| Current File : //usr/lib64/python3.6/site-packages/borg/platform/base.py |
import errno
import os
import socket
import uuid
from borg.helpers import safe_unlink
"""
platform base module
====================
Contains platform API implementations based on what Python itself provides. More specific
APIs are stubs in this module.
When functions in this module use platform APIs themselves they access the public
platform API: that way platform APIs provided by the platform-specific support module
are correctly composed into the base functionality.
"""
API_VERSION = '1.1_04'
fdatasync = getattr(os, 'fdatasync', os.fsync)
def acl_get(path, item, st, numeric_owner=False):
"""
Saves ACL Entries
If `numeric_owner` is True the user/group field is not preserved only uid/gid
"""
def acl_set(path, item, numeric_owner=False):
"""
Restore ACL Entries
If `numeric_owner` is True the stored uid/gid is used instead
of the user/group names
"""
try:
from os import lchflags
def set_flags(path, bsd_flags, fd=None):
lchflags(path, bsd_flags)
except ImportError:
def set_flags(path, bsd_flags, fd=None):
pass
def get_flags(path, st):
"""Return BSD-style file flags for path or stat without following symlinks."""
return getattr(st, 'st_flags', 0)
def sync_dir(path):
fd = os.open(path, os.O_RDONLY)
try:
os.fsync(fd)
except OSError as os_error:
# Some network filesystems don't support this and fail with EINVAL.
# Other error codes (e.g. EIO) shouldn't be silenced.
if os_error.errno != errno.EINVAL:
raise
finally:
os.close(fd)
def safe_fadvise(fd, offset, len, advice):
if hasattr(os, 'posix_fadvise'):
advice = getattr(os, 'POSIX_FADV_' + advice)
try:
os.posix_fadvise(fd, offset, len, advice)
except OSError:
# usually, posix_fadvise can't fail for us, but there seem to
# be failures when running borg under docker on ARM, likely due
# to a bug outside of borg.
# also, there is a python wrapper bug, always giving errno = 0.
# https://github.com/borgbackup/borg/issues/2095
# as this call is not critical for correct function (just to
# optimize cache usage), we ignore these errors.
pass
class SyncFile:
"""
A file class that is supposed to enable write ordering (one way or another) and data durability after close().
The degree to which either is possible varies with operating system, file system and hardware.
This fallback implements a naive and slow way of doing this. On some operating systems it can't actually
guarantee any of the above, since fsync() doesn't guarantee it. Furthermore it may not be possible at all
to satisfy the above guarantees on some hardware or operating systems. In these cases we hope that the thorough
checksumming implemented catches any corrupted data due to misordered, delayed or partial writes.
Note that POSIX doesn't specify *anything* about power failures (or similar failures). A system that
routinely loses files or corrupts file on power loss is POSIX compliant.
Calling SyncFile(path) for an existing path will raise FileExistsError, see comment in __init__.
TODO: Use F_FULLSYNC on OSX.
TODO: A Windows implementation should use CreateFile with FILE_FLAG_WRITE_THROUGH.
"""
def __init__(self, path, *, fd=None, binary=False):
"""
Open a SyncFile.
:param path: full path/filename
:param fd: additionally to path, it is possible to give an already open OS-level fd
that corresponds to path (like from os.open(path, ...) or os.mkstemp(...))
:param binary: whether to open in binary mode, default is False.
"""
mode = 'xb' if binary else 'x' # x -> raise FileExists exception in open() if file exists already
self.path = path
if fd is None:
self.f = open(path, mode=mode) # python file object
else:
self.f = os.fdopen(fd, mode=mode)
self.fd = self.f.fileno() # OS-level fd
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
def write(self, data):
self.f.write(data)
def sync(self):
"""
Synchronize file contents. Everything written prior to sync() must become durable before anything written
after sync().
"""
from .. import platform
self.f.flush()
platform.fdatasync(self.fd)
# tell the OS that it does not need to cache what we just wrote,
# avoids spoiling the cache for the OS and other processes.
safe_fadvise(self.fd, 0, 0, 'DONTNEED')
def close(self):
"""sync() and close."""
from .. import platform
dirname = None
try:
dirname = os.path.dirname(self.path)
self.sync()
finally:
self.f.close()
if dirname:
platform.sync_dir(dirname)
class SaveFile:
"""
Update file contents atomically.
