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.TH READV 2
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.SH NAME
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readv, writev, preadv, pwritev \- scatter/gather read and write
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.nf
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.ft L
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typedef
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struct IOchunk
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{
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	void		*addr;
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	ulong	len;
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} IOchunk;
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.fi
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.PP
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.B
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long readv(int fd, IOchunk *io, int nio)
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.PP
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.B
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long preadv(int fd, IOchunk *io, int nio, vlong off)
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.PP
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.B
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long writev(int fd, IOchunk *io, int nio)
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.PP
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.B
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long pwritev(int fd, IOchunk *io, int nio, vlong off)
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.SH DESCRIPTION
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These functions supplement the standard read and write operations of
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.IR read (2)
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with facilities for scatter/gather I/O.
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The set of I/O buffers is collected into an array of
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.B IOchunk
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structures passed as an argument.
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.PP
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.I Readv
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reads data from
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.I fd
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and returns the total number of bytes received.
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The received data is stored in the successive
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.I nio
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elements of the
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.B IOchunk
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array, storing
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.IB io [0].len
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bytes at
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.IB io [0].addr\f1,
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the next
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.IB io [1].len
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at
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.IB io [1].addr\f1,
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and so on.
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.I Preadv
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does the same, but implicitly seeks to I/O offset
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.I off
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by analogy with
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.IR readv .
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.PP
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.I Writev
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and
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.I pwritev
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are the analogous write routines.
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.SH SOURCE
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.B /sys/src/libc/9sys/readv.c
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.br
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.B /sys/src/libc/9sys/writev.c
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.SH SEE ALSO
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.IR intro (2),
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.IR read (2)
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.SH DIAGNOSTICS
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These functions set
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.IR errstr .
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.SH BUGS
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The implementations use
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.IR malloc (2)
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to build a single buffer for a standard call to
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.B read
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or
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.BR write .
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They are placeholders for possible future system calls.