Re: [Qemu-stable] [Qemu-devel] [PATCH 2/3] block/qcow2: fix the corruption when rebasing luks encrypted files

[Maxim Levitsky]

On Mon, 2019-09-09 at 12:56 +0200, Kevin Wolf wrote:
> Am 06.09.2019 um 21:17 hat Eric Blake geschrieben:
> > > -        assert((offset_in_cluster & ~BDRV_SECTOR_MASK) == 0);
> > > +        assert((guest_offset & ~BDRV_SECTOR_MASK) == 0);
> > > +        assert((host_offset & ~BDRV_SECTOR_MASK) == 0);
> > >          assert((bytes & ~BDRV_SECTOR_MASK) == 0);
> > 
> > Pre-existing, but we could use QEMU_IS_ALIGNED(x, BDRV_SECTOR_SIZE) for
> > slightly more legibility than open-coding the bit operation.
> > 
> > Neat trick about power-of-2 alignment checks:
> > 
> > assert(QEMU_IS_ALIGNED(offset_in_cluster | guest_offset |
> >                        host_offset | bytes, BDRV_SECTOR_SIZE));
> > 
> > gives the same result in one assertion.  (I've used it elsewhere in the
> > code base, but I'm not opposed to one assert per variable if you think
> > batching is too dense.)
> 
> A possible downside of this is that if a user reports an assertion
> failure, you can't tell any more which of the variables ended up in a
> bad state.
> 
> If you're lucky, you can still tell in gdb at least if the bug is
> reproducible, but I wouldn't be surprised if in release builds, half of
> the variables were actually optimised away, so that even this wouldn't
> work.
Agreed. I guess I'll keep the separate asserts anyway after all, even though
I prefer shorter code.


Best regards,
        Maxim Levitsky