1 files changed, 66 insertions, 27 deletions

diff --git a/block/cow.c b/block/cow.c
index 1cc2e89c7c..764b93fae0 100644
--- a/block/cow.c
+++ b/block/cow.c
@@ -106,7 +106,7 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags)
  * XXX(hch): right now these functions are extremely inefficient.
  * We should just read the whole bitmap we'll need in one go instead.
  */
-static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
+static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
 {
     uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
     uint8_t bitmap;
@@ -117,27 +117,52 @@ static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
        return ret;
     }
 
+    if (bitmap & (1 << (bitnum % 8))) {
+        return 0;
+    }
+
+    if (*first) {
+        ret = bdrv_flush(bs->file);
+        if (ret < 0) {
+            return ret;
+        }
+        *first = false;
+    }
+
     bitmap |= (1 << (bitnum % 8));
 
-    ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap));
+    ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
     if (ret < 0) {
        return ret;
     }
     return 0;
 }
 
-static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
+#define BITS_PER_BITMAP_SECTOR (512 * 8)
+
+/* Cannot use bitmap.c on big-endian machines.  */
+static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
 {
-    uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
-    uint8_t bitmap;
-    int ret;
+    return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
+}
 
-    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
-    if (ret < 0) {
-       return ret;
+static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
+{
+    int streak_value = value ? 0xFF : 0;
+    int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
+    int bitnum = start;
+    while (bitnum < last) {
+        if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
+            bitnum += 8;
+            continue;
+        }
+        if (cow_test_bit(bitnum, bitmap) == value) {
+            bitnum++;
+            continue;
+        }
+        break;
     }
-
-    return !!(bitmap & (1 << (bitnum % 8)));
+    return MIN(bitnum, last) - start;
 }
 
 /* Return true if first block has been changed (ie. current version is
@@ -146,24 +171,33 @@ static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, int *num_same)
 {
+    int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
+    uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
+    uint8_t bitmap[BDRV_SECTOR_SIZE];
+    int ret;
     int changed;
 
-    if (nb_sectors == 0) {
-	*num_same = nb_sectors;
-	return 0;
+    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
+    if (ret < 0) {
+        return ret;
     }
 
-    changed = is_bit_set(bs, sector_num);
-    if (changed < 0) {
-        return 0; /* XXX: how to return I/O errors? */
-    }
+    bitnum &= BITS_PER_BITMAP_SECTOR - 1;
+    changed = cow_test_bit(bitnum, bitmap);
+    *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
+    return changed;
+}
 
-    for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
-	if (is_bit_set(bs, sector_num + *num_same) != changed)
-	    break;
+static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, int *num_same)
+{
+    BDRVCowState *s = bs->opaque;
+    int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
+    int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
+    if (ret < 0) {
+        return ret;
     }
-
-    return changed;
+    return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
 }
 
 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
@@ -171,9 +205,10 @@ static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 {
     int error = 0;
     int i;
+    bool first = true;
 
     for (i = 0; i < nb_sectors; i++) {
-        error = cow_set_bit(bs, sector_num + i);
+        error = cow_set_bit(bs, sector_num + i, &first);
         if (error) {
             break;
         }
@@ -189,7 +224,11 @@ static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
     int ret, n;
 
     while (nb_sectors > 0) {
-        if (bdrv_co_is_allocated(bs, sector_num, nb_sectors, &n)) {
+        ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
+        if (ret < 0) {
+            return ret;
+        }
+        if (ret) {
             ret = bdrv_pread(bs->file,
                         s->cow_sectors_offset + sector_num * 512,
                         buf, n * 512);
@@ -314,7 +353,7 @@ static int cow_create(const char *filename, QEMUOptionParameter *options)
     }
 
 exit:
-    bdrv_delete(cow_bs);
+    bdrv_unref(cow_bs);
     return ret;
 }
 
@@ -344,7 +383,7 @@ static BlockDriver bdrv_cow = {
 
     .bdrv_read              = cow_co_read,
     .bdrv_write             = cow_co_write,
-    .bdrv_co_is_allocated   = cow_co_is_allocated,
+    .bdrv_co_get_block_status   = cow_co_get_block_status,
 
     .create_options = cow_create_options,
 };