Magic Folder: garbage-collect old versions of files on seeing a newer version

[daira]

When a Magic Folder client sees a newer version of a file in another client's DMD, it should unlink the older version from its own DMD. This ensures that old versions are not retained unnecessarily by garbage collection.

[daira]

Note that this is *not* required as part of OTF objective 4.

[dawuud]

When a magic-folder client discovers a new version of a file within the DMD... this means within the DMD but not in our own Tahoe upload directory. We must link the DMD file into the client's Tahoe upload dir... after unlinking the old file.

[daira]

Replying to dawuud:

When a magic-folder client discovers a new version of a file within the DMD... this means within the DMD but not in our own Tahoe upload directory. We must link the DMD file into the client's Tahoe upload dir... after unlinking the old file.

It's not necessary to link the new version into this client's DMD, because it is already in the other client's DMD, and we don't rely on all the DMDs being eventually the same. What I was intending was that if we are modifying our own DMD anyway, we "garbage collect" links to versions that are known to be old.

It would be possible to link the new version at the same time even though it isn't required, but that is a separate design decision and not what I was intending to refer to by this ticket.

[exarkun]

magic-folder has been split out into a separate project - ​https://github.com/leastauthority/magic-folder