[Cluster-devel] [PATCH dlm-tool] dlm_controld: better uevent filtering

[Alexander Aring]

Hi,

On Mon, Jan 16, 2023 at 5:36 AM Steven Whitehouse <swhiteho at redhat.com> wrote:
>
> Hi,
>
> On Fri, 2023-01-13 at 17:43 -0500, Alexander Aring wrote:
> > When I did test with dlm_locktorture module I got several log
> > messages
> > about:
> >
> > uevent message has 3 args: add@/module/dlm_locktorture
> > uevent message has 3 args: remove@/module/dlm_locktorture
> >
> > which are not expected and not able to parse by dlm_controld
> > process_uevent() function, because mismatch of argument counts.
> > Debugging it more, I figured out that those uevents are for
> > loading/unloading the dlm_locktorture module and there are uevents
> > for
> > loading and unloading modules which have nothing todo with dlm
> > lockspace
> > uevent handling.
> >
> > The current filter works as:
> >
> > if (!strstr(buf, "dlm"))
> >
> I think that is the problem. If you want to filter out all events
> except those sent by the DLM module, then you need to look at the
> variables sent along with the request. Otherwise whatever string you
> look for here might appear in some other random request from a
> different subsystem. The event variables are much easier to parse than
> the actual event string...
>
> See a similar example in decode_uevent(), etc here:
>
> https://github.com/andyprice/gfs2-utils/blob/91c3e9a69ed70d3d522f5b47015da5e5868722ec/group/gfs_controld/main.c
>
> There are probably nicer ways of doing that, than what I did there, but
> it makes it is easier to get at the variables that are passed with the
> notification, than to try and parse the first line of the response,

This requires us to switch to the kernel uevent trigger function call
from kobject_uevent() [0] to kobject_uevent_env() [1], because we
don't have those envs like SUBSYSTEM being sent right now.
I was curious because I was sure that I printed out the "raw string"
from udev netlink socket and didn't see those envs, otherwise I
probably would use it if I saw those. Now I figured out we need to
have a UAPI change for that.

Unfortunately, for me it looks like older dlm_controld versions cannot
handle such change.

- Alex

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/dlm/lockspace.c?h=v6.2-rc4#n200
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kobject_uevent.c?h=v6.2-rc4#n447