diff -r b1dcf22c0418 -r 891991677a7f librazor/razor.c
--- a/librazor/razor.c	Wed Feb 01 12:47:50 2012 +0000
+++ b/librazor/razor.c	Thu Feb 09 20:45:27 2012 +0000
@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2008  Kristian Høgsberg <krh@redhat.com>
  * Copyright (C) 2008  Red Hat, Inc
- * Copyright (C) 2009-2011  J. Ali Harlow <ali@juiblex.co.uk>
+ * Copyright (C) 2009-2012  J. Ali Harlow <ali@juiblex.co.uk>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -992,6 +992,32 @@
 	}
 }
 
+/*
+ * Does <package> have a requirement for <script> which is
+ * satisfied by <provider> ?
+ * Note: We already know that <provider> is to be added as part of this install
+ * so there is no need to check the relation.
+ */
+static int
+package_script_requires(struct razor_set *set, struct razor_package *package,
+			enum razor_property_flags script,
+			struct razor_package *provider)
+{
+	struct list *link;
+	struct razor_property *prop;
+
+	link = list_first(&package->properties, &set->property_pool);
+	for(; link; link = list_next(link)) {
+		prop = set->properties.data;
+		prop += link->data;
+		if ((prop->flags & RAZOR_PROPERTY_SCRIPT_MASK) & script &&
+		    (prop->flags & RAZOR_PROPERTY_TYPE_MASK) == RAZOR_PROPERTY_REQUIRES &&
+		    provider->name == prop->name)
+			return 1;
+	}
+	return 0;
+}
+
 RAZOR_EXPORT struct razor_install_iterator *
 razor_set_create_install_iterator(struct razor_set *set,
 				  struct razor_set *next)
@@ -1002,10 +1028,12 @@
 	 * A->B means action A should follow action B.
 	 */
 	struct graph follows;
-	struct install_action *actions, *ai, *aj;
+	struct install_action *actions, *ai, *aj, *an;
 	int i, j, count, vertex_added;
 	struct list *link;
 	struct razor_set *rs;
+	struct deque *order;
+	int barrier_needed;
 
 	assert (set != NULL);
 	assert (next != NULL);
@@ -1066,7 +1094,73 @@
 			graph_add_edge(&follows, i, i);
 	}
 
-	ii->order = graph_sort(&follows);
+	/*
+	 * Because files are installed and removed using razor_atomic,
+	 * but scripts are run with no regard for these, we need some
+	 * means for synchronisation between the two. We support this
+	 * via transaction barriers which are points where
+	 * razor_atomic_commit() should be called so that scripts can
+	 * rely on the files they need being present.
+	 *
+	 * Rules:
+	 *   1)	Transaction barriers never occur within a dependency
+	 *	loop. Since we can't guarantee any ordering of actions
+	 *	within such a loop, they make no sense.
+	 *   2) Otherwise the following table applies:
+	 *	Action I    Action J	Barrier between I and J iff
+	 *	ADD P	    ADD Q	%pre(Q) requires P
+	 *	ADD P	    REMOVE Q	%preun(Q) requires P
+	 *	REMOVE P    ADD Q	never
+	 *	REMOVE P    REMOVE Q	%postun(P) requires Q
+	 *
+	 * FIXME:
+	 *	This should take account of conflicts somehow.
+	 */
+	order = graph_sort(&follows);
+	ii->order = deque_new(0);
+	if (!deque_empty(order)) {
+		j = deque_pop(order);
+		deque_unshift(ii->order, j);
+	}
+	while (!deque_empty(order)) {
+		i = j;
+		j = deque_pop(order);
+		ai = actions + i;
+		aj = actions + j;
+		if (graph_is_connected(&follows, i, j) &&
+		    graph_is_connected(&follows, j, i))
+			barrier_needed = 0;
+		else if (ai->action == RAZOR_INSTALL_ACTION_ADD &&
+			 aj->action == RAZOR_INSTALL_ACTION_ADD &&
+			 package_script_requires(next, aj->package,
+						 RAZOR_PROPERTY_PRE,
+						 ai->package))
+			barrier_needed = 1;
+		else if (ai->action == RAZOR_INSTALL_ACTION_ADD &&
+			 aj->action == RAZOR_INSTALL_ACTION_REMOVE &&
+			 package_script_requires(set, aj->package,
+						 RAZOR_PROPERTY_PREUN,
+						 ai->package))
+			barrier_needed = 1;
+		else if (ai->action == RAZOR_INSTALL_ACTION_REMOVE &&
+			 aj->action == RAZOR_INSTALL_ACTION_REMOVE &&
+			 package_script_requires(set, ai->package,
+						 RAZOR_PROPERTY_POSTUN,
+						 aj->package))
+			barrier_needed = 1;
+		else
+			barrier_needed = 0;
+		if (barrier_needed) {
+			an = array_add(&ii->actions, sizeof *an);
+			actions = ii->actions.data;
+			an->package = NULL;
+			an->action = RAZOR_INSTALL_ACTION_COMMIT;
+			deque_unshift(ii->order, an - actions);
+		}
+		deque_unshift(ii->order, j);
+	}
+	deque_free(order);
+
 	ii->left = deque_dup(ii->order);
 	graph_release(&follows);
 
