Re: [PATCH v3 1/5] kernel/sysctl: support setting sysctl parameters from kernel command line

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On 4/27/20 8:33 PM, Andrew Morton wrote:
On Mon, 27 Apr 2020 20:04:29 +0200 Vlastimil Babka <vbabka@xxxxxxx> 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?

Vlastimil



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