On 2020-06-20T11:11:55 -0700, Yonghong Song wrote:
>
>
> On 6/20/20 9:22 AM, Matt Pallissard wrote:
> > New to bpf here.
> >
> > I'm trying to read values out of of mm_struct. I have code like this;
> >
> > unsigned long i[10] = {};
> > struct task_struct *t;
> > struct mm_rss_stat *rss;
> >
> > t = (struct task_struct *)bpf_get_current_task();
> > BPF_CORE_READ_INTO(&rss, t, mm, rss_stat);
> > BPF_CORE_READ_INTO(i, rss, count);
> >
> > However, all values in `i` appear to be 0 (i[MM_FILEPAGES], etc), as if no data gets copied. I'm about 100% confident that this is caused by a glaring oversight on my part.
>
> Maybe you want to check the return value of BPF_CORE_READ_INTO.
> Underlying it is using bpf_probe_read and bpf_probe_read may fail e.g., due
> to major fault.
Doh, I should have known to check the return codes! Yes, it was failing. I knew I was overlooking something trivial.
Thanks a bunch.
Matt Pallissard
