Re: [Qemu-devel] [PATCH v3 1/2] COW: Speed up writes

[Kevin Wolf]

Am 06.11.2013 um 16:59 hat Charlie Shepherd geschrieben:
> 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 <address@hidden>
> ---
>  block/cow.c | 87 
> ++++++++++++++++++++++++++++++++++---------------------------
>  1 file changed, 49 insertions(+), 38 deletions(-)

> @@ -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) {

block/cow.c: In function 'cow_update_bitmap':
block/cow.c:206:23: error: 'sector_bits' undeclared (first use in this function)

Kevin