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Date: Wed, 13 Nov 2013 13:59:12 +0100
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20131113125912.GC2633@dhcp-200-207.str.redhat.com>
References: <1383753568-15844-1-git-send-email-charlie@ctshepherd.com>
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In-Reply-To: <1383753568-15844-2-git-send-email-charlie@ctshepherd.com>
Subject: Re: [Qemu-devel] [PATCH v3 1/2] COW: Speed up writes
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To: Charlie Shepherd <charlie@ctshepherd.com>
Cc: pbonzini@redhat.com, gabriel@kerneis.info, qemu-devel@nongnu.org, stefanha@gmail.com

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 <charlie@ctshepherd.com>
> ---
>  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