1io_uring_prep_writev(3)         liburing Manual        io_uring_prep_writev(3)
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NAME

6       io_uring_prep_writev - prepare vector I/O write request
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SYNOPSIS

9       #include <sys/uio.h>
10       #include <liburing.h>
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12       void io_uring_prep_writev(struct io_uring_sqe *sqe,
13                                 int fd,
14                                 const struct iovec *iovecs,
15                                 unsigned nr_vecs,
16                                 __u64 offset);
17

DESCRIPTION

19       The  io_uring_prep_writev(3)  prepares a vectored IO write request. The
20       submission queue entry sqe is setup to use the file  descriptor  fd  to
21       start writing nr_vecs from 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 write
24       operation commences at the file offset, and the file offset  is  incre‐
25       mented  by  the number of bytes written. See write(2) for more details.
26       Note that for an async API, reading and updating the current file  off‐
27       set  may result in unpredictable behavior, unless access to the file is
28       serialized. It is not encouraged to use this feature if  it's  possible
29       to 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 one  iovec,
49       it  is  more  efficient  to use io_uring_prep_write(3) rather than this
50       function, as no state has to be maintained for a  non-vectored  IO  re‐
51       quest.   As with any request that passes in data in a struct, that data
52       must remain valid until the request has been successfully submitted. It
53       need not remain valid until completion. Once a request has been submit‐
54       ted, the in-kernel state is stable. Very early kernels  (5.4  and  ear‐
55       lier) required state to be stable until the completion occurred. Appli‐
56       cations can test for this behavior by inspecting  the  IORING_FEAT_SUB‐
57       MIT_STABLE 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_write(3), io_uring_prep_writev2(3),
61       io_uring_submit(3)
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65liburing-2.1                   November 15, 2021       io_uring_prep_writev(3)
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