Eryk Sun <eryk...@gmail.com> added the comment:
> C:\Users>fsutil file queryfileid u:\test\test.jpg
> File ID is 0x00000000000029d500000000000004ae
ReFS uses a 128-bit file ID, which I gather consists of a 64-bit directory ID
and a 64-bit relative ID. (Take this with a grain of salt. AFAIK, Microsoft
hasn't published a spec for ReFS.) The latter is 0 for the directory itself and
increments by 1 for each file created in the directory, with no reuse of
previous values if a file is deleted or moved. If that's correct, and if
"test.jpg" was created in "\test", then the directory ID of "\test" is 0x29d5,
and the relative file ID is 0x4ae.
> >>> from pathlib import Path
> >>> hex(Path('U:/test/test.jpg').stat().st_ino)
> '0x4000000004ae29d5'
os.stat calls WINAPI GetFileInformationByHandle, which returns a 64-bit file
ID. It appears that ReFS generates this ID by concatenating the relative ID and
directory ID in a way that is "not guaranteed to be unique" according to the
BY_HANDLE_FILE_INFORMATION [1] docs.
I haven't checked whether this 64-bit file ID can even be used successfully
with OpenFileById [2]. It could be that ReFS simply fails an open-by-ID request
unless it includes the full 128-bit ID (i.e. ExtendedFileIdType).
You can request the 128-bit ID as a FILE_ID_128 record (an array of 16 bytes)
via GetFileInformationByHandleEx: FileIdInfo [3][4]. Maybe os.stat should try
to query the 128-bit ID and use it as st_ino (or st_ino_128) if it's available.
However, looking into my crystal ball, I don't see this happening, unless
someone makes a strong case in its favor.
> The problem does *not* exist on an NTFS volume:
>
> C:\Users>fsutil file queryfileid o:\OneDrive\test\test.jpg
> File ID is 0x0000000000000000000300000001be39
NTFS uses a 64-bit file ID, which consists of a 48-bit MFT record number and a
16-bit sequence number. The latter gets incremented when an MFT record is
reused in order to detect stale references. In the above case, the 48-bit
record number is 0x00000001be39, and the sequence number is 0x0003.
[1]:
https://docs.microsoft.com/en-us/windows/win32/api/fileapi/ns-fileapi-by_handle_file_information
[2]:
https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-openfilebyid
[3]:
https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-getfileinformationbyhandleex
[4]:
https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-file_id_info
----------
nosy: +eryksun
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<https://bugs.python.org/issue40095>
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