On 10/10/2014 18:00, Bruce Dubbs wrote: > Anthony Wright wrote: >> I'm running a modified version of LFS 7.5 where I have an initramfs that >> populates /dev/ with busybox's mdev before handing over to the udevd >> that's part of LFS 7.5 >> >> Everything seemed to be fine until a partitioned a disk and discovered >> that the partition device nodes weren't created by udevd. When I do >> 'udevadm info -e' it lists the /dev/sda1, /dev/sda2 devices but they >> don't exists in /dev. >> >> I deleted all of /dev, re-created /dev/null and then tried to get udevd >> to re-populate it using the standard LFS commands (run udevd, then call >> udevadm trigger). However, while udevadm info listed all the devices, it >> only created a few symbolic links and did no mknod()s at all. >> >> I tried to track down the issue in the udev code with a view to putting >> in some debugging patches. However, while I can find a few mknod calls >> inside systemd, I can't find any that look like they are used by udev to >> create the device nodes in /dev/. >> >> Could anybody explain how the actual mknod() calls are made but udev. >> Are the calls made by udev itself or does it call out to something else >> to do this final step. Does it use mknod() to create the /dev entries or >> is there another mechanism that I'm unaware of. > > udev does not create the devices. The kernel does. What udev does is > create symlinks, change permissions, ownership, etc. Look at the udev > rules to see. > > -- Bruce > I spent the whole day looking at this, and finally discovered the devtmpfs filesystem. Version 176 of udev switched from using a tmpfs for /dev and doing the mknod()s itself to using a devtmpfs for /dev and letting the kernel do the mknod()s for it. This was particularly confusing for me since everybody says the purpose of udev is to populate /dev, and clearly that's not it's purpose any more.
Given that udev's role has clearly changed, I'd like to understand what it's role is now. It seems to be involved in doing the modprobes, but does it do more than that now? -- http://lists.linuxfromscratch.org/listinfo/lfs-support FAQ: http://www.linuxfromscratch.org/blfs/faq.html Unsubscribe: See the above information page Do not top post on this list. A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? http://en.wikipedia.org/wiki/Posting_style
