On 4/27/20 8:33 PM, Andrew Morton wrote:

On Mon, 27 Apr 2020 20:04:29 +0200 Vlastimil Babka [off-list ref] wrote:

quoted

...
 
+	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