[Buildroot] [RFC 3/6] system: add mdev-only /dev management (without devtmpfs)

[Luca Ceresoli]

Dear Arnout,

Arnout Vandecappelle wrote:
> On 09-09-15 13:29, Thomas Petazzoni wrote:
>> Luca,
>>
>> On Tue,  8 Sep 2015 23:28:51 +0200, Luca Ceresoli wrote:
>>> There are a few reasons for an embedded Linux system not to use devtmpfs,
>>> but still want to have dynamic /dev management. The most notable is to use
>>> a kernel < 2.6.32, which have no devtmpfs support.
>>>
>>> For such corner cases, we introduce the ability to use busybox mdev for
>>> /dev management even without devtmpfs.
>>>
>>> First, we need the BR2_ROOTFS_STATIC_DEVICE_TABLE just like the static
>>> /dev management, in order to have the very basic devices such as /dev/null
>>> and /dev/console until mdev is enabled.
>>
>> As said in another e-mail, this is not really true: we just need a very
>> simple, two devices long, hard-coded device table. There is no need to
>> allow the user to customize it. It would in fact be potentially
>> misleading because the user who would add more devices in this static
>> device table would not see them on the target: they would be
>> "overridden" by the tmpfs mounted in /dev.
>
>   Right! So:
>
> define BUSYBOX_DEVICES
> 	/dev/console c 666 0 0 5 1 - - -
> 	/dev/null c 666 0 0 1 3 0 0 -
> endef

Good idea, this saves creating a new device table.

-- 
Luca