linux-kernel - Re: allocate an official device major number for virtio device?

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Date:	Wed, 2 Mar 2016 17:48:24 -0800
From:	Jin Qian <jinqian@...roid.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, Jeff Sharkey <jsharkey@...gle.com>,
	David Turner <digit@...gle.com>, pprabhu@...gle.com,
	Yu Ning <yu.ning@...el.com>
Subject: Re: allocate an official device major number for virtio device?

Do you mean detecting device name string as in /dev/...?

Just checked latest virtio_blk code, it's dynamic but not using
anything specific to experimental range. I guess we're fine here but
Yu can confirm.

Thanks,
jin

On Wed, Mar 2, 2016 at 5:25 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Wed, Mar 02, 2016 at 05:08:00PM -0800, Jin Qian wrote:
>> Hi -
>>
>> Can we allocate an official device major number for virtio devices?
>> Currently it's using 240-254 (LOCAL/EXPERIMENTAL USE). The reason we
>> ask for this is because userspace will need to treat virtio block
>> devices differently and need a way to detect such device. For example,
>> it checks major number to detect scsi and mmc device.
>>
>> https://android-review.googlesource.com/#/c/195240
>>
>> With dynamic major numbers 240-254, we might treat other devices as
>> virtio block device incorrectly.
>
> You shouldn't treat them incorrectly, devtmpfs handles this for you
> automatically, so I'd recommend using the dynamic majors please.
>
> And what in-kernel code is using the "experimental" range today?  Do you
> have a pointer to that?  We should fix that now...
>
> thanks,
>
> greg k-h