linux-ext4 - Re: Ext4 and scsi commands resubmission

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Message-ID: <4D1ABC82.5050909@cs.wisc.edu>
Date:	Tue, 28 Dec 2010 22:43:46 -0600
From:	Mike Christie <michaelc@...wisc.edu>
To:	torn5 <torn5@...ftmail.org>
CC:	linux-ext4@...r.kernel.org,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: Ext4 and scsi commands resubmission

On 12/28/2010 04:41 AM, torn5 wrote:
> Hello all,
>
> in open-iscsi, when network connectivity is lost, scsi commands that
> were in-flight at the moment of disconnection are failed to the SCSI layer.
> These get resubmitted up to 5 times by the SCSI layer (or so is written
> in the open-iscsi docs) and after that they are held in the queue
> (device "blocked") until the network connection is restored.
>
> Now the question is: when SCSI resubmits commands to a device, I suppose
> they go to the end of the queue for the device, and not at the head like
> they were. Am I right?

The request goes to eh head. scsi layer calls 
blk_requeue_request->elv_requeue_request-> 
elv_insert(ELEVATOR_INSERT_REQUEUE) and ELEVATOR_INSERT_REQUEUE's case 
falls through to the ELEVATOR_INSERT_FRONT case.
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