121 lines
3.9 KiB
Groff
121 lines
3.9 KiB
Groff
.\" $NetBSD: dofileread.9,v 1.9 2010/12/02 12:54:13 wiz Exp $
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.\"
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.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd December 20, 2005
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.Dt DOFILEREAD 9
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.Os
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.Sh NAME
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.Nm dofileread ,
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.Nm dofilereadv ,
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.Nm dofilewrite ,
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.Nm dofilewritev
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.Nd high-level file operations
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.Sh SYNOPSIS
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.In sys/file.h
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.Ft int
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.Fn dofileread "struct lwp *l" "int fd" "struct file *fp" "void *buf" \
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"size_t nbyte" "off_t *offset" "int flags" "register_t *retval"
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.Ft int
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.Fn dofilewrite "struct lwp *l" "int fd" "struct file *fp" \
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"const void *buf" "size_t nbyte" "off_t *offset" "int flags" \
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"register_t *retval"
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.Ft int
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.Fn dofilereadv "struct lwp *l" "int fd" "struct file *fp" \
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"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \
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"register_t *retval"
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.Ft int
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.Fn dofilewritev "struct lwp *l" "int fd" "struct file *fp" \
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"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \
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"register_t *retval"
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.Sh DESCRIPTION
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The functions implement the underlying functionality of the
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.Xr read 2 ,
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.Xr write 2 ,
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.Xr readv 2 ,
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and
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.Xr writev 2
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system calls.
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They are also used throughout the kernel as high-level access routines
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for file I/O.
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.Pp
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The
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.Fn dofileread
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function attempts to read
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.Fa nbytes
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of data from the object referenced by file entry
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.Fa fp
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into the buffer pointed to by
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.Fa buf .
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The
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.Fn dofilewrite
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function attempts to write
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.Fa nbytes
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of data to the object referenced by file entry
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.Fa fp
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from the buffer pointed to by
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.Fa buf .
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.Pp
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The
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.Fn dofilereadv
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and
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.Fn dofilewritev
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functions perform the same operations, but scatter the data with the
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.Fa iovcnt
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buffers specified by the members of the
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.Fa iov
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array.
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.Pp
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The offset of the file operations is explicitly specified by
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.Fa *offset .
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The new file offset after the file operation is returned in
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.Fa *offset .
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If the FOF_UPDATE_OFFSET flag is specified in the
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.Fa flags
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argument, the file offset in the file entry
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.Fa fp
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is updated to reflect the new file offset, otherwise it remains
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unchanged after the operation.
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.Pp
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The file descriptor
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.Fa fd
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is largely unused except for use by the ktrace framework for reporting
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to userlevel the process's file descriptor.
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.Pp
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Upon successful completion the number of bytes which were transferred
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is returned in
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.Fa *retval .
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.Sh RETURN VALUES
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Upon successful completion zero is returned, otherwise an appropriate
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error is returned.
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.Sh CODE REFERENCES
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The framework for these file operations is implemented within the file
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.Pa sys/kern/sys_generic.c .
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.Sh SEE ALSO
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.Xr file 9
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