| Message ID | 20200512155234.1080379-1-yhs@fb.com |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | misc fixes for bpf_iter | expand |
On Tue, May 12, 2020 at 8:53 AM Yonghong Song <yhs@fb.com> wrote: > > Add a short comment in bpf_iter_run_prog() function to > explain how bpf_prog return value is converted to > seq_ops->show() return value: > bpf_prog return seq_ops()->show() return > 0 0 > 1 -EAGAIN > > When show() return value is -EAGAIN, the current > bpf_seq_read() will end. If the current seq_file buffer > is empty, -EAGAIN will return to user space. Otherwise, > the buffer will be copied to user space. > In both cases, the next bpf_seq_read() call will > try to show the same object which returned -EAGAIN > previously. > > Signed-off-by: Yonghong Song <yhs@fb.com> > --- Acked-by: Andrii Nakryiko <andriin@fb.com> [...]
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c index 30efd15cd4a0..0a45a6cdfabd 100644 --- a/kernel/bpf/bpf_iter.c +++ b/kernel/bpf/bpf_iter.c @@ -526,5 +526,11 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx) migrate_enable(); rcu_read_unlock(); + /* bpf program can only return 0 or 1: + * 0 : okay + * 1 : retry the same object + * The bpf_iter_run_prog() return value + * will be seq_ops->show() return value. + */ return ret == 0 ? 0 : -EAGAIN; }
Add a short comment in bpf_iter_run_prog() function to explain how bpf_prog return value is converted to seq_ops->show() return value: bpf_prog return seq_ops()->show() return 0 0 1 -EAGAIN When show() return value is -EAGAIN, the current bpf_seq_read() will end. If the current seq_file buffer is empty, -EAGAIN will return to user space. Otherwise, the buffer will be copied to user space. In both cases, the next bpf_seq_read() call will try to show the same object which returned -EAGAIN previously. Signed-off-by: Yonghong Song <yhs@fb.com> --- kernel/bpf/bpf_iter.c | 6 ++++++ 1 file changed, 6 insertions(+)