.

wcfs/client/wcfs.cpp

@@ -75,40 +75,31 @@
 //
 // Wcfs integrates with virtmem layer to support virtmem to handle dirtying
 // pages of read-only base-layer that wcfs client provides via isolated
-// Mapping. When a page is write-accessed, virtmem mmaps in a page of RAM in
-// place of accessed virtual memory, copies base-layer content into there, and
-// marks that page as read-write accessed.
+// Mapping. For wcfs-backed bigfiles every VMA is interlinked with Mapping:
+//
+//       VMA     -> BigFileH -> ZBigFile    --.
+//        ↑↓                                 ZODB
+//      Mapping  -> FileH    -> wcfs server --'
+//
+// When a page is write-accessed, virtmem mmaps in a page of RAM in place of
+// accessed virtual memory, copies base-layer content provided by Mapping into
+// there, and marks that page as read-write accessed.
 //
 // Upon receiving pin message, the pinner consults virtmem, whether
-// corresponding page was already dirtied, and if it was, the pinner does not
-// remmap virtual memory to wcfs/@revX/f and just leaves dirty page in its
-// place, remembering pin information in fileh._pinned.
+// corresponding page was already dirtied in virtmem's BigFileH, and if it was,
+// the pinner does not remmap virtual memory to wcfs/@revX/f and just leaves
+// dirty page in its place, remembering pin information in fileh._pinned.
 //
 // Once dirty pages are no longer needed (either after discard/abort or
 // writeout/commit), virtmem asks wcfs client to remmap corresponding regions
 // of Mapping in its place again.
 //
-// The scheme outlined above avoids splitting Mapping upon dirtying an inner
-// page.
-//
-//
-// - we can reuse virtmem code:
-//
-//   XXX review text
+// The scheme outlined above does not need to split Mapping upon dirtying an
+// inner page.
 //
-//   if RW page is added to mapping, pinner does not need to split the mmap -
-//   it just needs to check before overwriting that page with @revX/data
-//   whether RAM page was mmaped by virtmem or not. If RW page is already
-//   there, pinner does not overwrite it.
-//
-//   RW -> Uptodate: Virtmem calls pinner to remmap the page RO after commit or
-//   abort.
-//   - Mapping.remmap_blk (call from virtmem after RW -> RO)
-//
-//
-//  VMA     -> fileh -> file
-//   ↑↓          ↑↓ (XXX here ?)
-// Mapping     FileH
+// See bigfile_ops (wendelin/bigfile/file.h) for interface related to
+// base-layer overlaying from virtmem point of view. For wcfs, this interface
+// is provided by small wcfs client wrapper in bigfile/file_zodb.cpp .
 //
 // --------
 //
@@ -118,6 +109,7 @@
 //     that serves all connections simultaneously.
 // XXX (wcfs client-level file handle - see package overview) ?
 
+
 // XXX locking -> explain atMu + slaves and refer to "Locking" in wcfs.go
 //
 // Conn.atMu > Conn.mu > FileH.mu