io_uring_sqe_set_flags - set flags for submission queue entry
#include <liburing.h>
void io_uring_sqe_set_flags(struct io_uring_sqe *sqe,
unsigned flags);
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 liberally or without understanding the performance and efficiency
tradeoffs.
- 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
successfully.
- 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.