linux-kernel - Re: Device tree node to major/minor?

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Date:	Tue, 20 Nov 2012 22:32:33 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Simon Glass <sjg@...omium.org>
Cc:	lk <linux-kernel@...r.kernel.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Che-liang Chiou <clchiou@...omium.org>
Subject: Re: Device tree node to major/minor?

On Tue, Nov 20, 2012 at 10:23 PM, Simon Glass <sjg@...omium.org> wrote:
> Hi,
>
> I hope this is a stupid question with an easy answer, but I cannot find it.
>
> I have a device tree node for an mmc block device and I want to use
> that block device from another driver. I have a phandle which lets me
> get the node of the mmc device, but I am not sure how to convert that
> into a block_device. In order to do so, I think I need a major/minor
> number. Of course the phandle might in fact point to a SCSI driver and
> I want that to work correctly also.
>
> I imagine I might be able to search through the wonders of sysfs in
> user space, but is there a better way?

Do you /want/ to do it from userspace? What is your use case? Mounting
the rootfs?

Regardless, userspace can monitor the uevents when devices are added
(that's what udev does) and watch for the full path of the node you
want in the uevent attribute. Then you can look for the child device
with the block major/minor numbers in it.

g.
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