Re: Linux software RAID vs. udev

["Kevin P. Fleming" <kpfleming@backtobasicsmgmt.com>]

Neil Brown wrote:

>>looking through the md driver, I don't even see how the first unit (md0) 
>>is getting registered by default, unless for some reason the block layer 
>>is calling md_probe for unit 0 without even being asked to.
> 
> 
> init/do_mounts_md.c:md_run_setup

OK, I saw that file but disregarded it thinking it didn't apply if I 
didn't have any autostart arrays. I'll look again to satisfy my 
curiosity :-)

> I think it would be very poor form for udev to break established and
> working semantics.  If it doesn't let you pre-create devices in /dev
> and have then stay there, then I think that is a mistake.

udev does not prevent anyone from creating any nodes in /dev they wish. 
/dev is just any filesystem you want to use, you can put anything there 
you like. The issue is that those of us that are converting to 
hotplug-driven udev are using ramfs/tmpfs for /dev, so there is no 
persistence. That means (for now) manually creating all /dev/md nodes we 
might need to use during that boot, or manually creating any required 
nodes before attempting to run mdadm. Neither of these are horrible 
solutions, they're just not elegant :-)

Since all of this infrastructure is already in place for the dm 
subsystem, I guess this leads back to implementing the md personalities 
as dm targets, but that's a much larger issue. It would solve this 
problem completely, though.


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