Hi,
On 10/02/2009 05:31 AM, Neil Brown wrote:
<snip>
Problem 2: Discovery / Assembly
Several issues have forced dracut to punt on using mdadm -I. Instead
dracut copies mdadm.conf to the initramfs and uses mdadm -As after a
udevadm --settle. One low hanging issue is the fact that non-rootfs
arrays may only be partially assembled when dracut discovers and
switches to the final rootfs. Upon switching the in-progress map file
is lost. Moving /var/run/mdadm/map to /dev/.mdadm/map would appear to
solve this issue.
mdadm already uses /dev/.mdadm.map if /var/run is not writable. So is
this a solved problem, or do we need some other way to force mdadm not
to use /var/run too early.
So you are talking about commit cf3a3d78 [2]. I think the problem is
that /var/run/mdadm/map is writable in dracut so we never fall back to
/dev/.mdadm.map. Any reason to not make /dev/.mdadm.map the first
location to try?
Because (damn it) the file is not a device file, it is a
run-time-management file and so it belongs in /var/run. If we just
put things wherever was convenient instead of where they belonged we
would end up with something like /proc!
If there is a writable /var/run in early boot, presumably it is a
tmpfs filesystem.
Would it not be simple to
mount --bind /var/run /root/var/run
before the pivot_root, or maybe "mount --move"?
Then everything would benefit from a stable /var/run and nothing would
have to put silly inappropriate files in /dev.
On the other hand, if /var/run is not a tmpfs filesystem and is
normally part of the real /var, what is the justification for having a
writable /var/run in early boot? Sounds like a recipe for confusion.
There is no such thing in the initrd (a writable /var/run), but there is
a writable / (initrd == ramdisk), and mdadm will happily create /var/run
itself, if it would not do that, there would no issue.
Although I do wonder how later, when we do have a writable /var/run, mdadm
decides which file to use. Once it has used /dev/.mdadm.map once it should
keep on using that.
Regards,
Hans
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