Re: [Qemu-devel] segfault while booting from saved snapshot

[Shehbaz Jaffer]

Thankyou for your reply. I do not face the error using qemu.1.7.1 version.

1 quick question:

I want to create a qcow2 image file after my VM has completed booting; i.e., when I boot from this new snapshot, I should directly get to my VMs login prompt. How can i create such a qcow2 snapshot?

I tried stopped the VM using QMP after the VM had completed booting, and then using host CLI to create a qcow2 image :

qemu-img create -b ubuntu.qcow2 -f qcow2 newsnap.qcow2

This created a new qcow2 file - newsnap.qcow2 on top of ubuntu.qcow2, however when I boot using newsnap.qcow2, It takes me again through the complete boot process - till the login prompt.

Is there a way to create the qcow2 snapshot after VM has completed booting?

--

Shehbaz

On Tue, Apr 15, 2014 at 1:37 PM, Dr. David Alan Gilbert <address@hidden> wrote:

* Shehbaz Jaffer (address@hidden) wrote:
> Hi,
>
> I am running a Ubuntu 12.04 guest VM that I created using vm-builder on a
> Ubuntu 12.04 Operating System. I am using qemu-2.0.0-rc0 version. I want to
> boot from a saved snapshot instance of the guest VM, so I created a
> snapshot using the Qemu Monitor as follows:

Can you try something newer than -rc0; I remember there was a seg that looked
similar to this on migration (that I suspect is also in the snapshot path).

Dave

>
> <code>
> stop
> savevm new
> cont
> quit
> </code>
>
> I checked if the snapshot had been created, and I could see the snapshot
> for the qcow2 file:
>
> :~/qemu-2.0.0-rc0$ ./qemu-img snapshot -l ~/ubuntu-kvm/ubuntu.qcow2
> Snapshot list:
> ID        TAG                 VM SIZE                DATE       VM CLOCK
> 1                                   0 2014-04-14 17:25:39   00:00:01.100
> 4         new                     84M 2014-04-15 10:00:39   00:08:21.657
>
> However when I try to load the same vm during boot, I get the following bt:
>
> ~/qemu-2.0.0-rc0$ gdb ./x86_64-softmmu/qemu-system-x86_64
> GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
> Copyright (C) 2012 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
> >
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "x86_64-linux-gnu".
> For bug reporting instructions, please see:
> <http://bugs.launchpad.net/gdb-linaro/>...
> Reading symbols from
> /home/manan/qemu-2.0.0-rc0/x86_64-softmmu/qemu-system-x86_64...done.
> (gdb) r -hda ~/ubuntu-kvm/ubuntu.qcow2 -loadvm new2
> Starting program:
> /home/manan/qemu-2.0.0-rc0/x86_64-softmmu/qemu-system-x86_64 -hda
> ~/ubuntu-kvm/ubuntu.qcow2 -loadvm new2
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
> [New Thread 0x7fffedf07700 (LWP 4213)]
> [New Thread 0x7fffed323700 (LWP 4214)]
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x00007ffff5751fb6 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
> (gdb) bt
> #0  0x00007ffff5751fb6 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
> #1  0x00007ffff7e07ec9 in tlb_flush (cpu=<optimized out>,
> flush_global=<optimized out>)
>     at /usr/include/x86_64-linux-gnu/bits/string3.h:85
> #2  0x00007ffff7e0ca2c in cpu_common_post_load (opaque=<optimized out>,
> version_id=<optimized out>)
>     at /home/manan/qemu-2.0.0-rc0/exec.c:423
> #3  0x00007ffff7e00d2d in vmstate_load_state (f=0x7ffff8ad1400,
> vmsd=0x7ffff82c9660, opaque=0x7ffff89715a0, version_id=1)
>     at vmstate.c:87
> #4  0x00007ffff7e719d7 in vmstate_load (version_id=<optimized out>,
> se=0x7ffff8982210, f=0x7ffff8ad1400)
>     at /home/manan/qemu-2.0.0-rc0/savevm.c:435
> #5  qemu_loadvm_state (f=0x7ffff8ad1400) at
> /home/manan/qemu-2.0.0-rc0/savevm.c:805
> #6  0x00007ffff7e7227a in load_vmstate (name=<optimized out>) at
> /home/manan/qemu-2.0.0-rc0/savevm.c:1091
> #7  0x00007ffff7c5ab5c in main (argc=<optimized out>, argv=<optimized out>,
> envp=<optimized out>) at vl.c:4457
> (gdb)
>
> I even tried the command
>
> guest-fsfreeze-freeze as mentioned here:
>
> http://wiki.qemu.org/Features/Snapshots
>
> But the Qemu Monitor says the command doesnt exist. Do we need to issue a
> command to flush the tlb buffer? Please advise.
>
> --
> Shehbaz Jaffer

--
Dr. David Alan Gilbert / address@hidden / Manchester, UK