38 lines
1,001 B
Plaintext
38 lines
1,001 B
Plaintext
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.TH IOUNIT 2
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.SH NAME
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iounit \- return size of atomic I/O unit for file descriptor
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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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.B
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int iounit(int fd)
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.SH DESCRIPTION
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Reads and writes of files are transmitted using the 9P protocol (see
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.IR intro (5))
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and in general, operations involving large amounts of data must be
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broken into smaller pieces by the operating system.
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The `I/O unit' associated with each file descriptor records the maximum
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size, in bytes, that may be read or written without breaking up the transfer.
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.PP
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The
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.I iounit
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routine uses the
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.IR dup (3)
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interface to discover the I/O unit size for the file descriptor
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.I fd
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and returns its value.
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Certain file descriptors, particularly those associated with devices, may
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have no specific I/O unit, in which case
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.I iounit
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will return
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.BR 0 .
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.SH SOURCE
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.B /sys/src/libc/9sys
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.SH SEE ALSO
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.IR dup (3),
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.IR read (5)
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.SH DIAGNOSTICS
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Returns zero if any error occurs or if the I/O unit size of the fd is unspecified or unknown.
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