Re: [Qemu-devel] [PATCH 3/3] i2c: Add vmstate handling to the smbus eeprom

[Peter Maydell]

On 8 November 2018 at 17:58, Corey Minyard <address@hidden> wrote:
> On 11/8/18 8:08 AM, Peter Maydell wrote:
>> This doesn't do anything for migration of the actual data contents.
>> The current users of this device (hw/arm/aspeed.c and the
>> smbus_eeprom_init() function) doesn't do anything
>> to migrate the contents. For that matter, "user of the device
>> passes a pointer to a random lump of memory via a device property"
>> is a bit funky as an interface. The device should allocate its
>> own memory and migrate it, and the user should just pass the
>> initial required contents (default being "zero-initialize",
>> which is what everybody except the mips_fulong2e, mips_malta
>> and sam460ex want).

> I debated on this, and it depends on what the eeprom is used for.  If
> it's a DRAM eeprom, it shouldn't need to be transferred.

It's guest-visible data; the guest can write it and read it back.
So it needs to be migrated. Otherwise behaviour after migration
will not be the same as if the guest had never migrated.

>> Does this also break migration from an old QEMU to a new one?
>> (For Aspeed that's probably ok, but we should flag it up in the
>> commit message if so. x86 uses need care...)
>>
> There is no transfer before, so I don't see why it would break anything.
> Am I missing something?

I forget what the behaviour is where the source QEMU didn't
have a vmstate at all but the destination QEMU does expect
one. David can remind me...

thanks
- PMM