Messages in this thread | | | Date | Fri, 1 Apr 2022 11:37:07 +0800 | Subject | Re: [PATCH] sample: bpf: syscall_tp_user: print result of verify_map | From | Song Chen <> |
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在 2022/4/1 11:01, Yonghong Song 写道: > > > On 3/31/22 6:41 PM, Song Chen wrote: >> syscall_tp only prints the map id and messages when something goes wrong, >> but it doesn't print the value passed from bpf map. I think it's better >> to show that value to users. >> >> What's more, i also added a 2-second sleep before calling verify_map, >> to make the value more obvious. >> >> Signed-off-by: Song Chen <chensong_2000@189.cn> >> --- >> samples/bpf/syscall_tp_user.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/samples/bpf/syscall_tp_user.c >> b/samples/bpf/syscall_tp_user.c >> index a0ebf1833ed3..1faa7f08054e 100644 >> --- a/samples/bpf/syscall_tp_user.c >> +++ b/samples/bpf/syscall_tp_user.c >> @@ -36,6 +36,9 @@ static void verify_map(int map_id) >> fprintf(stderr, "failed: map #%d returns value 0\n", map_id); >> return; >> } >> + >> + printf("verify map:%d val: %d\n", map_id, val); > > I am not sure how useful it is or anybody really cares. > This is just a sample to demonstrate how bpf tracepoint works. > The error path has error print out already. > >> + >> val = 0; >> if (bpf_map_update_elem(map_id, &key, &val, BPF_ANY) != 0) { >> fprintf(stderr, "map_update failed: %s\n", strerror(errno)); >> @@ -98,6 +101,7 @@ static int test(char *filename, int num_progs) >> } >> close(fd); >> + sleep(2); > > The commit message mentioned this sleep(2) is > to make the value more obvious. I don't know what does this mean. > sleep(2) can be added only if it fixed a bug.
The value in bpf map means how many times trace_enter_open_at are triggered with tracepoint,sys_enter_openat. Sleep(2) is to enlarge the result, tell the user how many files are opened in the last 2 seconds.
It shows like this:
sudo ./samples/bpf/syscall_tp prog #0: map ids 4 5 verify map:4 val: 253 verify map:5 val: 252
If we work harder, we can also print those files' name and opened by which process.
It's just an improvement instead of a bug fix, i will drop it if reviewers think it's unnecessary.
Thanks.
BR
chensong > >> /* verify the map */ >> for (i = 0; i < num_progs; i++) { >> verify_map(map0_fds[i]); >
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