Re: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line

[Michal Hocko <mhocko@kernel.org>]

On Wed 25-03-20 17:20:40, Eric W. Biederman wrote:
> Vlastimil Babka <vbabka@suse.cz> writes:
[...]
> > +	if (strncmp(param, "sysctl.", sizeof("sysctl.") - 1))
> > +		return 0;
> 
> Is there any way we can use a slash separated path.  I know
> in practice there are not any sysctl names that don't have
> a '.' in them but why should we artifically limit ourselves?

Because this is the normal userspace interface? Why should it be any
different from calling sysctl?
[...]

> Further it will be faster to lookup the sysctls using the code from
> proc_sysctl.c as it constructs an rbtree of all of the entries in
> a directory.  The code might as well take advantage of that for large
> directories.

Sounds like a good fit for a follow up patch to me. Let's make this
as simple as possible for the initial version. But up to Vlastimil of
course.

[...]

> Hmm.  There is a big gotcha in here and I think it should be mentioned.
> This code only works because no one has done set_fs(KERNEL_DS).  Which
> means this only works with strings that are kernel addresses essentially
> by mistake.  A big fat comment documenting why it is safe to pass in
> kernel addresses to a function that takes a "char __user*" pointer
> would be very good.

Agreed

-- 
Michal Hocko
SUSE Labs