Re: [PATCH 2/2] moderr: add module error injection tool

[Daniel Gomez]

On Wed, Jan 22, 2025 at 09:02:19AM +0100, Alexei Starovoitov wrote:
> On Wed, Jan 22, 2025 at 5:12 AM Daniel Gomez <da.gomez@xxxxxxxxxxx> wrote:
> >
> > Add support for a module error injection tool. The tool
> > can inject errors in the annotated module kernel functions
> > such as complete_formation(), do_init_module() and
> > module_enable_rodata_after_init(). Module name and module function are
> > required parameters to have control over the error injection.
> >
> > Example: Inject error -22 to module_enable_rodata_ro_after_init for
> > brd module:
> >
> > sudo moderr --modname=brd --modfunc=module_enable_rodata_ro_after_init \
> > --error=-22 --trace
> > Monitoring module error injection... Hit Ctrl-C to end.
> > MODULE     ERROR FUNCTION
> > brd        -22   module_enable_rodata_after_init()
> >
> > Kernel messages:
> > [   89.463690] brd: module loaded
> > [   89.463855] brd: module_enable_rodata_ro_after_init() returned -22,
> > ro_after_init data might still be writable
> >
> > Signed-off-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
> > ---
> >  tools/bpf/Makefile            |  13 ++-
> >  tools/bpf/moderr/.gitignore   |   2 +
> >  tools/bpf/moderr/Makefile     |  95 +++++++++++++++++
> >  tools/bpf/moderr/moderr.bpf.c | 127 +++++++++++++++++++++++
> >  tools/bpf/moderr/moderr.c     | 236 ++++++++++++++++++++++++++++++++++++++++++
> >  tools/bpf/moderr/moderr.h     |  40 +++++++
> >  6 files changed, 510 insertions(+), 3 deletions(-)
> 
> The tool looks useful, but we don't add tools to the kernel repo.
> It has to stay out of tree.

Can you clarify what do you mean? There are other tools under tools/ and tools/
bpf [1].

[1] https://lore.kernel.org/bpf/20200114184230.GA204154@krava/

I will anyway move the tool to the suggested location in the other thread.

> 
> The value of error injection is not clear to me.
> Other places in the kernel use it to test paths in the kernel
> that are difficult to do otherwise.

By any chance do you know which tool are they using?

> These 3 functions don't seem to be in this category.

Luis already answered this.