.\"     $NetBSD: dofileread.9,v 1.9 2010/12/02 12:54:13 wiz Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
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.Dd December 20, 2005
.Dt DOFILEREAD 9
.Os
.Sh NAME
.Nm dofileread ,
.Nm dofilereadv ,
.Nm dofilewrite ,
.Nm dofilewritev
.Nd high-level file operations
.Sh SYNOPSIS
.In sys/file.h
.Ft int
.Fn dofileread "struct lwp *l" "int fd" "struct file *fp" "void *buf" \
"size_t nbyte" "off_t *offset" "int flags" "register_t *retval"
.Ft int
.Fn dofilewrite "struct lwp *l" "int fd" "struct file *fp" \
"const void *buf" "size_t nbyte" "off_t *offset" "int flags" \
"register_t *retval"
.Ft int
.Fn dofilereadv "struct lwp *l" "int fd" "struct file *fp" \
"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \
"register_t *retval"
.Ft int
.Fn dofilewritev "struct lwp *l" "int fd" "struct file *fp" \
"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \
"register_t *retval"
.Sh DESCRIPTION
The functions implement the underlying functionality of the
.Xr read 2 ,
.Xr write 2 ,
.Xr readv 2 ,
and
.Xr writev 2
system calls.
They are also used throughout the kernel as high-level access routines
for file I/O.
.Pp
The
.Fn dofileread
function attempts to read
.Fa nbytes
of data from the object referenced by file entry
.Fa fp
into the buffer pointed to by
.Fa buf .
The
.Fn dofilewrite
function attempts to write
.Fa nbytes
of data to the object referenced by file entry
.Fa fp
from the buffer pointed to by
.Fa buf .
.Pp
The
.Fn dofilereadv
and
.Fn dofilewritev
functions perform the same operations, but scatter the data with the
.Fa iovcnt
buffers specified by the members of the
.Fa iov
array.
.Pp
The offset of the file operations is explicitly specified by
.Fa *offset .
The new file offset after the file operation is returned in
.Fa *offset .
If the FOF_UPDATE_OFFSET flag is specified in the
.Fa flags
argument, the file offset in the file entry
.Fa fp
is updated to reflect the new file offset, otherwise it remains
unchanged after the operation.
.Pp
The file descriptor
.Fa fd
is largely unused except for use by the ktrace framework for reporting
to userlevel the process's file descriptor.
.Pp
Upon successful completion the number of bytes which were transferred
is returned in
.Fa *retval .
.Sh RETURN VALUES
Upon successful completion zero is returned, otherwise an appropriate
error is returned.
.Sh CODE REFERENCES
The framework for these file operations is implemented within the file
.Pa sys/kern/sys_generic.c .
.Sh SEE ALSO
.Xr file 9