krpc: unbootable ZFS-on-root after major upgrade to 11.2

[Eugene Grosbein]

On 19.10.2018 13:28, Andriy Gapon wrote:

>> It was brought to my attention that 10.x did not require availability
>> of krpc for ZFS-on-root system to be bootable but 11.x does.
>>
>> That is, major upgrade of 10.x ZFS-on-root system to 11.x
>> results in non-bootable broken system if it uses custom kernel without NFS bits
>> that automatically come with krpc, and the system was built with MODULES_OVERRIDE="zfs opensolaris"
>> and no krpc mentioned.
> 
> Could you please also describe specifics of the problem?
> It's kidn of strange that root-on-zfs requires krpc.

https://svnweb.freebsd.org/base/stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c?revision=339111&view=markup#l7146

This code uses some xdr(3) functions to parse zpool.cache
and kernel-side implementation of xdr(3) is contained in krpc.ko

Out of curiosity, I've commented out mentioned MODULE_DEPEND(zfsctrl, krpc, 1, 1, 1),
rebuilt zfs.ko and tried to kldload it using UFS-only system having no NFS code in the kernel
and it failed with a note in dmesg:

link_elf: symbol xdrmem_create undefined