Hello,

On 08/27/2010 10:24 PM, Mike Snitzer wrote:

quoted

* As __blk_rq_prep_clone() copies REQ_FUA, just advertising FUA
  support is enough to pass through REQ_FUA to targets.

You're doing blk_queue_flush(md->queue, REQ_FLUSH | REQ_FUA); in 2
places:
1) generic dm_init_md_queue -- used for bio-based and request-based
2) request-based specific dm_init_request_based_queue.

Well, there are two places creating queues.

Interestingly, we never used the old blk_queue_ordered() method for
bio-based DM yet it is now using blk_queue_flush().

Yeap, because now __make_request() filters out REQ_FLUSH bio's.

But how can we blindly assume/advertise REQ_FUA?

Should we be taking more care to check each block device that DM
consumes to see if FUA is supported and only then advertise REQ_FUA?
DM already does this for discard support (see:
dm_table_supports_discards).

Nope, REQ_FUA will be interpreted by queues lower in the stack.
Drivers in the middle just need to pass them through.

quoted

Lightly tested linear, stripe, raid1, snap and crypt targets.

I tested the bio-based code with the LVM2 test suite and all tests
passed.

quoted

Please proceed with caution as I'm not familiar with the code base.

As I shared in an earlier (private) mail, I'm unfortunately having
problems with request-based DM (when all patches in this series are
applied).  I'll be working on that more.

Heh... I probably should set up a simple dm-mpath and test it.  I'll
do it this weekend.

BTW, we can eliminate the dm_rq_is_flush_request() wrapper right?  I
think hch mentioned this at some point in one of the various threads.

Sure, that's a rather silly wrapper at this point.

Thanks.

-- 
tejun