migration state save/load of sdcard device is broken

[Gustavo Moreira]

I'm having different issues trying to have QEMU snapshots working using qemu-system-arm with vexpress-a15 board.

In this opportunity, I'm trying the git master head version:
# git rev-parse HEAD
af352675efb7e92a1f5f6461a042a12015ab3d12

$ /usr/local/bin/qemu-system-arm -kernel kernel/vmlinuz-4.10.0-42-generic -initrd kernel/initrd.img-4.10.0-42-generic -M vexpress-a15 -m 2048 -append 'root=/dev/mmcblk0 rootwait console=tty0' -sd vexpress-4G.qcow2 -dtb device-tree/vexpress-v2p-ca15-tc1.dtb
audio: Could not init `oss' audio driver

Later on, when the machine finishes booting I savevm ss and quit. However, when I try to restore it, I have that Missing section footer error:

$ /usr/local/bin/qemu-system-arm -kernel kernel/vmlinuz-4.10.0-42-generic -initrd kernel/initrd.img-4.10.0-42-generic -M vexpress-a15 -m 2048 -append 'root=/dev/mmcblk0 rootwait console=tty0' -sd vexpress-4G.qcow2 -dtb device-tree/vexpress-v2p-ca15-tc1.dtb -loadvm ss
audio: Could not init `oss' audio driver
qemu-system-arm: Missing section footer for sd-card
qemu-system-arm: Error -22 while loading VM state

OS: Ubuntu 16.04.3 LTS (xenial)

$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.5) 5.4.0 20160609

How have I built it?
# git clone git://git.qemu.org/qemu.git
# cd qemu
# git submodule update --init --checkout
# make clean && ./configure --target-list=arm-softmmu && make -j8
# sudo make install

I've also tried a different ./configure line, explicitly enabling some of the features, i.e. smartcard, with the same results:

./configure '--disable-user' '--enable-system' '--enable-linux-user' '--enable-modules' '--enable-linux-aio' '--audio-drv-list=pa' '--enable-attr' '--enable-brlapi' '--enable-virtfs' '--enable-cap-ng' '--enable-curl' '--enable-fdt' '--enable-gnutls' '--disable-gtk' '--disable-vte' '--enable-libiscsi' '--enable-curses' '--enable-smartcard' '--enable-rbd' '--enable-vnc-sasl' '--enable-seccomp' '--enable-spice' '--enable-libusb' '--enable-usb-redir' '--enable-xfsctl' '--enable-vnc' '--enable-vnc-jpeg' '--enable-vnc-png' '--enable-kvm' '--enable-vhost-net'

As a reference, and just in case these may be in some way related, I've just submitted another ticket for a different issue with snapshots using Ubuntu Qemu version (https://bugs.launchpad.net/qemu/+bug/1739371)

Cheers,
Gus

[Dr. David Alan Gilbert (dgilbert-h)]

From a quick look my guess would be the wpgrps_size in sd_vmstate is different on the source and destination for some reason - it's the only thing that seems to be variable.
(It could also be whether the subsection is transmitted or not, but that's supposed to sort itself out automatically).

[Gustavo Moreira (gmoreira)]

So, it should be only related to SD? Which virtual device/storage backend do you recommend for snapshots?

[Peter Maydell (pmaydell)]

On 20 December 2017 at 18:44, Dr. David Alan Gilbert
<email address hidden> wrote:
> From a quick look my guess would be the wpgrps_size in sd_vmstate is
> different on the source and destination for some reason

Good guess: I added a pre_save hook to sdcard.c's vmstate,
which reports wpgrps_size as 201, but in the pre_load hook
it is reported as 0.

This seems to be because nothing ever calls the sd_reset()
function. I suspect this is down to the "legacy" handling
of sd card setup in sd_init(), or possibly the generic handling
of reset for devices that connect to SD buses.

(sd_reset() eventually gets called when the guest OS
probes the SD controller and issues a card reset command,
which is why it's correctly set by the time we do a vmsave.)

thanks
-- PMM

[Peter Maydell (pmaydell)]

I think the sd card migration issue should be fixed by http://patchwork.ozlabs.org/patch/857554/

NB that you'll also need to use "-machine secure=off" on the command line, as there's a second bug where we don't successfully migrate with trustzone emulation enabled (which is the default now).

[Gustavo Moreira (gmoreira)]

Finally I could test it. Yeah man, awesome, that did the trick. It is working like a charm.
You can close the ticket.
Thanks

[Thomas Huth (th-huth)]

The patch has been merged here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=0cb57cc701839e7358918