On Fri, Dec 11, 2020 at 3:01 PM Jonathan Lemon [off-list ref] wrote:

On Fri, Dec 11, 2020 at 12:23:34PM -0800, Andrii Nakryiko wrote:

quoted

quoted

@@ -164,7 +164,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
                curr_files = get_files_struct(curr_task);
                if (!curr_files) {
                        put_task_struct(curr_task);
-                       curr_tid = ++(info->tid);
+                       curr_tid = curr_tid + 1;

Yonghong might know definitively, but it seems like we need to update
info->tid here as well:

info->tid = curr_tid;

If the search eventually yields no task, then info->tid will stay at
some potentially much smaller value, and we'll keep re-searching tasks
from the same TID on each subsequent read (if user keeps reading the
file). So corner case, but good to have covered.

That applies earlier as well:

                curr_task = task_seq_get_next(ns, &curr_tid, true);
                if (!curr_task) {
                        info->task = NULL;
                        info->files = NULL;
                        return NULL;
                }

True, info->tid = curr_tid + 1; seems to be needed here?

The logic seems to be "if task == NULL, then return NULL and stop".
Is the seq_iterator allowed to continue/restart if seq_next returns NULL?

I don't think we allow seeking, so no restarts. But nothing will
prevent the user to keep calling read() after it returns 0 byte, so
yes, continuation is possible.

--
Jonathan