linux/io_uring/query.h

// SPDX-License-Identifier: GPL-2.0
#ifndef IORING_QUERY_H
#define IORING_QUERY_H

#include <linux/io_uring_types.h>

int io_query(struct io_ring_ctx *ctx, void __user *arg, unsigned nr_args);

#endif
io_uring: introduce io_uring querying There are many parameters users might want to query about io_uring like available request types or the ring sizes. This patch introduces an interface for such slow path queries. It was written with several requirements in mind: - Can be used with or without an io_uring instance. Asking for supported setup flags before creating an instance as well as qeurying info about an already created ring are valid use cases. - Should be moderately fast. For example, users might use it to periodically retrieve ring attributes at runtime. As a consequence, it should be able to query multiple attributes in a single syscall. - Backward and forward compatible. - Should be reasobably easy to use. - Reduce the kernel code size for introducing new query types. It's implemented as a new registration opcode IORING_REGISTER_QUERY. The user passes one or more query strutctures linked together, each represented by struct io_uring_query_hdr. The header stores common control fields needed for processing and points to query type specific information. The header contains - The query type - The result field, which on return contains the error code for the query - Pointer to the query type specific information - The size of the query structure. The kernel will only populate up to the size, which helps with backward compatibility. The kernel can also reduce the size, so if the current kernel is older than the inteface the user tries to use, it'll get only the supported bits. - next_entry field is used to chain multiple queries. Apart from common registeration syscall failures, it can only immediately return an error code in case when the headers are incorrect or any other addresses and invalid. That usually mean that the userspace doesn't use the API right and should be corrected. All query type specific errors are returned in the header's result field. As an example, the patch adds a single query type for now, i.e. IO_URING_QUERY_OPCODES, which tells what register / request / etc. opcodes are supported, but there are particular plans to extend it. Note: there is a request probing interface via IORING_REGISTER_PROBE, but it's a mess. It requires the user to create a ring first, it only works for requests, and requires dynamic allocations. Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> 2025-09-08 00:03:00 +01:00			`// SPDX-License-Identifier: GPL-2.0`
			`#ifndef IORING_QUERY_H`
			`#define IORING_QUERY_H`

			`#include <linux/io_uring_types.h>`

			`int io_query(struct io_ring_ctx ctx, void __user arg, unsigned nr_args);`

			`#endif`