Don't immediately discard streams with 0 references

diff --git a/src/export_image.c b/src/export_image.c
index bfeef97ad6b41afc83970afd6315f072e991c4d3..8d449ea93439d634b002aacea0287c1f66c3a88b 100644 (file)
--- a/src/export_image.c
+++ b/src/export_image.c
@@ -87,10 +87,12 @@ lte_unexport(struct wim_lookup_table_entry *lte, void *_lookup_table)
 {
        struct wim_lookup_table *lookup_table = _lookup_table;
 
-       lte->refcnt -= lte->out_refcnt;
-       if (lte->refcnt == 0) {
-               lookup_table_unlink(lookup_table, lte);
-               free_lookup_table_entry(lte);
+       if (lte->out_refcnt) {
+               lte->refcnt -= lte->out_refcnt;
+               if (lte->refcnt == 0) {
+                       lookup_table_unlink(lookup_table, lte);
+                       free_lookup_table_entry(lte);
+               }
        }
        return 0;
 }

diff --git a/src/lookup_table.c b/src/lookup_table.c
index 889013e0ae4912a382354e08e6d4ce406830e0d5..ed0ab750c9b3746878a734c04c1c87a42787c080 100644 (file)
--- a/src/lookup_table.c
+++ b/src/lookup_table.c
@@ -235,10 +235,30 @@ free_lookup_table_entry(struct wim_lookup_table_entry *lte)
        }
 }
 
-/* Decrements the reference count for the lookup table entry @lte.  If its
- * reference count reaches 0, it is unlinked from the lookup table.  If,
- * furthermore, the entry has no opened file descriptors associated with it, the
- * entry is freed.  */
+/* Should this stream be retained even if it has no references?  */
+static bool
+should_retain_lte(const struct wim_lookup_table_entry *lte)
+{
+       return lte->resource_location == RESOURCE_IN_WIM;
+}
+
+static void
+finalize_lte(struct wim_lookup_table_entry *lte)
+{
+       if (!should_retain_lte(lte))
+               free_lookup_table_entry(lte);
+}
+
+/*
+ * Decrements the reference count for the lookup table entry @lte, which must be
+ * inserted in the stream lookup table @table.
+ *
+ * If the reference count reaches 0, this may cause @lte to be destroyed.
+ * However, we may retain entries with 0 reference count.  This does not affect
+ * correctness, but it prevents the entries for valid streams in a WIM archive,
+ * which will continue to be present after appending to the file, from being
+ * lost merely because we dropped all references to them.
+ */
 void
 lte_decrement_refcnt(struct wim_lookup_table_entry *lte,
                     struct wim_lookup_table *table)
@@ -257,7 +277,8 @@ lte_decrement_refcnt(struct wim_lookup_table_entry *lte,
                                unlink(lte->staging_file_name);
                #endif
                } else {
-                       lookup_table_unlink(table, lte);
+                       if (!should_retain_lte(lte))
+                               lookup_table_unlink(table, lte);
                }
 
                /* If FUSE mounts are enabled, we don't actually free the entry
@@ -266,7 +287,7 @@ lte_decrement_refcnt(struct wim_lookup_table_entry *lte,
 #ifdef WITH_FUSE
                if (lte->num_opened_fds == 0)
 #endif
-                       free_lookup_table_entry(lte);
+                       finalize_lte(lte);
        }
 }
 
@@ -277,7 +298,7 @@ lte_decrement_num_opened_fds(struct wim_lookup_table_entry *lte)
        wimlib_assert(lte->num_opened_fds != 0);
 
        if (--lte->num_opened_fds == 0 && lte->refcnt == 0)
-               free_lookup_table_entry(lte);
+               finalize_lte(lte);
 }
 #endif