Commit 26ae9804 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Stefan Hajnoczi
Browse files

cow: make writes go at a less indecent speed 



Only sync once per write, rather than once per sector.

Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 276cbc7f

block/cow.c

+16 −3
Original line number Diff line number Diff line
@@ -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;
@@ -117,9 +117,21 @@ 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;

    }
@@ -181,9 +193,10 @@ 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;

        }