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Date: Fri, 15 Nov 2013 18:43:48 +0000
From: Charlie Shepherd <charlie@ctshepherd.com>
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Subject: Re: [Qemu-devel] [PATCH v3 1/2] COW: Speed up writes
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To: Kevin Wolf <kwolf@redhat.com>
Cc: pbonzini@redhat.com, gabriel@kerneis.info, qemu-devel@nongnu.org, stefanha@gmail.com

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 <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)

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


Charlie