Re: [PATCH v4 bpf-next 4/4] selftests/bpf: add bpf_iter test with bpf_get_task_stack()

[Yonghong Song]

On 6/29/20 9:56 AM, Song Liu wrote:
> > On Jun 29, 2020, at 8:06 AM, Yonghong Song <yhs@xxxxxx> wrote:
> >
> >
> >
> > On 6/28/20 10:55 PM, Song Liu wrote:
> > > The new test is similar to other bpf_iter tests. It dumps all
> > > /proc/<pid>/stack to a seq_file. Here is some example output:
> > > pid:     2873 num_entries:        3
> > > [<0>] worker_thread+0xc6/0x380
> > > [<0>] kthread+0x135/0x150
> > > [<0>] ret_from_fork+0x22/0x30
> > > pid:     2874 num_entries:        9
> > > [<0>] __bpf_get_stack+0x15e/0x250
> > > [<0>] bpf_prog_22a400774977bb30_dump_task_stack+0x4a/0xb3c
> > > [<0>] bpf_iter_run_prog+0x81/0x170
> > > [<0>] __task_seq_show+0x58/0x80
> > > [<0>] bpf_seq_read+0x1c3/0x3b0
> > > [<0>] vfs_read+0x9e/0x170
> > > [<0>] ksys_read+0xa7/0xe0
> > > [<0>] do_syscall_64+0x4c/0xa0
> > > [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > Note: To print the output, it is necessary to modify the selftest.
> >
> > I do not know what this sentence means. It seems confusing
> > and probably not needed.
>
> It means current do_dummy_read() doesn't check/print the contents of the
> seq_file:
>
>          /* not check contents, but ensure read() ends without error */
>          while ((len = read(iter_fd, buf, sizeof(buf))) > 0)
>                  ;

I see. Thanks. It could be great if the commit message is more
explicit about what 'modify' is.

> > > Signed-off-by: Song Liu <songliubraving@xxxxxx>
> >
> > Acked-by: Yonghong Song <yhs@xxxxxx>
>
> Thanks!
>
> [...]