Re: [Qemu-devel] [PATCH 1/5] elf-loader: Allow late loading of elf

[Christian Borntraeger]

On 02/20/2017 04:33 PM, Thomas Huth wrote:
> On 20.02.2017 15:19, Cornelia Huck wrote:
>> From: Farhan Ali <address@hidden>
>>
>> The current QEMU ROM infrastructure rejects late loading of ROMs.
>> And ELFs are currently loaded as ROM, this prevents delayed loading
>> of ELFs. So when loading ELF, allow the user to specify if ELF should
>> be loaded as ROM or not.
>>
>> If an ELF is not loaded as ROM, then they are not restored on a
>> guest reboot/reset and so its upto the user to handle the reloading.
> 
> Could you maybe also explain here why you need such a delayed ELF
> loading? Why can't you load the s390-netboot.img at the same time as
> s390-ccw.img?

Please read the cover letter for some details how to build such a netrom.
This is a simple variant to implement a standard compliant network boot 
today but using a kernel+busybox+scripts.
Long term we certainly want to have a look at implementing something in
the ccw bios, but this (tcp stack, virtio net, etc) will take some (a lot?)
more time. Having a ramdisk+kernel loaded  all the time would be extremely
wasteful.

This patch (1) has another advantage.
Right now we load the ccw bios all the time, even for -kernel xxx boot,
to allow the guest user to use chreipl to reboot from a disk. With this
in place we can rework our ccw bios loader to load the ccw bios lazily
as well.

Christian