NAME

io_uring_prep_cancel - prepare a cancelation request

SYNOPSIS

#include <liburing.h>

void io_uring_prep_cancel64(struct io_uring_sqe *sqe,
                            __u64 user_data,
                            int flags);

void io_uring_prep_cancel(struct io_uring_sqe *sqe,
                          void *user_data,
                          int flags);

void io_uring_prep_cancel_fd(struct io_uring_sqe *sqe,
                          int fd,
                          int flags);

DESCRIPTION

The io_uring_prep_cancel(3) function prepares a cancelation request. The submission queue entry sqe is prepared to cancel an existing request identified by user_data. For the flags argument, see below.

io_uring_prep_cancel64(3) is identical to io_uring_prep_cancel(3), except it takes a 64-bit integer rather than a pointer type.

The cancelation request will attempt to find the previously issued request identified by user_data and cancel it. The identifier is what the previously issued request has in their user_data field in the SQE.

The io_uring_prep_cancel_fd(3) function prepares a cancelation request. The submission queue entry sqe is prepared to cancel an existing request that used the file descriptor fd. For the flags argument, see below.

The cancelation request will attempt to find the previously issued request that used fd as the file descriptor and cancel it.

By default, the first request matching the criteria given will be canceled. This can be modified with any of the following flags passed in:

IORING_ASYNC_CANCEL_ALL: Cancel all requests that match the given criteria, rather than just canceling the first one found. Available since 5.19.
IORING_ASYNC_CANCEL_FD: Match based on the file descriptor used in the original request rather than the user_data. This is what io_uring_prep_cancel_fd(3) sets up. Available since 5.19.
IORING_ASYNC_CANCEL_ANY: Match any request in the ring, regardless of user_data or file descriptor. Can be used to cancel any pending request in the ring. Available since 5.19.

RETURN VALUE

None

ERRORS

These are the errors that are reported in the CQE res field. If no flags are used to cancel multiple requests, 0 is returned on success. If flags are used to match multiple requests, then a positive value is returned indicating how many requests were found and canceled.

-ENOENT: The request identified by user_data could not be located. This could be because it completed before the cancelation request was issued, or if an invalid identifier is used.
-EINVAL: One of the fields set in the SQE was invalid.
-EALREADY: The execution state of the request has progressed far enough that cancelation is no longer possible. This should normally mean that it will complete shortly, either successfully, or interrupted due to the cancelation.

NOTES

Although the cancelation request uses async request syntax, the kernel side of the cancelation is always run synchronously. It is guaranteed that a CQE is always generated by the time the cancel request has been submitted. If the cancelation is successful, the completion for the request targeted for cancelation will have been posted by the time submission returns. For -EALREADY it may take a bit of time to do so. For this case, the caller must wait for the canceled request to post its completion event.