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.\" Copyright (c) 1996 Doug Rabson
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.\" $FreeBSD: head/share/man/man9/VOP_RDWR.9 206622 2010-04-14 19:08:06Z uqs $
.\"
.Dd July 24, 1996
.Dt VOP_RDWR 9
.Os
.Sh NAME
.Nm VOP_READ ,
.Nm VOP_WRITE
.Nd read or write a file
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.In sys/uio.h
.Ft int
.Fn VOP_READ "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
.Ft int
.Fn VOP_WRITE "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
.Sh DESCRIPTION
These entry points read or write the contents of a file
.Pp
The arguments are:
.Bl -tag -width ioflag
.It Fa vp
The vnode of the file.
.It Fa uio
The location of the data to be read or written.
.It Fa ioflag
Various flags.
.It Fa cnp
The credentials of the caller.
.El
.Pp
The
.Fa ioflag
argument is used to give directives and hints to the file system.
When attempting a read, the high 16 bits are used to provide a
read-ahead hint (in units of file system blocks) that the file system
should attempt.
The low 16 bits are a bit mask which can contain
the following flags:
.Bl -tag -width ".Dv IO_NODELOCKED"
.It Dv IO_UNIT
Do I/O as atomic unit.
.It Dv IO_APPEND
Append write to end.
.It Dv IO_SYNC
Do I/O synchronously.
.It Dv IO_NODELOCKED
Underlying node already locked.
.It Dv IO_NDELAY
.Dv FNDELAY
flag set in file table.
.It Dv IO_VMIO
Data already in VMIO space.
.El
.Sh LOCKS
The file should be locked on entry and will still be locked on exit.
.Sh RETURN VALUES
Zero is returned on success, otherwise an error code is returned.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EFBIG
An attempt was made to write a file that exceeds the process's file size
limit or the maximum file size.
.It Bq Er ENOSPC
The file system is full.
.It Bq Er EPERM
An append-only flag is set on the file, but the caller is attempting to
write before the current end of file.
.El
.Sh SEE ALSO
.Xr uiomove 9 ,
.Xr vnode 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .