From: Daira Hopwood Date: Sat, 6 Jun 2015 21:45:42 +0000 (+0100) Subject: Magic Folder design doc: rename "parent DMD" to "collective directory", and don't... X-Git-Tag: allmydata-tahoe-1.10.1b1~9 X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/file/about.html?a=commitdiff_plain;h=b062b767403a0439abcaf7512888d494287ffe29;p=tahoe-lafs%2Ftahoe-lafs.git Magic Folder design doc: rename "parent DMD" to "collective directory", and don't assume it is mutable. (An immutable collective directory could be interesting for some use cases, and is no more difficult to support.) 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 83d90f51..3e05b6cb 100644 --- a/docs/proposed/magic-folder/remote-to-local-sync.rst +++ b/docs/proposed/magic-folder/remote-to-local-sync.rst @@ -38,6 +38,8 @@ Folder: an abstract directory that is synchronized between clients. (A folder is not the same as the directory corresponding to it on any particular client, nor is it the same as a DMD.) +Collective: the set of clients subscribed to a given Magic Folder. + Descendant: a direct or indirect child in a directory or folder tree Subfolder: a folder that is a descendant of a magic folder @@ -83,8 +85,9 @@ Since it is a goal to allow multiple users to write to a Magic Folder, if the write coordination directive remains the same as above, then we will not be able to implement the Magic Folder as a single Tahoe-LAFS DMD. In general therefore, we will have multiple DMDs —spread across -clients— that together represent the Magic Folder. Each client polls -the other clients' DMDs in order to detect remote changes. +clients— that together represent the Magic Folder. Each client in a +Magic Folder collective polls the other clients' DMDs in order to detect +remote changes. Six possible designs were considered for the representation of subfolders of the Magic Folder: @@ -139,10 +142,11 @@ Here is a summary of advantages and disadvantages of each design: 123456+: All designs have the property that a recursive add-lease -operation starting from the parent Tahoe-LAFS DMD will find all of the -files and directories used in the Magic Folder representation. Therefore -the representation is compatible with `garbage collection`_, even when a -pre-Magic-Folder client does the lease marking. +operation starting from a *collective directory* containing all of +the client DMDs, will find all of the files and directories used in +the Magic Folder representation. Therefore the representation is +compatible with `garbage collection`_, even when a pre-Magic-Folder +client does the lease marking. .. _`garbage collection`: https://tahoe-lafs.org/trac/tahoe-lafs/browser/trunk/docs/garbage-collection.rst @@ -277,21 +281,21 @@ To enable representing empty directories, a client that creates a directory should link a corresponding zero-length file in its DMD, at a name that ends with the encoded directory separator character. -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. 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 clients. Note that a client DMD should not be unlinked from the -parent directory unless all of its files are first copied to some other -client DMD. +We want to enable dynamic configuration of the membership of a Magic +Folder collective, without having to reconfigure or restart each client +when another client joins. To support this, we have a single collective +directory that links to all of the client DMDs, named by their client +nicknames. If the collective directory is mutable, then it is possible +to change its contents in order to add clients. Note that a client DMD +should not be unlinked from the collective directory unless all of its +files are first copied to some other client DMD. 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. +to the collective directory 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 @@ -299,9 +303,9 @@ 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. +at a predetermined frequency. On each poll, it will reread the collective +directory (to allow for added or removed clients), and then read each +client DMD linked from it. "Hidden" files, and files with names matching the patterns used for backup, temporary, and conflicted files, will be ignored, i.e. not synchronized