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From: "Denis V. Lunev" <den@openvz.org>
Message-ID: <5739F9E8.7050609@openvz.org>
Date: Mon, 16 May 2016 19:48:40 +0300
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Subject: Re: [Qemu-devel] [PATCH 4/6] qcow2: add tracepoints for
 qcow2_co_write_zeroes
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To: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>

On 05/16/2016 07:32 PM, Eric Blake wrote:
> On 05/14/2016 06:01 AM, Denis V. Lunev wrote:
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> ---
>>   block/qcow2.c | 5 +++++
>>   trace-events  | 2 ++
>>   2 files changed, 7 insertions(+)
>>
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index 9a54bbd..97bf870 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -2435,6 +2435,9 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
>>       int head = sector_num % s->cluster_sectors;
>>       int tail = (sector_num + nb_sectors) % s->cluster_sectors;
>>   
>> +    trace_qcow2_write_zeroes_start_req(qemu_coroutine_self(), sector_num,
>> +                                       nb_sectors);
>> +
> Can we trace these by byte locations rather than by sector count?
> Ultimately, I think we want to move write_zeroes to a byte-based
> interface, even if we still assert internally that it is at least
> sector-aligned.
>
we can, but this patches traces for qcow2_co_writev

static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
                            int64_t sector_num,
                            int remaining_sectors,
                            QEMUIOVector *qiov)
{
     [...]
     trace_qcow2_writev_start_req(qemu_coroutine_self(), sector_num,
                                  remaining_sectors);

Thus I'd better either stick to this implementation or change
all tracepoints in QEMU code.