Re: [9fans] Persistent cache for cfs

["Douglas A. Gwyn" <DAGwyn@null.net>]

Matthew Weigel wrote:
> ... for special cases such as files that were edited both
> locally and on the fs while the client was disconnected could be
> presented as file.kfs-<modification-date> and
> file.fs-<modification-date>, so that the user could see both and decide
> what to do.

More thought is needed before inventing warts like this.
This is just a concurrent-update issue, widely studied
already.  It may be that nothing special needs to be done
about such occurrences; the last writer wins.

It seems to me that the only thing distinguishing a stash
from a normal filesystem from the user perspective is
that files have a new two-valued attribute, "temporary"
or "permanent", which is honored by the caching scheme.
Behind the scenes there must also be a mechanism for
specifying how to construct the stash filesystem, but
that can be as simple as an init rc script containing
some "copy permanent files into place" instructions.
You probably want additional specification capability
for what the stash needs to do when a nonexistent file
is accessed and also when the cache is full.  Also
what to do upon termination, again possibly an rc
script that copies out updated files.