Eryk Sun <[email protected]> added the comment:
In FSBO [1] section 6 "Time Stamps", note that the LastWriteTime value gets
updated when an IRP_MJ_FLUSH_BUFFERS is processed. In the Windows API, this is
a FlushFileBuffers [2] call. In the C runtime, it's a _commit [3] call, which
is an os.fsync [4] call in Python. Calling the latter will update the directory
entry for the file.
For an example implementation in the FAT32 filesystem, see
FatCommonFlushBuffers [5]. Note in the UserFileOpen case that it flushes any
cached data via FatFlushFile and then updates the directory entry from the file
control block (FCB) via FatUpdateDirentFromFcb, and finally it flushes the
parent directory control blocks (DCBs) -- and possibly also the volume.
Example with os.fsync:
import os
import time
import datetime
UPDATE_DIR = True
FILEPATH = 'C:/Temp/test/spam.txt'
def scan(filepath):
dir_path, filename = os.path.split(filepath)
with os.scandir(dir_path) as iter_dir:
for entry in iter_dir:
if entry.name == filename:
return entry
with open(FILEPATH, 'w') as f:
while True:
print('spam', file=f, flush=True)
if UPDATE_DIR:
os.fsync(f.fileno())
entry = scan(FILEPATH)
stat_result = entry.stat()
now = datetime.datetime.now()
print(f'st_mtime: {stat_result.st_mtime:0.3f}, '
f'delta_t: {now.timestamp() - stat_result.st_mtime:0.3f}')
time.sleep(1.0)
[1] https://go.microsoft.com/fwlink/?LinkId=140636
[2]
https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-flushfilebuffers
[3]
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/commit?view=vs-2019
[4] https://docs.python.org/3/library/os.html#os.fsync
[5]
https://github.com/microsoft/Windows-driver-samples/blob/9afd93066dfd9db12f66099cf9ec44b6fd734b2d/filesys/fastfat/flush.c#L145
----------
nosy: +eryksun
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