On Wed, Mar 10, 2010 at 4:54 PM, Jochen Kunz <jk...@unixag-kl.fh-kl.de> wrote: > On Wed, 10 Mar 2010 11:53:43 +0900 > Masao Uebayashi <uebay...@gmail.com> wrote: > > [device node ownership and modes on devfs] >> Is it acceptable for you to do such things by some layering? > Anything else but "chown jkunz.users /dev/ttyU0" is awkward to me. > So what ever solution for this problem is introduced (udevd, > rc.script, ...), I have to learn a special way to configure device > node ownership and modes on devfs. > > There could be some devd(8), that listens for ownership and modes > on devfs and stores it on disk. At next boot it could reconstruct > ownership and modes. But this looks a bit fragile to me. > >> > The Linux devfs solved this problem with an init-script, that changed >> > ownership and modes after each reboot. Looked a bit awkward to me when >> > I had to deal with it. >> A bit? I thought udevfs's config file is totally inacceptable for >> missiong critical embedded purposes. Why do we have to learn a new >> syntax to configure only a few device file permissions? > I talked about the long gone Linux devfs, not udev. But it doesn't > matter. Anything else then chmod(1) and chown(8) needs to be learned. > So it doesn't matter what new stuff I have to learn to get it done.
Fair enough. After some thinking, providing "traditional" view and persistent bits turns out to be not that difficult. /dev has a few reserved directory (like /dev/id). You have no freedom there. Any access other than that goes to devfsd. It has knowledge equivalt to sys/arch/*/conf/majors.* as reference. And it tracks mknod(2), rename(2), etc per-mount point. When you do mknod(/dev/wd0a); rename(/dev/wd0a, /dev/woah0a); open(/dev/woah0a), devfsd resoves it by using DBs and converts it to something like /dev/default/wd0a and pass it back to kernel. You have to shutdown cleanly, otherwise you lose DB. Initial mount needs some thought. > BTW: My dayjob is to programm an embedded system running Linux. > A (small) part of my work is to fight with udevd. And those systems > are used in mission critical applications. Are you happy about that? :) Masao
