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From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	linux-mm@kvack.org, Ivan Teterevkov <ivan.teterevkov@nutanix.com>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	"Guilherme G . Piccoli" <gpiccoli@canonical.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v3 1/5] kernel/sysctl: support setting sysctl parameters from kernel command line
Date: Tue, 28 Apr 2020 12:18:24 +0200	[thread overview]
Message-ID: <20200428101824.GM28637@dhcp22.suse.cz> (raw)
In-Reply-To: <d7d01e9e-6b6d-47ce-c750-cd7296e30613@suse.cz>

On Tue 28-04-20 10:09:37, Vlastimil Babka wrote:
> On 4/27/20 8:33 PM, Andrew Morton wrote:
> > On Mon, 27 Apr 2020 20:04:29 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:
> > 
> > > ...
> > > +	sysctl.*=	[KNL]
> > > +			Set a sysctl parameter, right before loading the init
> > > +			process, as if the value was written to the respective
> > > +			/proc/sys/... file. Both '.' and '/' are recognized as
> > > +			separators. Unrecognized parameters and invalid values
> > > +			are reported in the kernel log. Sysctls registered
> > > +			later by a loaded module cannot be set this way.
> > > +			Example: sysctl.vm.swappiness=40
> > 
> > Why support "."?  I think only supporting "/" is perfectly adequate and
> > simplifies documentation.  It aligns the command-line syntax with the
> > rest of the sysctl documentation.  I'm not seeing the need to provide
> > two ways of doing the same thing?
> 
> AFAIK the "." is traditional, and "/" is a newer artefact of moving from the
> binary syscall form to procfs based form. So by "command-line syntax" you
> mean echo and cat, not sysctl tool? Because "man sysctl" says:
> 
> variable
> 	The name of a key to read from.  An example is kernel.ostype.  The '/'
> separator is also accepted in place of a '.'.
> 
> So I'm not strongly against supporting only / but I expect most people are
> used to the . and it will take them two attempts to pass the sysctl boot
> parameter correctly if they don't use it regularly - first trying . form,
> wonder why it doesn't work, then read the doc and realize it's not
> supported?

Yes, I do agree. I have only recently learned that sysctl supports / as
well. Most people are simply used to . notation. The copy of the arch
and . -> / substitution is a trivial operation and I do not think it is
a real reason to introduce unnecessarily harder to use interface.
-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2020-04-28 10:18 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-27 18:04 [PATCH v3 0/5] support setting sysctl parameters from kernel command line Vlastimil Babka
2020-04-27 18:04 ` [PATCH v3 1/5] kernel/sysctl: " Vlastimil Babka
2020-04-27 18:33   ` Andrew Morton
2020-04-28  8:09     ` Vlastimil Babka
2020-04-28 10:18       ` Michal Hocko [this message]
2020-04-27 18:04 ` [PATCH v3 2/5] kernel/sysctl: support handling command line aliases Vlastimil Babka
2020-04-27 18:04 ` [PATCH v3 3/5] kernel/hung_task convert hung_task_panic boot parameter to sysctl Vlastimil Babka
2020-04-27 18:04 ` [PATCH v3 4/5] tools/testing/selftests/sysctl/sysctl.sh: support CONFIG_TEST_SYSCTL=y Vlastimil Babka
2020-04-27 18:39   ` Luis Chamberlain
2020-04-27 18:04 ` [PATCH v3 5/5] lib/test_sysctl: support testing of sysctl. boot parameter Vlastimil Babka
2020-04-27 18:39   ` Luis Chamberlain
2020-05-11 11:05     ` Vlastimil Babka
2020-05-11 18:31       ` Luis Chamberlain
2020-05-13  8:58         ` Vlastimil Babka
2020-05-13 13:15           ` Luis Chamberlain
2020-05-13 13:17             ` Luis Chamberlain
2020-05-15 16:02               ` Vlastimil Babka

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