Specification of enhancing Areca backup to support filesystem ACL and extended attributes

1. Overview

    For a backup tool, it should be able to record/restore ALL the data with
    ALL the permissions. If extended attribtues are not able to be included
    then that is not ALL the data, if ACLs are not included then that is not
    ALL the permissions. 


2. Requirement Specification
    R-1: Backup ACL, including ZFS ACL if it has.
    R-2: Backup extended attributes, including ZFS extended attributes
         if it has.

3. High Level Design
    
    3.1 Issues
    The existing Areca backup tool was developed by Java, it is using Java IO
    API to copy files from source to destination. Current architecture can
    recognize what platform is (Windows, Unix); and if it is Unix system,
    the Areca will just restore owner, group and basic permissions by running
    Unix command 'chown' and 'chmod'. It does not record any ACL and
    extended attribute information.

    3.2 Possible Solution

    3.2.1 Using existing tools

    On Solaris, user can use getfacl(1)/setfacl(1) to record ACL
    permissions; However, user has to use openat() programming API to
    interoperate with file system, see fsattr(5). 

    Solaris has cpio(1), tar(1) and pax(1) archive tools; they all support
    ACL and extended attributes. User can use one of these 3 tools to
    backup data. 

    On Linux, GNU cpio, tar and pax are also available. However, GNU pax is
    not officially released.

    Advantage:
        Less code change.

    Disadvantage:
        Lower performance, platform restriction (sort of hard-code).

    3.2.2 Using programming API

    Java Native Interface can let Java Code to call C programming
    interface. On Solaris, the cpio.h(3HEAD) is available and stable; on
    Linux the corresponding header file is also available. Using JNI to
    record/restore IO in stead of using Java IO on Unix (Solaris/Linux) can
    resolve the issue permanently.

    Advantage:
        Higher performance, independent of system tools/packages

    Disadvantage:
        More code change.

    3.3 Design Specification

    Due to the analyzing above, I would like to chose 3.2.2 as the total
    solution for this backup tool. There are areas which need to be enhanced
    to support R-1 and R-2.
    
    3.1 Can distinguish Solaris, Linux and Windows
        Areca will use different IO APIs for these different platforms.
	Areca needs to make sure R-1 and R-2 can be recorded on Solaris.

    3.2 JNI programming code for Solaris cpio.h
        Using Java Native Interface to include cpio.h to support ACL and
	extended attribute backup. 

4. Design Limitation
   
   It is hard to sync ACL, extend attributes definition among Windows,
   Linux and Solaris. It is even harder to sync them between FreeBSD and
   other Unix platform. This phase only support OpenSolaris. If
   there are requirements for any other system, like Linux, windowsNT, MacOS,
   using JNI to swith IO API should be applicable.