[RFC PATCH 1/3] bsg: add bsg_uring_cmd uapi structure

[Yang Xiuwei <yangxiuwei@kylinos.cn>]

Add the bsg_uring_cmd structure to the BSG UAPI header to support
io_uring-based SCSI passthrough operations via IORING_OP_URING_CMD.

This structure is designed to work with 128-byte SQE (IO_URING_F_SQE128)
and provides a compact interface similar to sg_io_v4, but optimized
for io_uring's async I/O model. The structure is packed to fit within
the 80-byte cmd field of a 128-byte SQE, with 16 bytes reserved for
future extensions.

Key features:
- CDB address and length for SCSI command passthrough
- Protocol and subprotocol identifiers (BSG_PROTOCOL_SCSI)
- Data transfer parameters supporting both flat buffers and iovec arrays
- Sense data buffer information for error reporting
- Timeout and flags for command control

Signed-off-by: Yang Xiuwei <yangxiuwei@kylinos.cn>

diff --git a/include/uapi/linux/bsg.h b/include/uapi/linux/bsg.h
index cd6302def5ed..24b08fece509 100644
--- a/include/uapi/linux/bsg.h
+++ b/include/uapi/linux/bsg.h
@@ -63,5 +63,23 @@ struct sg_io_v4 {
 	__u32 padding;
 };
 
+struct bsg_uring_cmd {
+	__u64 cdb_addr;
+	__u8  cdb_len;
+	__u8  protocol;		/* [i] protocol type (BSG_PROTOCOL_*) */
+	__u8  subprotocol;	/* [i] subprotocol type (BSG_SUB_PROTOCOL_*) */
+	__u8  reserved1;
+	__u32 din_iovec_count;	/* [i] 0 -> flat din transfer else
+				 * din_xferp points to array of iovec
+				 */
+	__u32 din_xfer_len;	/* [i] bytes to be transferred from device */
+	__u64 din_xferp;	/* [i] data in buffer address or iovec array
+				 * address
+				 */
+	__u32 dout_iovec_count;	/* [i] 0 -> flat dout transfer else
+				 * dout_xferp points to array of iovec
+				 */
+	__u32 dout_xfer_len;	/* [i] bytes to be transferred to device */
+	__u64 dout_xferp;	/* [i] data out buffer address or iovec array address */
+	__u32 sense_len;
+	__u64 sense_addr;
+	__u32 timeout_ms;
+	__u32 flags;		/* [i] bit mask (BSG_FLAG_*) - reserved for future use */
+	__u8  reserved[16];	/* reserved for future extension */
+} __packed;
 
 #endif /* _UAPIBSG_H */
-- 
2.25.1