On Mon, 2017-09-11 at 21:47 +0200, Raphael Hertzog wrote: > Hi Ben, > > On Mon, 11 Sep 2017, Ben Hutchings wrote: > > The answer seems to be that udev doesn't just listen for device events, > > but also uses inotify to watch block devices. But inotify operates on > > inodes, not the underlying devices. The chroot has a separate /dev > > directory and inodes, so writing to a block device through one of those > > inodes doesn't trigger the inotify watch. > > > > If I bind-mount /dev into the chroot before running mkfs there, udev > > does see the change events because mkfs opens the inodes that it's > > watching. > > This is strange because schroot does bind-mount /dev in the default > profile that I used: > $ grep profile /etc/schroot/chroot.d/sid-amd64 > profile=default > profile=default > $ grep /dev /etc/schroot/default/fstab > /dev /dev none rw,bind 0 0 > /dev/pts /dev/pts none rw,bind 0 0 > /dev/shm /dev/shm none rw,bind 0 0 > > (and a stat call inside the chroot and outside of it returns the same inode > number and the same device number)
Then I don't know what's going wrong in your chroot environment. > > So this is a limitation of udev and of the kernel's inotify interface, > > but I don't think it's a bug in either of them. vmdebootstrap should > > not assume that udev will notice changes made by mkfs unless they are > > operating on the same /dev filesystem (and even then, it should use > > 'udevadm settle' to avoid races). > > Assuming your analysis is right, what would be the right course of action? > > Calling "udevadm trigger <block-device>" after the mkfs call? I think that's right... except now I wonder whether it's reasonable to assume udevadm in a chroot can talk to udev on the outside. It looks like they would have to share /run/udev/control. It seems like maybe vmdebootstrap shouldn't be used in a chroot. Ben. > FWIW, this udevadm trigger call does work (as in the missing symlink gets > created)... and it works when called outside of the chroot but also when > called > within the chroot. > > And thanks for the investigation you made! -- Ben Hutchings Kids! Bringing about Armageddon can be dangerous. Do not attempt it in your own home. - Terry Pratchett and Neil Gaiman, `Good Omens'
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