From: "Morales, Alejandra" <alejandra.morales@tum.de>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Doubts on IO requests in USB subsystem
Thread-Topic: Doubts on IO requests in USB subsystem
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Date: Mon, 9 Sep 2013 08:20:06 +0000
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Dear all,

For my master thesis I am developing a user space power management tool. For that purpose
I am implementing a kernel module and one task this module does is to intercept calls to the
request_fn function for every scsi device in order to check when they are actually being requested
an IO operation.

I am testing with a regular SATA hard drive and with an external USB hard drive. Both are just
mounted and there is no application using them at the moment, so that I was expecting that none
of them receive file system requests. Indeed the SATA HD does not receive any requests unless I
mount or unmount it, but the USB HD receives a large number of file system requests and it seems
that it never enters into an idle state. Since any application is using it I think these requests may
come from the USB subsystem. Am I right? If so, how could I determine whether a request comes
from the USB subsystem or it is a file system request that actually moves blocks?

Thanks in advance.
Regards,
Alejandra--
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