On Tue, Aug 04, 2020 at 11:35:53PM -0700, Andrii Nakryiko wrote:
> On Sat, Aug 1, 2020 at 10:04 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding d_path helper function that returns full path for
> > given 'struct path' object, which needs to be the kernel
> > BTF 'path' object. The path is returned in buffer provided
> > 'buf' of size 'sz' and is zero terminated.
> >
> > bpf_d_path(&file->f_path, buf, size);
> >
> > The helper calls directly d_path function, so there's only
> > limited set of function it can be called from. Adding just
> > very modest set for the start.
> >
> > Updating also bpf.h tools uapi header and adding 'path' to
> > bpf_helpers_doc.py script.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 13 +++++++++
> > kernel/trace/bpf_trace.c | 48 ++++++++++++++++++++++++++++++++++
> > scripts/bpf_helpers_doc.py | 2 ++
> > tools/include/uapi/linux/bpf.h | 13 +++++++++
> > 4 files changed, 76 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index eb5e0c38eb2c..a356ea1357bf 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3389,6 +3389,18 @@ union bpf_attr {
> > * A non-negative value equal to or less than *size* on success,
> > * or a negative error in case of failure.
> > *
> > + * int bpf_d_path(struct path *path, char *buf, u32 sz)
>
> nit: probably would be good to do `const struct path *` here, even if
> we don't do const-ification properly in all helpers.
ok
>
> > + * Description
> > + * Return full path for given 'struct path' object, which
> > + * needs to be the kernel BTF 'path' object. The path is
> > + * returned in buffer provided 'buf' of size 'sz' and
>
> typo: in the provided buffer 'buf' of size ... ?
ugh, sure
>
> > + * is zero terminated.
> > + *
> > + * Return
> > + * On success, the strictly positive length of the string,
> > + * including the trailing NUL character. On error, a negative
> > + * value.
> > + *
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -3533,6 +3545,7 @@ union bpf_attr {
> > FN(skc_to_tcp_request_sock), \
> > FN(skc_to_udp6_sock), \
> > FN(get_task_stack), \
> > + FN(d_path), \
> > /* */
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index cb91ef902cc4..02a76e246545 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1098,6 +1098,52 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = {
> > .arg1_type = ARG_ANYTHING,
> > };
> >
> > +BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz)
> > +{
> > + int len;
> > + char *p;
> > +
> > + if (!sz)
> > + return -ENAMETOOLONG;
>
> if we are modeling this after bpf_probe_read_str(), sz == 0 returns
> success and just does nothing. I don't think anyone will ever handle
> or expect this error. I'd just return 0.
ook
thanks,
jirka
