Re: dracut is too "clever" at identifying modules to exclude.

[Harald Hoyer <harald-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 12.10.2015 22:30, Neil Brown wrote:
> Harald Hoyer <harald-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
> 
>> On 12.10.2015 05:02, Neil Brown wrote:
>>>
>>> If I have booted a kernel with md/raid built in (no modules) and
>>> I use dracut to build the initramfs for a different kernel which
>>> has the md code compiled as separate modules, then it does not include
>>> the required md modules in the initramfs.
>>>
>>> As a particular instance this happen when the root filesystem is on
>>> RAID0.  The 'raid0.ko' module is not included and boot fails.
>>>
>>> https://bugzilla.opensuse.org/show_bug.cgi?id=935993
>>>
>>> This only happens when 'host-only' is selected (which is the default for
>>> openSUSE).
>>>
>>> the modules.d/90mdraid/module-setup.sh code calls
>>>
>>>     instmods =drivers/md
>>>
>>> instmods calls
>>>    module_is_host_only "raid0"
>>> and this incorrectly fails.
>>>
>>> If raid0.ko didn't have any alias this would succeed, but it does.
>>>
>>> $ modinfo -F alias raid0
>>> md-level-0
>>> md-raid0
>>> md-personality-2
>>
>> Huh? Is the module not loaded?
> 
> No, because the running kernel has "md/raid built in (no modules)".
> 
> Thanks,
> NeilBrown
> 
>>
>>>
>>> However these aliases don't appear in any modalias file in /sys/devices,
>>> in /proc/crypto, or in /proc/modules.
>>>
>>> Maybe you could parse /proc/mdstat..
>>>
>>> if [ -f /proc/mdstat ]; then
>>>   while read _d _c _a _m _x; do
>>>    if [ "$_c" = ':' -a "$_a" = 'active' ]; then
>>>       host_modalias["md-$_m"]=1
>>>    fi
>>>   done < /proc/mdstat
>>> fi
>>>
>>> but it all seems rather fragile.  There are probably other modules that
>>> might miss out accidentally. dm?
>>>
>>> Do we really need the host_modalias stuff?
>>>
>>> Thanks,
>>> NeilBrown
>>>

Interesting... so we have to blow up the initramfs with the entire drivers/md
in the case, where you switch from "compiled in" to "not compiled in"..

I guess that happens not that often, so better be safe than sorry.