From: Mike Anderson <andmike@us.ibm.com>
To: Douglas Gilbert <dougg@torque.net>
Cc: Sachin Sant <sachinp@in.ibm.com>, linux-scsi@vger.kernel.org
Subject: Re: SCSI reserve / release support for SG
Date: Fri, 14 Nov 2003 09:05:30 -0800 [thread overview]
Message-ID: <20031114170530.GC3322@beaverton.ibm.com> (raw)
In-Reply-To: <3FB4C85C.9020907@torque.net>
Douglas Gilbert [dougg@torque.net] wrote:
> >If not then are there any plans to support reserve/release SCSI command
> >so that sg driver can provide these options for its users in its
> >open/close function It will make all I/O operation with sg driver more
> >reliable especially in data storage area.
>
> I'm getting this request from several angles. As someone
> wryly pointed out ... as if we haven't got enough trouble
> at the moment with the scsi subsystem implicitly issuing
> scsi commands :-)
Yes, a sub question in the following bugme bug also asks this question.
http://bugme.osdl.org/show_bug.cgi?id=1488
>
> Seriously, I don't think issuing reserve/release SCSI commands
> on the open and close of a pass-through interface is a good
> idea. At a stretch it could be a non-default parameter on the
> sg driver [lk 2.4 via /proc/scsi/sg; in lk 2.6 ...]
>
Doing a reserve operation on open is more than sg doing some action as
device state could have been altered without sg or any upper level
driver knowing about. This could cause a case where the reservation
would be lost, but upper level drivers would not be notified. I guess
you could use persistent reserves, but then you would need another
parameter for the key. If we need to do these actions plus revoking /
breaking reservations what is the gain of sg doing this on open vs.
doing this in user space. In theory I guess a device mapper target could
be created if someone was opposed to a user space daemon (this is just a
quick thought with very little investigation).
IIRC when updates where happening for scsi_error in relation to door
lock someone suggested that we need a general machanism to indicate what
state the device is in and restore it post recovery.
-andmike
--
Michael Anderson
andmike@us.ibm.com
prev parent reply other threads:[~2003-11-14 17:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-14 11:29 SCSI reserve / release support for SG Sachin Sant
2003-11-14 12:19 ` Douglas Gilbert
2003-11-14 17:05 ` Mike Anderson [this message]
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