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Re: [Qemu-devel] [PATCH 2/3] COW: Extend checking allocated bits to beyo
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] COW: Extend checking allocated bits to beyond one sector |
Date: |
Wed, 06 Nov 2013 13:32:11 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
Il 06/11/2013 13:23, Charlie Shepherd ha scritto:
> cow_co_is_allocated() only checks one sector's worth of allocated bits before
> returning. This is
> allowed but (slightly) inefficient, so extend it to check all of the file's
> metadata sectors.
>
> Signed-off-by: Charlie Shepherd <address@hidden>
> ---
> block/cow.c | 36 ++++++++++++++++++++++++++----------
> 1 file changed, 26 insertions(+), 10 deletions(-)
>
> diff --git a/block/cow.c b/block/cow.c
> index 66f1478..4a081cb 100644
> --- a/block/cow.c
> +++ b/block/cow.c
> @@ -152,18 +152,34 @@ static int coroutine_fn
> cow_co_is_allocated(BlockDriverState *bs,
> {
> int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
> uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
> - uint8_t bitmap[BDRV_SECTOR_SIZE];
> - int ret;
> - int changed;
> + bool first = true;
> + int changed, same = 0;
>
> - ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
> - if (ret < 0) {
> - return ret;
> - }
> + do {
> + int ret;
> + 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;
> + }
> +
> + if (first) {
> + changed = cow_test_bit(bitnum, bitmap);
> + first = false;
> + }
> +
> + same += cow_find_streak(bitmap, changed, bitnum, nb_sectors);
> +
> + bitnum += sector_bits;
> + nb_sectors -= sector_bits;
> + offset += BDRV_SECTOR_SIZE;
> + } while (nb_sectors);
>
> - bitnum &= BITS_PER_BITMAP_SECTOR - 1;
> - changed = cow_test_bit(bitnum, bitmap);
> - *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
> + *num_same = same;
> return changed;
> }
>
>
This one is good.
Reviewed-by: Paolo Bonzini <address@hidden>