Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution.

@(#)vwrite.2v 4.1 (Berkeley) 05/09/85

C 4 vwrite - write (virtually) to file

 vwrite(filedes, buffer, nbytes)  char *buffer; 

N.B.: This call is likely to be replaced by more general virtual memory facilities in the near future.

The vwrite system call is used in conjunction with vread to perform efficient updating of large files. After a call to vread and updating of the data in the buffer which was given to vread, a vwrite of the same buffer to the same filedes at the same offset in the file will cause data which has been modified since it was vread from (or vwritten to) the file to be returned to the file.

vread(2) Returns -1 on error: bad descriptor, buffer address, count or alignment as well as on physical I/O errors. The result of vwrite is defined only when no other vread's have occurred on buffer since the one matching the vwrite.

This call is peculiar to this version of UNIX. It will be superseded by more general virtual memory facilities in future versions of the system.