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.drobys...@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) { >