Index: uspace/lib/libblock/libblock.c
===================================================================
--- uspace/lib/libblock/libblock.c	(revision c91f2d1b74337f64f6bb816a3391eb3b801b5031)
+++ uspace/lib/libblock/libblock.c	(revision cd688d9d407ba17ea6df2aeaa333efe0c6c756d1)
@@ -306,4 +306,5 @@
 	b->refcnt = 1;
 	b->dirty = false;
+	b->toxic = false;
 	fibril_rwlock_initialize(&b->contents_lock);
 	link_initialize(&b->free_link);
Index: uspace/lib/libblock/libblock.h
===================================================================
--- uspace/lib/libblock/libblock.h	(revision c91f2d1b74337f64f6bb816a3391eb3b801b5031)
+++ uspace/lib/libblock/libblock.h	(revision cd688d9d407ba17ea6df2aeaa333efe0c6c756d1)
@@ -69,4 +69,6 @@
 	/** If true, the block needs to be written back to the block device. */
 	bool dirty;
+	/** If true, the blcok does not contain valid data. */
+	bool toxic;
 	/** Readers / Writer lock protecting the contents of the block. */
 	fibril_rwlock_t contents_lock;