Re: [Qemu-discuss] Qemu corrupted qcow2 system image

[Ivan Volosyuk]

I have 11 days old copy of the qcow2 file (with removed snapshots). I can post the bytes from it as well for comparison if it helpful. I have no idea how large is the corruption and is it possible to transplant pieces of the good qcow file into broken one.

On Thu, Nov 5, 2015 at 2:15 PM Ivan Volosyuk <address@hidden> wrote:

That doesn't sound too reassuring. Sounds it's time say good buy for my data and use pretty dated backup ;-) I thought qcow2 snapshots will help me. hexdump always annoys me that it swaps pairs of bytes to form u16s. Here it is:

0000000 4651 fb49 0000 0300 0000 0000 0000 0000

0000010 0000 0000 0000 1000 0000 0001 0000 0000

0000020 0000 0000 0000 0008 0000 0000 0300 0000

0000030 0000 0000 0100 0000 0000 0100 0000 0600

0000040 0000 2300 6f45 0000 0000 0000 0000 0200

0000050 0000 0000 0000 0000 0000 0000 0000 0000

0000060 0000 0400 0000 6800 0368 57f8 0000 9000

0000070 0000 6964 7472 2079 6962 0074 0000 0000

0000080 0000 0000 0000 0000 0000 0000 0000 0000

*

00000a0 0100 6f63 7272 7075 2074 6962 0074 0000

00000b0 0000 0000 0000 0000 0000 0000 0000 0000

*

00000d0 0001 616c 797a 7220 6665 6f63 6e75 7374

00000e0 0000 0000 0000 0000 0000 0000 0000 0000

*

0010000 0000 0000 0200 0000 0000 0000 0380 0000

0010010 0000 0100 1c00 0000 0000 0100 1e80 0000

0010020 0000 0200 0a00 0000 0000 0200 0d80 0000

0010030 0000 0300 1a00 0000 0000 0300 0380 0000

On Thu, Nov 5, 2015 at 2:08 PM Fam Zheng <address@hidden> wrote:

[Cc'ing qcow2 developers]

On Thu, 11/05 02:05, Ivan Volosyuk wrote:
> The image has some personal data and is pretty large 1T (140G allocated). I
> recompiled qemu-img and run through gdb:
> Program received signal SIGSEGV, Segmentation fault.
> get_refcount_ro4 (refcount_array=0x7fffc0edc010, index=246458459629569) at
> block/qcow2-refcount.c:179
> 179         return be16_to_cpu(((const uint16_t *)refcount_array)[index]);
> (gdb) bt
> #0  get_refcount_ro4 (refcount_array=0x7fffc0edc010, index=246458459629569)
> at block/qcow2-refcount.c:179
> #1  0x0000555555595851 in inc_refcounts
> (address@hidden,
> address@hidden,
>    address@hidden, address@hidden,
> res=0x7fffffffd730, res=0x7fffffffd730, bs=0x555555c76320)
>     at block/qcow2-refcount.c:1329
> #2  0x0000555555595a61 in check_refcounts_l1 (address@hidden,
> address@hidden, address@hidden
> =0x7fffffffd690,
>    address@hidden,
> l1_table_offset=-2294842463426117632, l1_size=335544320, address@hidden
> =0)

To avoid this crash, we should probably validate l1_table_offset against
refcount_table_size in check_refcounts_l1.

Regarding the image, apparently the l1 table offset doesn't make sense here,
the header may be corrupted.  Can you hexdump the first 512 bytes?

>     at block/qcow2-refcount.c:1487
> #3  0x0000555555595fcd in calculate_refcounts (address@hidden,
> address@hidden, address@hidden(unknown: 0),
>    address@hidden,
> address@hidden,
> address@hidden)
>     at block/qcow2-refcount.c:1811
> #4  0x000055555559893e in qcow2_check_refcounts (address@hidden,
> address@hidden, address@hidden(unknown: 0))
>     at block/qcow2-refcount.c:2199
> #5  0x0000555555592d15 in qcow2_check (bs=0x555555c76320,
> result=0x7fffffffd730, fix=(unknown: 0)) at block/qcow2.c:336
> #6  0x0000555555568b2b in collect_image_check (bs=0x555555c76320,
> check=0x555555ca8e40,
>     filename=0x7fffffffdc72 "/home/ivan/../vm-images/win81a.qcow2.broken",
> fix=<optimized out>, fmt=<optimized out>) at qemu-img.c:444
> #7  0x000055555556a53e in img_check (argc=<optimized out>, argv=<optimized
> out>) at qemu-img.c:570
> #8  0x000055555556559c in main (argc=3, argv=0x7fffffffd938) at
> qemu-img.c:3087
> --
> Regards,
> Ivan
>
> On Thu, Nov 5, 2015 at 12:29 PM Fam Zheng <address@hidden> wrote:
>
> > On Thu, 11/05 01:09, Ivan Volosyuk wrote:
> > > Yesterday, I did a few tweaks for my system which uses VGA passthrough.
> > > - I moved virtual CPUs to dedicated CPUs (isolcpus=4-7 kernel boot
> > argument)
> > > - I instructed my windows guest to use MSI IRQ
> > >
> > > Sound crackles disappeared, but after a few minutes of playing Starcraft
> > I
> > > got first ever reboot of windows 8.1 in virtual machine. When I tried to
> > > restart the virtual machine I got the message that qcow2 image is
> > corrupted.
> > > qemu-img check crashes with segfault now on the image.
> >
> > Is the convinient for you to provide the image? If not, can you post the
> > backtrace of "qemu-img check" crash?
> >
> > Fam
> >