move/refactor Archive._open_rb function to helpers.os_open

also:
- add and use OsOpen context manager
- add O_NONBLOCK, O_NOFOLLOW, O_NOCTTY (inspired by gnu tar)

src/borg/archive.py

@@ -38,6 +38,7 @@ from .helpers import StableDict
 from .helpers import bin_to_hex
 from .helpers import safe_ns
 from .helpers import ellipsis_truncate, ProgressIndicatorPercent, log_multi
+from .helpers import os_open, flags_normal
 from .helpers import msgpack
 from .patterns import PathPrefixPattern, FnmatchPattern, IECommand
 from .item import Item, ArchiveItem, ItemDiff
@@ -47,9 +48,6 @@ from .repository import Repository, LIST_SCAN_LIMIT
 
 has_lchmod = hasattr(os, 'lchmod')
 
-flags_normal = os.O_RDONLY | getattr(os, 'O_BINARY', 0)
-flags_noatime = flags_normal | getattr(os, 'O_NOATIME', 0)
-
 
 class Statistics:
 
@@ -197,6 +195,16 @@ def backup_io_iter(iterator):
         yield item
 
 
+@contextmanager
+def OsOpen(path, flags, noatime=False, op='open'):
+    with backup_io(op):
+        fd = os_open(path, flags, noatime)
+    try:
+        yield fd
+    finally:
+        os.close(fd)
+
+
 class DownloadPipeline:
 
     def __init__(self, repository, key):
@@ -826,18 +834,6 @@ Utilization of max. archive size: {csize_max:.0%}
             logger.warning('forced deletion succeeded, but the deleted archive was corrupted.')
             logger.warning('borg check --repair is required to free all space.')
 
-    @staticmethod
-    def _open_rb(path):
-        try:
-            # if we have O_NOATIME, this likely will succeed if we are root or owner of file:
-            return os.open(path, flags_noatime)
-        except PermissionError:
-            if flags_noatime == flags_normal:
-                # we do not have O_NOATIME, no need to try again:
-                raise
-            # Was this EPERM due to the O_NOATIME flag? Try again without it:
-            return os.open(path, flags_normal)
-
     @staticmethod
     def compare_archives_iter(archive1, archive2, matcher=None, can_compare_chunk_ids=False):
         """
@@ -1126,9 +1122,7 @@ class FilesystemObjectProcessors:
 
     def process_file(self, path, st, cache):
         with self.create_helper(path, st, None) as (item, status, hardlinked, hardlink_master):  # no status yet
-            with backup_io('open'):
-                fd = Archive._open_rb(path)
-            try:
+            with OsOpen(path, flags_normal, noatime=True) as fd:
                 with backup_io('fstat'):
                     curr_st = os.fstat(fd)
                 # XXX do some checks here: st vs. curr_st
@@ -1178,8 +1172,6 @@ class FilesystemObjectProcessors:
                     # we processed a special file like a regular file. reflect that in mode,
                     # so it can be extracted / accessed in FUSE mount like a regular file:
                     item.mode = stat.S_IFREG | stat.S_IMODE(item.mode)
-            finally:
-                os.close(fd)
             return status
 
 

src/borg/helpers/fs.py

@@ -189,6 +189,36 @@ def dash_open(path, mode):
         return open(path, mode)
 
 
+def O_(*flags):
+    result = 0
+    for flag in flags:
+        result |= getattr(os, 'O_' + flag, 0)
+    return result
+
+
+flags_base = O_('BINARY', 'NONBLOCK', 'NOCTTY')  # later: add 'NOFOLLOW'
+flags_normal = flags_base | O_('RDONLY')
+flags_noatime = flags_normal | O_('NOATIME')
+
+
+def os_open(path, flags, noatime=False):
+    _flags_normal = flags
+    if noatime:
+        _flags_noatime = _flags_normal | O_('NOATIME')
+        try:
+            # if we have O_NOATIME, this likely will succeed if we are root or owner of file:
+            fd = os.open(path, _flags_noatime)
+        except PermissionError:
+            if _flags_noatime == _flags_normal:
+                # we do not have O_NOATIME, no need to try again:
+                raise
+            # Was this EPERM due to the O_NOATIME flag? Try again without it:
+            fd = os.open(path, _flags_normal)
+    else:
+        fd = os.open(path, _flags_normal)
+    return fd
+
+
 def umount(mountpoint):
     env = prepare_subprocess_env(system=True)
     try:

src/borg/testsuite/archiver.py

@@ -32,7 +32,7 @@ except ImportError:
 
 import borg
 from .. import xattr, helpers, platform
-from ..archive import Archive, ChunkBuffer, flags_noatime, flags_normal
+from ..archive import Archive, ChunkBuffer
 from ..archiver import Archiver, parse_storage_quota
 from ..cache import Cache, LocalCache
 from ..constants import *  # NOQA
@@ -46,6 +46,7 @@ from ..helpers import EXIT_SUCCESS, EXIT_WARNING, EXIT_ERROR
 from ..helpers import bin_to_hex
 from ..helpers import MAX_S
 from ..helpers import msgpack
+from ..helpers import flags_noatime, flags_normal
 from ..nanorst import RstToTextLazy, rst_to_terminal
 from ..patterns import IECommand, PatternMatcher, parse_pattern
 from ..item import Item, ItemDiff