Re: [RFC] CONFIG_FORCE_MINIMALLY_SANE_CONFIG=y (was: Re: [RFC PATCH] x86/kconfig: Sanity-check config file during oldconfig)

[Ingo Molnar <mingo@kernel.org>]

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Jan 19, 2016 at 09:20:22AM +0100, Ingo Molnar wrote:
> > +	# newer systemd silently relies on the presence of the epoll system call:
> > +	select EPOLL
> > +	select ANON_INODES
> > +
> > +	# newer systemd silently hangs durig early init without these:
> > +	select PROC_SYSCTL
> > +	select SYSCTL
> > +	select POSIX_MQUEUE
> > +	select POSIX_MQUEUE_SYSCTL
> > +
> > +	# systemd needs this syscall:
> > +	select FHANDLE
> > +
> > +	# systemd needs devtmpfs: "systemd[1]: Failed to mount devtmpfs at /dev: No such device"
> > +	select DEVTMPFS
> > +
> > +	# systemd needs tmpfs: "systemd[1]: Failed to mount tmpfs at /sys/fs/cgroup: No such file or directory"
> > +	select SHMEM
> > +	select TMPFS
> > +
> > +	# systemd needs timerfd syscalls: "[    8.198625] systemd[1]: Failed to create timerfd: Function not implemented^"
> > +	select TIMERFD
> > +
> > +	# systemd needs signalfd support: "[   45.536725] systemd[1]: Failed to allocate manager object: Function not implemented"
> > +	select SIGNALFD
> > +
> > +	# systemd hangs during bootup without cgroup support:
> > +	select CGROUPS
> > +
> > +	# systemd fails during bootup without this option, with a nonsensical message: "[DEPEND] Dependency failed for File System Check on /dev/sda1."
> > +	select FILE_LOCKING
> > +
> > +	# systemd fails during bootup without this option:
> > +	select FSNOTIFY
> > +	select INOTIFY_USER
> 
> > And yes, many of these options are members of the 'SystemD debuggability Hall Of 
> > Shame'... It cost me many, many days of painful config-bisection to figure the 
> > often obscure dependencies out, so we might as well upstream this information.
> > 
> > Many braincells died to bring us this information!
> 
> So why not group those under CONFIG_SYSTEMD_BLOWS? I still dont have a
> machine with that turd on.

I'd definitely (try to) list the reasons for each quirk in the Kconfig lines (as I 
did above), but I'd still keep a single generic option not tied to systemd in 
particular, for the following reasons:

 - I am using many systemd systems, so the quirks are naturally mostly systemd
   related. There might be more non-systemd quirks that I never triggered
   personally. They can be added once people trigger them.

 - Also, even that considered, not all of the options I listed are systemd quirks,
   as I still have a single (albeit simple) non-systemd test machine.

 - I'd like to have a single superset option that principally makes the kernel
   'just work' for newbie testers - without them having to be even aware of
   whether their distro version uses systemd or something else.

Thanks,

	Ingo