.

wcfs/internal/wcfs_virtmem.cpp

@@ -46,6 +46,9 @@ using std::vector;
 typedef uint64_t Tid;   // XXX ok?
 typedef uint64_t Oid;   // XXX ok?
 
+// TidHead is invalid Tid which is larged Tid value and means @head
+const Tid TidHead = -1ULL;
+
 // XXX ok?
 struct IContext {
     virtual chan<structZ> done() = 0;
@@ -108,6 +111,8 @@ struct _Mapping {
         ASSERT((mem_stop - mem_start) % file->blksize == 0);
         return blk_start + (mem_stop - mem_start) / file->blksize;
     }
+
+    void _remmapblk(int64_t blk, Tid at);
 };
 
 
@@ -213,3 +218,36 @@ void Conn::_pin1(SrvReq *req) {
 
     wconn->_filemu.unlock();
 }
+
+// _remmapblk remmaps mapping memory for file[blk] to be viewing database as of @at state.
+//
+// at=None means unpin to head/ .   XXX -> C
+// NOTE this does not check wrt virtmem already mapped blk as RW.
+void _Mapping::_remmapblk(int64_t blk, Tid at) {
+    _Mapping *mmap = this;
+
+    ASSERT(mmap->blk_start <= blk && blk < mmap->blk_stop());
+    _File *f = mmap->file;
+
+    uint8_t *blkmem = mmap->mem_start + (blk - mmap->blk_start)*f->blksize;
+    if (at == TidHead) {
+        fsfile = f->headf;
+    }
+    else {
+        // TODO share @rev fd until wconn is resynced?
+        fsfile = f->wconn->_wc._open("@%s/bigfile/%s" % (h(at), h(f->foid)), "rb")
+        defer(fsfile.close)
+    }
+
+    _ = os.fstat(fsfile.fileno());
+    ASSERT(_.st_blksize == f->blksize);  // FIXME assert
+
+    // block is beyond file size - mmap with zeros   (assumes head/f size ↑=)
+    if ((blk+1)*f->blksize > _.st_size) {
+        mm.map_zero_into_ro(blkmem)
+    }
+    // block is inside file - mmap file data
+    else {
+        mm.map_into_ro(blkmem, fsfile.fileno(), blk*f->blksize)
+    }
+}