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Re: [PATCH v2 3/8] qemu-img: rebase: use backing files' BlockBackend for
From: |
Andrey Drobyshev |
Subject: |
Re: [PATCH v2 3/8] qemu-img: rebase: use backing files' BlockBackend for buffer alignment |
Date: |
Tue, 19 Sep 2023 12:26:26 +0300 |
User-agent: |
Mozilla Thunderbird |
On 9/19/23 11:18, Hanna Czenczek wrote:
> On 15.09.23 18:20, Andrey Drobyshev wrote:
>> Since commit bb1c05973cf ("qemu-img: Use qemu_blockalign"), buffers for
>> the data read from the old and new backing files are aligned using
>> BlockDriverState (or BlockBackend later on) referring to the target
>> image.
>> However, this isn't quite right, because buf_new is only being used for
>> reading from the new backing, while buf_old is being used for both
>> reading
>> from the old backing and writing to the target. Let's take that into
>> account
>> and use more appropriate values as alignments.
>>
>> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
>> ---
>> qemu-img.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/qemu-img.c b/qemu-img.c
>> index 50660ba920..d12e4a4753 100644
>> --- a/qemu-img.c
>> +++ b/qemu-img.c
>> @@ -3750,8 +3750,13 @@ static int img_rebase(int argc, char **argv)
>> int64_t n;
>> float local_progress = 0;
>> - buf_old = blk_blockalign(blk, IO_BUF_SIZE);
>> - buf_new = blk_blockalign(blk, IO_BUF_SIZE);
>> + if (blk_old_backing && bdrv_opt_mem_align(blk_bs(blk)) >
>> + bdrv_opt_mem_align(blk_bs(blk_old_backing))) {
>> + buf_old = blk_blockalign(blk, IO_BUF_SIZE);
>> + } else {
>> + buf_old = blk_blockalign(blk_old_backing, IO_BUF_SIZE);
>> + }
>
> As I read this, if blk_old_backing is NULL, we will go to the
> blk_blockalign(blk_old_backing, IO_BUF_SIZE) path. I think if it is
> NULL, we should align on blk instead.
>
> Hanna
You're right, thanks for noticing. Will fix that.
>
>> + buf_new = blk_blockalign(blk_new_backing, IO_BUF_SIZE);
>> size = blk_getlength(blk);
>> if (size < 0) {
>
- Re: [PATCH v2 4/8] qemu-img: add chunk size parameter to compare_buffers(), (continued)