 @@ -1,275 +1,275 @@
-.\"	$NetBSD: read.2,v 1.38 2019/08/07 19:13:49 wiz Exp $
+.\"	$NetBSD: read.2,v 1.39 2019/09/02 00:00:25 sevan Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\" 3. Neither the name of the University nor the names of its contributors
 .\"    may be used to endorse or promote products derived from this software
 .\"    without specific prior written permission.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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 .\"
 .\"     @(#)read.2	8.4 (Berkeley) 2/26/94
 .\"
-.Dd August 7, 2019
+.Dd September 2, 2019
 .Dt READ 2
 .Os
 .Sh NAME
 .Nm read ,
 .Nm readv ,
 .Nm pread ,
 .Nm preadv
 .Nd read input
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In unistd.h
 .Ft ssize_t
 .Fn read "int d" "void *buf" "size_t nbytes"
 .Ft ssize_t
 .Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
 .In sys/uio.h
 .Ft ssize_t
 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
 .Ft ssize_t
 .Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
 .Sh DESCRIPTION
 .Fn read
 attempts to read
 .Fa nbytes
 of data from the object referenced by the descriptor
 .Fa d
 into the buffer pointed to by
 .Fa buf .
 .Fn readv
 performs the same action, but scatters the input data
 into the
 .Fa iovcnt
 buffers specified by the members of the
 .Fa iov
 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
 .Fn pread
 and
 .Fn preadv
 perform the same functions, but read from the specified position in
 the file without modifying the file pointer.
 .Pp
 For
 .Fn readv
 and
 .Fn preadv ,
 the
 .Fa iovec
 structure is defined as:
 .Pp
 .Bd -literal -offset indent -compact
 struct iovec {
 	void *iov_base;
 	size_t iov_len;
 };
 .Ed
 .Pp
 Each
 .Fa iovec
 entry specifies the base address and length of an area
 in memory where data should be placed.
 .Fn readv
 will always fill an area completely before proceeding
 to the next.
 .Pp
 On objects capable of seeking, the
 .Fn read
 starts at a position
 given by the file pointer associated with
 .Fa d
 (see
 .Xr lseek 2 ) .
 Upon return from
 .Fn read ,
 the file pointer is incremented by the number of bytes actually read.
 .Pp
 Objects that are not capable of seeking always read from the current
 position.
 The value of the file pointer associated with such an object is undefined.
 .Pp
 Upon successful completion,
 .Fn read ,
 .Fn readv ,
 .Fn pread ,
 and
 .Fn preadv
 return the number of bytes actually read and placed in the buffer.
 The system guarantees to read the number of bytes requested if
 the descriptor references a normal file that has that many bytes left
 before the end-of-file, but in no other case.
 .Sh RETURN VALUES
 If successful, the
 number of bytes actually read is returned.
 Upon reading end-of-file, zero is returned.
 Otherwise, a \-1 is returned and the global variable
 .Va errno
 is set to indicate the error.
 .Sh ERRORS
 .Fn read ,
 .Fn readv ,
 .Fn pread ,
 and
 .Fn preadv
 will succeed unless:
 .Bl -tag -width Er
 .It Bq Er EAGAIN
 The file was marked for non-blocking I/O,
 and no data were ready to be read.
 .It Bq Er EBADF
 .Fa d
 is not a valid file or socket descriptor open for reading.
 .It Bq Er EFAULT
 .Fa buf
 points outside the allocated address space.
 .It Bq Er EINTR
 A read from a slow device
 (i.e. one that might block for an arbitrary amount of time)
 was interrupted by the delivery of a signal
 before any data arrived.
 See
 .Xr sigaction 2
 for more information on the interaction between signals and system
 calls.
 .It Bq Er EINVAL
 The file pointer associated with
 .Fa d
 was negative; or
 the total length of the I/O is more than can be expressed by the ssize_t
 return value.
 .It Bq Er EIO
 An I/O error occurred while reading from the file system.
 .It Bq Er EISDIR
 .Fa d
 refers to a directory and the implementation does not allow the directory
 to be read using
 .Fn read
 or
 .Fn pread .
 The
 .Fn readdir
 function should be used instead.
 .It Bq Er ENOBUFS
 A message was not delivered because it would have overflowed the buffer.
 .El
 .Pp
 In addition,
 .Fn readv
 and
 .Fn preadv
 may return one of the following errors:
 .Bl -tag -width Er
 .It Bq Er EFAULT
 Part of the
 .Fa iov
 points outside the process's allocated address space.
 .It Bq Er EINVAL
 .Fa iovcnt
 was less than or equal to 0, or greater than
 .Brq Dv IOV_MAX ;
 or one of the
 .Fa iov_len
 values in the
 .Fa iov
 array was negative; or
 the sum of the
 .Fa iov_len
 values in the
 .Fa iov
 array overflowed a 32-bit integer.
 .El
 .Pp
 The
 .Fn pread
 and
 .Fn preadv
 calls may also return the following errors:
 .Bl -tag -width Er
 .It Bq Er EINVAL
 The specified file offset is invalid.
 .It Bq Er ESPIPE
 The file descriptor is associated with a pipe, socket, or FIFO.
 .El
 .Sh SEE ALSO
 .Xr dup 2 ,
 .Xr fcntl 2 ,
 .Xr open 2 ,
 .Xr pipe 2 ,
 .Xr poll 2 ,
 .Xr select 2 ,
 .Xr sigaction 2 ,
 .Xr socket 2 ,
 .Xr socketpair 2
 .Sh STANDARDS
 The
 .Fn read
 function conforms to
 .St -p1003.1-90 .
 The
 .Fn readv
 and
 .Fn pread
 functions conform to
 .St -xpg4.2 .
 .Sh HISTORY
 The
 .Fn preadv
 function call
 appeared in
 .Nx 1.4 .
 The
 .Fn pread
 function call
 appeared in
 .At V.4 .
 The
 .Fn readv
 function call
 appeared in
 .Bx 4.2 .
 The
 .Fn read
 function call appeared in
-.At v2 .
+.At v1 .
 .Sh CAVEATS
 Error checks should explicitly test for \-1.
 Code such as
 .Bd -literal
 	while ((nr = read(fd, buf, sizeof(buf))) > 0)
 .Ed
 .Pp
 is not maximally portable, as some platforms allow for
 .Va nbytes
 to range between
 .Dv SSIZE_MAX
 and
 .Dv SIZE_MAX
 \- 2, in which case the return value of an error-free
 .Fn read
 may appear as a negative number distinct from \-1.
 Proper loops should use
 .Bd -literal
 	while ((nr = read(fd, buf, sizeof(buf))) != -1 && nr != 0)
 .Ed