Re: [PATCH 0/6] Save state error handling (kill off no_migrate)

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Oct 06, 2010 at 02:58:57PM -0600, Alex Williamson wrote:
> Our code paths for saving or migrating a VM are full of functions that
> return void, leaving no opportunity for a device to cancel a migration,
> either from error or incompatibility.  The ivshmem driver attempted to
> solve this with a no_migrate flag on the save state entry.  I think the
> more generic and flexible way to solve this is to allow driver save
> functions to fail.  This series implements that and converts ivshmem
> to uses a set_params function to NAK migration much earlier in the
> processes.  This touches a lot of files, but bulk of those changes are
> simply s/void/int/ and tacking a "return 0" to the end of functions.
> Thanks,
> 
> Alex

Well error handling is always tricky: it seems easier to
require save handlers to never fail.
So there's a bunch of code here but what exactly is the benefit?
Since save handlers have no idea what does the remote do,
what is the compatibility you mention?

> ---
> 
> Alex Williamson (6):
>       savevm: Remove register_device_unmigratable()
>       savevm: Allow set_params and save_live_state to error
>       virtio: Allow virtio_save() errors
>       pci: Allow pci_device_save() to return error
>       savevm: Allow vmsd->pre_save to return error
>       savevm: Allow SaveStateHandler() to return error
> 
> 
>  block-migration.c           |    4 +-
>  hw/adb.c                    |    8 +++-
>  hw/ads7846.c                |    4 +-
>  hw/arm_gic.c                |    4 +-
>  hw/arm_timer.c              |    6 ++-
>  hw/armv7m_nvic.c            |    4 +-
>  hw/cuda.c                   |    4 +-
>  hw/fdc.c                    |    3 +
>  hw/g364fb.c                 |    4 +-
>  hw/grackle_pci.c            |    4 +-
>  hw/gt64xxx.c                |    4 +-
>  hw/heathrow_pic.c           |    4 +-
>  hw/hpet.c                   |    3 +
>  hw/hw.h                     |   12 ++----
>  hw/i2c.c                    |    3 +
>  hw/ide/core.c               |    4 +-
>  hw/ivshmem.c                |   30 +++++++++++----
>  hw/lsi53c895a.c             |    4 +-
>  hw/m48t59.c                 |    4 +-
>  hw/mac_dbdma.c              |    4 +-
>  hw/mac_nvram.c              |    4 +-
>  hw/max111x.c                |    4 +-
>  hw/mipsnet.c                |    4 +-
>  hw/mst_fpga.c               |    3 +
>  hw/nand.c                   |    3 +
>  hw/openpic.c                |    4 +-
>  hw/pci.c                    |    9 +++-
>  hw/pci.h                    |    2 -
>  hw/piix4.c                  |    4 +-
>  hw/pl011.c                  |    4 +-
>  hw/pl022.c                  |    4 +-
>  hw/pl061.c                  |    4 +-
>  hw/ppc4xx_pci.c             |   11 ++++-
>  hw/ppce500_pci.c            |   11 ++++-
>  hw/pxa2xx.c                 |   28 ++++++++++----
>  hw/pxa2xx_dma.c             |    4 +-
>  hw/pxa2xx_gpio.c            |    4 +-
>  hw/pxa2xx_keypad.c          |    3 +
>  hw/pxa2xx_lcd.c             |    4 +-
>  hw/pxa2xx_mmci.c            |    4 +-
>  hw/pxa2xx_pic.c             |    4 +-
>  hw/pxa2xx_timer.c           |    4 +-
>  hw/rc4030.c                 |    4 +-
>  hw/rtl8139.c                |    4 +-
>  hw/serial.c                 |    3 +
>  hw/spitz.c                  |   14 +++++--
>  hw/ssd0323.c                |    4 +-
>  hw/ssi-sd.c                 |    4 +-
>  hw/stellaris.c              |   20 +++++++---
>  hw/stellaris_enet.c         |    4 +-
>  hw/stellaris_input.c        |    4 +-
>  hw/syborg_fb.c              |    4 +-
>  hw/syborg_interrupt.c       |    3 +
>  hw/syborg_keyboard.c        |    3 +
>  hw/syborg_pointer.c         |    3 +
>  hw/syborg_rtc.c             |    4 +-
>  hw/syborg_serial.c          |    4 +-
>  hw/syborg_timer.c           |    4 +-
>  hw/tsc2005.c                |    4 +-
>  hw/tsc210x.c                |    4 +-
>  hw/twl92230.c               |    3 +
>  hw/unin_pci.c               |    4 +-
>  hw/usb-uhci.c               |    3 +
>  hw/virtio-balloon.c         |    9 +++-
>  hw/virtio-blk.c             |   10 ++++-
>  hw/virtio-net.c             |   11 ++++-
>  hw/virtio-pci.c             |   10 ++++-
>  hw/virtio-serial-bus.c      |   10 ++++-
>  hw/virtio.c                 |   14 +++++--
>  hw/virtio.h                 |    4 +-
>  hw/wm8750.c                 |    3 +
>  hw/zaurus.c                 |    4 +-
>  qemu-common.h               |    2 -
>  savevm.c                    |   88 +++++++++++++++++++------------------------
>  slirp/slirp.c               |    6 ++-
>  target-arm/machine.c        |    3 +
>  target-cris/machine.c       |    3 +
>  target-i386/machine.c       |    7 ++-
>  target-microblaze/machine.c |    3 +
>  target-mips/machine.c       |    3 +
>  target-ppc/machine.c        |    3 +
>  target-s390x/machine.c      |    3 +
>  target-sparc/machine.c      |    3 +
>  83 files changed, 365 insertions(+), 181 deletions(-)
> --
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