[PATCH v5 1/8] fs: add write-stream management ioctls

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

From: Anuj Gupta <anuj20.g@samsung.com>

Add three ioctls for write stream management:

  FS_IOC_WRITE_STREAM_GET_MAX  number of streams the filesystem offers
  FS_IOC_WRITE_STREAM_ALLOC    reserve a stream, returns an fd
  FS_IOC_WRITE_STREAM_SET      set or clear a stream on a file

Write streams are a resource the kernel manages and applications ask
for.

ALLOC reserves a stream and returns a stream fd; the stream stays
reserved as long as that fd is open. ALLOC fails once all streams are
reserved.

SET assigns the stream named by the stream_fd in struct
fs_write_stream_set to an open file; the same stream fd can be used to
set the stream on any number of files. SET with FS_WRITE_STREAM_SET_CLEAR
and a stream_fd of -1 clears whatever stream the file carries.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
---
 include/uapi/linux/fs.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 34c6f219462a..1974052aa476 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -345,6 +345,21 @@ 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_set {
+	__s32		stream_fd;	/* IN: stream to attach, -1 to clear */
+	__u32		flags;		/* IN: FS_WRITE_STREAM_SET_* */
+};
+
+/* Clear the file's write stream. Requires stream_fd to be -1. */
+#define FS_WRITE_STREAM_SET_CLEAR	(1U << 0)
+
+/* GET_MAX returns the count through its argument; ALLOC returns a stream fd
+ * as the ioctl return value and takes none.
+ */
+#define FS_IOC_WRITE_STREAM_GET_MAX	_IOR(0x15, 3, __u32)
+#define FS_IOC_WRITE_STREAM_ALLOC	_IO(0x15, 4)
+#define FS_IOC_WRITE_STREAM_SET		_IOW(0x15, 5, struct fs_write_stream_set)
+
 /*
  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
  *
-- 
2.25.1