Man pages for the VFS extended attribute and access control list vnops.

Reviewed by:	eivind

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+.\"-
+.\" Copyright (c) 1999 Robert N. M. Watson
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"       $FreeBSD$
+.\"
+.Dd December 23, 1999
+.Os
+.Dt VOP_GETEXTATTR 9
+.Sh NAME
+.Nm VOP_GETEXTATTR
+.Nd Retrieve named extended attribute from a vnode
+.Sh SYNOPSIS
+.Fd #include <sys/param.h>
+.Fd #include <sys/vnode.h>
+.Fd #include <sys/extattr.h>
+.Ft int
+.Fn VOP_GETEXTATTR "struct vnode *vp" "char *name" "struct uio *uio" "struct ucred *cred" "struct proc *p"
+.Sh DESCRIPTION
+This vnode call may be used to retrieve a specific named extended attribute
+from a file or directory.
+.Pp
+Its arguments are:
+.Bl -tag -width type
+.It Ar vp
+the vnode of the file or directory
+.It Ar name
+pointer to a null-terminated character string containing the attribute name
+.It Ar uio
+the location of the data to be read or written
+.It Ar cred
+the user credentials to use in authorizing the request
+.It Ar p
+the process requesting the extended attribute
+.El
+.Pp
+The
+.Fa cred
+pointer may be NULL to indicate that access control checks are not to be
+performed, of possible.  This cred setting might be used to allow the 
+kernel to authorize extended attribute retrieval that the active process
+might not be permitted to do.
+.Pp
+Extended attribute semantics may vary by file system implementing the call.
+More information on extended attributes may be found in
+.Xr extattr 9 .
+.Sh LOCKS
+No locks are required to call this vnode method, and any locks held on
+entry will be held on exit.
+.Sh RETURN VALUES
+On success, zero will be returned, and the uio structure will be updated to
+reflect data read.  Otherwise, an appropriate error code is returned.
+.Sh ERRORS
+.Bl -tag -width Er
+.It Bq Er ENOENT
+The attribute name is not defined for this vnode
+.It Bq Er EACCES
+Permission denied
+.It Bq Er ENXIO
+The request was not valid in this file system for the specified vnode and
+attribute name.
+.It Bq Er ENOMEM
+Insufficient memory available to fulfill request
+.It Bq Er EFAULT
+The uio structure refers to an invalid userspace address.
+.It Bq Er EINVAL
+The 
+.Fa name
+or
+.Fa uio
+argument is invalid.
+.It Bq Er EOPNOTSUPP
+The file system does not support VOP_GETEXTATTR
+.El
+.Sh SEE ALSO
+.Xr extattr 9 ,
+.Xr vnode 9 ,
+.Xr VOP_SETEXTATTR 9