[fedora-virt] Re: virt-inspector calling guestfs_umount_all() before launch()?

Richard W.M. Jones rjones at redhat.com
Thu May 28 16:58:30 UTC 2009

On Thu, May 28, 2009 at 11:50:00AM -0500, Charles Duffy wrote:
> Richard W.M. Jones wrote:
>> Charles, can you see if this fixes the problem?
>> It's completely untested, and might even segfault the Perl bindings
>> because of BZ #501892 (which really needs to be fixed).

I'm still fixing this one ...

> It doesn't fix things completely, due to what appears to be a qemu bug  
> -- apparently, -snapshot doesn't work correctly with -drive, and  
> snapshot=on needs to be used instead. I've tested this by setting  
> LIBGUESTFS_QEMU to a wrapper which adds ,cache=off,snapshot=on to each  
> -drive parameter, which works correctly; using only -snapshot fails as  
> below.
> The generated command line correctly includes -snapshot, and qemu  
> correctly creates a read-only file to store changes to, but we still  
> fail (albeit differently) on attempted journal replay:
>    hda: max request size: 128KiB
>    hda: 2016 sectors (1 MB) w/256KiB Cache, CHS=2/16/63, (U)DMA
>    hda: cache flushes supported
>     hda:<4>hda: dma_timer_expiry: dma status == 0x61
>    hda: DMA timeout error
>    sock_read_event: 0x9ec8f0 g->state = 1, fd = 3, events = 0x1
>    stdout_event: 0x9ec8f0: child process died
>    wait_ready: guestfs_wait_ready failed, see earlier error messages at
>    /usr/bin/virt-inspector line 219.
>    closing guestfs handle 0x9ec8f0 (state 0)
> Manually creating a new, writable backing store (qemu-img create -b  
> da.qcow2 -f qcow2 da.tmp.qcow2) and running against that (with --force),  
> virt-inspector works correctly, just as it does with snapshot=on passed  
> to the individual -drive options and no global -snapshot flag at all.
> One other issue with that patch is that it passes an empty string rather  
> than no secondary parameter at all in place of the null:
>    /usr/bin/qemu-kvm -snapshot '' -drive file=da.qcow2 [...]

I think that's the same bug in the Perl bindings actually.  The
C code looks correct.


Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
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