Changed protocol spec to make SETCONFIG only store it persistently when run
during INITREMOTE. I see no reason to support storing it persistently at
other times, and doing so would unnecessarily complicate the code.
Also, letting that be done would probably result in use for storing data that
doesn't really belong there, and special remote authors who don't
understand how the union merging works would probably be surprised the
results.
That complicated special remote programs, because they had to avoid making
PREPARE fail if some configuration is missing, because the remote might not
be initialized yet. Instead, complicate git-annex slightly by only sending
PREPARE immediately before some other request other than INITREMOTE (or
PREPARE of course).
This has not been tested at all. It compiles!
The only known missing things are support for encryption, and for get/set
of special remote configuration, and of key state. (The latter needs
separate work to add a new per-key log file to store that state.)
Only thing I don't much like is that initremote needs to be passed both
type=external and externaltype=foo. It would be better to have just
type=foo
Most of this is quite straightforward code, that largely wrote itself given
the types. The only tricky parts were:
* Need to lock the remote when using it to eg make a request, because
in theory git-annex could have multiple threads that each try to use
a remote at the same time. I don't think that git-annex ever does
that currently, but better safe than sorry.
* Rather than starting up every external special remote program when
git-annex starts, they are started only on demand, when first used.
This will avoid slowdown, especially when running fast git-annex query
commands. Once started, they keep running until git-annex stops, currently,
which may not be ideal, but it's hard to know a better time to stop them.
* Bit of a chicken and egg problem with caching the cost of the remote,
because setting annex-cost in the git config needs the remote to already
be set up. Managed to finesse that.
This commit was sponsored by Lukas Anzinger.
