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.
> + * 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 ... ?
> + * 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.
> +
> + p = d_path(path, buf, sz);
> + if (IS_ERR(p)) {
> + len = PTR_ERR(p);
> + } else {
> + len = buf + sz - p;
> + memmove(buf, p, len);
> + }
> +
> + return len;
> +}
> +
[...]
