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Re: [Qemu-block] [Qemu-devel] [2.4 PATCH v3 16/19] hbitmap: truncate tes

From: Max Reitz
Subject: Re: [Qemu-block] [Qemu-devel] [2.4 PATCH v3 16/19] hbitmap: truncate tests
Date: Tue, 17 Mar 2015 13:28:50 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 
On 2015-03-17 at 13:21, John Snow wrote:



On 03/17/2015 10:53 AM, Max Reitz wrote:

On 2015-03-13 at 14:30, John Snow wrote:

The general approach is to set bits close to the boundaries of
where we are truncating and ensure that everything appears to
have gone OK.

We test growing and shrinking by different amounts:
- Less than the granularity
- Less than the granularity, but across a boundary
- Less than sizeof(unsigned long)
- Less than sizeof(unsigned long), but across a ulong boundary
- More than sizeof(unsigned long)

Signed-off-by: John Snow <address@hidden>
---
  tests/test-hbitmap.c | 247
+++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 247 insertions(+)

diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
index 8c902f2..65401ab 100644
--- a/tests/test-hbitmap.c
+++ b/tests/test-hbitmap.c
@@ -11,6 +11,8 @@
  #include <glib.h>
  #include <stdarg.h>
+#include <string.h>
+#include <sys/types.h>
  #include "qemu/hbitmap.h"
  #define LOG_BITS_PER_LONG          (BITS_PER_LONG == 32 ? 5 : 6)
@@ -23,6 +25,7 @@ typedef struct TestHBitmapData {
      HBitmap       *hb;
      unsigned long *bits;
      size_t         size;
+    size_t         old_size;
      int            granularity;
  } TestHBitmapData;
@@ -91,6 +94,44 @@ static void hbitmap_test_init(TestHBitmapData *data,
      }
  }
+static inline size_t hbitmap_test_array_size(size_t bits)
+{
+    size_t n = (bits + BITS_PER_LONG - 1) / BITS_PER_LONG;
+    return n ? n : 1;
+}
+
+static void hbitmap_test_truncate_impl(TestHBitmapData *data,
+                                       size_t size)
+{
+    size_t n;
+    size_t m;
+    data->old_size = data->size;
+    data->size = size;
+
+    if (data->size == data->old_size) {
+        return;
+    }
+
+    n = hbitmap_test_array_size(size);
+    m = hbitmap_test_array_size(data->old_size);
+    data->bits = g_realloc(data->bits, sizeof(unsigned long) * n);
+    if (n > m) {
+        memset(&data->bits[m], 0x00, sizeof(unsigned long) * (n - m));
+    }
+
+    /* If we shrink to an uneven multiple of sizeof(unsigned long),
+     * scrub the leftover memory. */
+    if (data->size < data->old_size) {
+        m = size % (sizeof(unsigned long) * 8);
+        if (m) {
+            unsigned long mask = (1ULL << m) - 1;
+            data->bits[n-1] &= mask;
+        }
+    }
+
+    hbitmap_truncate(data->hb, size);
+}
+
  static void hbitmap_test_teardown(TestHBitmapData *data,
                                    const void *unused)
  {
@@ -369,6 +410,190 @@ static void
test_hbitmap_iter_granularity(TestHBitmapData *data,
      g_assert_cmpint(hbitmap_iter_next(&hbi), <, 0);
  }
+static void hbitmap_test_set_boundary_bits(TestHBitmapData *data,
ssize_t diff)
+{
+    size_t size = data->size;
+
+    /* First bit */
+    hbitmap_test_set(data, 0, 1);
+    if (diff < 0) {
+        /* Last bit in new, shortened map */
+        hbitmap_test_set(data, size + diff - 1, 1);
+
+        /* First bit to be truncated away */
+        hbitmap_test_set(data, size + diff, 1);
+    }
+    /* Last bit */
+    hbitmap_test_set(data, size - 1, 1);
+    if (data->granularity == 0) {
+        hbitmap_test_check_get(data);
+    }
+}
+
+static void hbitmap_test_check_boundary_bits(TestHBitmapData *data)
+{
+    size_t size = MIN(data->size, data->old_size);
+
+    if (data->granularity == 0) {
+        hbitmap_test_check_get(data);
+        hbitmap_test_check(data, 0);
+    } else {
+        g_assert(hbitmap_get(data->hb, 0));
+        g_assert(hbitmap_get(data->hb, size - 1));
+        g_assert_cmpint(2 << data->granularity, ==,
hbitmap_count(data->hb));


