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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>
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