[PATCH bpf-next v3 04/21] bpf: support bpf tracing/iter programs for BPF_LINK_UPDATE

Yonghong Song
2020-05-07T05:40:30Z

Added BPF_LINK_UPDATE support for tracing/iter programs.
This way, a file based bpf iterator, which holds a reference
to the link, can have its bpf program updated without
creating new files.

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
kernel/bpf/bpf_iter.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 03f5832909db..0542a243b78c 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -23,6 +23,9 @@ struct bpf_iter_link {
static struct list_head targets = LIST_HEAD_INIT(targets);
static DEFINE_MUTEX(targets_mutex);

+/* protect bpf_iter_link changes */
+static DEFINE_MUTEX(link_mutex);
+
int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
{
struct bpf_iter_target_info *tinfo;
@@ -111,9 +114,37 @@ static void bpf_iter_link_dealloc(struct bpf_link *link)
kfree(iter_link);
}

+static int bpf_iter_link_replace(struct bpf_link *link,
+ struct bpf_prog *new_prog,
+ struct bpf_prog *old_prog)
+{
+ int ret = 0;
+
+ mutex_lock(&link_mutex);
+ if (old_prog && link->prog != old_prog) {
+ ret = -EPERM;
+ goto out_unlock;
+ }
+
+ if (link->prog->type != new_prog->type ||
+ link->prog->expected_attach_type != new_prog->expected_attach_type ||
+ link->prog->aux->attach_btf_id != new_prog->aux->attach_btf_id) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ old_prog = xchg(&link->prog, new_prog);
+ bpf_prog_put(old_prog);
+
+out_unlock:
+ mutex_unlock(&link_mutex);
+ return ret;
+}
+
static const struct bpf_link_ops bpf_iter_link_lops = {
.release = bpf_iter_link_release,
.dealloc = bpf_iter_link_dealloc,
+ .update_prog = bpf_iter_link_replace,
};

int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
--
2.24.1