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VOP_GETEXTATTR.9
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.\"-
.\" Copyright (c) 1999, 2000, 2001, 2003 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.
.\"
.Dd December 23, 1999
.Dt VOP_GETEXTATTR 9
.Os
.Sh NAME
.Nm VOP_GETEXTATTR
.Nd retrieve named extended attribute from a vnode
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.In sys/extattr.h
.Ft int
.Fo VOP_GETEXTATTR
.Fa "struct vnode *vp"
.Fa "int attrnamespace"
.Fa "const char *name"
.Fa "struct uio *uio"
.Fa "size_t *size"
.Fa "struct ucred *cred"
.Fa "struct thread *td"
.Fc
.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 ".Fa attrnamespace"
.It Fa vp
The vnode of the file or directory.
.It Fa attrnamespace
Integer constant indicating which extended attribute namespace the attribute
name is present in.
.It Fa name
Pointer to a null-terminated character string containing the attribute name.
.It Fa uio
The location of the data to be read.
.It Fa size
If not
.Dv NULL ,
on return it will contain the number of bytes required to read all of the
attribute data.
In most cases
.Fa uio
will be
.Dv NULL
when
.Fa size
is not, and vice versa.
.It Fa cred
The user credentials to use in authorizing the request.
.It Fa td
The thread requesting the extended attribute.
.El
.Pp
The
.Fa cred
pointer may be
.Dv NULL
to indicate that access control checks are not to be performed, if possible.
This
.Fa 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
The vnode will be locked on entry and should remain locked on return.
.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 ENOATTR
The requested attribute was not defined for this vnode.
.It Bq Er EACCES
The caller does not have the appropriate privilege.
.It Bq Er ENXIO
The request was not valid in this file system for the specified vnode and
attribute name.
.It Bq Er ENOMEM
Sufficient memory is not available to fulfill the request.
.It Bq Er EFAULT
The uio structure refers to an invalid userspace address.
.It Bq Er EINVAL
The
.Fa name ,
.Fa namespace ,
or
.Fa uio
argument is invalid.
.It Bq Er EOPNOTSUPP
The file system does not support
.Fn VOP_GETEXTATTR .
.El
.Sh SEE ALSO
.Xr extattr 9 ,
.Xr vnode 9 ,
.Xr VOP_LISTEXTATTR 9 ,
.Xr VOP_SETEXTATTR 9
.Sh BUGS
By passing in the empty string as the attribute name, some file systems
will return a list of defined names on the target vnode for the
requested namespace.
This is a bad API, and will be replaced by an explicit VOP.