client/common_lib/utils.py

#
# Copyright 2008 Google Inc. Released under the GPL v2

import os, pickle, random, re, resource, select, shutil, signal, StringIO
import socket, struct, subprocess, sys, time, textwrap, urlparse
import warnings, smtplib, logging, urllib2
try:
    import hashlib
except ImportError:
    import md5, sha
from autotest_lib.client.common_lib import error, logging_manager

def deprecated(func):
    """This is a decorator which can be used to mark functions as deprecated.
    It will result in a warning being emmitted when the function is used."""
    def new_func(*args, **dargs):
        warnings.warn("Call to deprecated function %s." % func.__name__,
                      category=DeprecationWarning)
        return func(*args, **dargs)
    new_func.__name__ = func.__name__
    new_func.__doc__ = func.__doc__
    new_func.__dict__.update(func.__dict__)
    return new_func


class _NullStream(object):
    def write(self, data):
        pass


    def flush(self):
        pass


TEE_TO_LOGS = object()
_the_null_stream = _NullStream()

DEFAULT_STDOUT_LEVEL = logging.DEBUG
DEFAULT_STDERR_LEVEL = logging.ERROR

# prefixes for logging stdout/stderr of commands
STDOUT_PREFIX = '[stdout] '
STDERR_PREFIX = '[stderr] '


def get_stream_tee_file(stream, level, prefix=''):
    if stream is None:
        return _the_null_stream
    if stream is TEE_TO_LOGS:
        return logging_manager.LoggingFile(level=level, prefix=prefix)
    return stream


class BgJob(object):
    def __init__(self, command, stdout_tee=None, stderr_tee=None, verbose=True,
                 stdin=None, stderr_level=DEFAULT_STDERR_LEVEL):
        self.command = command
        self.stdout_tee = get_stream_tee_file(stdout_tee, DEFAULT_STDOUT_LEVEL,
                                              prefix=STDOUT_PREFIX)
        self.stderr_tee = get_stream_tee_file(stderr_tee, stderr_level,
                                              prefix=STDERR_PREFIX)
        self.result = CmdResult(command)

        # allow for easy stdin input by string, we'll let subprocess create
        # a pipe for stdin input and we'll write to it in the wait loop
        if isinstance(stdin, basestring):
            self.string_stdin = stdin
            stdin = subprocess.PIPE
        else:
            self.string_stdin = None

        if verbose:
            logging.debug("Running '%s'" % command)
        self.sp = subprocess.Popen(command, stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE,
                                   preexec_fn=self._reset_sigpipe, shell=True,
                                   executable="/bin/bash",
                                   stdin=stdin)


    def output_prepare(self, stdout_file=None, stderr_file=None):
        self.stdout_file = stdout_file
        self.stderr_file = stderr_file


    def process_output(self, stdout=True, final_read=False):
        """output_prepare must be called prior to calling this"""
        if stdout:
            pipe, buf, tee = self.sp.stdout, self.stdout_file, self.stdout_tee
        else:
            pipe, buf, tee = self.sp.stderr, self.stderr_file, self.stderr_tee

        if final_read:
            # read in all the data we can from pipe and then stop
            data = []
            while select.select([pipe], [], [], 0)[0]:
                data.append(os.read(pipe.fileno(), 1024))
                if len(data[-1]) == 0:
                    break
            data = "".join(data)
        else:
            # perform a single read
            data = os.read(pipe.fileno(), 1024)
        buf.write(data)
        tee.write(data)


    def cleanup(self):
        self.stdout_tee.flush()
        self.stderr_tee.flush()
        self.sp.stdout.close()
        self.sp.stderr.close()
        self.result.stdout = self.stdout_file.getvalue()
        self.result.stderr = self.stderr_file.getvalue()


    def _reset_sigpipe(self):
        signal.signal(signal.SIGPIPE, signal.SIG_DFL)


def ip_to_long(ip):
    # !L is a long in network byte order
    return struct.unpack('!L', socket.inet_aton(ip))[0]


def long_to_ip(number):
    # See above comment.
    return socket.inet_ntoa(struct.pack('!L', number))


def create_subnet_mask(bits):
    return (1 << 32) - (1 << 32-bits)


def format_ip_with_mask(ip, mask_bits):
    masked_ip = ip_to_long(ip) & create_subnet_mask(mask_bits)
    return "%s/%s" % (long_to_ip(masked_ip), mask_bits)


def normalize_hostname(alias):
    ip = socket.gethostbyname(alias)
    return socket.gethostbyaddr(ip)[0]


