io_uring: enable per-io write streams

JIRA: https://issues.redhat.com/browse/RHEL-122870

commit 0204035
Author: Keith Busch <kbusch@kernel.org>
Date:   Tue May 6 17:47:27 2025 +0530

    io_uring: enable per-io write streams

    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 block devices
    max_write_streams sysfs attribute. Unsupported values are ignored by
    file operations that do not support write streams or rejected with an
    error by those that support them.

    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Keith Busch <kbusch@kernel.org>
    Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
    Link: https://lore.kernel.org/r/20250506121732.8211-7-joshi.k@samsung.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

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 {

io_uring/io_uring.c

@@ -3895,6 +3895,8 @@ 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);

io_uring/rw.c

@@ -291,6 +291,7 @@ 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);
 
 	if (req->ctx->flags & IORING_SETUP_IOPOLL)
 		rw->kiocb.ki_complete = io_complete_rw_iopoll;