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

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