def get_ip_local_port_range():
    match = re.match(r'\s*(\d+)\s*(\d+)\s*$',
                     read_one_line('/proc/sys/net/ipv4/ip_local_port_range'))
    return (int(match.group(1)), int(match.group(2)))


def set_ip_local_port_range(lower, upper):
    write_one_line('/proc/sys/net/ipv4/ip_local_port_range',
                   '%d %d\n' % (lower, upper))



def send_email(mail_from, mail_to, subject, body):
    """
    Sends an email via smtp

    mail_from: string with email address of sender
    mail_to: string or list with email address(es) of recipients
    subject: string with subject of email
    body: (multi-line) string with body of email
    """
    if isinstance(mail_to, str):
        mail_to = [mail_to]
    msg = "From: %s\nTo: %s\nSubject: %s\n\n%s" % (mail_from, ','.join(mail_to),
                                                   subject, body)
    try:
        mailer = smtplib.SMTP('localhost')
        try:
            mailer.sendmail(mail_from, mail_to, msg)
        finally:
            mailer.quit()
    except Exception, e:
        # Emails are non-critical, not errors, but don't raise them
        print "Sending email failed. Reason: %s" % repr(e)


def read_one_line(filename):
    return open(filename, 'r').readline().rstrip('\n')


def read_file(filename):
    f = open(filename)
    try:
        return f.read()
    finally:
        f.close()


def write_one_line(filename, line):
    open_write_close(filename, line.rstrip('\n') + '\n')


def open_write_close(filename, data):
    f = open(filename, 'w')
    try:
        f.write(data)
    finally:
        f.close()


def read_keyval(path):
    """
    Read a key-value pair format file into a dictionary, and return it.
    Takes either a filename or directory name as input. If it's a
    directory name, we assume you want the file to be called keyval.
    """
    if os.path.isdir(path):
        path = os.path.join(path, 'keyval')
    keyval = {}
    if os.path.exists(path):
        for line in open(path):
            line = re.sub('#.*', '', line).rstrip()
            if not re.search(r'^[-\.\w]+=', line):
                raise ValueError('Invalid format line: %s' % line)
            key, value = line.split('=', 1)
            if re.search('^\d+$', value):
                value = int(value)
            elif re.search('^(\d+\.)?\d+$', value):
                value = float(value)
            keyval[key] = value
    return keyval


def write_keyval(path, dictionary, type_tag=None):
    """
    Write a key-value pair format file out to a file. This uses append
    mode to open the file, so existing text will not be overwritten or
    reparsed.

    If type_tag is None, then the key must be composed of alphanumeric
    characters (or dashes+underscores). However, if type-tag is not
    null then the keys must also have "{type_tag}" as a suffix. At
    the moment the only valid values of type_tag are "attr" and "perf".
    """
    if os.path.isdir(path):
        path = os.path.join(path, 'keyval')
    keyval = open(path, 'a')

    if type_tag is None:
        key_regex = re.compile(r'^[-\.\w]+$')
    else:
        if type_tag not in ('attr', 'perf'):
            raise ValueError('Invalid type tag: %s' % type_tag)
        escaped_tag = re.escape(type_tag)
        key_regex = re.compile(r'^[-\.\w]+\{%s\}$' % escaped_tag)
    try:
        for key in sorted(dictionary.keys()):
            if not key_regex.search(key):
                raise ValueError('Invalid key: %s' % key)
            keyval.write('%s=%s\n' % (key, dictionary[key]))
    finally:
        keyval.close()


def is_url(path):
    """Return true if path looks like a URL"""
    # for now, just handle http and ftp
    url_parts = urlparse.urlparse(path)
    return (url_parts[0] in ('http', 'ftp'))


def urlopen(url, data=None, timeout=5):
    """Wrapper to urllib2.urlopen with timeout addition."""

    # Save old timeout
    old_timeout = socket.getdefaulttimeout()
    socket.setdefaulttimeout(timeout)
    try:
        return urllib2.urlopen(url, data=data)
    finally:
        socket.setdefaulttimeout(old_timeout)


def urlretrieve(url, filename, data=None, timeout=300):
    """Retrieve a file from given url."""
    logging.debug('Fetching %s -> %s', url, filename)

    src_file = urlopen(url, data=data, timeout=timeout)
    try:
        dest_file = open(filename, 'wb')
        try:
            shutil.copyfileobj(src_file, dest_file)
        finally:
            dest_file.close()
    finally:
        src_file.close()


def hash(type, input=None):
    """
    Returns an hash object of type md5 or sha1. This function is implemented in
    order to encapsulate hash objects in a way that is compatible with python
    2.4 and python 2.6 without warnings.

