diff options
| -rw-r--r-- | block/cow.c | 88 |
1 files changed, 50 insertions, 38 deletions
diff --git a/block/cow.c b/block/cow.c index 909c3e7182..f75949607c 100644 --- a/block/cow.c +++ b/block/cow.c @@ -103,40 +103,18 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags, return ret; } -/* - * 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, bool *first) +static inline void cow_set_bits(uint8_t *bitmap, int start, int64_t nb_sectors) { - uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8; - uint8_t bitmap; - int ret; - - ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap)); - if (ret < 0) { - return ret; - } - - if (bitmap & (1 << (bitnum % 8))) { - return 0; - } - - if (*first) { - ret = bdrv_flush(bs->file); - if (ret < 0) { - return ret; + int64_t bitnum = start, last = start + nb_sectors; + while (bitnum < last) { + if ((bitnum & 7) == 0 && bitnum + 8 <= last) { + bitmap[bitnum / 8] = 0xFF; + bitnum += 8; + continue; } - *first = false; + bitmap[bitnum/8] |= (1 << (bitnum % 8)); + bitnum++; } - - bitmap |= (1 << (bitnum % 8)); - - ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap)); - if (ret < 0) { - return ret; - } - return 0; } #define BITS_PER_BITMAP_SECTOR (512 * 8) @@ -204,18 +182,52 @@ static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs, static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num, int nb_sectors) { - int error = 0; - int i; + int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8; + uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE; bool first = true; + int sector_bits; + + for ( ; nb_sectors; + bitnum += sector_bits, + nb_sectors -= sector_bits, + offset += BDRV_SECTOR_SIZE) { + int ret, set; + uint8_t bitmap[BDRV_SECTOR_SIZE]; + + bitnum &= BITS_PER_BITMAP_SECTOR - 1; + sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum); + + ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap)); + if (ret < 0) { + return ret; + } + + /* Skip over any already set bits */ + set = cow_find_streak(bitmap, 1, bitnum, sector_bits); + bitnum += set; + sector_bits -= set; + nb_sectors -= set; + if (!sector_bits) { + continue; + } + + if (first) { + ret = bdrv_flush(bs->file); + if (ret < 0) { + return ret; + } + first = false; + } + + cow_set_bits(bitmap, bitnum, sector_bits); - for (i = 0; i < nb_sectors; i++) { - error = cow_set_bit(bs, sector_num + i, &first); - if (error) { - break; + ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap)); + if (ret < 0) { + return ret; } } - return error; + return 0; } static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num, |