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What still uses the block layer?

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From: Rob Landley <rob@...>
To: <linux-kernel@...>
Cc: <linux-scsi@...>, Jens Axboe <axboe@...>, Suparna Bhattacharya <suparna@...>, Nick Piggin <piggin@...>
Subject: What still uses the block layer?
Date: Thursday, October 11, 2007 - 9:11 pm

My impression from asking questions on the linux-scsi mailing list is that the 
scsi upper/middle/lower layers doesn't use the block layer described in 
Documentation/block/*.

For example, the scsi guys say:
http://marc.info/?l=linux-scsi&m=118633268527856&w=2

Instead of using the block layer, SCSI reinvents this particular wheel itself.  
There's a scsi "upper layer" that provides /dev nodes, scsi low-level 
drivers, and a gigantic glue layer in between call the "scsi midlayer" that's 
something like a networking stack, and is responsible for losing track of all 
your devices so that the one SATA disk hardwired into your laptop might be 
sda or sdc depending on whether or not you had a USB key plugged in when you 
booted up.  Anyway, the block layer isn't between any of these three, that I 
can tell.

Now that IDE disks have been rerouted through the scsi layer, SATA goes 
through the scsi layer, USB goes through the scsi layer, firewire goes 
through the scsi layer...  What's left?  It seems like everything but 
ramdisks have now been routed through the scsi layer.  My laptop hasn't got a 
single SCSI device but it also hasn't got any block devices that don't show 
up as scsi.

So what's still using the block layer?  How do the scsi layers and the block 
layer relate?  I'm confused!  (This is normal for me, but still...)

