NAME

       io_uring_prep_readv - prepare vector I/O read request

SYNOPSIS

       #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);

DESCRIPTION

       The io_uring_prep_readv(3) 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 read has been prepared it can be submitted with one of the submit functions.

RETURN VALUE

       None

ERRORS

       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.

NOTES

       Unless  an  application  explicitly  needs  to  pass  in  more  than one 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).

SEE ALSO

       io_uring_get_sqe(3), io_uring_prep_read(3), io_uring_prep_readv2(3), io_uring_submit(3)