1io_uring_prep_readv(3)          liburing Manual         io_uring_prep_readv(3)
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NAME

6       io_uring_prep_readv - prepare vector I/O read request
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SYNOPSIS

9       #include <sys/uio.h>
10       #include <liburing.h>
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12       void io_uring_prep_readv(struct io_uring_sqe *sqe,
13                                int fd,
14                                const struct iovec *iovecs,
15                                unsigned nr_vecs,
16                                __u64 offset);
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DESCRIPTION

19       The  io_uring_prep_readv(3)  prepares  a  vectored IO read request. The
20       submission queue entry sqe is setup to use the file  descriptor  fd  to
21       start reading nr_vecs into the iovecs array at the specified offset.
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23       On files that support seeking, if the offset is set to -1, the read op‐
24       eration commences at the file offset, and the  file  offset  is  incre‐
25       mented  by the number of bytes read. See read(2) for more details. Note
26       that for an async API, reading and updating the current file offset may
27       result  in unpredictable behavior, unless access to the file is serial‐
28       ized. It is not encouraged to use this feature,  if  it's  possible  to
29       provide the desired IO offset from the application or library.
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31       On files that are not capable of seeking, the offset must be 0 or -1.
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33       After  the  write has been prepared it can be submitted with one of the
34       submit functions.
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RETURN VALUE

38       None
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ERRORS

41       The CQE res field will contain the result of the operation. See the re‐
42       lated man page for details on possible values. Note that where synchro‐
43       nous system calls will return -1 on failure and set errno to the actual
44       error value, io_uring never uses errno.  Instead it returns the negated
45       errno directly in the CQE res field.
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NOTES

48       Unless an application explicitly needs to pass in more than  iovec,  it
49       is  more  efficient to use io_uring_prep_read(3) rather than this func‐
50       tion, as no state has to be maintained for a non-vectored  IO  request.
51       As with any request that passes in data in a struct, that data must re‐
52       main valid until the request has been successfully submitted.  It  need
53       not  remain  valid until completion. Once a request has been submitted,
54       the in-kernel state is stable. Very early kernels (5.4 and earlier) re‐
55       quired  state  to be stable until the completion occurred. Applications
56       can test for this behavior by inspecting the  IORING_FEAT_SUBMIT_STABLE
57       flag passed back from io_uring_queue_init_params(3).
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SEE ALSO

60       io_uring_get_sqe(3),   io_uring_prep_read(3),  io_uring_prep_readv2(3),
61       io_uring_submit(3)
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65liburing-2.1                   November 15, 2021        io_uring_prep_readv(3)
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