[7153] in linux-scsi channel archive
Re: Fixing the SCSI layer
daemon@ATHENA.MIT.EDU (tad-m2n@omoikane.co.jp)
Sun Sep 5 23:12:29 1999
Date: Mon, 06 Sep 1999 12:01:42 +0900
From: tad-m2n@omoikane.co.jp
To: groudier@club-internet.fr
Cc: alan@lxorguk.ukuu.org.uk, linux-kernel@vger.rutgers.edu,
linux-scsi@vger.rutgers.edu
In-Reply-To: In your message of "Sun, 5 Sep 1999 21:53:39 +0200 (MET DST)"
<Pine.LNX.3.95.990905210333.2179A-100000@localhost>
Genard wrote:
> > - have better sg driver (ex, abort handling, etc)
>
> What do you want to abort ? Once a command has been passed to the lower
> layer, it must complete with or without error, or time out.
Sending abort message to a device.
For expamle, you would want to stop a scanner when it does unwanted and
long operation without fail. (recent scanner is fast, though)
Adding message sending handle to SHT would not affect performance,
but it make mid-layer bigger...
> I suggest you to invest CAM3 specifications first. The FreeBSD CAM is a
> derivative and is very different from official CAM1/3 on some points. It
> has also some design/implementation errors in my opinion.
> For example, the SIM queuing (CAM3 10.4.2-10.4.3) implementation in
> FreeBSD can only have race conditions on error recovery (queue freeze), in
> my opinion.
I appreciate good advise. Thanks.
> > step2 : make a 'wrapper' of low driver to the CAM layer.
>
> Not a good idea, in my opinion. My suggestion is to allow both the CAM
> stack and the old SCSI stack to be configured in the kernel, allowing
> low-level drivers (SIMs) to be converted when time will allow.
Oh, sorry, I wanted to picture :
--------------------------------------------------------------------
|
low |
| low specialized to cam mid
+-------------------+
| |
| wrapped old low |
| |
----------------+---------------------------------------------------
|
old mid | cam mid
|
----------------+---------------------------------------------------
|
sd/sr/st/sg | new sd/sr/st/sg + s-net + s-target mode
|
--------------------------------------------------------------------
(Imagine wrapped old low has limited functionality but enough for sd.)
Ok, I am going to investigate CAM3 and FreeBSD CAM.
Thanks for advise!
--
Tadayoshi Ohkuma / tad@omoikane.co.jp
Omoikane Ltd. / http://www.omoikane.co.jp
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