[RFC] breakage in bsg

[Al Viro <viro@ZenIV.linux.org.uk>]

	* with "bsg: bind bsg to request_queue instead of gendisk" we
get all requests with NULL ->rq_disk.  SCSI can cope with that, anything
else is not promised to be able to surive that.  Indeed, quite a few
drivers do not.

	* WTF are these per-bd flags doing, seeing that you set them
on every ->read() and ->write()?  Just what will happen if you have
two openers?

	* cmd_filter thing is broken as well (we have no access to
gendisk in question and there's a lot of obvious issues when you have
several openers).

#2 and part of #3 are fixable, but I really don't see what to do with #1.
If nothing else, it's absolutely incompatible with cmd_filter, even if you
leave aside the issue with non-IDE/non-SCSI drivers.

Comments?