From: Baolin Liu <liubaolin@kylinos.cn>

This series implements persistent immutable, append-only and nodump flags
using a private $LINUXFLAGS EA in the standard NTFS $EA/$EA_INFORMATION
attributes. No new NTFS attribute type or formatter changes are needed.

The value is a little-endian u32 with immutable, append-only and nodump
in bits 0, 1 and 2. Inode loading restores the flags. Unknown bits are
preserved, and the entry is removed only when its entire value is zero.
The setter protects system metadata and sys_immutable-derived immutable
state, rejects direct writes to $LINUXFLAGS, and updates in-memory flags
only after the EA update succeeds. Fileattr queries also report mount-wide
case folding. Nodump is reported through both fileattr and statx.

Changes since v3 (the standalone revision of patch 2):
- Rename the private EA from $LXFLAGS to $LINUXFLAGS, as agreed with
  Hyunchul, to avoid the WSL-owned $LX namespace. Rename the related
  internal fields, helpers and constants, and update the documentation.
- Include the v3 patch-2 changes: ntfs_listxattr() reuses full-chain
  validation, including size-only queries, and returns EUCLEAN for
  malformed EA structures while preserving lower-level read errors.
- Resend the complete ten-patch series with Hyunchul's Reviewed-by tag.

Changes since v2:
- The EA rename above and the listxattr validation requested during
  review. The on-disk bit assignments and update/rollback behavior
  remain unchanged.

Patch overview:
- Patch 1 fixes the cached EA presence flag after creating or replacing
  the only entry.
- Patch 2 validates EA chains and links zero-terminated tails before
  appending entries.
- Patch 3 preserves EA write errors and reports truncate failures.
- Patch 4 distinguishes missing attributes from lookup failures and
  rejects incomplete EA attribute pairs.
- Patch 5 distinguishes empty EA values from deletion and rejects
  removal or replacement of absent entries.
- Patch 6 prepares the new list before updating attributes, restores
  both old attributes on failure, and shuts down if restoration fails.
- Patch 7 adds fileattr queries for existing inode flags and mount-wide
  case folding.
- Patch 8 introduces the $LINUXFLAGS storage and inode-load paths, adds
  immutable persistence, and protects system-imposed immutable state.
- Patch 9 extends the persistent interface to append-only.
- Patch 10 adds persistent nodump and reports it through fileattr and
  statx.

Testing on this revision:
- QEMU tests covered flag and EA readback, inode cache reclaim,
  read-only/read-write remount, unmount/mount and fresh-kernel reload.
  Checked immutable write/unlink denial, append-only enforcement,
  normal I/O after clearing flags, and read-only SETFLAGS rejection.
- Verified EPERM when clearing $Bitmap protection, including without
  sys_immutable, and when clearing sys_immutable-derived protection.
  $MFT rejects SETFLAGS with ENOTTY through its empty operations.
  Checked casefold reporting and STATX_ATTR_NODUMP.
- Exercised first-EA creation/removal, XATTR_CREATE/REPLACE, zero-length
  values, zero-terminated tails, unrelated EA preservation, unknown-bit
  preservation, and direct LINUXFLAGS write/removal rejection.
- listxattr tests covered exact names and sizes, zero-terminated and
  empty lists, short buffers, and malformed offsets, name terminators,
  values and entry headers. Size-only, full-buffer and tiny-buffer
  requests returned EUCLEAN for malformed chains after a successful open.
- Malformed LINUXFLAGS length, chain offsets, name termination, value
  length and query length returned EUCLEAN. A corrupt tail following
  LINUXFLAGS prevented an update without changing the existing flags.
  An invalid resident EA_INFORMATION length rejected earlier by the
  underlying attribute parser retained that parser's EIO.
- Fault injection covered allocation failure, failures after each EA
  attribute update and rollback failure. Tested creation, replacement
  and removal with no other EAs, resident EAs and an 8 KiB non-resident
  EA; checked old values and protection after failure and remount, and
  shutdown when restoration failed.
- Additional injection checked ENOSPC write errors, short writes,
  truncate errors, ENOMEM/EIO lookup errors and missing EA attribute
  pairs, with old EA contents verified after remount.
- Formatted a SanDisk USB partition inside QEMU using the final kernel,
  and created combined and individual flag probes through SETFLAGS.
  A fresh QEMU boot with both disk and mount read-only confirmed flags
  0x70/0x10/0x20/0x40 and LINUXFLAGS values 7/1/2/4, directory nodump,
  absence of the cleared entry, unchanged canary EA and statx nodump.

The USB was freshly formatted with the label LINUXFLAGS_V4. The final
read-only check verified that $LINUXFLAGS is present with the expected
four-byte values and that the obsolete $LXFLAGS entry is absent.

Windows compatibility testing with the new $LINUXFLAGS name completed
on Windows build 26200.9457 (ver: 10.0.26200.9457), using the LINUXFLAGS_V4
USB volume (serial 3B3F-1D09). Windows mounted the volume and accessed
the existing probes with dir/type. After changing the current directory
to C:\, chkdsk G: /f completed all three stages and reported no filesystem
problems and no further action required.

After returning the USB to Linux, a fresh QEMU guest running the final
v4 kernel checked it with both the virtual disk and NTFS mount read-only.
GETFLAGS and EA reads confirmed combined flags 0x70 and individual flags
0x10/0x20/0x40, with four-byte $LINUXFLAGS values 7/1/2/4 unchanged.
Directory nodump remained set, the cleared entry remained absent, the
unrelated canary EA was unchanged, and statx still reported nodump.
The obsolete $LXFLAGS entry was absent.

The tested Windows mount/access/CHKDSK sequence therefore preserved the
$LINUXFLAGS names, lengths and values on this Windows build.

Baolin Liu (10):
  ntfs: keep the EA presence flag after creating the first entry
  ntfs: validate EA chains and link zero-terminated tails
  ntfs: propagate EA write and truncate errors
  ntfs: preserve EA attribute lookup errors
  ntfs: distinguish empty EA values from removal
  ntfs: restore EA attributes when an update fails
  ntfs: add fileattr query support
  ntfs: persist immutable in the $LINUXFLAGS EA
  ntfs: persist append-only in the $LINUXFLAGS EA
  ntfs: persist nodump in the $LINUXFLAGS EA

 Documentation/filesystems/ntfs.rst |  24 ++
 fs/ntfs/ea.c                       | 483 +++++++++++++++--------------
 fs/ntfs/ea.h                       |   9 +
 fs/ntfs/file.c                     | 125 +++++++-
 fs/ntfs/inode.c                    |  12 +-
 fs/ntfs/inode.h                    |   2 +
 fs/ntfs/namei.c                    |   2 +
 fs/ntfs/ntfs.h                     |   4 +
 8 files changed, 423 insertions(+), 238 deletions(-)

-- 
2.51.0