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

[Josh Triplett]

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

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.

mountkernfs already mounts other kernel filesystems, so it seemed like
the right place to mount debugfs.  Obviously a debugfs-common package
could do the same thing, and packages which want to have debugfs enabled
by default could depend on that; on the other hand, it seems somewhat
silly to have a package for a five-line init script.

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.

- Josh Triplett