Thanks Alan!
--------------------------------------------------
From: "Alan Stern" <stern@xxxxxxxxxxxxxxxxxxx>
Sent: Wednesday, August 31, 2011 7:45 AM
To: "Chris Furlough" <chrisfurlough@xxxxxxxxxxx>
Cc: "Greg KH" <greg@xxxxxxxxx>; <linux-usb@xxxxxxxxxxxxxxx>
Subject: Re: HID device question.
On Tue, 30 Aug 2011, Chris Furlough wrote:
OK, hopefully my last couple of questions:
1. From the kernel, what's the best way to enumerate the devices that
are
already plugged in?
Kernel drivers aren't supposed to enumerate devices. But if you insist
on it, you can use the bus_for_each_dev routine.
2. I can use filp_open to open the devices in USBFS, this gives me a
struct
file, from which I can get the struct file_operations, from which I can
get
a pointer to the IOCTL function for that device. I can cast that as a
function pointer, and call it, but I believe that it's expecting the last
parameter to be a pointer to a buffer in userspace. Is there a correct
way to handle this?
The correct way is not to do it at all. There's no good reason for a
kernel driver to open a usbfs file.
However, if you call
set_fs(get_ds());
then the kernel will accept a kernelspace pointer in contexts where it
expects a userspace pointer. But be certain to store the original
value from get_fs() and restore it before returning to userspace!
Alan Stern
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