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From: Simon Glass <sjg@chromium.org>
To: Grant Likely <grant.likely@secretlab.ca>
Cc: lk <linux-kernel@vger.kernel.org>,
	Devicetree Discuss <devicetree-discuss@lists.ozlabs.org>,
	Che-liang Chiou <clchiou@chromium.org>
Subject: Re: Device tree node to major/minor?
Date: Tue, 20 Nov 2012 15:48:24 -0800	[thread overview]
Message-ID: <CAPnjgZ3jF7bdwqDCNzJXvSrwoP0PZVjcFO+nGOiLACLDX07Z7A@mail.gmail.com> (raw)
In-Reply-To: <CACxGe6t-ROJe+KXZh-nah50M2buM4yjncs=7musv39=C+73_FQ@mail.gmail.com>

Hi Grant,

On Tue, Nov 20, 2012 at 2:32 PM, Grant Likely <grant.likely@secretlab.ca> wrote:
> On Tue, Nov 20, 2012 at 10:23 PM, Simon Glass <sjg@chromium.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?

The use case is storing some raw data on a block device from within a
driver in the kernel. It is used to keep track of the verified boot
state.

>
> 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.

So is there a way to do this entirely in the kernel ex post? It might
need to happen during kernel boot, before user space.

>
> g.

Thanks,
Simon

  reply	other threads:[~2012-11-20 23:48 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-11-20 22:23 Device tree node to major/minor? Simon Glass
2012-11-20 22:32 ` Grant Likely
2012-11-20 23:48   ` Simon Glass [this message]
2012-11-21 15:47     ` Grant Likely
2012-11-21 20:48       ` Simon Glass
2012-11-21 23:07         ` Grant Likely

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