RE: [PATCH v2 1/7] exec: Fix for qemu_ram_resize() callback

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: David Hildenbrand [mailto:david@redhat.com]
> Sent: 10 February 2020 09:29
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> Igor Mammedov <imammedo@redhat.com>
> Cc: peter.maydell@linaro.org; xiaoguangrong.eric@gmail.com;
> mst@redhat.com; shannon.zhaosl@gmail.com; qemu-devel@nongnu.org;
> xuwei (O) <xuwei5@huawei.com>; Linuxarm <linuxarm@huawei.com>;
> eric.auger@redhat.com; qemu-arm@nongnu.org; lersek@redhat.com
> Subject: Re: [PATCH v2 1/7] exec: Fix for qemu_ram_resize() callback
> 
> >> Can you look the original value up somehow and us the resize callback
> >> only as a notification that something changed? (that value would have to
> >> be stored somewhere and migrated I assume - maybe that's already being
> >> done)
> >
> > Ok. I will take a look at that. But can we instead pass the block->used_length
> to
> > fw_cfg_add_file_callback(). That way we don’t have to change the
> qemu_ram_resize()
> > as well. I think Igor has suggested this before[1] and I had a go at it before
> coming up
> > with the "req_length" proposal here.
> 
> You mean, passing the old size as well? I don't see how that will solve
> the issue, but yeah, nothing speaks against simply sending the old and
> the new size.

Nope. I actually meant using the block->used_length to store in the 
s->files->f[index].size. 

virt_acpi_setup()
  acpi_add_rom_blob()
    rom_add_blob()
      rom_set_mr()  --> used_length  = page aligned blob size
        fw_cfg_add_file_callback()  --> uses actual blob size.


Right now what we do is use the actual blob size to store in FWCfgEntry.
Instead pass the RAMBlock used_length to fw_cfg_add_file_callback().
Of course by this, the firmware will see an aligned size, but that is fine I think.
But at the same time this means the qemu_ram_resize() can stay as it is 
because it will invoke the callback when the size changes beyond the aligned
page size. And also during migration, there won't be any inconsistency as everyone
works on aligned page size.

Does that make sense? Or I am again missing something here?

Thanks,
Shameer

> --
> Thanks,
> 
> David / dhildenb