At this point the RepoSize database is getting populated, and it
all seems to be working correctly. Incremental updates still need to be
done to make it performant.
Including locking on creation, handling of permissions errors, and
setting repo sizes.
I'm confident that locking is not needed while using this database.
Since writes happen in a single transaction. When there are two writers
that are recording sizes based on different git-annex branch commits,
one will overwrite what the other one recorded. Which is fine, it's only
necessary that the database stays consistent with the content of a
git-annex branch commit.
Plan is to run this when populating Annex.reposizes on demand.
So Annex.reposizes will be up-to-date with the journal, including
crucially journal entries for private repositories. But also
anything that has been written to the journal by another process,
especially if the process was ran with annex.alwayscommit=false.
From there, Annex.reposizes can be kept up to date with changes made
by the running process.
This will be used to prime the RepoSizes database, which will always
contain values that correpond to information in the git-annex branch, so
without anything from journal files.
Factored out overJournalFileContents which will later be used to
update Annex.reposizes to include information from journal files.
This will be partitcularly important to support private UUIDs which only
ever get to journal files and not to the branch.
5afbea25e7 changed it to ignore journal
files that did not correspond to a key in the git-annex branch. However,
when there is a private journal, that can happen.
Neither behavior is fully correct, so keep the old incorrect behavior
rather than introducing a new differently incorrect behavior.
I plan to eventually make git-annex info use Annex.reposizes instead of
calculating it itself, and once Annex.reposizes handles this all
correctly, this will be a moot problem.
This fully fixes --rebalance stability, and also deals with an issue
where a file is present in each balanced repository and it didn't want
to remove it from any.
git-annex info was displaying a message that didn't make sense in
context.
In calcRepoSizes, it seems better to return the information from the
git-annex branch, rather than giving up. Especially since balanced
preferred content uses it, and we can't just give up evaluating a
preferred content expression if git-annex is to be usable in such a
readonly repo.
Commit 6d7ecd9e5d nobly wanted git-annex
to behave the same with such unmerged branches as it does when it can
merge them. But for the purposes of preferred content, it seems to me
there's a sense that such an unmerged branch is the same as a remote we
have not pulled from. The balanced preferred content will either way
operate under outdated information, and so make not the best choices.
This is very innefficient, it will need to be optimised not to
calculate the sizes of repos every time.
Also, fixed a bug in balancedPicker that caused it to pick a too high
index when some repos were excluded due to being full.
The idea is that upon a merge of the git-annex branch, or a commit to
the git-annex branch, the reposize database will be updated. So it
should always accurately reflect the location log sizes, but it will
often be behind the actual current sizes.
Annex.reposizes will start with the value from the database, and get
updated with each transfer, so it will reflect a process's best
understanding of the current sizes.
When there are multiple processes all transferring to the same repo,
Annex.reposize will not reflect transfers made by the other processes
since the current process started. So when using balanced preferred
content, it may make suboptimal choices, including trying to transfer
content to the repo when another process has already filled it up.
But this is the same as if there are multiple processes running on
ifferent machines, so is acceptable. The reposize will eventually
get an accurate value reflecting changes made by other processes or in
other repos.
This deals with the possible security problem that someone could make an
unusually low UUID and generate keys that are all constructed to hash to
a number that, mod the number of repositories in the group, == 0.
So balanced preferred content would always put those keys in the
repository with the low UUID as long as the group contains the
number of repositories that the attacker anticipated.
Presumably the attacker than holds the data for ransom? Dunno.
Anyway, the partial solution is to use HMAC (sha256) with all the UUIDs
combined together as the "secret", and the key as the "message". Now any
change in the set of UUIDs in a group will invalidate the attacker's
constructed keys from hashing to anything in particular.
Given that there are plenty of other things someone can do if they can
write to the repository -- including modifying preferred content so only
their repository wants files, and numcopies so other repositories drom
them -- this seems like safeguard enough.
Note that, in balancedPicker, combineduuids is memoized.
This all works fine. But it doesn't check repository sizes yet, and
without repository size checking, once a repository gets full, there
will be no other repository that will want its files.
Use of sha2 seems unncessary, probably alder2 or md5 or crc would have
been enough. Possibly just summing up the bytes of the key mod the number
of repositories would have sufficed. But sha2 is there, and probably
hardware accellerated. I doubt very much there is any security benefit
to using it though. If someone wants to construct a key that will be
balanced onto a given repository, sha2 is certianly not going to stop
them.
