Re: [PATCH for-5.1 1/2] block: Require aligned image size to avoid assertion failure

[Kevin Wolf]

Am 15.07.2020 um 15:22 hat Nir Soffer geschrieben:
> On Mon, Jul 13, 2020 at 7:56 PM Kevin Wolf <kwolf@redhat.com> wrote:
> >
> > Am 13.07.2020 um 18:33 hat Nir Soffer geschrieben:
> > > On Fri, Jul 10, 2020 at 5:22 PM Kevin Wolf <kwolf@redhat.com> wrote:
> > > >
> > > > Unaligned requests will automatically be aligned to bl.request_alignment
> > > > and we don't want to extend requests to access space beyond the end of
> > > > the image, so it's required that the image size is aligned.
> > > >
> > > > With write requests, this could cause assertion failures like this if
> > > > RESIZE permissions weren't requested:
> > > >
> > > > qemu-img: block/io.c:1910: bdrv_co_write_req_prepare: Assertion 
> > > > `end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE' 
> > > > failed.
> > > >
> > > > This was e.g. triggered by qemu-img converting to a target image with 4k
> > > > request alignment when the image was only aligned to 512 bytes, but not
> > > > to 4k.
> > >
> > > Was it on NFS? Shouldn't this be fix by the next patch then?
> >
> > Patch 2 makes the problem go away for NFS because NFS doesn't even
> > require the 4k alignment. But on storage that legitimately needs 4k
> > alignment (or possibly other filesystems that are misdetected), you
> > would still hit the same problem.
> 
> I want to add oVirt point of view on this. We enforce raw image
> alignment of 4k on file based storage, and 128m on block storage, so
> our raw images cannot have this issue.

Yes, then you won't hit the problem.

> We have an issue with empty qcow2 images which are unaligned size, but
> we don't create such images in normal flows.

Can you give a reproducer where qcow2 images would be affected?
Generally speaking, the qcow2 driver either takes both WRITE and RESIZE
permissions or neither. So it should just automatically resize the image
as needed instead of crashing.

Kevin