Hm, where does this come from?
I assume you are referring to specifically the population count. On both grow and shrink operations, we should be left with only two real/physical bits set: the first and either the last or the formerly last bit in the bitmap.
For shrink operations, we truncate off two extra bits that exist within the now 'dead space.', leaving us with two.
For grow operations, we add empty space, leaving the first and formerly last bit set. (This is the MIN() call above.)
In both cases, we should have two real bits left. Adjusting for granularity (g=1 in my tests, here, when used) we should always find four "virtual bits" set.
Ooooh, yeah, I was wondering about the granularity adjustment. But of course, if you set one bit but your granularity is 2^x, you're basically setting x bits.
Confusingly, this even happens when the bitmap ends or is truncated on a virtual granularity boundary: e.g. a bitmap of 3 bits with a granularity of g=1 (2^1 - 2 bits). Setting the 3rd bit will set two virtual bits, giving us a popcount of 2, even though one of those bits is a phantom.
The boundary bits that I am checking here are set in test_set_boundary_bits, and are not checked explicitly for g=0 cases where we can rely on the shadow data that Paolo keeps track of. For g=1 cases, I check manually.
The implication here is that "test_check_boundary_bits" is only expected to avoid an assertion if it is called after "test_set_boundary_bits" and, in the shrinking case, a truncate operation.
I was about to propose making this a comment (I know it's only a test, but even tests deserve comments on what they're testing), but now I noticed that my main problem of understanding was simply the "you call hbitmap_set() once and it sets x bits if your granularity is 2^x", so I guess it can stay this way. 

Reviewed-by: Max Reitz <address@hidden>


+    }
+}
+
+/* Generic truncate test. */
+static void hbitmap_test_truncate(TestHBitmapData *data,
+                                  size_t size,
+                                  ssize_t diff,
+                                  int granularity)
+{
+    hbitmap_test_init(data, size, granularity);
+    hbitmap_test_set_boundary_bits(data, diff);
+    hbitmap_test_truncate_impl(data, size + diff);
+    hbitmap_test_check_boundary_bits(data);
+}
+
+static void test_hbitmap_truncate_nop(TestHBitmapData *data,
+                                      const void *unused)
+{
+    hbitmap_test_truncate(data, L2, 0, 0);
+}
+
+/**
+ * Grow by an amount smaller than the granularity, without crossing
+ * a granularity alignment boundary. Effectively a NOP.
+ */
+static void test_hbitmap_truncate_grow_negligible(TestHBitmapData *data, 
+                                                  const void *unused)
+{
+    size_t size = L2 - 1;
+    size_t diff = 1;
+    int granularity = 1;
+
+    hbitmap_test_truncate(data, size, diff, granularity);
+}
+
+/**
+ * Shrink by an amount smaller than the granularity, without crossing
+ * a granularity alignment boundary. Effectively a NOP.
+ */
+static void test_hbitmap_truncate_shrink_negligible(TestHBitmapData
*data,
+ const void *unused) 
+{
+    size_t size = L2;
+    ssize_t diff = -1;
+    int granularity = 1;
+
+    hbitmap_test_truncate(data, size, diff, granularity);
+}
+
+/**
+ * Grow by an amount smaller than the granularity, but crossing over
+ * a granularity alignment boundary.
+ */
+static void test_hbitmap_truncate_grow_tiny(TestHBitmapData *data,
+                                            const void *unused)
+{
+    size_t size = L2 - 2;
+    ssize_t diff = 1;
+    int granularity = 1;
+
+    hbitmap_test_truncate(data, size, diff, granularity);
+}
+
+/**
+ * Shrink by an amount smaller than the granularity, but crossing over
+ * a granularity alignment boundary.
+ */
+static void test_hbitmap_truncate_shrink_tiny(TestHBitmapData *data,
+                                              const void *unused)
+{
+    size_t size = L2 - 1;
+    ssize_t diff = -1;
+    int granularity = 1;
+
+    hbitmap_test_truncate(data, size, diff, granularity);
+}
+
+/**
+ * Grow by an amount smaller than sizeof(long), and not crossing over
+ * a sizeof(long) alignment boundary.
+ */
+static void test_hbitmap_truncate_grow_small(TestHBitmapData *data,
+                                             const void *unused)
+{
+    size_t size = L2 + 1;
+    size_t diff = sizeof(long) / 2;
+
+    hbitmap_test_truncate(data, size, diff, 0);
+}
+
+/**
+ * Shrink by an amount smaller than sizeof(long), and not crossing over 
+ * a sizeof(long) alignment boundary.
+ */
+static void test_hbitmap_truncate_shrink_small(TestHBitmapData *data,
+                                               const void *unused)
+{
+    size_t size = L2;
+    size_t diff = sizeof(long) / 2;
+
+    hbitmap_test_truncate(data, size, -diff, 0);
+}
+
+/**
+ * Grow by an amount smaller than sizeof(long), while crossing over
+ * a sizeof(long) alignment boundary.
+ */
+static void test_hbitmap_truncate_grow_medium(TestHBitmapData *data,
+                                              const void *unused)
+{
+    size_t size = L2 - 1;
+    size_t diff = sizeof(long) / 2;
+
+    hbitmap_test_truncate(data, size, diff, 0);
+}
+
+/**
+ * Shrink by an amount smaller than sizeof(long), while crossing over
+ * a sizeof(long) alignment boundary.
+ */
+static void test_hbitmap_truncate_shrink_medium(TestHBitmapData *data,
+                                                const void *unused)
+{
+    size_t size = L2 + 1;
+    size_t diff = sizeof(long) / 2;
+
+    hbitmap_test_truncate(data, size, -diff, 0);
+}
+
+/**
+ * Grow by an amount larger than sizeof(long).
+ */
+static void test_hbitmap_truncate_grow_large(TestHBitmapData *data,
+                                             const void *unused)
+{
+    size_t size = L2;
+    size_t diff = 8 * sizeof(long);
You can use L1 here. But you don't have to. Do as you please. (just saying) 

