From 2e3ed68bfcd9c5ca2cf8b88ba23a34992ccd0b1f Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 13 May 2020 11:02:18 -0700 Subject: bpf: Add comments to interpret bpf_prog return values 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 Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20200513180218.2949517-1-yhs@fb.com --- kernel/bpf/bpf_iter.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'kernel/bpf/bpf_iter.c') 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; } -- cgit v1.2.3-59-g8ed1b