Date: Wed, 2 Mar 2016 17:25:30 -0800
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Jin Qian <jinqian@android.com>
Cc: linux-kernel@vger.kernel.org, jsharkey@google.com, digit@google.com,
        pprabhu@google.com, Yu Ning <yu.ning@intel.com>
Subject: Re: allocate an official device major number for virtio device?
Message-ID: <20160303012530.GA23521@kroah.com>
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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