    Note that even though python 2.6 hashlib supports hash types other than
    md5 and sha1, we are artificially limiting the input values in order to
    make the function to behave exactly the same among both python
    implementations.

    @param input: Optional input string that will be used to update the hash.
    """
    if type not in ['md5', 'sha1']:
        raise ValueError("Unsupported hash type: %s" % type)

    try:
        hash = hashlib.new(type)
    except NameError:
        if type == 'md5':
            hash = md5.new()
        elif type == 'sha1':
            hash = sha.new()

    if input:
        hash.update(input)

    return hash


def get_file(src, dest, permissions=None):
    """Get a file from src, which can be local or a remote URL"""
    if src == dest:
        return

    if is_url(src):
        urlretrieve(src, dest)
    else:
        shutil.copyfile(src, dest)

    if permissions:
        os.chmod(dest, permissions)
    return dest


def unmap_url(srcdir, src, destdir='.'):
    """
    Receives either a path to a local file or a URL.
    returns either the path to the local file, or the fetched URL

    unmap_url('/usr/src', 'foo.tar', '/tmp')
                            = '/usr/src/foo.tar'
    unmap_url('/usr/src', 'http://site/file', '/tmp')
                            = '/tmp/file'
                            (after retrieving it)
    """
    if is_url(src):
        url_parts = urlparse.urlparse(src)
        filename = os.path.basename(url_parts[2])
        dest = os.path.join(destdir, filename)
        return get_file(src, dest)
    else:
        return os.path.join(srcdir, src)


def update_version(srcdir, preserve_srcdir, new_version, install,
                   *args, **dargs):
    """
    Make sure srcdir is version new_version

    If not, delete it and install() the new version.

    In the preserve_srcdir case, we just check it's up to date,
    and if not, we rerun install, without removing srcdir
    """
    versionfile = os.path.join(srcdir, '.version')
    install_needed = True

    if os.path.exists(versionfile):
        old_version = pickle.load(open(versionfile))
        if old_version == new_version:
            install_needed = False

    if install_needed:
        if not preserve_srcdir and os.path.exists(srcdir):
            shutil.rmtree(srcdir)
        install(*args, **dargs)
        if os.path.exists(srcdir):
            pickle.dump(new_version, open(versionfile, 'w'))


def get_stderr_level(stderr_is_expected):
    if stderr_is_expected:
        return DEFAULT_STDOUT_LEVEL
    return DEFAULT_STDERR_LEVEL


def run(command, timeout=None, ignore_status=False,
        stdout_tee=None, stderr_tee=None, verbose=True, stdin=None,
        stderr_is_expected=None, args=()):
    """
    Run a command on the host.

    @param command: the command line string.
    @param timeout: time limit in seconds before attempting to kill the
            running process. The run() function will take a few seconds
            longer than 'timeout' to complete if it has to kill the process.
    @param ignore_status: do not raise an exception, no matter what the exit
            code of the command is.
    @param stdout_tee: optional file-like object to which stdout data
            will be written as it is generated (data will still be stored
            in result.stdout).
    @param stderr_tee: likewise for stderr.
    @param verbose: if True, log the command being run.
    @param stdin: stdin to pass to the executed process (can be a file
            descriptor, a file object of a real file or a string).
    @param args: sequence of strings of arguments to be given to the command
            inside " quotes after they have been escaped for that; each
            element in the sequence will be given as a separate command
            argument

    @return a CmdResult object

    @raise CmdError: the exit code of the command execution was not 0
    """
    if isinstance(args, basestring):
        raise TypeError('Got a string for the "args" keyword argument, '
                        'need a sequence.')

    for arg in args:
        command += ' "%s"' % sh_escape(arg)
    if stderr_is_expected is None:
        stderr_is_expected = ignore_status

    bg_job = join_bg_jobs(
        (BgJob(command, stdout_tee, stderr_tee, verbose, stdin=stdin,
               stderr_level=get_stderr_level(stderr_is_expected)),),
        timeout)[0]
    if not ignore_status and bg_job.result.exit_status:
        raise error.CmdError(command, bg_job.result,
                             "Command returned non-zero exit status")

    return bg_job.result


def run_parallel(commands, timeout=None, ignore_status=False,
                 stdout_tee=None, stderr_tee=None):
    """
    Behaves the same as run() with the following exceptions:

    - commands is a list of commands to run in parallel.
    - ignore_status toggles whether or not an exception should be raised
      on any error.

    @return: a list of CmdResult objects
    """
    bg_jobs = []
    for command in commands:
        bg_jobs.append(BgJob(command, stdout_tee, stderr_tee,
                             stderr_level=get_stderr_level(ignore_status)))

    # Updates objects in bg_jobs list with their process information
    join_bg_jobs(bg_jobs, timeout)

    for bg_job in bg_jobs:
        if not ignore_status and bg_job.result.exit_status:
            raise error.CmdError(command, bg_job.result,
                                 "Command returned non-zero exit status")

    return [bg_job.result for bg_job in bg_jobs]


@deprecated
def run_bg(command):
    """Function deprecated. Please use BgJob class instead."""
    bg_job = BgJob(command)
    return bg_job.sp, bg_job.result


def join_bg_jobs(bg_jobs, timeout=None):
    """Joins the bg_jobs with the current thread.

    Returns the same list of bg_jobs objects that was passed in.
    """
    ret, timeout_error = 0, False
    for bg_job in bg_jobs:
        bg_job.output_prepare(StringIO.StringIO(), StringIO.StringIO())

    try:
        # We are holding ends to stdin, stdout pipes
        # hence we need to be sure to close those fds no mater what
        start_time = time.time()
        timeout_error = _wait_for_commands(bg_jobs, start_time, timeout)

        for bg_job in bg_jobs:
            # Process stdout and stderr
            bg_job.process_output(stdout=True,final_read=True)
            bg_job.process_output(stdout=False,final_read=True)
    finally:
        # close our ends of the pipes to the sp no matter what
        for bg_job in bg_jobs:
            bg_job.cleanup()

    if timeout_error:
        # TODO: This needs to be fixed to better represent what happens when
        # running in parallel. However this is backwards compatable, so it will
        # do for the time being.
        raise error.CmdError(bg_jobs[0].command, bg_jobs[0].result,
                             "Command(s) did not complete within %d seconds"
                             % timeout)


    return bg_jobs


def _wait_for_commands(bg_jobs, start_time, timeout):
    # This returns True if it must return due to a timeout, otherwise False.

    # To check for processes which terminate without producing any output
    # a 1 second timeout is used in select.
    SELECT_TIMEOUT = 1

    read_list = []
    write_list = []
    reverse_dict = {}

    for bg_job in bg_jobs:
        read_list.append(bg_job.sp.stdout)
        read_list.append(bg_job.sp.stderr)
        reverse_dict[bg_job.sp.stdout] = (bg_job, True)
        reverse_dict[bg_job.sp.stderr] = (bg_job, False)
        if bg_job.string_stdin is not None:
            write_list.append(bg_job.sp.stdin)
            reverse_dict[bg_job.sp.stdin] = bg_job

    if timeout:
        stop_time = start_time + timeout
        time_left = stop_time - time.time()
    else:
        time_left = None # so that select never times out

    while not timeout or time_left > 0:
        # select will return when we may write to stdin or when there is
        # stdout/stderr output we can read (including when it is
        # EOF, that is the process has terminated).
        read_ready, write_ready, _ = select.select(read_list, write_list, [],
                                                   SELECT_TIMEOUT)

        # os.read() has to be used instead of
        # subproc.stdout.read() which will otherwise block
        for file_obj in read_ready:
            bg_job, is_stdout = reverse_dict[file_obj]
            bg_job.process_output(is_stdout)

        for file_obj in write_ready:
            # we can write PIPE_BUF bytes without blocking
            # POSIX requires PIPE_BUF is >= 512
            bg_job = reverse_dict[file_obj]
            file_obj.write(bg_job.string_stdin[:512])
            bg_job.string_stdin = bg_job.string_stdin[512:]
            # no more input data, close stdin, remove it from the select set
            if not bg_job.string_stdin:
                file_obj.close()
                write_list.remove(file_obj)
                del reverse_dict[file_obj]

        all_jobs_finished = True
        for bg_job in bg_jobs:
            if bg_job.result.exit_status is not None:
                continue

            bg_job.result.exit_status = bg_job.sp.poll()
            if bg_job.result.exit_status is not None:
                # process exited, remove its stdout/stdin from the select set
                read_list.remove(bg_job.sp.stdout)
                read_list.remove(bg_job.sp.stderr)
                del reverse_dict[bg_job.sp.stdout]
                del reverse_dict[bg_job.sp.stderr]
            else:
                all_jobs_finished = False

        if all_jobs_finished:
            return False

        if timeout:
            time_left = stop_time - time.time()

    # Kill all processes which did not complete prior to timeout
    for bg_job in bg_jobs:
        if bg_job.result.exit_status is not None:
            continue

        logging.warn('run process timeout (%s) fired on: %s', timeout,
                     bg_job.command)
        nuke_subprocess(bg_job.sp)
        bg_job.result.exit_status = bg_job.sp.poll()

    return True


def pid_is_alive(pid):
    """
    True if process pid exists and is not yet stuck in Zombie state.
    Zombies are impossible to move between cgroups, etc.
    pid can be integer, or text of integer.
    """
    path = '/proc/%s/stat' % pid

    try:
        stat = read_one_line(path)
    except IOError:
        if not os.path.exists(path):
            # file went away
            return False
        raise

    return stat.split()[2] != 'Z'


def signal_pid(pid, sig):
    """
    Sends a signal to a process id. Returns True if the process terminated
    successfully, False otherwise.
    """
    try:
        os.kill(pid, sig)
    except OSError:
        # The process may have died before we could kill it.
        pass

    for i in range(5):
        if not pid_is_alive(pid):
            return True
        time.sleep(1)

    # The process is still alive
    return False


def nuke_subprocess(subproc):
    # check if the subprocess is still alive, first
    if subproc.poll() is not None:
        return subproc.poll()

    # the process has not terminated within timeout,
    # kill it via an escalating series of signals.
    signal_queue = [signal.SIGTERM, signal.SIGKILL]
    for sig in signal_queue:
        signal_pid(subproc.pid, sig)
        if subproc.poll() is not None:
            return subproc.poll()


def nuke_pid(pid, signal_queue=(signal.SIGTERM, signal.SIGKILL)):
    # the process has not terminated within timeout,
    # kill it via an escalating series of signals.
    for sig in signal_queue:
        if signal_pid(pid, sig):
            return

    # no signal successfully terminated the process
    raise error.AutoservRunError('Could not kill %d' % pid, None)


def system(command, timeout=None, ignore_status=False):
    """
    Run a command

    @param timeout: timeout in seconds
    @param ignore_status: if ignore_status=False, throw an exception if the
            command's exit code is non-zero
            if ignore_stauts=True, return the exit code.

    @return exit status of command
            (note, this will always be zero unless ignore_status=True)
    """
    return run(command, timeout=timeout, ignore_status=ignore_status,
               stdout_tee=TEE_TO_LOGS, stderr_tee=TEE_TO_LOGS).exit_status


def system_parallel(commands, timeout=None, ignore_status=False):
    """This function returns a list of exit statuses for the respective
    list of commands."""
    return [bg_jobs.exit_status for bg_jobs in
            run_parallel(commands, timeout=timeout, ignore_status=ignore_status,
                         stdout_tee=TEE_TO_LOGS, stderr_tee=TEE_TO_LOGS)]


def system_output(command, timeout=None, ignore_status=False,
                  retain_output=False, args=()):
    """
    Run a command and return the stdout output.

    @param command: command string to execute.
    @param timeout: time limit in seconds before attempting to kill the
            running process. The function will take a few seconds longer
            than 'timeout' to complete if it has to kill the process.
    @param ignore_status: do not raise an exception, no matter what the exit
            code of the command is.
    @param retain_output: set to True to make stdout/stderr of the command
            output to be also sent to the logging system
    @param args: sequence of strings of arguments to be given to the command
            inside " quotes after they have been escaped for that; each
            element in the sequence will be given as a separate command
            argument

    @return a string with the stdout output of the command.
    """
    if retain_output:
        out = run(command, timeout=timeout, ignore_status=ignore_status,
                  stdout_tee=TEE_TO_LOGS, stderr_tee=TEE_TO_LOGS,
                  args=args).stdout
    else:
        out = run(command, timeout=timeout, ignore_status=ignore_status,
                  args=args).stdout
    if out[-1:] == '\n':
        out = out[:-1]
    return out


def system_output_parallel(commands, timeout=None, ignore_status=False,
                           retain_output=False):
    if retain_output:
        out = [bg_job.stdout for bg_job
               in run_parallel(commands, timeout=timeout,
                               ignore_status=ignore_status,
                               stdout_tee=TEE_TO_LOGS, stderr_tee=TEE_TO_LOGS)]
    else:
        out = [bg_job.stdout for bg_job in run_parallel(commands,
                                  timeout=timeout, ignore_status=ignore_status)]
    for x in out:
        if out[-1:] == '\n': out = out[:-1]
    return out


def strip_unicode(input):
    if type(input) == list:
        return [strip_unicode(i) for i in input]
    elif type(input) == dict:
        output = {}
        for key in input.keys():
            output[str(key)] = strip_unicode(input[key])
        return output
    elif type(input) == unicode:
        return str(input)
    else:
        return input


def get_cpu_percentage(function, *args, **dargs):
    """Returns a tuple containing the CPU% and return value from function call.

    This function calculates the usage time by taking the difference of
    the user and system times both before and after the function call.
    """
    child_pre = resource.getrusage(resource.RUSAGE_CHILDREN)
    self_pre = resource.getrusage(resource.RUSAGE_SELF)
    start = time.time()
    to_return = function(*args, **dargs)
    elapsed = time.time() - start
    self_post = resource.getrusage(resource.RUSAGE_SELF)
    child_post = resource.getrusage(resource.RUSAGE_CHILDREN)

    # Calculate CPU Percentage
    s_user, s_system = [a - b for a, b in zip(self_post, self_pre)[:2]]
    c_user, c_system = [a - b for a, b in zip(child_post, child_pre)[:2]]
    cpu_percent = (s_user + c_user + s_system + c_system) / elapsed

    return cpu_percent, to_return


def get_arch(run_function=run):
    """
    Get the hardware architecture of the machine.
    run_function is used to execute the commands. It defaults to
    utils.run() but a custom method (if provided) should be of the
    same schema as utils.run. It should return a CmdResult object and
    throw a CmdError exception.
    """
    arch = run_function('/bin/uname -m').stdout.rstrip()
    if re.match(r'i\d86$', arch):
        arch = 'i386'
    return arch


def get_num_logical_cpus_per_socket(run_function=run):
    """
    Get the number of cores (including hyperthreading) per cpu.
    run_function is used to execute the commands. It defaults to
    utils.run() but a custom method (if provided) should be of the
    same schema as utils.run. It should return a CmdResult object and
    throw a CmdError exception.
    """
    siblings = run_function('grep "^siblings" /proc/cpuinfo').stdout.rstrip()
    num_siblings = map(int,
                       re.findall(r'^siblings\s*:\s*(\d+)\s*$',
                                  siblings, re.M))
    if len(num_siblings) == 0:
        raise error.TestError('Unable to find siblings info in /proc/cpuinfo')
    if min(num_siblings) != max(num_siblings):
        raise error.TestError('Number of siblings differ %r' %
                              num_siblings)
    return num_siblings[0]


def merge_trees(src, dest):
    """
    Merges a source directory tree at 'src' into a destination tree at
    'dest'. If a path is a file in both trees than the file in the source
    tree is APPENDED to the one in the destination tree. If a path is
    a directory in both trees then the directories are recursively merged
    with this function. In any other case, the function will skip the
    paths that cannot be merged (instead of failing).
    """
    if not os.path.exists(src):
        return # exists only in dest
    elif not os.path.exists(dest):
        if os.path.isfile(src):
            shutil.copy2(src, dest) # file only in src
        else:
            shutil.copytree(src, dest, symlinks=True) # dir only in src
        return
    elif os.path.isfile(src) and os.path.isfile(dest):
        # src & dest are files in both trees, append src to dest
        destfile = open(dest, "a")
        try:
            srcfile = open(src)
            try:
                destfile.write(srcfile.read())
            finally:
                srcfile.close()
        finally:
            destfile.close()
    elif os.path.isdir(src) and os.path.isdir(dest):
        # src & dest are directories in both trees, so recursively merge
        for name in os.listdir(src):
            merge_trees(os.path.join(src, name), os.path.join(dest, name))
    else:
        # src & dest both exist, but are incompatible
        return


class CmdResult(object):
    """
    Command execution result.