@@ -1105,12 +1199,99 @@
 				(*count)++;
 		}
 		razor_package_iterator_destroy(pi);
-	} else
+	} else if (a->action == RAZOR_INSTALL_ACTION_ADD)
 		*count = 1;
 
 	return 1;
 }
 
+static int
+action_is_included(struct razor_install_iterator *ii, struct deque *done,
+		   struct razor_package *package,
+		   enum razor_install_action action)
+{
+	struct deque *t;
+	struct install_action *a;
+	int retval;
+
+	t = deque_dup(done);
+
+	while(!deque_empty(t)) {
+		a = (struct install_action *)ii->actions.data + deque_pop(t);
+		if (a->package == package && a->action == action)
+			break;
+	}
+	retval = !deque_empty(t);
+
+	deque_free(t);
+
+	return retval;
+}
+
+RAZOR_EXPORT struct razor_set *
+razor_install_iterator_commit_set(struct razor_install_iterator *ii)
+{
+	struct razor_merger *merger;
+	struct razor_set *set;
+	struct razor_package *n, *nend, *npkgs, *s, *send, *spkgs;
+	struct deque *done;
+	size_t pos;
+	char *npool, *spool;
+	int cmp;
+
+	done = deque_dup(ii->order);
+	pos = razor_install_iterator_tell(ii);
+	while(deque_length(done) > pos)
+		deque_shift(done);
+
+	s = ii->set->packages.data;
+	spkgs = ii->set->packages.data;
+	send = ii->set->packages.data + ii->set->packages.size;
+	spool = ii->set->string_pool.data;
+
+	n = ii->next->packages.data;
+	npkgs = ii->next->packages.data;
+	nend = ii->next->packages.data + ii->next->packages.size;
+	npool = ii->next->string_pool.data;
+
+	merger = razor_merger_create(ii->set, ii->next);
+	while (s < send || n < nend) {
+		if (s < send && n < nend)
+			cmp = strcmp(&spool[s->name], &npool[n->name]);
+		else if (s < send)
+			cmp = -1;
+		else
+			cmp = 1;
+
+		if (cmp < 0) {
+			if (!action_is_included(ii, done, s,
+						RAZOR_INSTALL_ACTION_REMOVE))
+				razor_merger_add_package(merger, s);
+			s++;
+		} else if (cmp == 0) {
+			if (!action_is_included(ii, done, s,
+						RAZOR_INSTALL_ACTION_REMOVE))
+				razor_merger_add_package(merger, s);
+			if (action_is_included(ii, done, n,
+					       RAZOR_INSTALL_ACTION_ADD))
+				razor_merger_add_package(merger, n);
+
+			s++;
+			n++;
+		} else {
+			if (action_is_included(ii, done, n,
+					       RAZOR_INSTALL_ACTION_ADD))
+				razor_merger_add_package(merger, n);
+			n++;
+		}
+	}
+
+	set = razor_merger_commit(merger);
+	razor_merger_destroy(merger);
+
+	return set;
+}
+
 RAZOR_EXPORT void
 razor_install_iterator_rewind(struct razor_install_iterator *ii)
 {
@@ -1118,6 +1299,35 @@
 	ii->left=deque_dup(ii->order);
 }
 
+RAZOR_EXPORT size_t
+razor_install_iterator_tell(struct razor_install_iterator *ii)
+{
+	return deque_length(ii->order) - deque_length(ii->left);
+}
+
+RAZOR_EXPORT size_t
+razor_install_iterator_seek(struct razor_install_iterator *ii, size_t pos)
+{
+	size_t current_pos;
+
+	if (pos > deque_length(ii->order))
+		pos = deque_length(ii->order);
+
+	current_pos = razor_install_iterator_tell(ii);
+
+	if (pos < current_pos) {
+		razor_install_iterator_rewind(ii);
+		current_pos = 0;
+	}
+
+	while(current_pos < pos) {
+		(void) deque_pop(ii->left);
+		current_pos++;
+	}
+
+	return current_pos;
+}
+
 RAZOR_EXPORT void
 razor_install_iterator_destroy(struct razor_install_iterator *ii)
 {