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Re: [Qemu-devel] [PATCH v5 15/21] block: Resize bitmaps on bdrv_truncate


From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH v5 15/21] block: Resize bitmaps on bdrv_truncate
Date: Fri, 17 Apr 2015 15:25:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 09.04.2015 00:19, John Snow wrote:
Signed-off-by: John Snow <address@hidden>
---
  block.c                | 18 ++++++++++++++++++
  include/qemu/hbitmap.h | 10 ++++++++++
  util/hbitmap.c         | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
  3 files changed, 76 insertions(+)

diff --git a/block.c b/block.c
index 16209a2..42839a0 100644
--- a/block.c
+++ b/block.c
@@ -113,6 +113,7 @@ 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;
@@ -3583,6 +3584,7 @@ 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);
          }
@@ -5593,6 +5595,22 @@ 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;
diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
index c19c1cb..a75157e 100644
--- a/include/qemu/hbitmap.h
+++ b/include/qemu/hbitmap.h
@@ -65,6 +65,16 @@ 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.
   * @b: The bitmap to merge into @a.
diff --git a/util/hbitmap.c b/util/hbitmap.c
index ba11fd3..1ad3bf3 100644
--- a/util/hbitmap.c
+++ b/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) - num_elements;

Shouldn't this be s/num_elements/start/?

Max

+
+        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.




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