Il 06/11/2013 16:59, Charlie Shepherd ha scritto:
> Process a whole sector's worth of COW bits by reading a sector, setting the
> bits after skipping
> any already set bits, then writing it out again. Make sure we only flush once
> before writing
> metadata, and only if we need to write metadata.
>
> Signed-off-by: Charlie Shepherd <char...@ctshepherd.com>
> ---
> block/cow.c | 87
> ++++++++++++++++++++++++++++++++++---------------------------
> 1 file changed, 49 insertions(+), 38 deletions(-)
>
> diff --git a/block/cow.c b/block/cow.c
> index 909c3e7..bf447fd 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 +182,51 @@ 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;
>
> - for (i = 0; i < nb_sectors; i++) {
> - error = cow_set_bit(bs, sector_num + i, &first);
> - if (error) {
> - break;
> + 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;
> + int 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);
> +
> + 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,
>
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
