linux-kernel - cgq vs bdi names, was "cfq-iosched: fix a kernel OOPs when usb key is inserted"

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Message-ID: <20100920130318.GA29565@lst.de>
Date:	Mon, 20 Sep 2010 15:03:18 +0200
From:	Christoph Hellwig <hch@....de>
To:	vgoyal@...hat.com
Cc:	jaxboe@...ionio.com, linux-kernel@...r.kernel.org
Subject: cgq vs bdi names, was "cfq-iosched: fix a kernel OOPs when usb key is inserted"

Hi Vivek, hi Jens,

where was http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff_plain;h=44c74d6292e97f8bd9adfa6b0df3cb4f3c42a6dc posted  on the mailinglist?

I can't find it in my lkml or fsdevel inboxes.  Either way I don't think
just papering over the underlying issue like this is a good idea.  

The big issue is that cfq tries to scanf the textual representation of
the dev_t from the request_queue by abusing the bdi.  But the reason why
we don't have a dev_t in the request_queue is that it's still not
unique.  If it was we could easily add a dev_t into the request_queue
and be done with it.

So the fix is either to get rid of the last remaining users of shared
request_queues (IIRC the various floppy drivers) and just add a dev_t
in the request_queue for the bdi, tracing and cfq, or add a dev_t into
the request_queue and add a flag for shared request queues that the
floppy driver and whoever needs it set and let the bdi sysfs code, cfq
and blocktrace ignore theis request_queue.  This will also allow to
get rid of the crap about ignoring failures due to already register
or prematurely unregistered bdis and actually add real error handling
to that code.
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