io_uring_sqe_set_flags - Man Page

set flags for submission queue entry

Synopsis

#include <liburing.h>

void io_uring_sqe_set_flags(struct io_uring_sqe *sqe,
                            unsigned flags);

Description

The io_uring_sqe_set_flags(3) function allows the caller to change the behavior of the submission queue entry by specifying flags. It enables the flags belonging to the sqe submission queue entry param.

flags is a bit mask of 0 or more of the following values ORed together:

IOSQE_FIXED_FILE

The file descriptor in the SQE refers to the index of a previously registered file or direct file descriptor, not a normal file descriptor.

IOSQE_ASYNC

Normal operation for io_uring is to try and issue an sqe as non-blocking first, and if that fails, execute it in an async manner. To support more efficient overlapped operation of requests that the application knows/assumes will always (or most of the time) block, the application can ask for an sqe to be issued async from the start. Note that this flag immediately causes the SQE to be offloaded to an async helper thread with no initial non-blocking attempt. This may be less efficient and should not be used sporadically.

IOSQE_IO_LINK

When this flag is specified, the SQE forms a link with the next SQE in the submission ring. That next SQE will not be started before the previous request completes. This, in effect, forms a chain of SQEs, which can be arbitrarily long. The tail of the chain is denoted by the first SQE that does not have this flag set. Chains are not supported across submission boundaries. Even if the last SQE in a submission has this flag set, it will still terminate the current chain. This flag has no effect on previous SQE submissions, nor does it impact SQEs that are outside of the chain tail. This means that multiple chains can be executing in parallel, or chains and individual SQEs. Only members inside the chain are serialized. A chain of SQEs will be broken if any request in that chain ends in error.

IOSQE_IO_HARDLINK

Like IOSQE_IO_LINK , except the links aren't severed if an error or unexpected result occurs.

IOSQE_IO_DRAIN

When this flag is specified, the SQE will not be started before previously submitted SQEs have completed, and new SQEs will not be started before this one completes.

IOSQE_CQE_SKIP_SUCCESS

Request that no CQE be generated for this request, if it completes successfully. This can be useful in cases where the application doesn't need to know when a specific request completed, if it completed succesfully.

IOSQE_BUFFER_SELECT

If set, and if the request types supports it, select an IO buffer from the indicated buffer group. This can be used with requests that read or receive data from a file or socket, where buffer selection is deferred until the kernel is ready to transfer data, instead of when the IO is originally submitted. The application must also set the buf_group field in the SQE, indicating which previously registered buffer group to select a buffer from.

Return Value

None

See Also

io_uring_submit(3), io_uring_register(3) io_uring_register_buffers(3) io_uring_register_buf_ring(3)

Referenced By

io_uring_sqe_set_flags(3).

liburing-2.1 liburing Manual