svn commit: r348737 - head/sys/kern

[Ian Lepore]

On Thu, 2019-06-06 at 12:04 -0600, Alan Somers wrote:
> On Thu, Jun 6, 2019 at 12:01 PM John Baldwin <jhb at freebsd.org> wrote:
> > 
> > On 6/6/19 10:39 AM, Alan Somers wrote:
> > > On Thu, Jun 6, 2019 at 11:35 AM Rodney W. Grimes
> > > <freebsd at gndrsh.dnsmgr.net> wrote:
> > > > 
> > > > > Author: asomers
> > > > > Date: Thu Jun  6 15:04:50 2019
> > > > > New Revision: 348737
> > > > > URL: https://svnweb.freebsd.org/changeset/base/348737
> > > > > 
> > > > > Log:
> > > > >   Add a testing facility to manually reclaim a vnode
> > > > > 
> > > > >   Add the debug.try_reclaim_vnode sysctl. When a pathname is
> > > > > written to it, it
> > > > >   will be reclaimed, as long as it isn't already or doomed.
> > > > > The purpose is to
> > > > >   gain test coverage for vnode reclamation, which is
> > > > > otherwise hard to
> > > > >   achieve.
> > > > > 
> > > > >   Add the debug.ftry_reclaim_vnode sysctl.  It does the same
> > > > > thing, except
> > > > >   that its argument is a file descriptor instead of a
> > > > > pathname.
> > > > 
> > > > Should not this all be wrapped in some #ifdef or other
> > > > protection,
> > > > is it really a good idea to have this on every single box
> > > > running
> > > > FreeBSD?
> > > 
> > > I initially thought so too, but kib thought that it could be
> > > useful
> > > for debugging problems in the field.  The potential downside is
> > > limited, because only root can write to the sysctls, and the
> > > worse-case damage is similar to a "umount -f".
> > 
> > A compromise might be to stick this in a kernel module instead of
> > in the
> > base kernel.  You could still kldload it in the field for debugging
> > but
> > not necessarily have it directly available out of the box.
> > 
> > --
> > John Baldwin
> 
> If we already had such a module, it would make sense to put these
> sysctls in there.  But I don't want to create an entire module for
> just a few dozen LOC.  Nor do I want to mediate a bike shed.  So
> let's
> vote.  kib already registered a vote for making them available all of
> the time.  rgrimes voted to guard them by INVARIANTS.  Anybody else
> who cares can reply to this thread.  I'll count the votes in 24
> hours.
> -Alan
> 

If our new policy is to remove sysctls that aren't used often "because
something bad might happen" (without any requirement for the complainer
to elaborate on just what might happen or why it's so much worse than
the damage a root user could do with any other sysctl), I think several
people could be employed full time doing that removal work.  Or we
could all just get on with doing some real work.

-- Ian