Re: [PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment
On 29.08.23 09:06, Andrey Drobyshev wrote:
On 8/25/23 17:29, Hanna Czenczek wrote:
On 01.06.23 21:28, Andrey Drobyshev via 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 target image is only being
written to and has nothing to do with those buffers. Let's fix that.
I don’t understand. The write to the target image does use one of those
buffers (buf_old, specifically).
This change is correct for buf_new/blk_new_backing, but for buf_old, in
theory, we need a buffer that fulfills both the alignment requirements
of blk and blk_old_backing. (Not that this patch really makes the
situation worse for buf_old.)
Hanna
Hmm, you're right. In which case the right thing to do would probably
be smth like:
float local_progress = 0;
-buf_old = blk_blockalign(blk, IO_BUF_SIZE);
-buf_new = blk_blockalign(blk, IO_BUF_SIZE);
+if (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);
+}
+buf_new = blk_blockalign(blk_new_backing, IO_BUF_SIZE);
size = blk_getlength(blk);
I'll include this in v2 if you don't have any objections.
Looks good to me, thanks!
Re: [PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment
On 8/25/23 17:29, Hanna Czenczek wrote:
> On 01.06.23 21:28, Andrey Drobyshev via 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 target image is only being
>> written to and has nothing to do with those buffers. Let's fix that.
>
> I don’t understand. The write to the target image does use one of those
> buffers (buf_old, specifically).
>
> This change is correct for buf_new/blk_new_backing, but for buf_old, in
> theory, we need a buffer that fulfills both the alignment requirements
> of blk and blk_old_backing. (Not that this patch really makes the
> situation worse for buf_old.)
>
> Hanna
>
Hmm, you're right. In which case the right thing to do would probably
be smth like:
> float local_progress = 0;
>
> -buf_old = blk_blockalign(blk, IO_BUF_SIZE);
> -buf_new = blk_blockalign(blk, IO_BUF_SIZE);
> +if (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);
> +}
> +buf_new = blk_blockalign(blk_new_backing, IO_BUF_SIZE);
>
> size = blk_getlength(blk);
I'll include this in v2 if you don't have any objections.
Re: [PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment
On 01.06.23 21:28, Andrey Drobyshev via 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 target image is only being
written to and has nothing to do with those buffers. Let's fix that.
I don’t understand. The write to the target image does use one of those
buffers (buf_old, specifically).
This change is correct for buf_new/blk_new_backing, but for buf_old, in
theory, we need a buffer that fulfills both the alignment requirements
of blk and blk_old_backing. (Not that this patch really makes the
situation worse for buf_old.)
Hanna
Re: [PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment
On 6/1/23 21:28, 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 target image is only being
written to and has nothing to do with those buffers. Let's fix that.
Signed-off-by: Andrey Drobyshev
---
qemu-img.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 78433f3746..60f4c06487 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3746,8 +3746,8 @@ 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);
+buf_old = blk_blockalign(blk_old_backing, IO_BUF_SIZE);
+buf_new = blk_blockalign(blk_new_backing, IO_BUF_SIZE);
size = blk_getlength(blk);
if (size < 0) {
Reviewed-by: Denis V. Lunev
[PATCH 3/6] qemu-img: rebase: use backing files' BlockBackend for buffer alignment
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 target image is only being
written to and has nothing to do with those buffers. Let's fix that.
Signed-off-by: Andrey Drobyshev
---
qemu-img.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 78433f3746..60f4c06487 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3746,8 +3746,8 @@ 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);
+buf_old = blk_blockalign(blk_old_backing, IO_BUF_SIZE);
+buf_new = blk_blockalign(blk_new_backing, IO_BUF_SIZE);
size = blk_getlength(blk);
if (size < 0) {
--
2.31.1
