Re: [PATCH bpf-next v12 2/2] selftests/bpf: test for bpf_get_file_path() from tracepoint

[Wenbo Zhang <ethercflow@gmail.com>]

> 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.

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?