Synnefo » snf-image-creator

# -*- coding: utf-8 -*-

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# Copyright 2012 GRNET S.A. All rights reserved.

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"""This module provides various helper functions to be used by other parts of

the package.

"""

import sh

import hashlib

import time

import os

class FatalError(Exception):

    """Fatal Error exception of snf-image-creator"""

    pass

def get_command(command):

    """Return a file system binary command"""

    def find_sbin_command(command, exception):

        search_paths = ['/usr/local/sbin', '/usr/sbin', '/sbin']

        for fullpath in map(lambda x: "%s/%s" % (x, command), search_paths):

            if os.path.exists(fullpath) and os.access(fullpath, os.X_OK):

                return sh.Command(fullpath)

        raise exception

    try:

        return sh.__getattr__(command)

    except sh.CommandNotFound as e:

        return find_sbin_command(command, e)

def try_fail_repeat(command, *args):

    """Execute a command multiple times until it succeeds"""

    times = (0.1, 0.5, 1, 2)

    i = iter(times)

    while True:

        try:

            command(*args)

            return

        except sh.ErrorReturnCode:

            try:

                wait = i.next()

            except StopIteration:

                break

            time.sleep(wait)

    raise FatalError("Command: `%s %s' failed" % (command, " ".join(args)))

def free_space(dirname):

    """Compute the free space in a directory"""

    stat = os.statvfs(dirname)

    return stat.f_bavail * stat.f_frsize

def check_guestfs_version(ghandler, major, minor, release):

    """Checks if the version of the used libguestfs is smaller, equal or

    greater than the one specified by the major, minor and release triplet

    Returns:

        < 0 if the installed version is smaller than the specified one

        = 0 if they are equal

        > 0 if the installed one is greater than the specified one

    """

    ver = ghandler.version()

    for (a, b) in (ver['major'], major), (ver['minor'], minor), \

            (ver['release'], release):

        if a != b:

            return a - b

    return 0

class MD5:

    """Represents MD5 computations"""

    def __init__(self, output):

        """Create an MD5 instance"""

        self.out = output

    def compute(self, filename, size):

        """Compute the MD5 checksum of a file"""

        MB = 2 ** 20

        BLOCKSIZE = 4 * MB  # 4MB

        prog_size = ((size + MB - 1) // MB)  # in MB

        progressbar = self.out.Progress(prog_size, "Calculating md5sum", 'mb')

        md5 = hashlib.md5()

        with open(filename, "r") as src:

            left = size

            while left > 0:

                length = min(left, BLOCKSIZE)

                data = src.read(length)

                md5.update(data)

                left -= length

                progressbar.goto((size - left) // MB)

        checksum = md5.hexdigest()

        progressbar.success(checksum)

        return checksum

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