Re: [Qemu-block] [VDSM] travis tests fail consistently since Apr 14

[Eric Blake]

On 06/11/2018 11:19 AM, Kevin Wolf wrote:

> > > Opened the following bug:
> > >    https://bugzilla.redhat.com/1589738
> >
> > Adding qemu-block
>
> It's related to the unaligned image size. Correct image files should be
> aligned to 512 byte sectors, so something is wrong with your image to
> start with (hard disks don't have half sectors).
>
> Anyway, git bisects points to this one:
>
> a290f085901b528265787cd27ebda19c970be4ee is the first bad commit
> commit a290f085901b528265787cd27ebda19c970be4ee
> Author: Eric Blake <address@hidden>
> Date:   Tue Feb 13 14:26:44 2018 -0600
>
>      file-posix: Switch to .bdrv_co_block_status()

Hmm, definitely fallout from my changes.

> I think the problem is a bit higher up the call stack, but I'm not
> completely sure yet. It manifests in img_map(), in this code:
>
>          while (curr.start + curr.length < length) {
>              ...
>              n = QEMU_ALIGN_DOWN(MIN(1 << 30, length - offset), 
> BDRV_SECTOR_SIZE);
>              ret = get_block_status(bs, offset, n, &next);
>
> The loop condition is still true because a single byte is left to be
> processed, but n is aligned down to 0. I'm not sure why the
> QEMU_ALIGN_DOWN() is even there.
>
> Eric, would just removing the QEMU_ALIGN_DOWN() be correct?

I think so, but I'm testing it now. If so, the real culprit was that I 
added the rounding in commit 5e344dd8 when I switched qemu-img.c 
get_block_status() to take bytes but operate in sectors, but didn't 
remove it when I later removed sector-based limitations in commit 237d78f8.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org