From: Daira Hopwood Date: Tue, 26 May 2015 14:54:42 +0000 (+0100) Subject: Expand on how DMDs are configured and polled. X-Git-Url: https://git.rkrishnan.org/frontends/reliability?a=commitdiff_plain;h=refs%2Fheads%2F2418.remote-to-local-sync.1;p=tahoe-lafs%2Ftahoe-lafs.git Expand on how DMDs are configured and polled. Signed-off-by: Daira Hopwood --- diff --git a/docs/proposed/magic-folder/remote-to-local-sync.rst b/docs/proposed/magic-folder/remote-to-local-sync.rst index 2815c7ca..975ace59 100644 --- a/docs/proposed/magic-folder/remote-to-local-sync.rst +++ b/docs/proposed/magic-folder/remote-to-local-sync.rst @@ -255,10 +255,37 @@ this project. Therefore, design 1 was chosen. That is: -All subfolders written by a given Magic Folder client are collapsed -into a single client DMD, containing immutable files. The child name of -each file encodes the full subpath of that file relative to the Magic -Folder. + All subfolders written by a given Magic Folder client are collapsed + into a single client DMD, containing immutable files. The child name + of each file encodes the full subpath of that file relative to the + Magic Folder. + +We want to enable dynamic configuration of the set of clients subscribed +to a Magic Folder, without having to reconfigure or restart each client +when another client joins or leaves. To support this, we have a single +parent DMD that links to all of the client DMDs, named by their client +nicknames. Then it is possible to change the contents of the parent DMD +in order to add or remove clients. + +A client needs to be able to write to its own DMD, and read from other DMDs. +To be consistent with the `Principle of Least Authority`_, each client's +reference to its own DMD is a write capability, whereas its reference +to the parent DMD is a read capability. The latter transitively grants +read access to all of the other client DMDs and the files linked from +them, as required. + +.. _`Principle of Least Authority`: http://www.eros-os.org/papers/secnotsep.pdf + +Design and implementation of the user interface for maintaining this +DMD structure and configuration will be addressed in Objectives 5 and 6. + +During operation, each client will poll for changes on other clients +at a predetermined frequency. On each poll, it will reread the parent DMD +(to allow for added or removed clients), and then read each client DMD +linked from the parent. + +[TODO: discuss how magic folder db is used -- or should this go in the +Fire Dragon section?] Conflict Detection and Resolution @@ -620,6 +647,14 @@ Ticket `#2431`_ has been opened to track this idea. Fire Dragons: Distinguishing conflicts from overwrites '''''''''''''''''''''''''''''''''''''''''''''''''''''' +It is also necessary to distinguish between overwrites, in which the +remote side was aware of your most recent version and overwrote it with a +new version, and conflicts, in which the remote side was unaware of your +most recent version when it published its new version. Those two cases +have to be handled differently — the latter needs to be raised to the +user as an issue the user will have to resolve and the former must not +bother the user. + alice sees a change by bob to 'foo' and needs to know whether that change is an overwrite or a conflict i.e. is it "based on" the version that alice already had