[PATCH v3 1/6] fs: add generic write-stream management ioctl

[Kanchan Joshi <joshi.k@samsung.com>]

Wire up the userspace interface for write stream management via a new
vfs ioctl 'FS_IOC_WRITE_STEAM'.
Application communictes the intended operation using the 'op_flags'
field of the passed 'struct fs_write_stream'.
Valid flags are:
FS_WRITE_STREAM_OP_GET_MAX: Returns the number of available streams.
FS_WRITE_STREAM_OP_SET: Assign a specific stream value to the file.
FS_WRITE_STREAM_OP_GET: Query what stream value is set on the file.

Application should query the available streams by using
FS_WRITE_STREAM_OP_GET_MAX first.
If returned value is N, valid stream values for the file are 0 to N.
Stream value 0 implies that no stream is set on the file.
Setting a larger value than available streams is rejected.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
---
 include/uapi/linux/fs.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 13f71202845e..9e87271e610b 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -338,6 +338,20 @@ struct file_attr {
 /* Get logical block metadata capability details */
 #define FS_IOC_GETLBMD_CAP		_IOWR(0x15, 2, struct logical_block_metadata_cap)
 
+struct fs_write_stream {
+	__u32		op_flags;	/* IN: operation flags */
+	union {
+		__u32		stream_id;	/* IN/OUT:  stream value to assign/guery */
+		__u32		max_streams;	/* OUT: max streams values supported */
+	};
+	__u64		rsvd;
+};
+
+#define FS_WRITE_STREAM_OP_GET_MAX		(1 << 0)
+#define FS_WRITE_STREAM_OP_GET			(1 << 1)
+#define FS_WRITE_STREAM_OP_SET			(1 << 2)
+
+#define FS_IOC_WRITE_STREAM		_IOWR('f', 135, struct fs_write_stream)
 /*
  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
  *
-- 
2.25.1