uncow.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# uncow, a simple script to uncow files copied into a fresh btrfs subvolume
#
# (C)opyright 2012 Alex Bennée
# License: GPLv3
#
# Usage:
#  - create a new btrfs subvolume with nodatacow mount option
#  - move all the data you want into the new subvolume
#  - find <SPEC> | xargs uncow.py
#
# What the script does:
#  - create a new file
#  - copy the contents of the old file to new
#  - rm the old file
#  - rename the new file to the old files name
#

import sys,os
import argparse
from uuid import uuid3, NAMESPACE_URL
from shutil import copyfile
from subprocess import check_output,check_call,STDOUT,CalledProcessError
from re import search
from array import array
from fcntl import ioctl

# IOCTL constants, ganked from strace of lsattr/chattr
FS_GET_FLAGS=0x80086601
FS_SET_FLAGS=0x40086602
FS_NOWCOW_FL=0x00800000

checked_dirs=dict()

def check_attributes(verbose, directory):
    flags=array('I', [0])
    fd=os.open(directory, os.O_DIRECTORY)
    ioctl(fd, FS_GET_FLAGS, flags, 1)
    if verbose: print "check_for_nowcow(%s) => %x" % (directory, flags[0])
    os.close(fd)
    return flags[0]

def check_and_modify_dir(verbose, directory):
    """
    check directory has +C attribute, if not set it
    """
    if directory in checked_dirs:
        return

    flags=check_attributes(verbose, directory)
    if flags & FS_NOWCOW_FL:
        checked_dirs[directory]=1
    else:
        fd=os.open(directory, os.O_DIRECTORY)
        new_flags=array('I', [flags|FS_NOWCOW_FL])
        if verbose: print "setting +C/%x for %s" % (new_flags[0], directory)
        try:
            ioctl(fd, FS_SET_FLAGS, new_flags)
        except:
            print "Error setting +C for %s" % (directory)
            sys.exit(-2)
        if verbose: print "new flags now %x" % (check_attributes(verbose, directory))

        os.close(fd)
        

parser = argparse.ArgumentParser(description='Create new non-COW files with old data.',
                                 epilog='If passed a directory instead of a file it will just make '+
                                 'the attributes changes for new files')

parser.add_argument('files', metavar='FILE', nargs='+', help='filepath to uncow')
parser.add_argument('-v', '--verbose', action='store_true', default=False, help="Verbose output")
args = parser.parse_args()

for p in args.files:
    absp = os.path.abspath(p)
    if os.path.exists(absp):
        if os.path.isdir(absp):
            check_and_modify_dir(args.verbose, absp)
        elif os.path.isfile(absp):
            old_filename=os.path.basename(absp)
            dirname=os.path.dirname(absp)
            check_and_modify_dir(args.verbose, dirname)
            
            new_filename="%s/%s-%s" % (dirname, old_filename, uuid3(NAMESPACE_URL, old_filename))
            try:
                if args.verbose: print "creating new file %s" % (new_filename)
                copyfile(absp, new_filename)
                if args.verbose: print "removing old file %s" % (absp)
                os.unlink(absp)
                if args.verbose: print "renaming %s to %s" % (new_filename, absp)
                os.rename(new_filename, absp)
            except:
                print "error with %s, %s" % (absp, new_filename)
                exit -1
        else:
            print "can't operate on things that aren't directories or files (%s)" % (absp)
            exit -1