Posted Nov 21, 2012 21:28 UTC (Wed) by mezcalero (subscriber, #45103)
Parent article: Gentoo's udev fork
Ahem, it would be nice to mention that there's actually nothing in upstream *udev* that would make split-off /usr impossible or that would even complain about it. Let's clarify this:
a) *udev* doesn't care at all whether /usr is split off.
b) *systemd* will print a *warning* at boot if /usr is not found to be pre-mounted. But that's systemd, not udev. If you don't use systemd, then you will never see this warning. Despite this warning systemd will continue to go on booting, and will in itself not create any problems, as we carefully made sure that the build tree is neatly separated in stuff that goes into / and stuff that goes into /usr if split-off /usr is used, to make this all work. All you need to do for that is use --prefix= and --with-rootprefix= on the configure command line with the right path names.
c) systemd is hence merely the messenger and supports split-off /usr just fine, and if you don't use systemd but only udev, then you won't notice anything at all that has changed.
Hence: the Gentoo Tea Party never used systemd, so they never saw the warning, and even if they had, then it would just have been a warning, and that's it. The split-off /usr thing is hence nothing but a red herring.
And: there's nothing to fix in udev about this. Nothing at all. To make udev itself work fine on split-off /usr requires exactly ZERO patches, because it supports that just fine, out-of-the-box.
Of course, ignoring the warning we print won't win you anything, as you still need to fix the rest of the stack to support split-off /usr. There's simply way too much code in our stack that assumes /usr was already there in early boot. And this is also documented in detail here: http://freedesktop.org/wiki/Software/systemd/separate-usr... -- there's also an non-comprehensive list of packages that are broken in this regard. And again: systemd/udev is not one of those broken packages.
May I ask the editors to update the article to clarify that split-off /usr cannot be fixed by forking udev, because there simply is nothing to fix. In particularly the sentence "Whether a fork like eudev can address those concerns remains to be seen." appears very much misleading to me.