On Mon, May 24 2010 at 6:00am -0400,
Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx> wrote:
> Hi Mike,
>
> On 05/24/2010 06:44 AM +0900, Mike Snitzer wrote:
> > But this new series eliminates v7's locking between table_load() and
> > do_resume() -- fixed md->type made this possible. So these changes
> > may be more desirable overall (adds some clearer exclusion and state
> > transitions that I feel help DM without being too restrictive).
>
> Yes, I think it's reasonable.
OK.
> > This work has expanded in scope somewhat (based on Mikulas' suggestion
> > that I pursue more constrained table/device type switching to avoid
> > Kiyoshi's locking concerns). A mapped_device now has a specific type
> > (md->type) that is managed in table_{load,clear} (see patch 3/6).
>
> Cancelling the type by table_clear() keeps the code/model complex
> even after changing model.
> I think the feature to cancel the type is not required any userspace
> tools nor admins at least for now. So dropping the feature and
> completely fixing the type at the first table loading time may be
> a good meeting point to make the kernel code simple.
I initially thought it best to keep table_clear() more "friendly".. so
as not to impose a user explicitly delete a DM device just to switch
from bio-based to request-based tables (or vice-versa).
But I think I've come full-circle:
- I'm not against imposing your suggestion (never reset md->type).
Certainly keeps the DM code simpler! :)
- We don't know all existing userspace code -- people could be using
DM's clear ioctl and we'd break their assumptions; but do we _really_
care? They'll adapt (they'd have to do a device delete, device
create, table load).
> I had only a quick look, so I may find some more comments. But I'd
> like to have more review after we reach an agreement about the basic
> implementation design above.
Yes, wish I had the restraint to avoid making dm_clear_md_type() work ;)
But pulling out that support will be easy and will also simplify other
code:
- will eliminate concern for "rq -> bio -> rq" in
dm_init_request_based_queue()
- can remove dm_clear_request_based_queue()
- maybe more...
Thanks,
Mike
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