.

bigfile/virtmem.c

@@ -288,7 +288,7 @@ int fileh_mmap(VMA *vma, BigFileH *fileh, pgoff_t pgoffset, pgoff_t pglen)
             if (!(pgoffset <= page->f_pgoffset && page->f_pgoffset < pgoffset + pglen))
                 continue; /* page is out of requested mmap coverage */
 
-            // XXX notify watcher that we mmap RAM page in its range?
+            // XXX notify watcher that we mmap RAM page in its range? -> no need
             vma_mmap_page(vma, page);
         }
     }

include/wendelin/bigfile/file.h

@@ -81,9 +81,21 @@ struct bigfile_ops {
      *
      * The mapping will be used as the base read-only layer for vma.
      *
-     * XXX bigfile backend owns setup mapping and can change it dynamically
-     * e.g. due to changes to the file from outside. However it should XXX
-     * check dirtyv and if dirty=1 not change that page until remmap_blk_read.
+     * After setup bigfile backend manages the mapping and can change it dynamically
+     * e.g. due to changes to the file from outside. However before changing a page,
+     * the backend must check if that page was already dirtied by virtmeme and if
+     * so don't change that page until virtmem calls .remmap_blk_read.
+     *
+     * The checking has to be done with virtmem lock held. A sketch of mapping
+     * update sequence is as below:
+     *
+     *      # backend detects that block is changed from outside
+     *      # fileh is vma->fileh - file handle with which the vma is associated
+     *      virt_lock()
+     *      if (!fileh_blk_isdirty(fileh, blk)) {
+     *          // update mappings for all fileh's vma that cover blk
+     *      }
+     *      virt_unlock()
      *
      * XXX called under virtmem lock?
      *
@@ -96,7 +108,9 @@ struct bigfile_ops {
     void* (*mmap_setup_read) (BigFile *file, blk_t blk, size_t blklen, VMA *vma);
 
 
-    // XXX
+    // remmap_blk_read is called to remmap a block into vma again, after e.g.
+    // RW dirty page was discarded.
+    //
     // XXX called under virtmem lock?
     //
     // XXX error -> bug (must not fail)

wcfs/__init__.py

@@ -21,7 +21,7 @@
 """Module wcfs.py provides python gateway for spawning and interoperating with wcfs server
 
 Join(zurl) joins wcfs server. If wcfs server for zurl is not yet running, it
-will be automatically started if `autostart=True` parameter is passed to join.
+will be automatically started if `autostart=True` is passed to join.
 It will also be automatically started by default unless
 $WENDELIN_CORE_WCFS_AUTOSTART=no is specified in environment.
 
@@ -233,10 +233,16 @@ def _pin1(wconn, req):
 
             trace('\tremmapblk %d @%s' % (req.blk, (h(req.at) if req.at else "head")))
             # FIXME check if virtmem did not mapped RW page into this block already
-            mmap._remmapblk(req.blk, req.at)
+            #    -> check if virtmem did not dirtied page corresponding to this block already
+            virt_lock()
+            if not fileh_blk_isdirty(mmap.fileh, req.blk):
+                mmap._remmapblk(req.blk, req.at)
+            virt unlock()
             trace('\t-> remmaped')
 
         # update f.pinned
+        # XXX do it before ^^^ remmapblk (so that e.g. concurrent
+        # discard/writeout see correct f.pinned) ?
         if req.at is None:
             f.pinned.pop(req.blk, None)     # = delete(f.pinned, req.blk)  -- unpin to @head
         else: