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[Qemu-block] [PATCH v2 06/17] hbitmap: add hbitmap_merge
From: |
John Snow |
Subject: |
[Qemu-block] [PATCH v2 06/17] hbitmap: add hbitmap_merge |
Date: |
Mon, 2 Mar 2015 18:19:52 -0500 |
We add a bitmap merge operation to assist in error cases
where we wish to combine two bitmaps together.
This is algorithmically O(bits) provided HBITMAP_LEVELS remains
constant. For a full bitmap on a 64bit machine:
sum(bits/64^k, k, 0, HBITMAP_LEVELS) ~= 1.01587 * bits
We may be able to improve running speed for particularly sparse
bitmaps by using iterators, but the running time for dense maps
will be worse.
We present the simpler solution first, and we can refine it later
if needed.
Signed-off-by: John Snow <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
include/qemu/hbitmap.h | 11 +++++++++++
util/hbitmap.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 43 insertions(+)
diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
index 550d7ce..c19c1cb 100644
--- a/include/qemu/hbitmap.h
+++ b/include/qemu/hbitmap.h
@@ -65,6 +65,17 @@ struct HBitmapIter {
HBitmap *hbitmap_alloc(uint64_t size, int granularity);
/**
+ * hbitmap_merge:
+ * @a: The bitmap to store the result in.
+ * @b: The bitmap to merge into @a.
+ *
+ * Merge two bitmaps together.
+ * A := A (BITOR) B.
+ * B is left unmodified.
+ */
+bool hbitmap_merge(HBitmap *a, const HBitmap *b);
+
+/**
* hbitmap_empty:
* @hb: HBitmap to operate on.
*
diff --git a/util/hbitmap.c b/util/hbitmap.c
index ab13971..962ff29 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -395,3 +395,35 @@ HBitmap *hbitmap_alloc(uint64_t size, int granularity)
hb->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
return hb;
}
+
+/**
+ * Given HBitmaps A and B, let A := A (BITOR) B.
+ * Bitmap B will not be modified.
+ */
+bool hbitmap_merge(HBitmap *a, const HBitmap *b)
+{
+ int i, j;
+ uint64_t size;
+
+ if ((a->size != b->size) || (a->granularity != b->granularity)) {
+ return false;
+ }
+
+ if (hbitmap_count(b) == 0) {
+ return true;
+ }
+
+ /* This merge is O(size), as BITS_PER_LONG and HBITMAP_LEVELS are constant.
+ * It may be possible to improve running times for sparsely populated maps
+ * by using hbitmap_iter_next, but this is suboptimal for dense maps.
+ */
+ size = a->size;
+ for (i = HBITMAP_LEVELS - 1; i >= 0; i--) {
+ size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
+ for (j = 0; j < size; j++) {
+ a->levels[i][j] |= b->levels[i][j];
+ }
+ }
+
+ return true;
+}
--
1.9.3
- [Qemu-block] [PATCH v2 00/17] block: transactionless incremental backup series, John Snow, 2015/03/02
- [Qemu-block] [PATCH v2 03/17] qmp: Ensure consistent granularity type, John Snow, 2015/03/02
- [Qemu-block] [PATCH v2 06/17] hbitmap: add hbitmap_merge,
John Snow <=
- [Qemu-block] [PATCH v2 04/17] qmp: Add block-dirty-bitmap-add and block-dirty-bitmap-remove, John Snow, 2015/03/02
- [Qemu-block] [PATCH v2 01/17] docs: incremental backup documentation, John Snow, 2015/03/02
- [Qemu-block] [PATCH v2 02/17] qapi: Add optional field "name" to block dirty bitmap, John Snow, 2015/03/02
- [Qemu-block] [PATCH v2 07/17] block: Add bitmap disabled status, John Snow, 2015/03/02