Towards replacing rpm + yum (0.1):

- drop the filelists from the main package set file, split out to a

  secondary file.  for package sets that depend on other package sets,

  we need to be able to generate properties with owning packages that

  are in another set.  this way, a package that requires a file, will

  look up the provides in the set and find the package that owns it

  and then try mark that for update.

- installer part:

   - pre install check; check that dirs can be created (no files where

     want to create dirs), move config files according to file

     flags. (.rpmnew etc)

   - store rpm headers for installed packages.

   - implement rpm uninstall and update.

   - triggers? just say no?

- rpm seems to consider glibc > 2.6.90 to mean greater than

  2.6.90-anything.  That is, a comparison that doesn't mention the

  release field, shouldn't regard the release field of pkgs it

  compares against.  glibc-common-2.6.90 has

	conflicts: glibc < 2.6.90, glibc > 2.6.90

  since rpm doesn't let you do glibc != 2.6.90, and

	requires: glibc = 2.6.90

  will always pull in glibc.  But even with a != relation, would

  glibc-2.6.90-16 be equal to 2.6.90?  glibc 2.7.90-8 dropped it in

  favor of requires = 2.7.90-8 (#225806).

- signed packages

- space calculation before transaction, but ideally, do a number of

  smaller transactions.

- pre-link changing binaries and libs on disk screwing up checksum?

- pipelined download and install; topo-sort packages in update set,

  pick one with all deps in the current set, add it to the current set

  and satisfy deps against update set => result: minimal update

  transaction.  Queue download and install/update transaction for the

  packages in the minimal set, start over.  This also makes the

  installation phase much more interruptible, basically just stop

  after a sub-transaction finishes.  As we keep the update set around

  as a target, we can restart if needed.  Probably don't need to, can

  just do a new update.  During a sub-transaction we should keep the

  target set (i.e. the current set to be) around as a lock file

  (system.rzdb.lock or so, see git) so that razor updates are

  prevented if the systems crashes during an update.

- implement depsolving between multiple package sets by creating an

  iterator that has a sorted list of all installed pkgs from all sets,

  all installed requires from all sets, all installed provides from

  all sets etc.  could be a list of tuples (pkgs index, set index).

  should simplify even the two-set depsolving a bit since we can

  pretend there's just one set.  this should also be useful for the

  'overlay set' idea where the system set is actually made up of a

  number of sets, but typically a read-only set from a read-only fs

  and a read-write set from a r/w fs.

- locking: we use advisory file locking on the system set

  (/var/lib/razor/system.rzdb) to indicate a transaction is in

  progress.  The locking algorithm is as follows:

    1. obtain advisory lock on system set.  if this is already taken,

       we know that a process is actively modifying the system set and

       we have to wait.  there's a fcntl that lets you block for the

       lock to go away.

    2. if a system-next.rzdb file already exists an earlier razor

       process was interrupted or crashed and we may want to clean

       that up.  the system-next.rzdb file will record what the

       previous instance was trying to do and we can just replay that

       to clean up.

    3. create the new package set whichever way and write it to

       system-next.rzdb, then start installing/removing rpms.

    4. When the update is complete, rename system-next.rzdb to

       system.rzdb and remove the advisory lock.

  we should probably introduce a new object that encapsulates this

  sequence, the filename conventions, rpm cache, e.g. struct

  razor_image, with operations such as

	#define RAZOR_IMAGE_READ	0x01

	#define RAZOR_IMAGE_WRITE	0x02

	struct razor_image *

	razor_image_open(const char *root, unsigned int flags);

	int

	razor_image_begin_transaction(struct razor_image *image,

				      struct razor_set *target);

	int

	razor_image_finish_transaction(struct razor_image *image);

  the transaction pipelineing described above sits on top of this,

  since each step there needs to complete a full transaction that

  writes out a new package set.

  for overlay package sets we could do something like

	struct razor_image *

	razor_image_open_with_base(const char *root, unsigned int flags,

				   struct razor_image *base);

  where base specifies the r/o package set it's layered on.  this

  allows for stacking several layers of images.

Package set file format items:

- nail down byte-order of repo file.

- version the sections in the file, put the element size in the header

  so we can add stuff to elements in a backwards compatible way.

  maybe not necessary, we can just add sections that augment the

  sections we want to add to (similar to how rpm has add versioned

  deps).

Misc ideas:

- keep history of installed packages/journal of package transaction,

  so we can roll back to yesterday, or see what got installed in the

  latest yum update.

- use hash table for package and property lists so we only store

  unique lists (like for string pool).

- use existing, running system as repo; eg

	razor update razor://other-box.local evince

  to pull eg the latest evince and dependencies from another box.  We

  should be able to regenerate a rzr pkg from the system so we can

  reuse the signature from the originating repo.

- Ok, maybe the fastest package set merge method in the end is to use

  the razor_importer, but use a hash table for the properties.  This

  way we can assign them unique IDs immediately (like tokenizing

  strings).

- test suite should be easy, just keep .rzdb files around and test

  different type of upgrades that way (obsoletes, conflicts, file

  conflicts, file/dir problems etc).  Or maybe just keep a simple file

  format ad use a custom importer to create the .rzdb files.

- overlay package sets?  mount a read-only /usr over nfs or from the

  virt-host and have a local package set overlaid over the read-only

  one.  shouldn't need new features in the core package set data

  structure, but should be just conventions on top.  we have the base

  package set from the r/o system, the overlay set from the local

  system and we can have an effective package set which is the merge

  of everything from the overlay into the base set.  the effective set

  is easy to compute and we could do it on the fly or cache it.  or

  maybe the effective set is the on-disk representation and the

  overlay can be computed when needed, we just keep a link back to the

  base.

- incremental rawhide repo updates? instead of downloading 10MB zipped

  repo every time, download a diff rzdb?  Should be pretty small,

  especially if we don't have file checksums in metadata.  Filenames

  and properties are for the most part already present, typically just

  a version bump plus maybe tweaking a couple requires.  The upstream

  repo can store multiple incremental updates in one big file and

  provide an index file that maps updates for a given date (we should

  use repo-file checksums though) to a range in the file: Download the

  index file, search for a match for your latest rawhide.rzdb file,

  download range of updates that brings it up to date.

- use hash tables for dirs when importing files to avoid qsorting all

  files in rawhide.

Bugs:

- eliminate duplicate entries in package property lists.