    command:     String containing the command line itself
    exit_status: Integer exit code of the process
    stdout:      String containing stdout of the process
    stderr:      String containing stderr of the process
    duration:    Elapsed wall clock time running the process
    """


    def __init__(self, command="", stdout="", stderr="",
                 exit_status=None, duration=0):
        self.command = command
        self.exit_status = exit_status
        self.stdout = stdout
        self.stderr = stderr
        self.duration = duration


    def __repr__(self):
        wrapper = textwrap.TextWrapper(width = 78,
                                       initial_indent="\n    ",
                                       subsequent_indent="    ")

        stdout = self.stdout.rstrip()
        if stdout:
            stdout = "\nstdout:\n%s" % stdout

        stderr = self.stderr.rstrip()
        if stderr:
            stderr = "\nstderr:\n%s" % stderr

        return ("* Command: %s\n"
                "Exit status: %s\n"
                "Duration: %s\n"
                "%s"
                "%s"
                % (wrapper.fill(self.command), self.exit_status,
                self.duration, stdout, stderr))


class run_randomly:
    def __init__(self, run_sequentially=False):
        # Run sequentially is for debugging control files
        self.test_list = []
        self.run_sequentially = run_sequentially


    def add(self, *args, **dargs):
        test = (args, dargs)
        self.test_list.append(test)


    def run(self, fn):
        while self.test_list:
            test_index = random.randint(0, len(self.test_list)-1)
            if self.run_sequentially:
                test_index = 0
            (args, dargs) = self.test_list.pop(test_index)
            fn(*args, **dargs)


def import_site_module(path, module, dummy=None, modulefile=None):
    """
    Try to import the site specific module if it exists.

    @param path full filename of the source file calling this (ie __file__)
    @param module full module name
    @param dummy dummy value to return in case there is no symbol to import
    @param modulefile module filename

    @return site specific module or dummy

    @raises ImportError if the site file exists but imports fails
    """
    short_module = module[module.rfind(".") + 1:]

    if not modulefile:
        modulefile = short_module + ".py"

    if os.path.exists(os.path.join(os.path.dirname(path), modulefile)):
        return __import__(module, {}, {}, [short_module])
    return dummy


def import_site_symbol(path, module, name, dummy=None, modulefile=None):
    """
    Try to import site specific symbol from site specific file if it exists

    @param path full filename of the source file calling this (ie __file__)
    @param module full module name
    @param name symbol name to be imported from the site file
    @param dummy dummy value to return in case there is no symbol to import
    @param modulefile module filename

    @return site specific symbol or dummy

    @raises ImportError if the site file exists but imports fails
    """
    module = import_site_module(path, module, modulefile=modulefile)
    if not module:
        return dummy

    # special unique value to tell us if the symbol can't be imported
    cant_import = object()

    obj = getattr(module, name, cant_import)
    if obj is cant_import:
        logging.debug("unable to import site symbol '%s', using non-site "
                      "implementation", name)
        return dummy

    return obj


def import_site_class(path, module, classname, baseclass, modulefile=None):
    """
    Try to import site specific class from site specific file if it exists

    Args:
        path: full filename of the source file calling this (ie __file__)
        module: full module name
        classname: class name to be loaded from site file
        baseclass: base class object to return when no site file present or
            to mixin when site class exists but is not inherited from baseclass
        modulefile: module filename

    Returns: baseclass if site specific class does not exist, the site specific
        class if it exists and is inherited from baseclass or a mixin of the
        site specific class and baseclass when the site specific class exists
        and is not inherited from baseclass

    Raises: ImportError if the site file exists but imports fails
    """

    res = import_site_symbol(path, module, classname, None, modulefile)
    if res:
        if not issubclass(res, baseclass):
            # if not a subclass of baseclass then mix in baseclass with the
            # site specific class object and return the result
            res = type(classname, (res, baseclass), {})
    else:
        res = baseclass

    return res


def import_site_function(path, module, funcname, dummy, modulefile=None):
    """
    Try to import site specific function from site specific file if it exists

    Args:
        path: full filename of the source file calling this (ie __file__)
        module: full module name
        funcname: function name to be imported from site file
        dummy: dummy function to return in case there is no function to import
        modulefile: module filename

    Returns: site specific function object or dummy

    Raises: ImportError if the site file exists but imports fails
    """

    return import_site_symbol(path, module, funcname, dummy, modulefile)


def _get_pid_path(program_name):
    my_path = os.path.dirname(__file__)
    return os.path.abspath(os.path.join(my_path, "..", "..",
                                        "%s.pid" % program_name))


def write_pid(program_name):
    """
    Try to drop <program_name>.pid in the main autotest directory.

    Args:
      program_name: prefix for file name
    """
    pidfile = open(_get_pid_path(program_name), "w")
    try:
        pidfile.write("%s\n" % os.getpid())
    finally:
        pidfile.close()


def delete_pid_file_if_exists(program_name):
    """
    Tries to remove <program_name>.pid from the main autotest directory.
    """
    pidfile_path = _get_pid_path(program_name)

    try:
        os.remove(pidfile_path)
    except OSError:
        if not os.path.exists(pidfile_path):
            return
        raise


def get_pid_from_file(program_name):
    """
    Reads the pid from <program_name>.pid in the autotest directory.

