Some updates... On Sunday 02 February 2025 16:23:43 Pali Rohár wrote: > And how many bit flags are needed? I have done some investigation. Lets > start with table which describes all 32 possible bit flags which are > used by Windows system and also by filesystems FAT / exFAT / NTFS / ReFS > and also by SMB over network: > > bit / attrib.exe flag / SDK constant / description > > 0 - R - FILE_ATTRIBUTE_READONLY - writing to file or deleting it is disallowed > 1 - H - FILE_ATTRIBUTE_HIDDEN - inode is hidden > 2 - S - FILE_ATTRIBUTE_SYSTEM - inode is part of operating system > 3 - - FILE_ATTRIBUTE_VOLUME - inode is the disk volume label entry > 4 - - FILE_ATTRIBUTE_DIRECTORY - inode is directory > 5 - A - FILE_ATTRIBUTE_ARCHIVE - inode was not archived yet (when set) > 6 - - FILE_ATTRIBUTE_DEVICE - inode represents in-memory device (e.g. C:\), flag not stored on filesystem > 7 - - FILE_ATTRIBUTE_NORMAL - no other flag is set (value 0 means to not change flags, bit 7 means to clear all flags) > 8 - - FILE_ATTRIBUTE_TEMPORARY - inode data do not have to be flushed to disk > 9 - - FILE_ATTRIBUTE_SPARSE_FILE - file is sparse with holes > 10 - - FILE_ATTRIBUTE_REPARSE_POINT - inode has attached reparse point (symlink is also reparse point) > 11 - - FILE_ATTRIBUTE_COMPRESSED - file is compressed, for directories it means that newly created inodes would have this flag set > 12 - O - FILE_ATTRIBUTE_OFFLINE - HSM - inode is used by HSM > 13 - I - FILE_ATTRIBUTE_NOT_CONTENT_INDEXED - inode will not be indexed by content indexing service > 14 - - FILE_ATTRIBUTE_ENCRYPTED - file is encrypted, for directories it means that newly created inodes would have this flag set > 15 - V - FILE_ATTRIBUTE_INTEGRITY_STREAM - fs does checksumming of data and metadata when reading inode, read-only FILE_ATTRIBUTE_INTEGRITY_STREAM can be enabled for individual inode via FSCTL_SET_INTEGRITY_INFORMATION or FSCTL_SET_INTEGRITY_INFORMATION_EX fs ioctl call, available on Windows and also via SMB protocol. So de-facto it is read-write attribute, just over SMB requires separate operation for changing it. In similar way can be modified also FILE_ATTRIBUTE_COMPRESSED and FILE_ATTRIBUTE_ENCRYPTED attributes. > 16 - - FILE_ATTRIBUTE_VIRTUAL - inode is in %LocalAppData%\VirtualStore, flag not stored on filesystem > 17 - X - FILE_ATTRIBUTE_NO_SCRUB_DATA - do not use scrubber (proactive background data integrity scanner) on this file, for directories it means that newly created inodes would have this flag set > 18 - - FILE_ATTRIBUTE_EA - inode has xattrs, (not in readdir output, shares same bit with FILE_ATTRIBUTE_RECALL_ON_OPEN) > 18 - - FILE_ATTRIBUTE_RECALL_ON_OPEN - HSM - inode is not stored locally (only in readdir output, shares same bit with FILE_ATTRIBUTE_EA) > 19 - P - FILE_ATTRIBUTE_PINNED - HSM - inode data content must be always stored on locally > 20 - U - FILE_ATTRIBUTE_UNPINNED - HSM - inode data content can be removed from local storage > 21 - - - reserved > 22 - - FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS - HSM - inode data content is not stored locally > 23 - - - reserved > 24 - - - reserved > 25 - - - reserved > 26 - - - reserved > 27 - - - reserved > 28 - - - reserved > 29 - B - FILE_ATTRIBUTE_STRICTLY_SEQUENTIAL - SMR Blob, unknown meaning, read-only > 30 - - - reserved > 31 - - - reserved > > (HSM means Hierarchical Storage Management software, which uses reparse > points to make some remote file/folder available on the local > filesystem, for example OneDrive or DropBox) > > From above list only following bit flags are suitable for modification > over some Linux API: > - FILE_ATTRIBUTE_READONLY > - FILE_ATTRIBUTE_HIDDEN > - FILE_ATTRIBUTE_SYSTEM > - FILE_ATTRIBUTE_ARCHIVE > - FILE_ATTRIBUTE_TEMPORARY > - FILE_ATTRIBUTE_COMPRESSED > - FILE_ATTRIBUTE_OFFLINE > - FILE_ATTRIBUTE_NOT_CONTENT_INDEXED > - FILE_ATTRIBUTE_ENCRYPTED > - FILE_ATTRIBUTE_NO_SCRUB_DATA > - FILE_ATTRIBUTE_PINNED > - FILE_ATTRIBUTE_UNPINNED Hence this list needs to be extended by FILE_ATTRIBUTE_INTEGRITY_STREAM attribute. FILE_ATTRIBUTE_INTEGRITY_STREAM is interesting attribute as it allows to enable checksumming of file content. > And if I'm looking correctly the FILE_ATTRIBUTE_COMPRESSED can be > already mapped to Linux FS_COMPR_FL / STATX_ATTR_COMPRESSED, which has > same meaning. Also FILE_ATTRIBUTE_ENCRYPTED can be mapped to > FS_ENCRYPT_FL / STATX_ATTR_ENCRYPTED. Note that these two flags cannot > be set over WinAPI or SMB directly and it is required to use special > WinAPI or SMB ioctl. > > So totally are needed 10 new bit flags. And for future there are 9 > reserved bits which could be introduced by MS in future. > > Additionally there are get-only attributes which can be useful for statx > purposes (for example exported by cifs.ko SMB client): > - FILE_ATTRIBUTE_REPARSE_POINT > - FILE_ATTRIBUTE_INTEGRITY_STREAM > - FILE_ATTRIBUTE_RECALL_ON_OPEN > - FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS > - FILE_ATTRIBUTE_STRICTLY_SEQUENTIAL > > From the above list of flags suitable for modification, following bit > flags have no meaning for kernel and it is up to userspace how will use > them. What is needed from kernel and/or filesystem driver is to preserve > those bit flags. > - FILE_ATTRIBUTE_HIDDEN > - FILE_ATTRIBUTE_SYSTEM > - FILE_ATTRIBUTE_ARCHIVE > - FILE_ATTRIBUTE_NOT_CONTENT_INDEXED > > Following are bit flags which kernel / VFS / fsdriver would have to > handle specially, to provide enforcement or correct behavior of them: > - FILE_ATTRIBUTE_READONLY - enforce that data modification or unlink is disallowed when set > - FILE_ATTRIBUTE_COMPRESSED - enforce compression on filesystem when set > - FILE_ATTRIBUTE_ENCRYPTED - enforce encryption on filesystem when set > > Then there are HSM flags which for local filesystem would need some > cooperation with userspace synchronization software. For network > filesystems (SMB / NFS4) they need nothing special, just properly > propagating them over network: > - FILE_ATTRIBUTE_OFFLINE > - FILE_ATTRIBUTE_PINNED > - FILE_ATTRIBUTE_UNPINNED > > About following 2 flags, I'm not sure if the kernel / VFS / fs driver > has to do something or it can just store bits to fs: > - FILE_ATTRIBUTE_TEMPORARY > - FILE_ATTRIBUTE_NO_SCRUB_DATA
