ntfs: add named stream ioctls support

NTFS supports multiple named $DATA attributes, commonly known as alternate
data streams. Add NTFS-specific ioctls to list, read, write, and remove
named streams through an opened base file or directory.

The UAPI provides separate commands for each operation.

  - NTFS_IOC_STREAM_READ
  - NTFS_IOC_STREAM_WRITE
  - NTFS_IOC_STREAM_REMOVE
  - NTFS_IOC_LIST_STREAMS

Read and write requests use struct ntfs_stream to specify the stream name,
byte offset, and transfer length. Writes create the stream if it does not
already exist. A write failure after creation may leave the new stream
visible. It is not rolled back because another caller may already have
opened it. Userspace can remove it with NTFS_IOC_STREAM_REMOVE.

The list command returns variable-length entries containing each named
stream's data size, allocated size, and name. If the buffer is too small,
the command returns -ENOSPC without copying entries. bytes_returned reports
the required buffer size, and stream_count reports the number of streams.

Stream names use the mounted filesystem NLS by default. Set
NTFS_STREAM_FL_UTF16 to pass or receive raw UTF-16LE names. In NLS mode,
names that cannot be represented by the mounted character set are omitted
from the list. Use UTF-16 mode for lossless enumeration. Read and write
transfers are limited to 16 MiB per request.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

1 files changed, 130 insertions, 0 deletions

diff --git a/include/uapi/linux/ntfs.h b/include/uapi/linux/ntfs.h
new file mode 100644
index 000000000000..f5b3d4997a56
--- /dev/null
+++ b/include/uapi/linux/ntfs.h
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2026 LG Electronics Co., Ltd.
+ */
+
+#ifndef _UAPI_LINUX_NTFS_H
+#define _UAPI_LINUX_NTFS_H
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define NTFS_IOC_MAGIC	0xEF
+
+/*
+ * Flags for ntfs_stream.flags and ntfs_list_streams.flags.
+ *
+ * NTFS_STREAM_FL_UTF16 makes stream names raw UTF-16LE, exactly as stored on
+ * disk, instead of encoding them with the mounted filesystem NLS. This
+ * allows lossless round-tripping of stream names whose characters are not
+ * representable by the mount NLS (e.g. for Wine, which works in UTF-16
+ * natively). When set, the name length fields count bytes of UTF-16LE and
+ * must therefore be even.
+ */
+#define NTFS_STREAM_FL_UTF16		0x1
+
+/*
+ * ntfs named stream read, write, and remove ioctl structure.
+ *
+ * @stream_offset:	Offset within the named stream for read/write.
+ * @io_len:		Number of bytes to read/write. Must be zero for remove.
+ * @bytes_returned:	Actual bytes transferred on success (out).
+ * @name_len:		Stream name length in bytes, not including any
+ *			terminating NUL. When NTFS_STREAM_FL_UTF16 is set,
+ *			this counts UTF-16LE bytes and must be even.
+ * @flags:		Bit mask of NTFS_STREAM_FL_* flags. Other bits must
+ *			be zero.
+ * @reserved:		Must be zero.
+ * @buffer:		Bare stream name followed by stream data for read/write.
+ *
+ * The stream name is encoded with the mounted filesystem NLS, or as raw
+ * UTF-16LE when NTFS_STREAM_FL_UTF16 is set. A write creates the stream if
+ * it does not already exist. A write failure after creation may leave the
+ * new stream behind; it can be removed separately.
+ *
+ * For NTFS_IOC_STREAM_READ, a successful short read indicates EOF. If a read
+ * fails, the ioctl returns an error and copies no stream data to userspace.
+ *
+ * NTFS_IOC_STREAM_WRITE is not atomic. Write errors may leave partial data
+ * changes and an extended stream size. On error, bytes_returned is not valid.
+ * The ioctl does not report the completed byte count.
+ */
+struct ntfs_stream {
+	__aligned_u64 stream_offset;
+	__aligned_u64 io_len;
+	__aligned_u64 bytes_returned;
+	__u32 name_len;
+	__u32 flags;
+	__aligned_u64 reserved;
+	__u8 buffer[];
+};
+
+/*
+ * Single stream entry returned by NTFS_IOC_LIST_STREAMS.
+ *
+ * @next_entry_off:	Byte offset from the start of this entry to the next
+ *			entry, or zero for the last entry. Always a multiple
+ *			of 8. Consumers must use this to advance instead of
+ *			computing the stride themselves.
+ * @size:		Stream data size in bytes.
+ * @alloc_size:		Bytes allocated for the stream (cluster aligned for
+ *			non-resident streams).
+ * @name_len:		Stream name length in bytes, not including a NUL
+ *			terminator (none is stored). Counts UTF-16LE bytes
+ *			when NTFS_STREAM_FL_UTF16 was requested.
+ * @name_offset:	Byte offset from the start of this entry to @name.
+ * @reserved:		Must be zero.
+ * @name:		Bare stream name; NLS encoded, or raw UTF-16LE when
+ *			NTFS_STREAM_FL_UTF16 was requested.
+ *
+ * New fixed fields may be added after @reserved and before @name. Consumers
+ * must use @name_offset to locate the name and @next_entry_off to advance to
+ * the next entry.
+ */
+struct ntfs_stream_entry {
+	__aligned_u64 next_entry_off;
+	__aligned_u64 size;
+	__aligned_u64 alloc_size;
+	__u32 name_len;
+	__u32 name_offset;
+	__u32 reserved;
+	__u8 name[];
+};
+
+/*
+ * ntfs list streams ioctl structure.
+ *
+ * @buffer_size:	user buffer size(in).
+ * @bytes_returned:	actual bytes written or required(out).
+ * @stream_count:	number of streams(out).
+ * @flags:		Bit mask of NTFS_STREAM_FL_* flags controlling the
+ *			encoding of the returned names; other bits must be zero.
+ * @reserved:		Must be zero.
+ * @buffer:		ntfs_stream_entry array.
+ *
+ * The variable-length entries follow the header in @buffer, each aligned on
+ * an 8-byte boundary and chained via ntfs_stream_entry.next_entry_off. If
+ * @buffer_size is too small, no data is copied, @stream_count and
+ * @bytes_returned report the required values and the ioctl fails with
+ * -ENOSPC. In NLS mode, names that cannot be represented by the mounted
+ * character set are omitted; use NTFS_STREAM_FL_UTF16 to list all
+ * names without conversion loss.
+ */
+struct ntfs_list_streams {
+	__aligned_u64 buffer_size;
+	__aligned_u64 bytes_returned;
+	__aligned_u64 stream_count;
+	__u32 flags;
+	__u32 reserved;
+	__u8 buffer[];
+};
+
+#define NTFS_IOC_STREAM_READ \
+	_IOWR(NTFS_IOC_MAGIC, 1, struct ntfs_stream)
+#define NTFS_IOC_STREAM_WRITE \
+	_IOWR(NTFS_IOC_MAGIC, 2, struct ntfs_stream)
+#define NTFS_IOC_STREAM_REMOVE \
+	_IOWR(NTFS_IOC_MAGIC, 3, struct ntfs_stream)
+#define NTFS_IOC_LIST_STREAMS \
+	_IOWR(NTFS_IOC_MAGIC, 4, struct ntfs_list_streams)
+
+#endif /* _UAPI_LINUX_NTFS_H */