block: Resize bitmaps on bdrv_truncate

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1429314609-29776-16-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -114,6 +114,7 @@ static void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector,
                            int nr_sectors);
 static void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
                              int nr_sectors);
+static void bdrv_dirty_bitmap_truncate(BlockDriverState *bs);
 /* If non-zero, use only whitelisted block drivers */
 static int use_bdrv_whitelist;
 
@@ -3610,6 +3611,7 @@ int bdrv_truncate(BlockDriverState *bs, int64_t offset)
     ret = drv->bdrv_truncate(bs, offset);
     if (ret == 0) {
         ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS);
+        bdrv_dirty_bitmap_truncate(bs);
         if (bs->blk) {
             blk_dev_resize_cb(bs->blk);
         }
@@ -5659,6 +5661,22 @@ BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
     return parent;
 }
 
+/**
+ * Truncates _all_ bitmaps attached to a BDS.
+ */
+static void bdrv_dirty_bitmap_truncate(BlockDriverState *bs)
+{
+    BdrvDirtyBitmap *bitmap;
+    uint64_t size = bdrv_nb_sectors(bs);
+
+    QLIST_FOREACH(bitmap, &bs->dirty_bitmaps, list) {
+        if (bdrv_dirty_bitmap_frozen(bitmap)) {
+            continue;
+        }
+        hbitmap_truncate(bitmap->bitmap, size);
+    }
+}
+
 void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap)
 {
     BdrvDirtyBitmap *bm, *next;

include/qemu/hbitmap.h

@@ -64,6 +64,16 @@ struct HBitmapIter {
  */
 HBitmap *hbitmap_alloc(uint64_t size, int granularity);
 
+/**
+ * hbitmap_truncate:
+ * @hb: The bitmap to change the size of.
+ * @size: The number of elements to change the bitmap to accommodate.
+ *
+ * truncate or grow an existing bitmap to accommodate a new number of elements.
+ * This may invalidate existing HBitmapIterators.
+ */
+void hbitmap_truncate(HBitmap *hb, uint64_t size);
+
 /**
  * hbitmap_merge:
  * @a: The bitmap to store the result in.

util/hbitmap.c

@@ -400,6 +400,54 @@ HBitmap *hbitmap_alloc(uint64_t size, int granularity)
     return hb;
 }
 
+void hbitmap_truncate(HBitmap *hb, uint64_t size)
+{
+    bool shrink;
+    unsigned i;
+    uint64_t num_elements = size;
+    uint64_t old;
+
+    /* Size comes in as logical elements, adjust for granularity. */
+    size = (size + (1ULL << hb->granularity) - 1) >> hb->granularity;
+    assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
+    shrink = size < hb->size;
+
+    /* bit sizes are identical; nothing to do. */
+    if (size == hb->size) {
+        return;
+    }
+
+    /* If we're losing bits, let's clear those bits before we invalidate all of
+     * our invariants. This helps keep the bitcount consistent, and will prevent
+     * us from carrying around garbage bits beyond the end of the map.
+     */
+    if (shrink) {
+        /* Don't clear partial granularity groups;
+         * start at the first full one. */
+        uint64_t start = QEMU_ALIGN_UP(num_elements, 1 << hb->granularity);
+        uint64_t fix_count = (hb->size << hb->granularity) - start;
+
+        assert(fix_count);
+        hbitmap_reset(hb, start, fix_count);
+    }
+
+    hb->size = size;
+    for (i = HBITMAP_LEVELS; i-- > 0; ) {
+        size = MAX(BITS_TO_LONGS(size), 1);
+        if (hb->sizes[i] == size) {
+            break;
+        }
+        old = hb->sizes[i];
+        hb->sizes[i] = size;
+        hb->levels[i] = g_realloc(hb->levels[i], size * sizeof(unsigned long));
+        if (!shrink) {
+            memset(&hb->levels[i][old], 0x00,
+                   (size - old) * sizeof(*hb->levels[i]));
+        }
+    }
+}
+
+
 /**
  * Given HBitmaps A and B, let A := A (BITOR) B.
  * Bitmap B will not be modified.