linux-kernel - Re: Why is CONFIG

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Date:   Tue, 31 Dec 2019 02:40:54 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Rob Landley <rob@...dley.net>
Cc:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: Why is CONFIG_VT forced on?

On Mon, Dec 30, 2019 at 08:04:35PM -0600, Rob Landley wrote:
> 
> 
> On 12/30/19 7:45 PM, Rob Landley wrote:
> > On 12/30/19 6:59 PM, Randy Dunlap wrote:
> >> #
> >> # Character devices
> >> #
> >> CONFIG_TTY=y
> >> # CONFIG_VT is not set
> >>
> >> But first you must set/enable EXPERT.  See the bool prompt.
> > 
> > Wait, the if doesn't _disable_ the symbol? It disables _editability_ of the
> > symbol, but the symbol can still be on (and displayed) when the if is false?
> > (Why would...)
> > 
> > Ok. Thanks for pointing that out. Any idea why the menuconfig help text has no
> > mention of this?
> 
> So if I disable CONFIG_EXPERT, using miniconfig I then need to manually switch on:
> 
> ./init/Kconfig:	bool "Namespaces support" if EXPERT
> ./init/Kconfig:	bool "Multiple users, groups and capabilities support" if EXPERT
> ./init/Kconfig:	bool "Sysfs syscall support" if EXPERT
> ./init/Kconfig:	bool "open by fhandle syscalls" if EXPERT
> ./init/Kconfig:	bool "Posix Clocks & timers" if EXPERT
> ./init/Kconfig:	bool "Enable support for printk" if EXPERT
> ./init/Kconfig:	bool "BUG() support" if EXPERT
> ./init/Kconfig:	bool "Enable ELF core dumps" if EXPERT
> ./init/Kconfig:	bool "Enable full-sized data structures for core" if EXPERT
> ./init/Kconfig:	bool "Enable futex support" if EXPERT
> ./init/Kconfig:	bool "Enable eventpoll support" if EXPERT
> ./init/Kconfig:	bool "Enable signalfd() system call" if EXPERT
> ./init/Kconfig:	bool "Enable timerfd() system call" if EXPERT
> ./init/Kconfig:	bool "Enable eventfd() system call" if EXPERT
> ./init/Kconfig:	bool "Use full shmem filesystem" if EXPERT
> ./init/Kconfig:	bool "Enable AIO support" if EXPERT
> ./init/Kconfig:	bool "Enable IO uring support" if EXPERT
> ./init/Kconfig:	bool "Enable madvise/fadvise syscalls" if EXPERT
> ./init/Kconfig:	bool "Enable membarrier() system call" if EXPERT
> ./init/Kconfig:	bool "Load all symbols for debugging/ksymoops" if EXPERT
> ./init/Kconfig:	bool "Enable rseq() system call" if EXPERT
> ./init/Kconfig:	bool "Enabled debugging of rseq() system call" if EXPERT
> ./init/Kconfig:	bool "PC/104 support" if EXPERT
> ./init/Kconfig:	bool "Enable VM event counters for /proc/vmstat" if EXPERT

No.  What you need is
	* actually attempt to flip CONFIG_EXPERT (go to "General setup" submenu and
set "Configure standard kernel features (expert users)" there)
	* check the resulting .config (or look at the items in question via
menuconfig)
	* get enlightened

Rob, if you are in a mood for a long wank, it's your business.  But try to avoid
spraying the results over public lists.