[Qemu-devel] [PATCH 2/2] qapi: Fix memleak in string visitors on int lists

[Eric Blake]

Commit 7f8f9ef1 introduced the ability to store a list of
integers as a sorted list of ranges, but when merging ranges,
it leaks one or more ranges.  It was also using range_get_last()
incorrectly within range_compare() (a range is a start/end pair,
but range_get_last() is for start/len pairs), and will also
mishandle a range ending in UINT64_MAX (remember, we document
that no range covers 2**64 bytes, but that ranges that end on
UINT64_MAX have end < begin).

The whole merge algorithm was rather complex, especially since
we are hard-coding things to a list of ranges; so just rewrite
the thing to open-code the traversal and comparisons, making
the range_compare() helper function give us a nicer answer,
avoiding the need to pass any callbacks to g_list_*(). And
reusing range_extend() ensures we cover the corner cases
correctly.

Drop the now-unused range_merge() and ranges_can_merge().

Doing this lets test-string-{input,output}-visitor pass under
valgrind without leaks.

CC: address@hidden
Signed-off-by: Eric Blake <address@hidden>
---
 include/qemu/range.h | 78 +++++++++++++++++++++-------------------------------
 1 file changed, 31 insertions(+), 47 deletions(-)

diff --git a/include/qemu/range.h b/include/qemu/range.h
index 4a4801b..9955cca 100644
--- a/include/qemu/range.h
+++ b/include/qemu/range.h
@@ -59,67 +59,51 @@ static inline int ranges_overlap(uint64_t first1, uint64_t 
len1,
     return !(last2 < first1 || last1 < first2);
 }

-/* 0,1 can merge with 1,2 but don't overlap */
-static inline bool ranges_can_merge(Range *range1, Range *range2)
+/* Return -1 if @a < b, 1 if greater, and 0 if they overlap. */
+static inline int range_compare(Range *a, Range *b)
 {
-    return !(range1->end < range2->begin || range2->end < range1->begin);
-}
-
-static inline void range_merge(Range *range1, Range *range2)
-{
-    if (range1->end < range2->end) {
-        range1->end = range2->end;
-    }
-    if (range1->begin > range2->begin) {
-        range1->begin = range2->begin;
-    }
-}
-
-static inline gint range_compare(gconstpointer a, gconstpointer b)
-{
-    Range *ra = (Range *)a, *rb = (Range *)b;
-    if (ra->begin == rb->begin && ra->end == rb->end) {
-        return 0;
-    } else if (range_get_last(ra->begin, ra->end) <
-               range_get_last(rb->begin, rb->end)) {
+    if (a->end && a->end < b->begin) {
         return -1;
-    } else {
+    }
+    if (b->end && a->begin > b->end) {
         return 1;
     }
+    return 0;
 }

+/* Insert @data into @list of ranges; caller no longer owns @data */
 static inline GList *range_list_insert(GList *list, Range *data)
 {
-    GList *l, *next = NULL;
-    Range *r, *nextr;
+    GList *l = list;

-    if (!list) {
-        list = g_list_insert_sorted(list, data, range_compare);
-        return list;
+    /* Range lists require no empty ranges */
+    assert(data->begin || data->end);
+
+    /* Skip all list elements strictly less than data */
+    while (l && range_compare(l->data, data) < 0) {
+        l = l->next;
+    }
+
+    /* If no list, or rest of list exceeds data, insert data and done */
+    if (!l || range_compare(l->data, data) > 0) {
+        return g_list_insert_before(list, l, data);
     }

-    nextr = data;
-    l = list;
-    while (l && l != next && nextr) {
-        r = l->data;
-        if (ranges_can_merge(r, nextr)) {
-            range_merge(r, nextr);
-            l = g_list_remove_link(l, next);
-            next = g_list_next(l);
-            if (next) {
-                nextr = next->data;
-            } else {
-                nextr = NULL;
-            }
-        } else {
-            l = g_list_next(l);
+    /* Merge data into current list element */
+    range_extend(l->data, data);
+    g_free(data);
+
+    /* Merge any subsequent list elements that now also overlap */
+    while (l->next && range_compare(l->data, l->next->data) == 0) {
+        range_extend(l->data, l->next->data);
+        g_free(l->next->data);
+        /* We know we aren't deleting the list head, so shave time
+         * by passing l instead of list */
+        if (g_list_delete_link(l, l->next) != l) {
+            abort();
         }
     }

-    if (!l) {
-        list = g_list_insert_sorted(list, data, range_compare);
-    }
-
     return list;
 }

-- 
2.5.5