NAME

VOP_READ, VOP_WRITE — read or write a file

SYNOPSIS

#include <sys/param.h>
#include <sys/vnode.h>
#include <sys/uio.h>

int
VOP_READ(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred);

int
VOP_WRITE(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred);

DESCRIPTION

These entry points read or write the contents of a file.

The arguments are:

vp: The vnode of the file.
uio: The location of the data to be read or written.
ioflag: Various flags.
cnp: The credentials of the caller.

The 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:

IO_UNIT: Do I/O as atomic unit.
IO_APPEND: Append write to end.
IO_SYNC: Do I/O synchronously.
IO_NODELOCKED: Underlying node already locked.
IO_NDELAY: FNDELAY flag set in file table.
IO_VMIO: Data already in VMIO space.

LOCKS

The file should be locked on entry and will still be locked on exit. Rangelock covering the whole i/o range should be owned around the call.

RETURN VALUES

Zero is returned on success, otherwise an error code is returned.

ERRORS

[EFBIG]: An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.
[ENOSPC]: The file system is full.
[EPERM]: An append-only flag is set on the file, but the caller is attempting to write before the current end of file.

AUTHORS

This manual page was written by Doug Rabson.