Re: Ethernet Interface disappear after exit from grub command prompt

[Andrei Borzenkov]

23.02.2017 15:11, Wasim Khan пишет:
> Hi,
> 
> I am working on a EDK2 based UEFI solution for arm64 architecture board. I am 
> trying Pxeboot to boot Linux from network.
> 
> I am doing below steps:
> 
> *         From UEFI boot Menu, select Pxeboot on a particular interface (say 
> eth0).
> 
> *         After getting the grub.efi from network, select a menu entry from 
> grub menu.
> 
> *         If a file corresponding to selected grub menu entry is not present 
> on tftp server, grub menu is displayed again.
> 
> *         Now go to grub command prompt and run 'exit' command.
> 
> *         I am coming back to UEFI boot menu, but if I go to UEFI SHELL, 
> interface eth0 is not visible in ifconfig command.
> 
> Same behavior is observed on arm64 QEMU virtual machine UEFI firmware .
> http://snapshots.linaro.org/components/kernel/leg-virt-tianocore-edk2-upstream/latest/QEMU-AARCH64/DEBUG_GCC5/
> 
> Is it a bug in grub OR is it by design?

Both.

GRUB only supports Simple Network Protocol and expects it is the only
consumer of physical interface. Most moder systems default to Managed
Network Protocol stack where there are multiple consumers on top of
physical interface. It was found that in this configuration firmware
competes with grub for incoming packets resulting in connection failure.
So grub was modified to open physical interface exclusively, which
deactivated MNP stack.

This behavior fixed connection issues but caused other problems, like
the one you observed.

It is recognized and plans are to add MNP support to grub. Just needs
someone to actually code it :)

> Can someone help me understand the exit process, that why exit from grub 
> command prompt (after tftp fail) is making the interface down ?
> 
> Thanks,
> Wasim
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