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[37.188.130.62]) by smtp.gmail.com with ESMTPSA id h3sm24489313wrm.73.2020.04.28.03.18.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2020 03:18:25 -0700 (PDT) Date: Tue, 28 Apr 2020 12:18:24 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Andrew Morton , Luis Chamberlain , Kees Cook , Iurii Zaikin , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , David Rientjes , Matthew Wilcox , "Eric W . Biederman" , "Guilherme G . Piccoli" , Alexey Dobriyan , Thomas Gleixner , Greg Kroah-Hartman , Christian Brauner , Masami Hiramatsu Subject: Re: [PATCH v3 1/5] kernel/sysctl: support setting sysctl parameters from kernel command line Message-ID: <20200428101824.GM28637@dhcp22.suse.cz> References: <20200427180433.7029-1-vbabka@suse.cz> <20200427180433.7029-2-vbabka@suse.cz> <20200427113331.f0c1e8e7cee98644260448d3@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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