mirror of https://github.com/GnoConsortium/gno.git
192 lines
5.1 KiB
Groff
192 lines
5.1 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)read.2 8.4 (Berkeley) 2/26/94
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.\"
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.TH READ 2 "23 January 1997" GNO "System Calls"
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.SH NAME
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.BR read ,
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.BR readv
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\- read input
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.SH SYNOPSIS
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#include <sys/types.h>
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.br
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#include <sys/uio.h>
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.br
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#include <unistd.h>
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.sp 1
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ssize_t
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\fBread\fR (int \fId\fR, void *\fIbuf\fR, size_t \fInbytes\fR);
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.sp 1
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ssize_t
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\fBreadv\fR (int \fId\fR, const struct iovec *\fIiov\fR, int \fIiovcnt\fR);
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.SH DESCRIPTION
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.BR read
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attempts to read
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.I nbytes
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of data from the object referenced by the descriptor
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.I d
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into the buffer pointed to by
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.IR buf .
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.BR readv
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performs the same action, but scatters the input data
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into the
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.I iovcnt
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buffers specified by the members of the
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.I iov
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array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
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.LP
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For
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.BR readv ,
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the
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.I iovec
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structure is defined as:
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.LP
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.nf
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struct iovec {
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void *iov_base;
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size_t iov_len;
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};
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.fi
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.LP
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Each
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.I iovec
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entry specifies the base address and length of an area
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in memory where data should be placed.
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.BR readv
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will always fill an area completely before proceeding
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to the next.
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.LP
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On objects capable of seeking, the
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.BR read
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starts at a position
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given by the pointer associated with
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.I d
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(see
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.BR lseek (2)).
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Upon return from
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.BR read ,
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the pointer is incremented by the number of bytes actually read.
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.LP
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Objects that are not capable of seeking always read from the current
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position. The value of the pointer associated with such an
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object is undefined.
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.LP
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Upon successful completion,
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.BR read
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and
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.BR readv
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return the number of bytes actually read and placed in the buffer.
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The system guarantees to read the number of bytes requested if
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the descriptor references a normal file that has that many bytes left
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before the end-of-file, but in no other case.
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.LP
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If the file was opened with the GNO-specific flag
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.BR O_TRANS ,
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then newline translation will occur; any carridge return character (0x0d)
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read from descriptor
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.I d
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will be converted to a line feed (0x0a).
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.SH RETURN VALUES
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If successful, the
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number of bytes actually read is returned. Upon reading end-of-file,
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zero is returned.
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Otherwise, a -1 is returned and the global variable
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.IR errno
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is set to indicate the error.
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.SH ERRORS
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.BR read
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and
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.BR readv
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will succeed unless:
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.RS
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.IP \fBEBADF\fR
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.I D
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is not a valid file or socket descriptor open for reading.
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.IP \fBEFAULT\fR
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.I Buf
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points outside the allocated address space.
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.IP \fBEIO\fR
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An I/O error occurred while reading from the file system.
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.IP \fBEINTR\fR
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A read from a slow device was interrupted before
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any data arrived by the delivery of a signal.
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.IP \fBEINVAL\fR
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The pointer associated with
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.I d
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was negative.
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.IP \fBEAGAIN\fR
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The file was marked for non-blocking I/O,
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and no data were ready to be read.
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.RE
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.LP
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In addition,
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.BR readv
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may return one of the following errors:
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.RS
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.IP \fBEINVAL\fR
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.I Iovcnt
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was less than or equal to 0, or greater than 16.
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.IP \fBEINVAL\fR
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One of the
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.I iov_len
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values in the
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.I iov
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array was negative.
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.IP \fBEINVAL\fR
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The sum of the
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.I iov_len
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values in the
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.I iov
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array overflowed a 32-bit integer.
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.RE
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.SH SEE ALSO
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.BR dup (2),
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.BR fcntl (2),
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.BR open (2),
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.BR pipe (2),
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.BR select (2),
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.BR socket (2),
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.BR socketpair (2)
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.SH STANDARDS
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.BR Read
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is expected to conform to IEEE Std 1003.1-1988 (POSIX).
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.SH HISTORY
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The
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.BR readv
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function call
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appeared in 4.2BSD.
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A
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.BR read
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function call
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appeared in
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Version 6 AT&T UNIX.
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