Max


+
+    hbitmap_test_truncate(data, size, diff, 0);
+}
+
+/**
+ * Shrink by an amount larger than sizeof(long).
+ */
+static void test_hbitmap_truncate_shrink_large(TestHBitmapData *data,
+                                               const void *unused)
+{
+    size_t size = L2;
+    size_t diff = 8 * sizeof(long);
+
+    hbitmap_test_truncate(data, size, -diff, 0);
+}
+
  static void hbitmap_test_add(const char *testpath,
                                     void (*test_func)(TestHBitmapData
*data, const void *user_data))
  {
@@ -395,6 +620,28 @@ int main(int argc, char **argv)
hbitmap_test_add("/hbitmap/reset/empty", test_hbitmap_reset_empty); 
      hbitmap_test_add("/hbitmap/reset/general", test_hbitmap_reset);
hbitmap_test_add("/hbitmap/granularity", test_hbitmap_granularity); 
+
+    hbitmap_test_add("/hbitmap/truncate/nop",
test_hbitmap_truncate_nop);
+    hbitmap_test_add("/hbitmap/truncate/grow/negligible",
+                     test_hbitmap_truncate_grow_negligible);
+    hbitmap_test_add("/hbitmap/truncate/shrink/negligible",
+ test_hbitmap_truncate_shrink_negligible);
+    hbitmap_test_add("/hbitmap/truncate/grow/tiny",
+                     test_hbitmap_truncate_grow_tiny);
+    hbitmap_test_add("/hbitmap/truncate/shrink/tiny",
+                     test_hbitmap_truncate_shrink_tiny);
+    hbitmap_test_add("/hbitmap/truncate/grow/small",
+                     test_hbitmap_truncate_grow_small);
+    hbitmap_test_add("/hbitmap/truncate/shrink/small",
+                     test_hbitmap_truncate_shrink_small);
+    hbitmap_test_add("/hbitmap/truncate/grow/medium",
+                     test_hbitmap_truncate_grow_medium);
+    hbitmap_test_add("/hbitmap/truncate/shrink/medium",
+                     test_hbitmap_truncate_shrink_medium);
+    hbitmap_test_add("/hbitmap/truncate/grow/large",
+                     test_hbitmap_truncate_grow_large);
+    hbitmap_test_add("/hbitmap/truncate/shrink/large",
+                     test_hbitmap_truncate_shrink_large);
      g_test_run();
      return 0;
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