Hi Ludo, On Mon, 12 Mar 2018 23:14:59 +0100 ludo@gnu.org (Ludovic Courtès) wrote: > > One of the devnames created statically is the one for btrfs, so not writing or > > using devnames is not going to end well. > > We’re fine because btrfs, 9p, overlay, etc. all have an “fs-btrfs”, > “fs-9p”, etc. alias, which shows up in “modules.alias”. No need for > “modules.devname” AFAICS. The other filesystems are not such a problem - but BTRFS has its own snapshotting/ multivolume functionality - and it's possible that someone accesses /dev/btrfs-control "too early" for that. I applied your patches to a fresh clone of guix master now, ran the btrfs-root-os system check, and indeed I get (tried two rounds, happened both times): $ make TESTS=btrfs-root-os check-system [...] Scanning for Btrfs filesystems WARNING: failed to open /dev/btrfs-control, skipping device registration: No suy ERROR: there are 1 errors while registering devices File system check on /dev/vda2 failed; spawning Bourne-like REPL GNU Guile 2.2.3 Copyright (C) 1995-2017 Free Software Foundation, Inc. Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'. This program is free software, and you are welcome to redistribute it under certain conditions; type `,show c' for details. Enter `,help' for help. (can't evaluate anything here) > > (I'd also copy the modules.builtin (from Linux). > > Also, what happens if we load a module which has as dependency a builtin? > > Will we try to load the builtin as a .ko file and fail the entire thing?) > > The dependency of a builtin is necessarily a builtin, Yes. >and the kernel won’t invoke modprobe for a builtin, will it? I've read Linux's __request_module and I can't find where they pre-check anything - neither whether there's already a builtin nor whether it's loaded already. They probably don't check. But I'll read it again, more carefully... (request_module isn't that popular so it makes sense for them not to complicate the kernel by these checks when there are like 8 callers in total - and all on init) >Thanks for the insightful review! You're welcome :)