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

[Peter Korsgaard <peter@korsgaard.com>]

>>>>> "Arnout" == Arnout Vandecappelle <arnout@mind.be> writes:

Hi,

 > On 15-09-15 14:01, Peter Korsgaard wrote:
 >> Or alternatively, extend the S10mdev logic to detect that it need to
 >> create a tmpfs on /dev (by looking for devtmpfs in /proc/filesystems or
 >> detecting that /dev is RO) and have all the fixup there. That way it
 >> atleast doesn't add any more complications to the rest of Buildroot /
 >> users.

 >  That's a great idea, because it actually simplifies the buildroot code (no
 > longer needed to force devtmpfs in the kernel when mdev is selected).

 >  To detect, it's as simple as:

 > if [ "$(cut -d ' ' -f 2,3 /proc/mounts | sed -n '/^\/dev /s///p')" != devtmpfs ]

Or simply 'grep -q devtmpfs /proc/filesystems'. It doesn't check if /dev
is really a devtmpfs, but as we force DEVTMPFS_MOUNT=y (and the cpio
init wrapper) that is probably good enough.

For mdev, I think it makes more sense to check if /dev is writable, as
that is the really what mdev requires (E.G. we could be in an initramfs
on a <2.6.32 kernel or similar.

-- 
Venlig hilsen,
Peter Korsgaard