bpftool: Handle EAGAIN error code properly in pids collection

When the error code is EAGAIN, the kernel signals the user
space should retry the read() operation for bpf iterators.
Let us do it.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200818222312.2181675-1-yhs@fb.com

diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
index e3b116325403bea81a56a03e58f06b8206440dce..df7d8ec7603616ac915f764b663e65fbeb579cb0 100644 (file)
--- a/tools/bpf/bpftool/pids.c
+++ b/tools/bpf/bpftool/pids.c
@@ -134,6 +134,8 @@ int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
        while (true) {
                ret = read(fd, buf, sizeof(buf));
                if (ret < 0) {
+                       if (errno == EAGAIN)
+                               continue;
                        err = -errno;
                        p_err("failed to read PID iterator output: %d", err);
                        goto out;