NetBSD/share/man/man9/fetch.9

.\"	$NetBSD: fetch.9,v 1.5 1997/11/11 10:07:10 mrg Exp $
.\"
.\" Copyright (c) 1996 Jason R. Thorpe.
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.\" This code is derived from software contributed by Kenneth Stailey.
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.Dd Jan 7, 1996
.Dt FETCH 9
.Os NetBSD
.Sh NAME
.Nm fetch ,
.Nm fubyte     ,
.Nm fuibyte ,
.Nm fusword ,
.Nm fuswintr ,
.Nm fuword ,
.Nm fuiword
.Nd fetch data from user-space
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/systm.h>
.Ft int
.Fn fubyte "void *base"
.Ft int
.Fn fusword "void *base"
.Ft int
.Fn fuswintr "void *base"
.Ft int
.Fn fuword "void *base"
.Sh DESCRIPTION
The
.Nm
functions are designed to copy small amounts of data from user-space.
.Pp
The
.Nm
routines provide the following functionality:
.Bl -tag -width "fuswintr()"
.It Fn fubyte
Fetches a byte of data from the user-space address
.Fa base .
.It Fn fusword
Fetches a short word of data from the user-space address
.Fa base .
.It Fn fuswintr
Fetches a short word of data from the user-space address
.Fa base .
This function is safe to call during an interrupt context.
.It Fn fuword
Fetches a word of data from the user-space address
.Fa base .
.El
.Sh RETURN VALUES
The
.Nm
functions return the data fetched or -1 on failure.
Note that these functions all do "unsigned" access, and
therefore will never sign extend byte or short values.
This prevents ambiguity with the error return value
for all functions except
.Fn fuword .
.Sh BUGS
.Pp
The function
.Fn fuword
has no way to unambiguously signal an error, because the
data it reads might legetimately be the same as the -1
used to indicate an error.  The other functions do not
have this problem because the unsigned values returned
by those can never match the -1 error return value.
.Sh SEE ALSO
.Xr copy 9 ,
.Xr store 9 .