Must be used as a context manager (defining the scope of the transaction).
On a journaling file system the file contents are always updated
atomically and won't become corrupted, even on power failures or
crashes (for caveats see SyncFile).
SaveFile can safely by used in parallel (e.g. by multiple processes) to write
to the same target path. Whatever writer finishes last (executes the os.replace
last) "wins" and has successfully written its content to the target path.
Internally used temporary files are created in the target directory and are
named <BASENAME>-<RANDOMCHARS>.tmp and cleaned up in normal and error conditions.
"""
def __init__(self, path, binary=False):
self.binary = binary
self.path = path
self.dir = os.path.dirname(path)
self.tmp_prefix = os.path.basename(path) + '-'
self.tmp_fd = None # OS-level fd
self.tmp_fname = None # full path/filename corresponding to self.tmp_fd
self.f = None # python-file-like SyncFile
def __enter__(self):
from .. import platform
from ..helpers import mkstemp_mode
self.tmp_fd, self.tmp_fname = mkstemp_mode(prefix=self.tmp_prefix, suffix='.tmp', dir=self.dir, mode=0o666)
self.f = platform.SyncFile(self.tmp_fname, fd=self.tmp_fd, binary=self.binary)
return self.f
def __exit__(self, exc_type, exc_val, exc_tb):
from .. import platform
self.f.close() # this indirectly also closes self.tmp_fd
self.tmp_fd = None
if exc_type is not None:
safe_unlink(self.tmp_fname) # with-body has failed, clean up tmp file
return # continue processing the exception normally
try:
os.replace(self.tmp_fname, self.path) # POSIX: atomic rename
except OSError:
safe_unlink(self.tmp_fname) # rename has failed, clean up tmp file
raise
finally:
platform.sync_dir(self.dir)
def swidth(s):
"""terminal output width of string <s>
For western scripts, this is just len(s), but for cjk glyphs, 2 cells are used.
"""
return len(s)
# patched socket.getfqdn() - see https://bugs.python.org/issue5004
def getfqdn(name=''):
"""Get fully qualified domain name from name.
An empty argument is interpreted as meaning the local host.
"""
name = name.strip()
if not name or name == '0.0.0.0':
name = socket.gethostname()
try:
addrs = socket.getaddrinfo(name, None, 0, socket.SOCK_DGRAM, 0, socket.AI_CANONNAME)
except socket.error:
pass
else:
for addr in addrs:
if addr[3]:
name = addr[3]
break
return name
# for performance reasons, only determine hostname / fqdn / hostid once.
# XXX this sometimes requires live internet access for issuing a DNS query in the background.
hostname = socket.gethostname()
fqdn = getfqdn(hostname)
# some people put the fqdn into /etc/hostname (which is wrong, should be the short hostname)
# fix this (do the same as "hostname --short" cli command does internally):
hostname = hostname.split('.')[0]
# uuid.getnode() is problematic in some environments (e.g. OpenVZ, see #3968) where the virtual MAC address
# is all-zero. uuid.getnode falls back to returning a random value in that case, which is not what we want.
# thus, we offer BORG_HOST_ID where a user can set an own, unique id for each of his hosts.
hostid = os.environ.get('BORG_HOST_ID')
if not hostid:
hostid = '%s@%s' % (fqdn, uuid.getnode())
def get_process_id():
"""
Return identification tuple (hostname, pid, thread_id) for 'us'.
This always returns the current pid, which might be different from before, e.g. if daemonize() was used.
Note: Currently thread_id is *always* zero.
"""
thread_id = 0
pid = os.getpid()
return hostid, pid, thread_id
def process_alive(host, pid, thread):
"""
Check if the (host, pid, thread_id) combination corresponds to a potentially alive process.
"""
raise NotImplementedError
def local_pid_alive(pid):
"""Return whether *pid* is alive."""
raise NotImplementedError