linux-kernel - Re: generic_make_request fucntion for scsi

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Message-Id: <1245507640.4255.6.camel@mulgrave.site>
Date:	Sat, 20 Jun 2009 09:20:40 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Ravish Tayal <ravish.tayal@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: generic_make_request fucntion for scsi_disk

On Sat, 2009-06-20 at 19:35 +0530, Ravish Tayal wrote:
> I am debugging Filesystem code for USB mass storage devices.  I need
> help to figure out after generic_make_request how the request is
> placed to scsi disk (sd) requeset queue and than how sd qeueuecommand
> to usb_storeage thread.  (in which context, is it system call context)

requests out of the lower end of block come from the elevators.  The
elevators can operate in a variety of contexts: user, kernel thread or
softirq depending on state.

The mechanism for queueing to the USB thread is in
scsiglue.c:queuecommand() it's basically a simple single command
consumer model: fill in slot and wake thread.

James


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