Re: [Xenomai-core] [PATCH 00/23] [git pull] procfs overflow fixes and seq_file conversions

[Philippe Gerum <rpm@xenomai.org>]

On Mon, 2010-04-26 at 19:09 +0200, Gilles Chanteperdrix wrote: 
> Jan Kiszka wrote:
> > Jan Kiszka wrote:
> >> The following changes since commit 113ea4d56e8b215cb56ae7673013163ea5a5987d:
> >>   Gilles Chanteperdrix (1):
> >>         switchtest: increase stack sizes
> >>
> >> are available in the git repository at:
> >>
> >>   git://git.xenomai.org/xenomai-jki.git queues/proc
> >>
> >> This series fixes some of the potential (but when they happen fatal)
> >> overflows in our procfs outputs. Specifically, it fixes all issues in
> >> RTDM (one of them hit us in the field) and the recently reported
> >> overflow in /proc/xenomai/heap. Moreover, Wolfgang started the lengthy
> >> conversion of the registry by introducing a new seq_file-based interface
> >> and already moving the native skin over.
> >>
> >> The future belongs to seq_file, so some of the patches are strictly
> >> spoken not yet required. But we better start this effort before the last
> >> legacy interface user was converted and the old interface is suddenly
> >> dropped from the kernel. This may not be that far away. A patch of mine
> >> to improve error reporting of the old interface was rejected with
> >> "->read_proc is going to be removed, so there is no point."
> > 
> > Did you already have a chance to look into this series?
> 
> Not yet, that is a big series. With a high potential for kernel crashes,
> memory leaks and other things like that. I am trying to find a way to
> test it. Maybe we can try and run it with kmemcheck?
> 

Looking at this series, I eventually made my mind about the kind of
support I'd wish in this area. It boils down to:

- getting rid of the PAGE_SIZE limitation on read as this series does,
- reducing the impact on latency of large outputs,
- hiding discrepancies between linux kernel
releases, regarding the proper way to export kernel object states
to userland (like the planned deprecation of read procs).
- providing a common encapsulation to do that, which brings all the
previous properties in a normalized way, and helps removing direct
dependencies of other core code on PROC_FS
- rebasing the registry support on top of this feature, so that skins
are automatically feature-enabled when going through the registry to
export stuff to userland (as they should).

To this end, I came up with the so-called "virtual file" (aka vfile)
support for the nucleus, and have toyed with those ideas here: 
git://git.xenomai.org/xenomai-rpm.git	queue/vfile

This is still early work in progress, not all the codebase was converted
to use the vfiles (registry and native API were), and I tested the
result only in a very limited manner; so this is not for inclusion into
2.5.x given the amount of code that touches anyway. But I will likely
submit this for inclusion at some point into any upcoming 2.6.x, if
vfiles turn out to fit the job.

-- 
Philippe.