From: KP Singh <kpsingh@chromium.org>
To: Jiri Olsa <jolsa@redhat.com>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
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>,
Andrii Nakryiko <andriin@fb.com>,
Brendan Gregg <bgregg@netflix.com>,
Florent Revest <revest@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Florent Revest <revest@chromium.org>
Subject: Re: [PATCH v4 bpf-next 10/14] bpf: Add d_path helper
Date: Fri, 17 Jul 2020 01:13:23 +0200 [thread overview]
Message-ID: <6f3fd6b0-cc3d-57e7-0444-dcaf399e6abd@chromium.org> (raw)
In-Reply-To: <20200628194242.GB2988321@krava>
On 6/28/20 9:42 PM, Jiri Olsa wrote:
> On Fri, Jun 26, 2020 at 01:38:27PM -0700, Andrii Nakryiko wrote:
>> On Thu, Jun 25, 2020 at 4:49 PM Jiri Olsa <jolsa@kernel.org> wrote:
>>>
>>> Adding d_path helper function that returns full path
>>> for give 'struct path' object, which needs to be the
>>> kernel BTF 'path' object.
>>>
>>> The helper calls directly d_path function.
>>>
>>> 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 | 14 +++++++++-
>>> kernel/trace/bpf_trace.c | 47 ++++++++++++++++++++++++++++++++++
>>> scripts/bpf_helpers_doc.py | 2 ++
>>> tools/include/uapi/linux/bpf.h | 14 +++++++++-
>>> 4 files changed, 75 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>>> index 0cb8ec948816..23274c81f244 100644
>>> --- a/include/uapi/linux/bpf.h
>>> +++ b/include/uapi/linux/bpf.h
>>> @@ -3285,6 +3285,17 @@ union bpf_attr {
>>> * Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
>>> * Return
>>> * *sk* if casting is valid, or NULL otherwise.
>>> + *
>>> + * int bpf_d_path(struct path *path, char *buf, u32 sz)
>>> + * 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'.
>>> + *
>>> + * Return
>>> + * length of returned string on success, or a negative
>>> + * error in case of failure
>>
>> It's important to note whether string is always zero-terminated (I'm
>> guessing it is, right?).
>
> right, will add
Also note that bpf_probe_read_{kernel, user}_str return the length including
the NUL byte:
* Return
* On success, the strictly positive length of the string,
* including the trailing NUL character. On error, a negative
* value.
It would be good to keep this uniform. So you will need a len += 1 here as well.
- KP
>
>>
>>> + *
>>> */
>>> #define __BPF_FUNC_MAPPER(FN) \
>>> FN(unspec), \
>>> @@ -3427,7 +3438,8 @@ union bpf_attr {
>>> FN(skc_to_tcp_sock), \
>>> FN(skc_to_tcp_timewait_sock), \
>>> FN(skc_to_tcp_request_sock), \
>>> - FN(skc_to_udp6_sock),
>>> + FN(skc_to_udp6_sock), \
>>> + FN(d_path),
>>>
>>> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>>> * function eBPF program intends to call
>>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>>> index b124d468688c..6f31e21565b6 100644
>>> --- a/kernel/trace/bpf_trace.c
>>> +++ b/kernel/trace/bpf_trace.c
>>> @@ -1060,6 +1060,51 @@ 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)
>>> +{
>>> + char *p = d_path(path, buf, sz - 1);
>>> + int len;
>>> +
>>> + if (IS_ERR(p)) {
>>> + len = PTR_ERR(p);
>>> + } else {
>>> + len = strlen(p);
>>> + if (len && p != buf) {
>>> + memmove(buf, p, len);
>>> + buf[len] = 0;
>>
>> if len above is zero, you won't zero-terminate it, so probably better
>> to move buf[len] = 0 out of if to do unconditionally
>
> good catch, will change
>
>>
>>> + }
>>> + }
>>> +
>>> + return len;
>>> +}
>>> +
>>> +BTF_SET_START(btf_whitelist_d_path)
>>> +BTF_ID(func, vfs_truncate)
>>> +BTF_ID(func, vfs_fallocate)
>>> +BTF_ID(func, dentry_open)
>>> +BTF_ID(func, vfs_getattr)
>>> +BTF_ID(func, filp_close)
>>> +BTF_SET_END(btf_whitelist_d_path)
>>> +
>>> +static bool bpf_d_path_allowed(const struct bpf_prog *prog)
>>> +{
>>> + return btf_id_set_contains(&btf_whitelist_d_path, prog->aux->attach_btf_id);
>>> +}
>>> +
>>
>> This looks pretty great and clean, considering what's happening under
>> the covers. Nice work, thanks a lot!
