From: Yonghong Song <yhs@fb.com>
To: Wenbo Zhang <ethercflow@gmail.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"ast@kernel.org" <ast@kernel.org>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
"andrii.nakryiko@gmail.com" <andrii.nakryiko@gmail.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v12 2/2] selftests/bpf: test for bpf_get_file_path() from tracepoint
Date: Tue, 17 Dec 2019 04:13:44 +0000 [thread overview]
Message-ID: <71c53be6-add4-2557-bc8f-8acb8e4a2f39@fb.com> (raw)
In-Reply-To: <CABtjQmZtzZT+OmZCn=eL9pvTeeCQ+TzKUMGgFJcGzwJDqyk6vw@mail.gmail.com>
On 12/16/19 8:01 PM, Wenbo Zhang wrote:
>> In non-bpf .c file, typically we do not add 'inline' attribute.
>> It is up to compiler to decide whether it should be inlined.
>
> Thank you, I'll fix this.
>
>>> +struct sys_enter_newfstat_args {
>>> + unsigned long long pad1;
>>> + unsigned long long pad2;
>>> + unsigned int fd;
>>> +};
>
>> The BTF generated vmlinux.h has the following structure,
>> struct trace_entry {
>> short unsigned int type;
>> unsigned char flags;
>> unsigned char preempt_count;
>> int pid;
>> };
>> struct trace_event_raw_sys_enter {
>> struct trace_entry ent;
>> long int id;
>> long unsigned int args[6];
>> char __data[0];
>> };
>
>> The third parameter type should be long, otherwise,
>> it may have issue on big endian machines?
>
> Sorry, I don't understand why there is a problem on big-endian machines.
> Would you please explain that in more detail? Thank you.
The kernel will actually have 8 bytes of memory to store fd
based on trace_event_raw_sys_enter.
For little endian machine, the lower 4 bytes are read based on
your sys_enter_newfstat_args, which is "accidentally" the lower
4 bytes in u64, so you get the correct answer.
For big endian machine, the lower 4 bytes read based on
your sys_enter_newfstat_args will be high 4 bytes in u64, which
is incorrect.
>
> Yonghong Song <yhs@fb.com> 于2019年12月16日周一 上午12:25写道:
>>
>>
>>
>> On 12/14/19 8:01 PM, Wenbo Zhang wrote:
>>> trace fstat events by tracepoint syscalls/sys_enter_newfstat, and handle
>>> events only produced by test_file_get_path, which call fstat on several
>>> different types of files to test bpf_get_file_path's feature.
>>>
>>> v4->v5: addressed Andrii's feedback
>>> - pass NULL for opts as bpf_object__open_file's PARAM2, as not really
>>> using any
>>> - modify patch subject to keep up with test code
>>> - as this test is single-threaded, so use getpid instead of SYS_gettid
>>> - remove unnecessary parens around check which after if (i < 3)
>>> - in kern use bpf_get_current_pid_tgid() >> 32 to fit getpid() in
>>> userspace part
>>> - with the patch adding helper as one patch series
>>>
>>> v3->v4: addressed Andrii's feedback
>>> - use a set of fd instead of fds array
>>> - use global variables instead of maps (in v3, I mistakenly thought that
>>> the bpf maps are global variables.)
>>> - remove uncessary global variable path_info_index
>>> - remove fd compare as the fstat's order is fixed
>>>
>>> v2->v3: addressed Andrii's feedback
>>> - use global data instead of perf_buffer to simplified code
>>>
>>> v1->v2: addressed Daniel's feedback
>>> - rename bpf_fd2path to bpf_get_file_path to be consistent with other
>>> helper's names
>>>
>>> Signed-off-by: Wenbo Zhang <ethercflow@gmail.com>
>>> ---
>>> .../selftests/bpf/prog_tests/get_file_path.c | 171 ++++++++++++++++++
>>> .../selftests/bpf/progs/test_get_file_path.c | 43 +++++
>>> 2 files changed, 214 insertions(+)
>>> create mode 100644 tools/testing/selftests/bpf/prog_tests/get_file_path.c
>>> create mode 100644 tools/testing/selftests/bpf/progs/test_get_file_path.c
>>>
>>> diff --git a/tools/testing/selftests/bpf/prog_tests/get_file_path.c b/tools/testing/selftests/bpf/prog_tests/get_file_path.c
>>> new file mode 100644
>>> index 000000000000..7ec11e43e0fc
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/prog_tests/get_file_path.c
>>> @@ -0,0 +1,171 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +#define _GNU_SOURCE
>>> +#include <test_progs.h>
>>> +#include <sys/stat.h>
>>> +#include <linux/sched.h>
>>> +#include <sys/syscall.h>
>>> +
>>> +#define MAX_PATH_LEN 128
>>> +#define MAX_FDS 7
>>> +#define MAX_EVENT_NUM 16
>>> +
>>> +static struct file_path_test_data {
>>> + pid_t pid;
>>> + __u32 cnt;
>>> + __u32 fds[MAX_EVENT_NUM];
>>> + char paths[MAX_EVENT_NUM][MAX_PATH_LEN];
>>> +} src, dst;
>>> +
>>> +static inline int set_pathname(int fd)
>>
>> In non-bpf .c file, typically we do not add 'inline' attribute.
>> It is up to compiler to decide whether it should be inlined.
