io_uring_prep_cancel(3)

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,
                          const void *user_data,
                          int flags);

void io_uring_prep_cancel_fd(struct io_uring_sqe *sqe,
                          int fd,
                          unsigned 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_FD_FIXED
    Set in conjunction with IORING_ASYNC_CANCEL_FD , indicating that the file descriptor given is a direct descriptor rather than a normal file descriptor. Available since 6.0.

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.

IORING_ASYNC_CANCEL_USERDATA
    Match request based on the user data field set in the original request. This is the default lookup key, if no other key matching has been specified. Available since 6.6.

IORING_ASYNC_CANCEL_OP
    Use the original request opcode as the matching key. The opcopde requested must be set in the sqe len field after using one of the generic cancel preparation helpers. Available since 6.6.

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.

SEE ALSO
io_uring_prep_poll_remove(3), io_uring_get_sqe(3), io_uring_submit(3)