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)

liburing-2.1                                    November 15, 2021                         io_uring_prep_readv(3)