>>
>>> +{
>>> + char buf[MAX_PATH_LEN];
>>> +
>>> + snprintf(buf, MAX_PATH_LEN, "/proc/%d/fd/%d", src.pid, fd);
>>> + src.fds[src.cnt] = fd;
>>> + return readlink(buf, src.paths[src.cnt++], MAX_PATH_LEN);
>>> +}
>>> +
>> [...]
>>> diff --git a/tools/testing/selftests/bpf/progs/test_get_file_path.c b/tools/testing/selftests/bpf/progs/test_get_file_path.c
>>> new file mode 100644
>>> index 000000000000..eae663c1262a
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/progs/test_get_file_path.c
>>> @@ -0,0 +1,43 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#include <linux/bpf.h>
>>> +#include <linux/ptrace.h>
>>> +#include <string.h>
>>> +#include <unistd.h>
>>> +#include "bpf_helpers.h"
>>> +#include "bpf_tracing.h"
>>> +
>>> +#define MAX_PATH_LEN 128
>>> +#define MAX_EVENT_NUM 16
>>> +
>>> +static struct file_path_test_data {
>>> + pid_t pid;
>>> + __u32 cnt;
>>> + __u32 fds[MAX_EVENT_NUM];
>>> + char paths[MAX_EVENT_NUM][MAX_PATH_LEN];
>>> +} data;
>>> +
>>> +struct sys_enter_newfstat_args {
>>> + unsigned long long pad1;
>>> + unsigned long long pad2;
>>> + unsigned int fd;
>>> +};
>>
>> The BTF generated vmlinux.h has the following structure,
>> struct trace_entry {
>> short unsigned int type;
>> unsigned char flags;
>> unsigned char preempt_count;
>> int pid;
>> };
>> struct trace_event_raw_sys_enter {
>> struct trace_entry ent;
>> long int id;
>> long unsigned int args[6];
>> char __data[0];
>> };
>>
>> The third parameter type should be long, otherwise,
>> it may have issue on big endian machines?
next prev parent reply other threads:[~2019-12-17 4:14 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 13:27 [PATCH bpf-next v10 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-11-19 13:27 ` [PATCH bpf-next v10 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-11-23 3:18 ` Alexei Starovoitov
2019-11-23 4:43 ` Al Viro
2019-11-23 4:51 ` Al Viro
2019-11-23 5:19 ` Alexei Starovoitov
2019-11-23 5:35 ` Al Viro
2019-11-23 6:04 ` Alexei Starovoitov
2019-12-13 19:51 ` Brendan Gregg
2019-12-05 4:20 ` [PATCH bpf-next v11 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-12-05 4:20 ` [PATCH bpf-next v11 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-05 7:19 ` Alexei Starovoitov
2019-12-05 9:47 ` Wenbo Zhang
2019-12-15 4:01 ` [PATCH bpf-next v12 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-12-15 4:01 ` [PATCH bpf-next v12 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-15 16:05 ` Yonghong Song
2019-12-17 6:26 ` Wenbo Zhang
2019-12-17 6:33 ` Yonghong Song
2019-12-15 16:10 ` Yonghong Song
2019-12-17 6:27 ` Wenbo Zhang
2019-12-16 22:09 ` Brendan Gregg
2019-12-17 4:05 ` Wenbo Zhang
2019-12-17 9:47 ` [PATCH bpf-next v13 0/2] bpf: adding get_fd_path helper Wenbo Zhang
2019-12-17 9:47 ` [PATCH bpf-next v13 1/2] bpf: add new helper get_fd_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-17 16:29 ` Yonghong Song
2019-12-17 19:39 ` Daniel Borkmann
2019-12-18 0:11 ` Wenbo Zhang
2019-12-18 0:06 ` Wenbo Zhang
2019-12-18 0:56 ` [PATCH bpf-next v14 0/2] bpf: adding get_fd_path helper Wenbo Zhang
2019-12-18 0:56 ` [PATCH bpf-next v14 1/2] bpf: add new helper get_fd_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-18 3:27 ` Yonghong Song
2019-12-19 16:14 ` Daniel Borkmann
2019-12-20 3:35 ` Wenbo Zhang
2020-01-16 8:59 ` Jiri Olsa
2020-02-10 4:43 ` Brendan Gregg
2020-02-11 0:01 ` Daniel Borkmann
2020-02-12 15:21 ` Jiri Olsa
2020-06-01 14:17 ` Wenbo Zhang
2020-06-01 16:38 ` Alexei Starovoitov
2020-06-02 3:04 ` Wenbo Zhang
2020-06-02 8:14 ` Jiri Olsa
2019-12-18 0:56 ` [PATCH bpf-next v14 2/2] selftests/bpf: test for bpf_get_fd_path() from tracepoint Wenbo Zhang
2019-12-18 3:27 ` Yonghong Song
2019-12-17 9:47 ` [PATCH bpf-next v13 " Wenbo Zhang
2019-12-17 16:32 ` Yonghong Song
2019-12-15 4:01 ` [PATCH bpf-next v12 2/2] selftests/bpf: test for bpf_get_file_path() " Wenbo Zhang
2019-12-15 16:24 ` Yonghong Song
2019-12-17 4:01 ` Wenbo Zhang
2019-12-17 4:13 ` Yonghong Song [this message]
2019-12-17 9:44 ` Wenbo Zhang
2019-12-05 4:20 ` [PATCH bpf-next v11 " Wenbo Zhang
2019-11-19 13:27 ` [PATCH bpf-next v10 " Wenbo Zhang
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