Generation numbers to catch write back of stale copies

[empserver] / src / lib / common / file.c

diff --git a/src/lib/common/file.c b/src/lib/common/file.c
index 908b024b7051e0cea7ce1871a4e35f5889ef8bbf..16633eee94d01963869f715800399b305800ed49 100644 (file)
--- a/src/lib/common/file.c
+++ b/src/lib/common/file.c
@@ -52,9 +52,12 @@ static int do_read(struct empfile *, void *, int, int);
 static int do_write(struct empfile *, void *, int, int);
 static unsigned get_seqno(struct empfile *, int);
 static void new_seqno(struct empfile *, void *);
+static void must_be_fresh(struct empfile *, void *);
 static void do_blank(struct empfile *, void *, int, int);
 static int ef_check(int);
 
+static unsigned ef_generation;
+
 /*
  * Open the file-backed table TYPE (EF_SECTOR, ...).
  * HOW are flags to control operation.  Naturally, immutable flags are
@@ -338,6 +341,7 @@ ef_read(int type, int id, void *into)
        cachep = ep->cache + (id - ep->baseid) * ep->size;
     }
     memcpy(into, cachep, ep->size);
+    ef_mark_fresh(type, into);
 
     if (ep->postread)
        ep->postread(id, into);
@@ -500,9 +504,11 @@ ef_write(int type, int id, void *from)
        if (ep->onresize && ep->onresize(type) < 0)
            return 0;
     }
-    if (id >= ep->baseid && id < ep->baseid + ep->cids)
+    if (id >= ep->baseid && id < ep->baseid + ep->cids) {
        cachep = ep->cache + (id - ep->baseid) * ep->size;
-    else
+       if (cachep != from)
+           must_be_fresh(ep, from);
+    } else
        cachep = NULL;
     if (ep->prewrite)
        ep->prewrite(id, cachep, from);
@@ -586,6 +592,35 @@ new_seqno(struct empfile *ep, void *buf)
     elt->seqno = old_seqno + 1;
 }
 
+void
+ef_make_stale(void)
+{
+    ef_generation++;
+}
+
+void
+ef_mark_fresh(int type, void *buf)
+{
+    struct empfile *ep;
+
+    if (ef_check(type) < 0)
+       return;
+    ep = &empfile[type];
+    if (!(ep->flags & EFF_TYPED))
+       return;
+    ((struct emptypedstr *)buf)->generation = ef_generation;
+}
+
+static void
+must_be_fresh(struct empfile *ep, void *buf)
+{
+    struct emptypedstr *elt = buf;
+
+    if (!(ep->flags & EFF_TYPED))
+       return;
+    CANT_HAPPEN(elt->generation != ef_generation);
+}
+
 /*
  * Extend table TYPE by COUNT elements.
  * Any pointers obtained from ef_ptr() become invalid.
@@ -663,6 +698,7 @@ ef_blank(int type, int id, void *buf)
        elt = buf;
        elt->seqno = get_seqno(ep, elt->uid);
     }
+    ef_mark_fresh(type, buf);
 }
 
 /*