linux-kernel - Re: What still uses the block layer?

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Message-ID: <47139F15.7050702@s5r6.in-berlin.de>
Date:	Mon, 15 Oct 2007 19:10:45 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Matthew Wilcox <matthew@....cx>
CC:	Rob Landley <rob@...dley.net>,
	David Newall <david@...idnewall.com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Nick Piggin <piggin@...erone.com.au>
Subject: Re: What still uses the block layer?

Matthew Wilcox wrote:
> On Mon, Oct 15, 2007 at 04:26:04AM -0500, Rob Landley wrote:
>> Combining USB and IDE into the same /dev/sd? namespace makes enumerating the 
>> IDE devices much harder than in the traditional "/dev/hdb doesn't move 
>> without a screwdriver" model.  The merger creates a new problem for IDE, one 
>> which didn't exist before: the addition or removal of other unrelated types 
>> of devices may change this device's location next boot.  It may be possible 
>> to add additional complication to the system to compensate, but what was the 
>> advantage of merging the namespaces in the first place?
> 
> It's not something anyone particularly set out to do, it's just how
> it worked out.  It was justified by saying "ok, this goes from a 99%
> solution to a 96% solution, but there's 100% solution called uuids".
> I don't particularly agree with this line of argumentation, but it did
> hold sway.

Low-level networking drivers suggest a default interface name (per
interface or as a template like eth%d into which the networking core
inserts a lowest spare number).  Userspace can rename interfaces, but
nevertheless it's nice to have different default kernel names for
ethernet, wlan etc..

Could low-level SCSI drivers provide similar name templates which give a
hint on the transport involved?  It's a bit more difficult as with
networking interfaces though because
  - SCSI devices can have sd, sr, st, osst, ch, sg interfaces,
  - SCSI device files share a namespace with all other device files.

E.g.
/dev/sd-ide-b	- second IDE HDD,
/dev/sd-iscsi-e	- fifth iSCSI direct access device,
/dev/sr-sata-0	- first SATA CD-ROM,
/dev/sr-usb-0	- a USB CD-ROM,
/dev/st-fw-0	- a FireWire tape drive,
/dev/sda	- a device whose transport driver didn't propose a name

Of course the really interesting names will still be provided by
udev-generated symlinks.
-- 
Stefan Richter
-=====-=-=== =-=- -====
http://arcgraph.de/sr/
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