inject_diskio_delay.stp

global inject, delay_cnt

probe begin {
    println("injdect diskio delay begin.\n");
}

probe procfs("cnt").read {
    $value = sprintf("%d\n", delay_cnt);
}

probe procfs("inject").write {
    inject = $value;
    printf("inject count %d, delay_cnt %s", delay_cnt, inject);
}

probe vfs.read.return {
    if ($return && devname == @1 && inject == "on\n") {
        delay_cnt++;
        udelay($2);
    }
}

probe vfs.write.return {
    if ($return && devname == @1 && inject == "on\n") {
        delay_cnt++;
        udelay($3);
    }
}

eg:
sudo stap -p4 -DMAXSKIPPED=9999 -m idd -g inject_diskio_delay.stp sda6 300
sudo staprun idd.ko
echo on|sudo tee /proc/systemtap/idd/inject && sleep 60 && echo off|sudo tee /proc/systemtap/idd/inject