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

[Charlie Shepherd]

On 13/11/2013 12:59, Kevin Wolf wrote:
> 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)

Sorry I should have caught that, resending a new version.


Charlie