libc/sys/extattr.2

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.\" $FreeBSD: src/lib/libc/sys/extattr_get_file.2,v 1.19 2008/01/29 18:15:38 trhodes Exp $
.\"
.Dd May 8, 2010
.Dt EXTATTR 2
.Os
.Sh NAME
.Nm extattr_get_file ,
.Nm extattr_set_file ,
.Nm extattr_delete_file
.Nd system calls to manipulate VFS extended attributes
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/extattr.h
.Ft ssize_t
.Fn extattr_get_file "const char *path" "int attrnamespace" "const char *attrname" "void *data" "size_t nbytes"
.Ft int
.Fn extattr_set_file "const char *path" "int attrnamespace" "const char *attrname" "const void *data" "size_t nbytes"
.Ft int
.Fn extattr_delete_file "const char *path" "int attrnamespace" "const char *attrname"
.Sh DESCRIPTION
Named extended attributes are meta-data associated with vnodes
representing files and directories.
They exist as
.Qq Li name=value
pairs within a set of namespaces.
.Pp
The
.Fn extattr_get_file
system call retrieves the value of the specified extended attribute into
a buffer pointed to by
.Fa data
of size
.Fa nbytes .
The
.Fn extattr_set_file
system call sets the value of the specified extended attribute to the data
described by
.Fa data .
The
.Fn extattr_delete_file
system call deletes the extended attribute specified.
The
.Fn extattr_get_file
call consumes the
.Fa data
and
.Fa nbytes
arguments in the style of
.Xr read 2 ;
.Fn extattr_set_file
consumes these arguments in the style of
.Xr write 2 .
.Pp
If
.Fa data
is
.Dv NULL
in a call to
.Fn extattr_get_file
then the size of defined extended attribute data will be returned, rather
than the quantity read, permitting applications to test the size of the
data without performing a read.
.Pp
The following arguments are common to all the system calls described here:
.Bl -tag -width attrnamespace
.It Fa attrnamespace
the namespace in which the extended attribute resides; see
.Xr extattr 9
.It Fa attrname
the name of the extended attribute
.El
.Pp
Named extended attribute semantics vary by file system implementing the call.
Not all operations may be supported for a particular attribute.
Additionally, the format of the data in
.Fa data
is attribute-specific.
.Pp
For more information on named extended attributes, please see
.Xr extattr 9 .
.Sh CAVEAT
This interface is under active development, and as such is subject to
change as applications are adapted to use it.
Developers are discouraged from relying on its stability.
.Sh RETURN VALUES
If successful, the
.Fn extattr_get_file
and
.Fn extattr_set_file
calls return the number of bytes
that were read or written from the
.Fa data ,
respectively, or if
.Fa data
was
.Dv NULL ,
then
.Fn extattr_get_file
returns the number of bytes available to read.
If any of the calls are unsuccessful, the value \-1 is returned
and the global variable
.Va errno
is set to indicate the error.
.Pp
.Rv -std extattr_delete_file
.Sh ERRORS
The following errors may be returned by the system calls themselves.
Additionally, the file system implementing the call may return any
other errors it desires.
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa attrnamespace
and
.Fa attrname
arguments,
or the memory range defined by
.Fa data
and
.Fa nbytes
point outside the process's allocated address space.
.It Bq Er ENAMETOOLONG
The attribute name was longer than
.Dv EXTATTR_MAXNAMELEN .
.El
.Pp
Additionally, the
.Fn extattr_get_file ,
.Fn extattr_set_file ,
and
.Fn extattr_delete_file
calls may also fail due to the following errors:
.Bl -tag -width Er
.It Bq Er ENOATTR
The requested attribute was not defined for this file.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
A component of the path name that must exist does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" XXX are any missing?
.El
.Sh SEE ALSO
.\".Xr extattr 3 ,
.\".Xr getextattr 8 ,
.\".Xr setextattr 8 ,
.Xr extattr 9 ,
.Xr VOP_GETEXTATTR 9 ,
.Xr VOP_SETEXTATTR 9
.Sh HISTORY
Extended attribute support was developed as part of the
.Tn TrustedBSD
Project, and introduced in
.Fx 5.0 .
It was developed to support security extensions requiring additional labels
to be associated with each file or directory.
.Sh BUGS
In earlier versions of this API, passing an empty string for the
attribute name to
.Fn extattr_get_file
would return the list of attributes defined for the target object.
This interface has been deprecated in preference to using the explicit
list API, and should not be used.