Re: [9fans] replica (was: ipv6)

[rsc@plan9.bell-labs.com]

> The file is consistent but is the directory? I.e. if I was copying over a whole bunch of files,
> could he not have gotten in when I was half way through?

Pull doesn't walk the entire file system looking
for changes.  Instead, it relies on changes being
listed in a change log /n/sources/dist/replica/plan9.log.

If I run a pull (so I'm up-to-date) and then you
change files on sources, future pulls won't notice
any of them until they're added to the change log.

The change log gets updated by running mk scan
in /sys/lib/dist.  This happens half-hourly via cron.
If the cron job happened while the copy was in
progress, then yes, until the next scan you'd only
get half the new files.  If the cron job didn't exist,
so that mk scan couldn't happen while you were
halfway through updating things, then there'd be
no way for me to get just some of the changes if I
were up-to-date except for those changes.

I guess my point in all this was that you cannot
get into a state where the client machine has the
wrong idea of what it has and doesn't have.

For example, a priori you might worry that if I copy
down a file as it is changing, I'll get a weird merge
of the two files that will persist until the file changes
again.  Or I'd get the old file but think I had the new
one, so that I wouldn't download the new one the
next time around.  None of those things can happen.

Russ