[PATCHv12 07/12] io_uring: enable per-io write streams

[Keith Busch]

From: Keith Busch <kbusch at kernel.org>

Allow userspace to pass a per-I/O write stream in the SQE:

      __u8 write_stream;

The __u8 type matches the size the filesystems and block layer support.

Application can query the supported values from the statx
max_write_streams field. Unsupported values are ignored by file
operations that do not support write streams or rejected with an error
by those that support them.

Signed-off-by: Keith Busch <kbusch at kernel.org>
---
 include/uapi/linux/io_uring.h | 4 ++++
 io_uring/io_uring.c           | 2 ++
 io_uring/rw.c                 | 1 +
 3 files changed, 7 insertions(+)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 38f0d6b10eaf7..986a480e3b9c2 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -92,6 +92,10 @@ struct io_uring_sqe {
 			__u16	addr_len;
 			__u16	__pad3[1];
 		};
+		struct {
+			__u8	write_stream;
+			__u8	__pad4[3];
+		};
 	};
 	union {
 		struct {
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index a8cbe674e5d63..978d0617d7af8 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3868,6 +3868,8 @@ static int __init io_uring_init(void)
 	BUILD_BUG_SQE_ELEM(44, __s32,  splice_fd_in);
 	BUILD_BUG_SQE_ELEM(44, __u32,  file_index);
 	BUILD_BUG_SQE_ELEM(44, __u16,  addr_len);
+	BUILD_BUG_SQE_ELEM(44, __u8,   write_stream);
+	BUILD_BUG_SQE_ELEM(45, __u8,   __pad4[0]);
 	BUILD_BUG_SQE_ELEM(46, __u16,  __pad3[0]);
 	BUILD_BUG_SQE_ELEM(48, __u64,  addr3);
 	BUILD_BUG_SQE_ELEM_SIZE(48, 0, cmd);
diff --git a/io_uring/rw.c b/io_uring/rw.c
index 04e4467ab0ee8..b8aa2dfcbf48c 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -322,6 +322,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	rw->kiocb.dio_complete = NULL;
 	rw->kiocb.ki_flags = 0;
+	rw->kiocb.ki_write_stream = READ_ONCE(sqe->write_stream);
 
 	rw->addr = READ_ONCE(sqe->addr);
 	rw->len = READ_ONCE(sqe->len);
-- 
2.43.5