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.

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.

SEE ALSO

     uiomove(9), vnode(9)

AUTHORS

     This manual page was written by Doug Rabson.