Binary Updates for DragonFly

[Matthew Dillon]

    Here's my opinion on binary updates.  I considered two scenarios:

    (1) Distribute the object tree and use the normal make installkernel,
	installworld, and make upgrade mechanisms to update.

    (2) Distribute the binaries and write a custom installkernel and 
	installworld mechanism, but keep using 'make upgrade' to deal
	with the final clean up.

    I think option #2 is probably our best bet as for the most part everything
    done by instalkernel or installworld can be packaged together into a 
    single tar file that one just extracts, with only some minor renames
    of critical library files to avoid blowing the system up.

    * The binary dist creates a tar file.  The name of the tar file includes
      the rev and date... basically a unique naming convention that can be
      used to programmatically glue binary diffs together.

    * Binary diffs would be relative to older tar files and use a self
      identifying naming scheme so a script or application can verify
      that the correct binary diffs are available and applicable to the
      correct base file(s).

    * The tar files can be gzipped for distribution (but diffs are based on
      the non-gzipped version).  The gzipped tar file would remain on the
      target host as a basis for future binary patches.  The installed
      binaries would NOT be used as a basis for future binary patches, only
      the tar file.

    * A streaming patch to apply the binary diffs would be the best thing, so
      the tar file can be left on-disk in gzipped format.  I don't know if
      the binary diff mentioned in the thread can do that.  e.g. some sort
      of 'gunzip < tar | binary_patch <patchfile> | tar xvpf -' sequence
      to apply a binary patch and extract at the same time.  A similar 
      sequence could be used to generate the new tar file.  Again, the
      binary patch has to be against the NON gzipped tar file or it will
      never work.

    * Patches would contain the MD5 of the final result for validation
      (ungzipped MD5).

    * The tar file is installed on the machine.  Certain critical files
      (main library files like libc.so) are named differently in the tar
      file.  The next-to-last step after application of the tar file
      renames them to the official names, replacing the current system
      library files as a final step.

      e.g. in the tar libc.so would be 'libc.so.new' and then as a
      second-to-last step after extraction libc.so.new would be renamed
      to libc.so.

    * Enough of /usr/src is included in the patch to make 'make upgrade'
      work as it does now.  'make upgrade' is run as a final step.  We
      don't need the whole /usr/src tree, just a small part of it.  I don't
      want to have a separate upgrade mechanism for the cleanup step.  I
      want us to use 'make upgrade' even for this system.

    I see many advantages to this mechanism.

    * The upgrade can be reapplied to a system with no harm done if it was
      botched the first time... we don't want to be left with a non-working
      system no matter what.

    * Low impact on developers.  'make upgrade' is used for the final step
      either way.

    * Easy management of base tar's and patches.

    * Easy to generate the tar file(s) using existing buildworld &
      installworld mechanisms (something similar to how we build releases
      with nrelease).  e.g. a /usr/src/binarydists build system that
      leverages off of existing systems.

				KERNEL UPDATES

    Best way to do these is to have named kernel builds and maintain a base
    dist and patch system for each named build you want to distribute.  
    Official sites would distribute maybe half a dozen different kernel builds,
    but more importantly any administrator could set up a 'build' machine
    with all of his custom builds and do his own binary dists given the
    build infrastructure we would include in e.g. /usr/src/binarydists or
    /usr/src/binarybuild or whatever we want to call it.

    As a final note I would say that we have used our /usr/src/ based build
    system to great advantage over the years.  We need to leverage it as much
    as possible when introducing a binary update option.

						-Matt