>>
>>> +BTF_ID_LIST(bpf_d_path_btf_ids)
>>> +BTF_ID(struct, path)
>>
>> this is a bit more confusing to read and error-prone, but I couldn't
>> come up with any better way to do this... Still better than
>> alternatives.
>>
>>> +
>>> +static const struct bpf_func_proto bpf_d_path_proto = {
>>> + .func = bpf_d_path,
>>> + .gpl_only = true,
>>
>> Does it have to be GPL-only? What's the criteria? Sorry if this was
>> brought up previously.
>
> I don't think it's needed to be gpl_only, I'll set it to false
>
> thanks,
> jirka
>
next prev parent reply other threads:[~2020-07-16 23:13 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 22:12 [PATCH v4 bpf-next 00/14] bpf: Add d_path helper Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 01/14] bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object Jiri Olsa
2020-06-26 20:53 ` Andrii Nakryiko
2020-06-26 21:09 ` Yonghong Song
2020-06-28 19:09 ` Alexei Starovoitov
2020-06-28 19:35 ` Jiri Olsa
2020-06-28 20:53 ` Yonghong Song
2020-06-25 22:12 ` [PATCH v4 bpf-next 02/14] bpf: Compile resolve_btfids tool at kernel compilation start Jiri Olsa
2020-06-26 21:28 ` Andrii Nakryiko
2020-06-28 19:48 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 03/14] bpf: Add BTF_ID_LIST/BTF_ID macros Jiri Olsa
2020-06-26 21:32 ` Andrii Nakryiko
2020-06-28 19:50 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 04/14] bpf: Resolve BTF IDs in vmlinux image Jiri Olsa
2020-06-26 21:34 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 05/14] bpf: Remove btf_id helpers resolving Jiri Olsa
2020-06-26 21:36 ` Yonghong Song
2020-06-26 21:40 ` Andrii Nakryiko
2020-06-26 23:29 ` Yonghong Song
2020-06-28 18:50 ` Alexei Starovoitov
2020-06-28 20:00 ` Andrii Nakryiko
2020-06-28 20:16 ` Jiri Olsa
2020-06-28 20:59 ` Yonghong Song
2020-06-28 21:20 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 06/14] bpf: Use BTF_ID to resolve bpf_ctx_convert struct Jiri Olsa
2020-06-26 21:44 ` Andrii Nakryiko
2020-06-26 21:44 ` Yonghong Song
2020-06-28 19:52 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 07/14] bpf: Allow nested BTF object to be refferenced by BTF object + offset Jiri Olsa
2020-06-30 1:52 ` Andrii Nakryiko
2020-06-30 13:54 ` Jiri Olsa
2020-06-30 20:05 ` Andrii Nakryiko
2020-06-30 20:07 ` Andrii Nakryiko
2020-07-02 10:08 ` Jiri Olsa
2020-07-06 23:15 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 08/14] bpf: Add BTF_SET_START/END macros Jiri Olsa
2020-06-26 21:49 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 09/14] bpf: Add info about .BTF.ids section to btf.rst Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 10/14] bpf: Add d_path helper Jiri Olsa
2020-06-26 20:38 ` Andrii Nakryiko
2020-06-28 19:42 ` Jiri Olsa
2020-07-16 23:13 ` KP Singh [this message]
2020-07-17 8:28 ` Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 11/14] tools headers: Adopt verbatim copy of btf_ids.h from kernel sources Jiri Olsa
2020-06-26 21:51 ` Andrii Nakryiko
2020-06-25 22:13 ` [PATCH v4 bpf-next 12/14] selftests/bpf: Add verifier test for d_path helper Jiri Olsa
2020-06-30 1:30 ` Andrii Nakryiko
2020-06-25 22:13 ` [PATCH v4 bpf-next 13/14] selftests/bpf: Add " Jiri Olsa
2020-06-26 21:55 ` Andrii Nakryiko
2020-06-28 19:55 ` Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 14/14] selftests/bpf: Add test for resolve_btfids Jiri Olsa
2020-06-30 1:43 ` Andrii Nakryiko
2020-06-30 14:27 ` Jiri Olsa
2020-06-30 18:13 ` Andrii Nakryiko
2020-06-30 1:54 ` [PATCH v4 bpf-next 00/14] bpf: Add d_path helper Andrii Nakryiko
2020-06-30 13:55 ` Jiri Olsa
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