never blocks, but does(?)
*) Always returns read(2) = 0
*) Never returns EOF
I'm trying to read out the contents silently via a shell script prior to
starting syslog-ng. I.e., "drain it".
One would think any I/O manipulation utility (dd/pax/cpio/cat, etc.) would
work. The problem is that dd(1) w/ count=1 && bs=1 will always hang after
reading the last byte is read.
If I had some way of couting the bytes that could be read using stat(1) or
fstat(1), I could pass the correct count=$val
I've been staring at syslogd.c on FreeBSD for a while, but I'm still at a
lost as to the logic of how it even gets into klog_read(); I don't see
any select(2) or stat(2) logic.
Anyway, this perl script sort of explains where I'm trying to go:
$BUFSIZ=1;
sysopen(KLOG, "/dev/klog", O_RDONLY|O_NONBLOCK);
$oldbuffer="init";
while (1) {
undef($rv);
$rv = sysread(KLOG, $buffer, $BUFSIZ);
if (!defined($rv) && $! == EAGAIN) {
# would block
print "$rv\n";
print "Would block";
exit;
} else {
#successfully read $rv bytes from HANDLE
print "No Block";
print "$rv\n";
print "Buffer: \"" . $buffer . "\"\n";
chomp($buffer);
print "Buffer Chomped: \"" . $buffer . "\"\n";
print "Old Buffer: \"" . $oldbuffer . "\"\n";
print "Old Buffer Unchomped: \"" . $oldbufferunchomped . "\"\n";
#if ( ($buffer eq "") && ($oldbuffer eq "")) {
if ($buffer eq "") {
print "match, exit!\n";
}
$oldbuffer = $buffer
}
}
sysclose (KLOG);
~BAS
l8*
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