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Date: Sat, 2 Apr 2022 10:38:39 +0800 From: Song Chen <chensong_2000@....cn> To: Yonghong Song <yhs@...com>, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, kafai@...com, songliubraving@...com, john.fastabend@...il.com, kpsingh@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] sample: bpf: syscall_tp_user: print result of verify_map Hi, 在 2022/4/2 00:28, Yonghong Song 写道: > > > On 3/31/22 8:37 PM, Song Chen wrote: >> >> >> 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@....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. > > Considering we already have > printf("prog #%d: map ids %d %d\n", i, map0_fds[i], map1_fds[i]); > I think your proposed additional printout > printf("verify map:%d val: %d\n", map_id, val); > might be okay. The commit message should be rewritten > to justify this change something like: > we already print out > prog <some number>: map ids <..> <...> > further print out > verify map: ... > will help user to understand the program runs successfully. > > I think sleep(2) is unnecessary. will do, many thanks. BR Song > >>> >>>> + >>>> 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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