I've noticed that on 2.6.29-rcX, with Andi's patch
(ab4c1424882be9cd70b89abf2b484add355712fa, dm: support barriers on
simple devices) barriers are still getting rejected on these simple devices.
The problem is in __generic_make_request():
if (bio_barrier(bio) && bio_has_data(bio) &&
(q->next_ordered == QUEUE_ORDERED_NONE)) {
err = -EOPNOTSUPP;
goto end_io;
}
and dm isn't flagging its queue as supporting ordered writes, so it's
rejected here.
Doing something like this:
+ if (t->barriers_supported)
+ blk_queue_ordered(q, QUEUE_ORDERED_DRAIN, NULL);
somewhere in dm (I stuck it in dm_table_set_restrictions() - almost
certainly the wrong thing to do) did get my dm-linear device to mount
with xfs, w/o xfs complaining that its mount-time barrier tests failed.
So what's the right way around this? What should dm (or md for that
matter) advertise on their queues about ordered-ness? Should there be
some sort of "QUEUE_ORDERED_PASSTHROUGH" or something to say "this level
doesn't care, ask the next level" or somesuch? Or should it inherit the
flag from the next level down? Ideas?
Thanks,
-Eric
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