    @param program_name the name of the program
    @return the pid if the file exists, None otherwise.
    """
    pidfile_path = _get_pid_path(program_name)
    if not os.path.exists(pidfile_path):
        return None

    pidfile = open(_get_pid_path(program_name), 'r')

    try:
        try:
            pid = int(pidfile.readline())
        except IOError:
            if not os.path.exists(pidfile_path):
                return None
            raise
    finally:
        pidfile.close()

    return pid


def program_is_alive(program_name):
    """
    Checks if the process is alive and not in Zombie state.

    @param program_name the name of the program
    @return True if still alive, False otherwise
    """
    pid = get_pid_from_file(program_name)
    if pid is None:
        return False
    return pid_is_alive(pid)


def signal_program(program_name, sig=signal.SIGTERM):
    """
    Sends a signal to the process listed in <program_name>.pid

    @param program_name the name of the program
    @param sig signal to send
    """
    pid = get_pid_from_file(program_name)
    if pid:
        signal_pid(pid, sig)


def get_relative_path(path, reference):
    """Given 2 absolute paths "path" and "reference", compute the path of
    "path" as relative to the directory "reference".

    @param path the absolute path to convert to a relative path
    @param reference an absolute directory path to which the relative
        path will be computed
    """
    # normalize the paths (remove double slashes, etc)
    assert(os.path.isabs(path))
    assert(os.path.isabs(reference))

    path = os.path.normpath(path)
    reference = os.path.normpath(reference)

    # we could use os.path.split() but it splits from the end
    path_list = path.split(os.path.sep)[1:]
    ref_list = reference.split(os.path.sep)[1:]

    # find the longest leading common path
    for i in xrange(min(len(path_list), len(ref_list))):
        if path_list[i] != ref_list[i]:
            # decrement i so when exiting this loop either by no match or by
            # end of range we are one step behind
            i -= 1
            break
    i += 1
    # drop the common part of the paths, not interested in that anymore
    del path_list[:i]

    # for each uncommon component in the reference prepend a ".."
    path_list[:0] = ['..'] * (len(ref_list) - i)

    return os.path.join(*path_list)


def sh_escape(command):
    """
    Escape special characters from a command so that it can be passed
    as a double quoted (" ") string in a (ba)sh command.

    Args:
            command: the command string to escape.

    Returns:
            The escaped command string. The required englobing double
            quotes are NOT added and so should be added at some point by
            the caller.

    See also: http://www.tldp.org/LDP/abs/html/escapingsection.html
    """
    command = command.replace("\\", "\\\\")
    command = command.replace("$", r'\$')
    command = command.replace('"', r'\"')
    command = command.replace('`', r'\`')
    return command


def configure(extra=None, configure='./configure'):
    """
    Run configure passing in the correct host, build, and target options.

    @param extra: extra command line arguments to pass to configure
    @param configure: which configure script to use
    """
    args = []
    if 'CHOST' in os.environ:
        args.append('--host=' + os.environ['CHOST'])
    if 'CBUILD' in os.environ:
        args.append('--build=' + os.environ['CBUILD'])
    if 'CTARGET' in os.environ:
        args.append('--target=' + os.environ['CTARGET'])
    if extra:
        args.append(extra)

    system('%s %s' % (configure, ' '.join(args)))


def compare_versions(ver1, ver2):
    """Version number comparison between ver1 and ver2 strings.

    >>> compare_tuple("1", "2")
    -1
    >>> compare_tuple("foo-1.1", "foo-1.2")
    -1
    >>> compare_tuple("1.2", "1.2a")
    -1
    >>> compare_tuple("1.2b", "1.2a")
    1
    >>> compare_tuple("1.3.5.3a", "1.3.5.3b")
    -1

    Args:
        ver1: version string
        ver2: version string

    Returns:
        int:  1 if ver1 >  ver2
              0 if ver1 == ver2
             -1 if ver1 <  ver2
    """
    ax = re.split('[.-]', ver1)
    ay = re.split('[.-]', ver2)
    while len(ax) > 0 and len(ay) > 0:
        cx = ax.pop(0)
        cy = ay.pop(0)
        maxlen = max(len(cx), len(cy))
        c = cmp(cx.zfill(maxlen), cy.zfill(maxlen))
        if c != 0:
            return c
    return cmp(len(ax), len(ay))