# io_uring_prep_readv2

## NAME



           io_uring_prep_readv2 - prepare vector I/O read request with flags
    


## SYNOPSIS



           **#include <sys/uio.h>**
           **#include <liburing.h>**
    
           **void io_uring_prep_readv2(struct io_uring_sqe ***_sqe_**,**
                                     **int** _fd_**,**
                                     **const struct iovec ***_iovecs_**,**
                                     **unsigned** _nr_vecs_**,**
                                     **__u64** _offset_**,**
                                     **int** _flags_**);**
    


## DESCRIPTION



           The io_uring_prep_readv2(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_.  The behavior of the function can be controlled with the
           _flags_ parameter.
    
           Supported values for _flags_ are:
    
           **RWF_HIPRI**
                  High priority request, poll if possible
    
           **RWF_DSYNC**
                  per-IO O_DSYNC
    
           **RWF_SYNC**
                  per-IO O_SYNC
    
           **RWF_NOWAIT**
                  per-IO, return **-EAGAIN** if operation would block
    
           **RWF_APPEND**
                  per-IO O_APPEND
    
           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).
    


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