Xml in packaging system

[Matthew Dillon]

    What I envision in a packaging system is something that makes the 
    port maintainer's life as easy as possible.

    Lets say you are developing a new port, libabcd, which depends on a
    number of other libraries which are also ports in the system.

    As a developer I want to be able to do something like this:

    % vfsenvironment empty 'csh'

    (Now you would be in a vfs-sandboxed shell.  You can map-in other ports
    which you have already installed on the system):

    % vfsrecord "build_depend"
    ok, recording mappings as 'build_depend'
    % vfsmap libgettextsrc:0.12.11
    ok
    % vfsmap libexpat		(map in the highest installed version)
    ok
    % vfsmap libc
    ok
    % vfsmap gmake
    % vfsrename /usr/local/bin/gmake /usr/local/bin/make

    Once you have built an environment you could then attempt to build
    your new port natively simply by running the port's native build
    (at least initially).  If things are missing you can vfsunmap and vfsmap
    additional required elements.

    Modifications to the port distribution itself could also be done through
    the VFS.  In this case the VFS would be acting like a unionfs in that it
    would record whiteouts (deletions) and copy files that are modified into
    a higher layer which would be stored in the VFS environment process's
    memory (sufficient as long as no more then 2G worth of changes are made).

    % vfsunion ~dillon/original_distribution work

    (make your modifications to the work.  edit files, rm files, rename, 
    whatever).

    When you are satisfied that the build is working you can save the vfs
    state, which will also 'diff' any modifications you have made and record
    file/directory deletions.  The output file would be human readable and
    human editable (though it's easier for the developer to just enter the
    vfs environment and make modifications within the environment)

    % vfsrecord -w
    all changes recorded in 'build_depend.vfs'
    % exit

    --------------------

    Ok.  So there you have it, you now have the VFS environment and the
    patches required to build your new port!

    Similar action would be taken for install and run-time dependancies.
    Run-time dependancies would be more restrictive since under normal
    conditions you might not want to have to run every port wrapped in a 
    VFS.  e.g. simple ports like when you run 'less'.  But more involved
    ports, like OpenOffice, might always run in some sort of VFS environment.

    Note that the VFS environment I am contemplating does not take over
    the entire filesystem space.  That is, in the above example, the mainstream
    directories /usr/local/lib and /usr/local/bin would be selectively enabled
    and/or modified within the VFS but other directories, like your home
    directory for example (really all other directories not involved with
    mapping operations) would simply be passed through.  You would have to
    explicitly tell the VFS to map something as a union in order for the VFS
    to record your modifications within that target.

    In anycase, that is my idea... to approach it from the port maintainer's
    point of view rather then from a technical standpoint.

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>