Hello Monks, I need your wisdom.

A lot of children writes its status to a file. I'm using
LOCK_EX and LOCK_SH to avoin concurrency. I'm using
sysopen, syswrite, sysseek.

Ok, now my problem (see below the strace):
lseek(5, 147, SEEK_SET) = 147
gettimeofday({1255627303, 624276}, NULL) = 0
gettimeofday({1255627303, 624380}, NULL) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
gettimeofday({1255627303, 624572}, NULL) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/var/log/bloonix/bloonix-server.log", {st_mode=S_IFREG|0640, st_
+size=154119, ...}) = 0
stat("/var/log/bloonix/bloonix-server.log", {st_mode=S_IFREG|0640, st_
+size=154119, ...}) = 0
flock(3, LOCK_EX) = 0
write(3, "Oct 15 19:21:43 [WARNING] (0.0013"..., 61) = 61
flock(3, LOCK_UN)                   = 0
flock(5, LOCK_EX)                 = 0
lseek(5, 0, SEEK_CUR)                       = 808
gettimeofday({1255627303, 625664}, NULL)     = 0
gettimeofday({1255627303, 625771}, NULL) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
gettimeofday({1255627303, 625961}, NULL) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2309, ...}) = 0
stat("/var/log/bloonix/bloonix-server.log", {st_mode=S_IFREG|0640, st_
+size=154180, ...}) = 0
stat("/var/log/bloonix/bloonix-server.log", {st_mode=S_IFREG|0640, st_
+size=154180, ...}) = 0
flock(3, LOCK_EX)                       = 0
write(3, "Oct 15 19:21:43 [WARNING] (0.0013"..., 139)                 
+              = 139
flock(3, LOCK_UN)                       = 0
write(5, "cl  "..., 4)                   = 4
lseek(5, 0, SEEK_CUR)                = 1020

[download]
I want to jump to position 147 to write 2 bytes to the
file - that seems to work - but then the 2 bytes are
written at position 808.

I am really confused.

Short:

lseek(5, 147, SEEK_SET) = 147
flock(5, LOCK_EX)                 = 0
lseek(5, 0, SEEK_CUR)                       = 808
write(5, "cl  "..., 4)                   = 4
lseek(5, 0, SEEK_CUR)                = 1020

[download]
My code: 
# Example:
$self->_sysseek(147);
$self->_syswrite("cl", 4);

sub _sysseek {
    my ($self, $pos) = @_;
    my $fh = $self->{fh};

    my $cur_pos = sysseek($fh, 0, SEEK_CUR);

    if (!defined $cur_pos) {
        $cur_pos = "";
    }

    warn "+ $$ $pos $cur_pos" if $$ != PROCESS_ID && $WRITE;

    while ( 1 ) {
        $cur_pos = sysseek($fh, $pos, SEEK_SET);

        if (!defined $cur_pos) {
            die "system seek error: $!";
        }

        if ($cur_pos == $pos) {
            last;
        }

        $DEBUG = 1;
        warn "unable to seek to pos $pos (curpos $cur_pos), try again"
+;
    }

    warn "- $$ $pos $cur_pos\n" if $$ != PROCESS_ID && $WRITE;
}

sub _syswrite {
    my ($self, $data, $size) = @_;
    my $fh     = $self->{fh};
    my $offset = 0;
    my $length = length($data);

    if ($length < $size) {
        $data .= $SEPARATOR x ($size - $length);
    }

    flock($fh, LOCK_EX) or die "unable to lock file";

    while ($size) {
        my $pos = sysseek($fh, 0, SEEK_CUR);
        warn "start to write at pos $pos" if $WRITE;
        my $written = syswrite $fh, $data, $size, $offset;


        if (!defined $written) {
            die "system write error: $!";
        } elsif ($written) {
            $size   -= $written;
            $offset += $written;
            $pos = sysseek($fh, 0, SEEK_CUR);
            warn "written $written newpos $pos" if $WRITE;
        }
    }

    flock($fh, LOCK_UN) or die "unable to unlock file";
}

[download]
Please ignore the lines for debugging.

Any ideas to my problem?

Cheers

Update:
titel updated
Code updated

In reply to sysseek and syswrite fails by bloonix

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