[Gnu-arch-users] Mirror feature enhancement

[chth]

1) mirroring checks first if a file '=meta-info/mirror-inhibit' exists,
If so then mirroring is instantly stopped.
Rationale: sometimes one knows that his archive is broken, an archive is
freezed and don't need to be updated anymore, some traffic quota is
reached towards the end of the month or one is up to fix some things on
the archive and don't want this to be mirrored until the inhibit
condition is fixed.

2) mirroring checks if a file '=meta-info/mirror-serial' exists, If so
then the contents of the remote file are compared against the local
mirrored '=meta-info/mirror-serial'. When these both files differ the
local mirror will be completely rebuild (rm -rf or backuped and fetched
again). Rationale: this gives a archive owner some control over broken
mirrors without maintainace involvement of the mirror administrator.

Caveats: Changing these flags don't need to be *fully* transaction
protected, mirroring is likely to look for the inhibit flag at every
transaction commit. The serial only needs to be compared once before
mirroring. If one of this flags is changed while a mirroring is in
progress it will be stopped in case of the inhibit flag is set or
refetch the archive on the next mirroring cycle if the serial-flag is
changed. There is a small chance of breaking the mirror by this, but it
is far better than what we have now. While full transactional access
will complicate the implementation and make the mirroring turnaround
much slower.

        Christian