[PATCH v4 1/6] fs: add write-stream management ioctls

From: Anuj Gupta <[email protected]>

Wire up the userspace interface for write stream management via four
ioctls:

  FS_IOC_WRITE_STREAM_GET_MAX  query the max streams supported
  FS_IOC_WRITE_STREAM_OPEN     open a stream id, returns a stream fd
  FS_IOC_WRITE_STREAM_SET      attach the stream fd to an open file
  FS_IOC_WRITE_STREAM_GET      query the stream id value set on a file

Application should query the available streams by using
FS_IOC_WRITE_STREAM_GET_MAX. If returned value is N, valid stream id for
the file are 1 to N.

Application calls FS_IOC_WRITE_STREAM_OPEN to get fd for a stream-id.
By default, kernel picks an available stream-id and returns the fd for
it. The flag FS_WRITE_STREAM_OPEN_EXACT can be used to request a
specific stream_id. This is useful if application cares about keeping a
stable stream-id-to-spatial-isolation-bucket mapping across restarts.

Suggested-by: Christoph Hellwig <[email protected]>
Co-developed-by: Kanchan Joshi <[email protected]>
Signed-off-by: Anuj Gupta <[email protected]>
Signed-off-by: Kanchan Joshi <[email protected]>
---
 include/uapi/linux/fs.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index bd87262f2e34..a756d27bdf84 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -345,6 +345,22 @@ 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_open {
+	__u32		stream_id;	/* IN: requested id if OPEN_EXACT set; OUT: assigned id */
+	__u32		flags;		/* IN: FS_WRITE_STREAM_OPEN_* */
+};
+
+/*
+ * Flag to ask for specific stream_id, otherwise kernel can return any.
+ * Fails with -EBUSY if that stream_id is already held
+ */
+#define FS_WRITE_STREAM_OPEN_EXACT	(1 << 0)
+
+#define FS_IOC_WRITE_STREAM_GET_MAX	_IOR('f', 135, __u32)
+#define FS_IOC_WRITE_STREAM_OPEN	_IOWR('f', 136, struct fs_write_stream_open)
+#define FS_IOC_WRITE_STREAM_SET		_IOW('f', 137, __s32)
+#define FS_IOC_WRITE_STREAM_GET		_IOR('f', 138, __u32)
+
 /*
  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
  *
-- 
2.25.1