[PATCH 4/8] io_uring: add support for IORING_OP_URING_CMD

[Jens Axboe <axboe@kernel.dk>]

This is a file private kind of request. io_uring doesn't know what's
in this command type, it's for the file_operations->uring_cmd()
handler to deal with.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c            | 54 ++++++++++++++++++++++++++++++++++++++++
 include/linux/io_uring.h | 16 ++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fecf10e0625f..a66f953f71d4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -770,6 +770,7 @@ struct io_kiocb {
 		struct io_shutdown	shutdown;
 		struct io_rename	rename;
 		struct io_unlink	unlink;
+		struct io_uring_cmd	uring_cmd;
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
@@ -1002,6 +1003,7 @@ static const struct io_op_def io_op_defs[] = {
 	[IORING_OP_RENAMEAT] = {},
 	[IORING_OP_UNLINKAT] = {},
 	[IORING_OP_URING_CMD] = {
+		.needs_file		= 1,
 		.offsets		= 1,
 	},
 };
@@ -3565,6 +3567,53 @@ static int io_unlinkat(struct io_kiocb *req, unsigned int issue_flags)
 	return 0;
 }
 
+/*
+ * Called by consumers of io_uring_cmd, if they originally returned
+ * -EIOCBQUEUED upon receiving the command.
+ */
+void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret)
+{
+	struct io_kiocb *req = container_of(cmd, struct io_kiocb, uring_cmd);
+
+	if (ret < 0)
+		req_set_fail_links(req);
+	io_req_complete(req, ret);
+}
+EXPORT_SYMBOL(io_uring_cmd_done);
+
+static int io_uring_cmd_prep(struct io_kiocb *req,
+			     const struct io_uring_sqe *sqe)
+{
+	const struct io_uring_cmd_sqe *csqe = (const void *) sqe;
+	struct io_uring_cmd *cmd = &req->uring_cmd;
+
+	if (!req->file->f_op->uring_cmd)
+		return -EOPNOTSUPP;
+
+	cmd->op = READ_ONCE(csqe->op);
+	cmd->len = READ_ONCE(csqe->len);
+
+	/*
+	 * The payload is the last 40 bytes of an io_uring_cmd_sqe, with the
+	 * type being defined by the recipient.
+	 */
+	memcpy(&cmd->pdu, &csqe->pdu, sizeof(cmd->pdu));
+	return 0;
+}
+
+static int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct file *file = req->file;
+	int ret;
+
+	ret = file->f_op->uring_cmd(&req->uring_cmd, issue_flags);
+	/* queued async, consumer will call io_uring_cmd_done() when complete */
+	if (ret == -EIOCBQUEUED)
+		return 0;
+	io_uring_cmd_done(&req->uring_cmd, ret);
+	return 0;
+}
+
 static int io_shutdown_prep(struct io_kiocb *req,
 			    const struct io_uring_sqe *sqe)
 {
@@ -5858,6 +5907,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_renameat_prep(req, sqe);
 	case IORING_OP_UNLINKAT:
 		return io_unlinkat_prep(req, sqe);
+	case IORING_OP_URING_CMD:
+		return io_uring_cmd_prep(req, sqe);
 	}
 
 	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
@@ -6114,6 +6165,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 	case IORING_OP_UNLINKAT:
 		ret = io_unlinkat(req, issue_flags);
 		break;
+	case IORING_OP_URING_CMD:
+		ret = io_uring_cmd(req, issue_flags);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 9761a0ec9f95..fd5c8ca40a70 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -30,7 +30,20 @@ struct io_uring_task {
 	struct callback_head	task_work;
 };
 
+/*
+ * Note that the first member here must be a struct file, as the
+ * io_uring command layout depends on that.
+ */
+struct io_uring_cmd {
+	struct file	*file;
+	__u16		op;
+	__u16		unused;
+	__u32		len;
+	__u64		pdu[5];	/* 40 bytes available inline for free use */
+};
+
 #if defined(CONFIG_IO_URING)
+void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret);
 struct sock *io_uring_get_socket(struct file *file);
 void __io_uring_task_cancel(void);
 void __io_uring_files_cancel(struct files_struct *files);
@@ -52,6 +65,9 @@ static inline void io_uring_free(struct task_struct *tsk)
 		__io_uring_free(tsk);
 }
 #else
+static inline void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret)
+{
+}
 static inline struct sock *io_uring_get_socket(struct file *file)
 {
 	return NULL;
-- 
2.31.0