Le 22/08/2017 à 01:27, Adam Borowski a écrit :
Hi!
Do you remember when for decades we had to populate /dev using mknod
(using makedev or something) -- both on Linux and on Unices that predated
it? Then when udev came to make device creation dynamic.
I just installed a new server, not using d-i but manual debootstrap. Not
even regular debootstrap but with --variant=minbase as --exclude is still
buggy and fails to exclude THE THING THAT SHOULDN'T BE NAMED. Everything
worked fine, except for one detail: somehow /dev/ttyUSB* were mode 600
root:root instead of 660 root:dialout.
Turns out, udev was not installed. Nor mdev, nothing. No initrd either.
Yet it boots and works correctly. fstab has no entries except for / -- and
even this is pointless if you mount rootfs rw on cmdline (the ro + remount
dance does nothing good on any modern fs other than ext4). If there was any
userland configuration, it is done by openrc by default.
Hotplugging USB devices seems to work fine, new nodes get created without
udev's involvement.
Obviously, I guess running without udev is a bad idea in the long run -- you
want correct permissions to get applied, hotplug hooks to be run, etc. But
this suggests 90% of udev/mdev/vdev code can be thrown out.
That the kernel can now do most of this work by itself is news to me.
This is the result of enabling devtmpfs when building the kernel.
Devtmpfs was implemented a few years ago and is, in my opinion, a
reaction of the bad behaviour of Udev developpers. For the same reason
(explicitely), the kernel now loads the firmware automatically instead
of requesting it to the hotplugger. Definitely, the hotplugger has less
and less to do, and, definitely, I think Mdev could do it pretty well.
Didier
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