io_uring_prep_readv - prepare vector I/O read request
#include <sys/uio.h>
#include <liburing.h>
void io_uring_prep_readv(struct io_uring_sqe *sqe,
int fd,
const struct iovec *iovecs,
unsigned nr_vecs,
__u64 offset);
The prepares a vectored IO read request. The
submission queue entry
sqe is setup to use the file descriptor
fd to start reading
nr_vecs into the
iovecs array at the
specified
offset.
On files that support seeking, if the offset is set to
-1, the read
operation commences at the file offset, and the file offset is incremented by
the number of bytes read. See
read(2) for more details. Note that for
an async API, reading and updating the current file offset may result in
unpredictable behavior, unless access to the file is serialized. It is not
encouraged to use this feature, if it's possible to provide the desired IO
offset from the application or library.
On files that are not capable of seeking, the offset must be 0 or -1.
After the write has been prepared it can be submitted with one of the submit
functions.
None
The CQE
res field will contain the result of the operation. See the
related man page for details on possible values. Note that where synchronous
system calls will return
-1 on failure and set
errno to the
actual error value, io_uring never uses
errno. Instead it returns the
negated
errno directly in the CQE
res field.
Unless an application explicitly needs to pass in more than iovec, it is more
efficient to use
io_uring_prep_read(3) rather than this function, as no
state has to be maintained for a non-vectored IO request. As with any request
that passes in data in a struct, that data must remain valid until the request
has been successfully submitted. It need not remain valid until completion.
Once a request has been submitted, the in-kernel state is stable. Very early
kernels (5.4 and earlier) required state to be stable until the completion
occurred. Applications can test for this behavior by inspecting the
IORING_FEAT_SUBMIT_STABLE flag passed back from
io_uring_queue_init_params(3).
io_uring_get_sqe(3),
io_uring_prep_read(3),
io_uring_prep_readv2(3),
io_uring_submit(3)