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.
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Messages in current thread:
What still uses the block layer?, Rob Landley, (Thu Oct 11, 9:11 pm)
Re: What still uses the block layer?, Matthew Wilcox, (Sat Oct 13, 6:05 pm)
Re: What still uses the block layer?, James Bottomley, (Sun Oct 14, 6:24 pm)
Re: What still uses the block layer?, Luben Tuikov, (Sun Oct 14, 8:45 pm)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 2:51 am)
Re: What still uses the block layer?, Luben Tuikov, (Mon Oct 15, 4:37 am)
Re: What still uses the block layer?, Rob Landley, (Sun Oct 14, 7:45 pm)
Re: What still uses the block layer?, James Bottomley, (Mon Oct 15, 9:10 am)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 5:51 pm)
Re: What still uses the block layer?, Greg KH, (Mon Oct 15, 2:00 am)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 4:36 am)
Re: What still uses the block layer?, Greg KH, (Mon Oct 15, 1:25 pm)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 6:54 pm)
Re: What still uses the block layer?, Jeff Garzik, (Mon Oct 15, 2:46 pm)
Re: What still uses the block layer?, Bill Davidsen, (Wed Oct 17, 7:43 pm)
Re: What still uses the block layer?, Stefan Richter, (Tue Oct 16, 2:33 am)
Re: What still uses the block layer?, Matthew Wilcox, (Mon Oct 15, 2:00 pm)
Re: What still uses the block layer?, Arjan van de Ven, (Mon Oct 15, 10:00 am)
Re: What still uses the block layer?, Matthew Garrett, (Mon Oct 15, 2:56 pm)
Re: What still uses the block layer?, Alan Cox, (Mon Oct 15, 9:08 am)
Re: What still uses the block layer?, Christoph Hellwig, (Mon Oct 15, 4:52 am)
Re: What still uses the block layer?, Theodore Tso, (Sun Oct 14, 9:45 pm)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 4:04 am)
Re: What still uses the block layer?, , (Wed Oct 17, 1:34 am)
Re: What still uses the block layer?, , (Wed Oct 17, 2:07 am)
Re: What still uses the block layer?, Theodore Tso, (Mon Oct 15, 9:21 am)
Re: What still uses the block layer?, , (Mon Oct 15, 10:51 pm)
Re: What still uses the block layer?, Douglas Gilbert, (Mon Oct 15, 10:46 am)
Re: What still uses the block layer?, Alan Cox, (Mon Oct 15, 9:29 am)
Re: What still uses the block layer?, Jeff Garzik, (Mon Oct 15, 1:44 pm)
Re: What still uses the block layer?, Theodore Tso, (Mon Oct 15, 9:35 am)
Re: What still uses the block layer?, Loïc Grenié, (Mon Oct 15, 6:32 am)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 5:09 pm)
Re: What still uses the block layer?, Julian Calaby, (Mon Oct 15, 5:06 am)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 6:08 am)
Re: What still uses the block layer?, Greg KH, (Mon Oct 15, 1:33 pm)
Re: What still uses the block layer?, , (Mon Oct 15, 10:54 pm)
Re: What still uses the block layer?, Matthew Wilcox, (Tue Oct 16, 12:04 am)
Re: What still uses the block layer?, Greg KH, (Tue Oct 16, 12:21 am)
Re: What still uses the block layer?, , (Tue Oct 16, 1:00 am)
Re: What still uses the block layer?, Arjan van de Ven, (Tue Oct 16, 12:11 am)
Re: What still uses the block layer?, , (Tue Oct 16, 12:15 am)
OOM killer gripe (was Re: What still uses the block layer?), Nick Piggin, (Mon Oct 15, 9:37 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Andrew Morton, (Tue Oct 16, 4:37 pm)
Re: OOM killer gripe (was Re: What still uses the block laye..., Eric W. Biederman, (Mon Oct 15, 11:55 pm)
Re: OOM killer gripe (was Re: What still uses the block laye..., Nick Piggin, (Tue Oct 16, 2:59 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Eric W. Biederman, (Tue Oct 16, 12:38 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rob Landley, (Tue Oct 16, 2:38 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Alan Cox, (Tue Oct 16, 6:28 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rob Landley, (Tue Oct 16, 7:59 pm)
Re: OOM killer gripe (was Re: What still uses the block laye..., Eric W. Biederman, (Tue Oct 16, 5:31 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Nick Piggin, (Tue Oct 16, 3:34 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rogier Wolff, (Thu Oct 18, 9:00 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rob Landley, (Fri Oct 19, 2:49 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rogier Wolff, (Fri Oct 19, 3:21 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., , (Tue Oct 16, 12:10 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Eric W. Biederman, (Tue Oct 16, 12:45 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Theodore Tso, (Mon Oct 15, 7:40 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Pavel Machek, (Sat Oct 20, 5:50 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Rob Landley, (Mon Oct 15, 5:52 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Pavel Machek, (Sat Oct 20, 5:48 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., Nick Piggin, (Mon Oct 15, 11:08 am)
Re: OOM killer gripe (was Re: What still uses the block laye..., David Newall, (Tue Oct 16, 2:22 am)
Re: What still uses the block layer?, David Newall, (Sun Oct 14, 1:54 am)
Re: What still uses the block layer?, Stefan Richter, (Sun Oct 14, 1:46 pm)
Re: What still uses the block layer?, Rob Landley, (Sun Oct 14, 7:36 pm)
Re: What still uses the block layer?, Stefan Richter, (Mon Oct 15, 1:44 am)
Re: What still uses the block layer?, Rob Landley, (Mon Oct 15, 5:26 am)
Re: What still uses the block layer?, Wilfried Klaebe, (Mon Oct 15, 4:29 pm)
Re: What still uses the block layer?, Matthew Wilcox, (Mon Oct 15, 12:08 pm)
Re: What still uses the block layer?, Stefan Richter, (Mon Oct 15, 1:10 pm)
Re: What still uses the block layer?, , (Mon Oct 15, 11:06 pm)
Re: What still uses the block layer?, Alan Cox, (Tue Oct 16, 6:19 am)
Re: What still uses the block layer?, , (Tue Oct 16, 3:54 pm)
Re: What still uses the block layer?, Matthew Wilcox, (Tue Oct 16, 3:54 pm)
Re: What still uses the block layer?, , (Tue Oct 16, 4:55 pm)
Re: What still uses the block layer?, Gabor Gombas, (Wed Oct 17, 5:48 am)
Re: What still uses the block layer?, , (Wed Oct 17, 5:04 pm)
Re: What still uses the block layer?, Stefan Richter, (Wed Oct 17, 1:23 pm)
Re: What still uses the block layer?, Alan Cox, (Tue Oct 16, 5:49 pm)
Re: What still uses the block layer?, Theodore Tso, (Tue Oct 16, 4:34 pm)
Re: What still uses the block layer?, Stefan Richter, (Tue Oct 16, 4:56 pm)
Re: What still uses the block layer?, Stefan Richter, (Tue Oct 16, 4:18 pm)
Re: What still uses the block layer?, Stefan Richter, (Tue Oct 16, 1:56 am)
Re: What still uses the block layer?, Tilman Schmidt, (Sun Oct 14, 6:35 pm)