[Pkg-sysvinit-devel] Bug#539352: Bug#539352: /etc/init.d/mountkernfs.sh: Please mount debugfs when available in the kernel

[Henrique de Moraes Holschuh]

On Sat, 01 Aug 2009, Josh Triplett wrote:
> On Fri, Jul 31, 2009 at 11:33:28PM +0200, Petter Reinholdtsen wrote:
> > [Josh Triplett]
> > > Please consider automatically mounting debugfs on /sys/kernel/debug
> > > when available.
> > 
> > Why should this be done in the init.d scripts installed on each Debian
> > system, and not in some special package handling debugfs?  What is
> > debugfs and who is using it?
> 
> debugfs provides an interface to in-kernel tracing and debugging
> facilities.  The Debian kernels have debugfs available.  Various

Eh?  It is supposed to provide an interface to in-kernel *KERNEL* debugging
facilities.  It is NOT covered by the stable kernel-userspace ABI rules (in
fact, debugfs is the only thing that isn't covered by those rules), and we
(userspace distros) *REALLY* want to make a major pest of ourselves to
anyone trying to abuse debugfs in kernel-land to avoid doing his interface
design properly on sysfs, relayfs, /dev, or using netlink...

> subsystems have debugfs interfaces, including ftrace, usbmon, dri, kvm,
> and wireless.

IMHO, we should support it, yes.  In /etc/fstab but using "noauto".

> I'd suggest mounting debugfs by default because doing so will allow
> tracing tools like sysprof (packaged in Debian) and trace-cmd to work
> without additional configuration.  Mounting debugfs does not entail any
> overhead apart from the time for one call to mount.

Are you sure?  It should at least waste some memory for inodes and other
crap.  It is also the sort of thing one would *expect* to often disclose a
lot more information about devices, device drivers, etc.  And also to have
people be even less careful about security issues than normal.  I *wouldn't*
like it mounted with anything but mode 0700 on any system of mine, and I'd
rather not have it mounted at all.

> Note that /etc/fstab seems like the *wrong* place to mount debugfs,
> because that would generate an error if booting a kernel without
> debugfs, and because that would require additional configuration before
> packages using debugfs would work.

It generates no errors if you give it the "noauto" option ;-)

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh