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Sun, 27 Apr 2008

Detailed POHMELFS roadmap.

Transaction support will be added into kernel client. It is possible that it will be exported to userspace (thus it will be synchronous write-through operations).
Also kernel client will get locking support (fcntl() ones first, then more fine-grained ones), this is different from byte-range read/write locking, which will be done on server. It is possible to export it to client too (and will be part of POHMELFS locking API actually, which will be used for fcntl() too).
The simplest case is data invalidation in client's cache (i.e. if one client issued a writeback for given page, it has to be marked as not up-to-date on other clients). Likely it will be done at the beginning of the next week. So far it will be the last cache coherency item. Task is relly simple because of asynchronous processing of all data in kernel client. Server will have to store not only index of directories to watch for object changes there, but also per-object set of pages, read by client, so that appropriate users could be notified, that page is no longer up-to-date and has to be refreshed.

Userspace server will get parallel and distributed facilities. Parallel processing will be done first by allowing lookup and readdir callbacks return inormation about objects, which will contain address of the server where object is actually located, so that server could read, write or check status there. So far the whole file will be stored on a server, i.e. for the first implementation there will not be a possibility to store half of the file on one server and another half on different one. Then it can be extended.
Server will get ability to store data on different root directories (so that client was not able to see shadow copies). There will be simple regexp policies for data storing, for example '*.jpg' has to be stored in root1 and root2, '*.txt' only in root1 and so on. Each root directory can be local or remote mounted one, userspace does not care about this issues.

Main part is already completed: I have a vision of what system has to provide and how it will look like, so with good design of the low-level mechanisms it becomes a doable task for the predictible timeframe.

Stay tuned!

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