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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Wenbo Zhang <ethercflow@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Brendan Gregg <bgregg@netflix.com>,
	Florent Revest <revest@chromium.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v9 bpf-next 10/14] bpf: Add d_path helper
Date: Tue, 4 Aug 2020 23:35:53 -0700
Message-ID: <CAEf4BzY5b8GhoovkKZgT4YSUUW=GPZBU0Qjg4eqeHNjoPHCMTw@mail.gmail.com> (raw)
In-Reply-To: <20200801170322.75218-11-jolsa@kernel.org>

On Sat, Aug 1, 2020 at 10:04 AM Jiri Olsa <jolsa@kernel.org> 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@kernel.org>
> ---
>  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;
> +}
> +

[...]

  parent reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-01 17:03 [PATCH v9 bpf-next 00/14] " Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 01/14] tools resolve_btfids: Add size check to get_id function Jiri Olsa
2020-08-05  6:00   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 02/14] tools resolve_btfids: Add support for set symbols Jiri Olsa
2020-08-05  6:04   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 03/14] bpf: Move btf_resolve_size into __btf_resolve_size Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 04/14] bpf: Add elem_id pointer as argument to __btf_resolve_size Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 05/14] bpf: Add type_id " Jiri Olsa
2020-08-05  6:05   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 06/14] bpf: Remove recursion call in btf_struct_access Jiri Olsa
2020-08-05  6:12   ` Andrii Nakryiko
2020-08-05 17:36     ` Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 07/14] bpf: Factor btf_struct_access function Jiri Olsa
2020-08-05  6:18   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 08/14] bpf: Add btf_struct_ids_match function Jiri Olsa
2020-08-05  6:27   ` Andrii Nakryiko
2020-08-05 17:56     ` Jiri Olsa
2020-08-05 21:31       ` Jiri Olsa
2020-08-05 21:57         ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 09/14] bpf: Add BTF_SET_START/END macros Jiri Olsa
2020-08-05  6:29   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 10/14] bpf: Add d_path helper Jiri Olsa
2020-08-02  3:13   ` Alexei Starovoitov
2020-08-02 18:26     ` Jiri Olsa
2020-08-05  6:35   ` Andrii Nakryiko [this message]
2020-08-05 17:58     ` Jiri Olsa
2020-08-05 21:01       ` Jiri Olsa
2020-08-05 21:09         ` Andrii Nakryiko
2020-08-07  0:31   ` KP Singh
2020-08-07  8:35     ` Jiri Olsa
2020-08-07  9:42       ` KP Singh
2020-08-01 17:03 ` [PATCH v9 bpf-next 11/14] bpf: Update .BTF_ids section in btf.rst with sets info Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 12/14] selftests/bpf: Add verifier test for d_path helper Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 13/14] selftests/bpf: Add " Jiri Olsa
2020-08-05  6:40   ` Andrii Nakryiko
2020-08-05 18:00     ` Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 14/14] selftests/bpf: Add set test to resolve_btfids Jiri Olsa
2020-08-05  6:41   ` Andrii Nakryiko

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