pkg/53490: sysutils/grub2: module loaded even if feature is builtin

[triaxx%NetBSD.org@localhost]

>Number:         53490
>Category:       pkg
>Synopsis:       sysutils/grub2: module loaded even if feature is builtin
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Aug 01 15:10:00 +0000 2018
>Originator:     Frédéric Fauberteau
>Release:        netbsd-8-0-RELEASE (pkgsrc-2018Q2)
>Organization:
>Environment:
NetBSD hydralisk 8.0 NetBSD 8.0 (HYDRALISK) #1: Tue Jul 31 18:43:06 CEST 2018  root@hydralisk:/usr/obj/sys/arch/amd64/compile/HYDRALISK amd64
>Description:
At boot, the following errors at printed due to grub2 that loads ffs.kmod:

--- dmesg ---
NetBSD 8.0 (HYDRALISK) #1: Tue Jul 31 18:43:06 CEST 2018
    root@hydralisk:/usr/obj/sys/arch/amd64/compile/HYDRALISK
total memory = 3839 MB
avail memory = 3704 MB
kobj_checksyms, 1003: [ffs.kmod]: linker error: global symbol `ffs_vnodeop_opv_desc' redefined
kobj_checksyms, 1003: [ffs.kmod]: linker error: global symbol `ffs_snapshot_fini' redefined
*** idem ***
kobj_checksyms, 1003: [ffs.kmod]: linker error: global symbol `ufs_direnter' redefined
WARNING: module error: unable to load `ffs.kmod' pushed by boot loader, error 8
--- /dmesg ---

Actually, ffs is builtin:

--- modstat ---
$ modstat | grep "^ffs"
ffs                     vfs      builtin  -        2       - wapbl
--- /modstat ---
>How-To-Repeat:
# grub-mkconfig -o /grub/grub.cfg

The NetBSD prober (/usr/pkg/etc/grub/10_netbsd) detects fs type of the root filesystem and loads the corresponding module unconditionally.
>Fix:
pgoyette@ suggests teaching grub not to "push" modules that are already built-in.