Re: [PATCH 01/20] block, blk_filter: enable block device filters

[Sergei Shtepa]

Thank you, Christoph, for your attention to the patch.

I am preparing the next version of the patch. In it, I planned to
simplify the bdev_filer code.
I will make changes in it, in accordance with your comments, and
will add your code and check it on my test labs.

But I'm not sure if using the blk_mq_freeze_queue() is appropriate.
If I understood the code correctly, it is based on the expectation
that the counter q->q_usage_counter will decrease to zero.
To increase it, a blk_queue_enter() is used. And at the time of
calling the filter_bio() in the submit_bio_noacct(), this counter
has not yet been increased. I will double check this and try to
get rid of the bdev->bd_filter_lock.