From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael S. Zick Date: Tue, 13 Dec 2011 08:58:08 -0600 Subject: [Buildroot] Question about using mdev for /dev management In-Reply-To: <201112130939.34100.arnout@mind.be> References: <4EDD1149.8060104@carallon.com> <201112130939.34100.arnout@mind.be> Message-ID: <201112130858.10405.minimod@morethan.org> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net On Tue December 13 2011, Arnout Vandecappelle wrote: > On Monday 05 December 2011 19:45:29 Will Wagner wrote: > > Firstly it replaces $(TARGET_DIR)/init with fs/cpio/init which attempts > > to mount devtmpfs. My kernel doesn't support this (it's too old) and I'd > > rather not get this trace in the boot (it worries other developers). > > I didn't realize that mdev worked without devtmpfs in the kernel... > It does, and it has for nearly a decade. ;-) With tmpfs sysfs available in the kernel and a tmpfs mounted on /dev - an mdev -s will populate it for you. It was only recent changes to the BR configuration dependences that make (when looking at the BR menu) that mdev/udev requires devtmpfs. That was just a decision by the project to move forward with the new and drop the old but it isn't dropped in the kernel. ;-) Mike > If devtmpfs exists (and it does for all currently supported kernels), then > it should be mounted as soon as possible. It is normally mounted > automatically by the kernel, except when it runs /init for an initramfs. > That's why we have this extra /init script for the cpio rootfs. > > You could add a check to the init script that mounts a normal tmpfs on > /dev if the mount fails (and redirect its output to /dev/null). > > > I assume that for mdev we could not replace init but instead make sure > > that /dev/console (and possibly /dev/null?) exist? > > Yeah, actually, I think /dev/console and /dev/null should be created > on the rootfs even if devtmpfs is used. Which brings us to: > > > > The other small issue I have is that mdev fails to spot one of the > > kernel devices (as the driver doesn't have a sysfs entry) so it needs > > adding manually. I do that by adding an entry to BR2_ROOTFS_DEVICE_TABLE > > which works fine, but doesn't seem ideal as I thought device entries > > were meant to be set in BR2_ROOTFS_STATIC_DEVICE_TABLE, but that is not > > offered unless static devices used. Is there a better way to do this or > > should I just leave it as is? > > If you ask me, it's OK to add /dev entries in the BR2_ROOTFS_DEVICE_TABLE. > In fact, I think /dev/console and /dev/null should be put in there. But > I've never gotten around to roll a patch for it. > > Regards, > Arnout >