File-system ID may be duplicated among databases located on different volumes
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Key: CORE-6323
URL: http://tracker.firebirdsql.org/browse/CORE-6323
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 4.0 Beta 2, 3.0.5, 2.5.9, 4.0 Beta 1, 3.0.4, 3.0.3,
2.5.8, 4.0 Alpha 1, 3.0.2, 2.5.7, 3.0.1, 2.5.6, 3.0.0, 4.0 Initial, 2.5.5,
2.5.4, 2.5.3 Update 1, 2.1.7, 2.5.3, 2.5.2 Update 1, 2.5.2, 2.5.1, 2.5.0
Environment: Windows only
Reporter: Dmitry Yemanov
Firebird uses file-system ID of the open database file to uniquely name its
dependent shared memory files - lock table, event table, etc. File-system ID is
retrieved using GetFileInformationByHandle() API and composed from the three
fields (dwVolumeSerialNumber, nFileIndexHigh, nFileIndexLow) that are
documented in MSDN as providing a unique combination:
https://docs.microsoft.com/ru-ru/windows/win32/api/fileapi/nf-fileapi-getfileinformationbyhandle
"You can compare the VolumeSerialNumber and FileIndex members returned in the
BY_HANDLE_FILE_INFORMATION structure to determine if two paths map to the same
target; for example, you can compare two file paths and determine if they map
to the same directory."
The problem, however, is that Volume Serial Number (VSN) is not guaranteed to
be unique. It's generated when then the volume is formatted and it's stored
inside the volume's master boot record. But if the volume is cloned at the
physical block level, or if a virtual (preformatted) drive is used, or if a
volume snapshot (created by storage system like Dell EMC) is attached as a
different logical drive, then VSN may duplicate an existing VSN. This may cause
two different databases (located on different volumes) to share the same
file-system ID thus sharing the same lock table, causing unexpected freezes and
other undesired side-effects.
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