Commit 990afac1 authored by Kirill Smelkov's avatar Kirill Smelkov

X wcfs/client: Package overview (draft)

parent 9c95dbd9
......@@ -23,7 +23,7 @@
# Package _wcfs provides Python-wrappers for C++ wcfs client package.
#
# It wraps WCFS/Conn/FileH/Mapping and WatchLink to help wcfs_test.py unit-test
# It wraps WCFS/Conn/FileH/Mapping and WatchLink to help client_test.py unit-test
# WCFS base-layer mmap functionality. At functional level WCFS client (and especially
# pinner) is verified when running wendelin.core array tests in wcfs mode.
......
......@@ -19,7 +19,33 @@
// Package wcfs provides WCFS client integrated with user-space virtual memory manager.
//
// XXX view service provided
// This client package takes care about WCFS isolation protocol details and
// provides to clients simple interface to isolated file data similar to
// regular files: given a particular revision of database @at, it provides
// synthetic read-only bigfile mappings with data corresponding to @at state,
// but using /head/bigfile/* most of the time to build and maintain the mappings.
//
// For its data a mapping to bigfile X mostly reuses kernel cache for
// /head/bigfile/X with amount of data not associated with kernel cache for
// /head/bigfile/X being proportional to δ(bigfile/X, at..head). In the usual
// case where many client workers simultaneously serve requests, their database
// views are a bit outdated, but close to head, which means that in practice
// the kernel cache for /head/bigfile/* is being used almost 100% of the time.
//
// A mapping for bigfile X @at is built from OS-level memory mapping of on-WCFS
// files as
//
// ___ /@revA/bigfile/X
// __ /@revB/bigfile/X
// _ /@revC/bigfile/X
// + ...
// ─── ───── ────────────────────────── ───── /head/bigfile/X
//
// where @revR mmaps are being dynamically added/removed by this client package
// to maintain X@at data view according to WCFS invalidation protocol(*).
//
//
// API overview
//
// - `WCFS` represents filesystem-level connection to wcfs server.
// - `Conn` represents logical connection that provides view of data on wcfs
......@@ -27,8 +53,21 @@
// - `FileH` represent isolated file view under Conn.
// - `Mapping` represents one memory mapping of FileH.
//
// XXX text
// XXX provides isolated view.
//
// Integration with wendelin.core virtmem layer
//
// This client package can be used standalone, but additionally provides
// integration with wendelin.core userspace virtual memory manager: when a
// Mapping is created it can be associated as serving base layer for a
// particular virtmem VMA via FileH.mmap(vma=...). In that case, since virtmem
// itself adds another layer of dirty pages over read-only base provided by
// Mapping(+), the Mapping will interact with virtmem layer to coordinate
// mapping memory updates.
//
// --------
//
// (*) see wcfs.go documentation for overview and details of WCFS isolation protocol.
// (+) Mapping is already 2-layer as depicted above.
#ifndef _NXD_WCFS_H_
#define _NXD_WCFS_H_
......
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