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# -*- coding: utf-8 -*-
#
# Copyright © 2009, 2010, 2012 Red Hat, Inc.
# Authors:
# Nils Philippsen <nils@redhat.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""This module contains helper functions for dealing with files."""
__all__ = ["issamefile", "linkfile", "copyfile", "linkorcopyfile",
"overwrite_safely"]
import os
import selinux
import shutil
import tempfile
import errno
BLOCKSIZE = 1024
def _issamefile(path1, path2):
s1 = os.stat(path1)
s2 = os.stat(path2)
return os.path.samestat(s1, s2)
def issamefile(path1, path2, catch_stat_exceptions=[]):
"""Check whether two paths point to the same file (i.e. are hardlinked)."""
if catch_stat_exceptions == True:
catch_stat_exceptions = Exception
try:
return _issamefile(path1, path2)
except catch_stat_exceptions:
return False
def linkfile(srcpath, dstpath):
"""Hardlink srcpath to dstpath.
Attempt to atomically replace dstpath if it exists."""
if issamefile(srcpath, dstpath, catch_stat_exceptions=OSError):
return
dstpath = os.path.abspath(dstpath)
dstdname = os.path.dirname(dstpath)
dstbname = os.path.basename(dstpath)
hardlinked = False
for attempt in xrange(tempfile.TMP_MAX):
_dsttmp = tempfile.mktemp(prefix=dstbname + os.extsep, dir=dstdname)
try:
os.link(srcpath, _dsttmp)
except OSError, e:
if e.errno == errno.EEXIST:
# try another name
pass
else:
raise
else:
hardlinked = True
break
if hardlinked:
os.rename(_dsttmp, dstpath)
def copyfile(srcpath, dstpath, copy_mode_from_dst=True, run_restorecon=True):
"""Copy srcpath to dstpath.
Abort operation if e.g. not enough space is available. Attempt to
atomically replace dstpath if it exists."""
if issamefile(srcpath, dstpath, catch_stat_exceptions=OSError):
return
dstpath = os.path.abspath(dstpath)
dstdname = os.path.dirname(dstpath)
dstbname = os.path.basename(dstpath)
srcfile = open(srcpath, "rb")
dsttmpfile = tempfile.NamedTemporaryFile(prefix=dstbname + os.path.extsep,
dir=dstdname, delete=False)
mode_copied = False
if copy_mode_from_dst:
# attempt to copy mode from destination file (if it exists,
# otherwise fall back to copying it from the source file below)
try:
shutil.copymode(dstpath, dsttmpfile.name)
mode_copied = True
except (shutil.Error, OSError):
pass
if not mode_copied:
shutil.copymode(srcpath, dsttmpfile.name)
data = None
while data != "":
data = srcfile.read(BLOCKSIZE)
try:
dsttmpfile.write(data)
except:
srcfile.close()
dsttmpfile.close()
os.unlink(dsttmpfile.name)
raise
srcfile.close()
dsttmpfile.close()
os.rename(dsttmpfile.name, dstpath)
if run_restorecon and selinux.is_selinux_enabled() > 0:
selinux.restorecon(dstpath)
def linkorcopyfile(srcpath, dstpath, copy_mode_from_dst=True,
run_restorecon=True):
"""First attempt to hardlink srcpath to dstpath, if hardlinking isn't
possible, attempt copying srcpath to dstpath."""
try:
linkfile(srcpath, dstpath)
return
except OSError, e:
if e.errno not in (errno.EMLINK, errno.EPERM, errno.EXDEV):
# don't bother copying
raise
else:
# try copying
pass
copyfile(srcpath, dstpath, copy_mode_from_dst, run_restorecon)
def symlink_atomically(srcpath, dstpath, force=False, preserve_context=True):
"""Create a symlink, optionally replacing dstpath atomically, optionally
setting or preserving SELinux context."""
dstdname = os.path.dirname(dstpath)
dstbname = os.path.basename(dstpath)
run_restorecon = False
ctx = None
if preserve_context and selinux.is_selinux_enabled() <= 0:
preserve_context = False
else:
try:
ret, ctx = selinux.lgetfilecon(dstpath)
if ret < 0:
raise RuntimeError("getfilecon(%r) failed" % dstpath)
except OSError, e:
if e.errno == errno.ENOENT:
run_restorecon = True
else:
raise
if not force:
os.symlink(srcpath, dstpath)
if preserve_context:
selinux.restorecon(dstpath)
else:
dsttmp = None
for attempt in xrange(tempfile.TMP_MAX):
_dsttmp = tempfile.mktemp(prefix=dstbname + os.extsep, dir=dstdname)
try:
os.symlink(srcpath, _dsttmp)
except OSError, e:
if e.errno == errno.EEXIST:
# try again
continue
raise
else:
dsttmp = _dsttmp
break
if dsttmp is None:
raise IOError(errno.EEXIST,
"No suitable temporary symlink could be created.")
if preserve_context and not run_restorecon:
selinux.lsetfilecon(dsttmp, ctx)
try:
os.rename(dsttmp, dstpath)
except:
# clean up
os.remove(dsttmp)
raise
if run_restorecon:
selinux.restorecon(dstpath)
def overwrite_safely(path, content, preserve_mode=True, preserve_context=True):
"""Safely overwrite a file by creating a temporary file in the same
directory, writing it, moving it over the original file, eventually
preserving file mode and SELinux context."""
path = os.path.realpath(path)
dir_ = os.path.dirname(path)
base = os.path.basename(path)
fd = None
f = None
tmpname = None
exists = os.path.exists(path)
if preserve_context and selinux.is_selinux_enabled() <= 0:
preserve_context = False
try:
fd, tmpname = tempfile.mkstemp(prefix=base + os.path.extsep,
dir=dir_)
if exists and preserve_mode:
shutil.copymode(path, tmpname)
if exists and preserve_context:
ret, ctx = selinux.getfilecon(path)
if ret < 0:
raise RuntimeError("getfilecon(%r) failed" % path)
f = os.fdopen(fd, "w")
fd = None
f.write(content)
f.close()
f = None
os.rename(tmpname, path)
if preserve_context:
if exists:
selinux.setfilecon(path, ctx)
else:
selinux.restorecon(path)
finally:
if f:
f.close()
elif fd:
os.close(fd)
if tmpname and os.path.isfile(tmpname):
try:
os.unlink(tmpname)
except:
pass