Re: [PATCH] Skip resizing image to the same size

[Michael Tokarev]

20.01.2025 23:17, Fahrzin Hemmati wrote:
> My apologies, I saw the Signed-off-by requirement at first, but as I followed the docs I got to "git publish" and didn't realize "git publish" was 
> actually able to send emails on my system (I don't remember setting up any SMTP settings). By that time, I forgot and thought this patch was short 
> enough to not warrant much of a commit message.
>
> The main practical advantage is for users that call "qemu-img resize" via scripts or other systems (like Packer in my case) that don't check the image 
> size ahead of time. I can upstream this change into them (by using "qemu-img info —output=json ...") but I figured it would be useful to more users here.
>
> This could trivially be added to block/io.c:bdrv_co_truncate(), as well as blockdev.c:qmp_block_resize() with a little more work. I'm not familiar 
> with those workflows, but if needed I can do that as well.
>
> Here's the new patch:
>
>  From 17f5c5f03d930c4816b92b97e0e54db0725d7b94 Mon Sep 17 00:00:00 2001
> From: Fahrzin Hemmati <fahhem@fahhem.com <mailto:fahhem@fahhem.com>>
> Date: Mon, 20 Jan 2025 01:56:24 -0800
> Subject: [PATCH] Skip resizing image to the same size
>
> Higher-level software, such as Packer, blindly call "qemu-img resize"
> even when the size is the same. This change can be pushed to those
> users, but it's very cheap to check and can save many other users more
> time here.
>
> Signed-off-by: Fahrzin Hemmati <fahhem@fahhem.com <mailto:fahhem@fahhem.com>>
> ---
> qemu-img.c | 6 ++++++
> tests/qemu-iotests/061 | 8 ++++++++
> tests/qemu-iotests/061.out | 9 +++++++++
> 3 files changed, 23 insertions(+)
>
> diff --git a/qemu-img.c b/qemu-img.c
> index 2f2fac90e8..3345c4e63f 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -4184,6 +4184,12 @@ static int img_resize(int argc, char **argv)
> goto out;
> }
>
> + if (total_size == current_size) {
> + qprintf(quiet, "Image already has the desired size.\n");
> + ret = 0;
> + goto out;
> + }


I don't think this is necessary: the actual operation is a no-op
anyway, there's no need to special-case it.

Please also refrain from changing qemu-img until my refresh
patchset is either accepted or rejected.  It was a large work
and it'd be sad to lose it.

Thanks,

/mjt