Re: [PATCH v2 bpf-next 1/3] bpf: Introduce bpf_timer

On 6/14/21 8:33 PM, Alexei Starovoitov wrote:

On Fri, Jun 11, 2021 at 3:12 PM Yonghong Song [off-list ref] wrote:

quoted

quoted

+struct bpf_hrtimer {
+     struct hrtimer timer;
+     struct bpf_map *map;
+     struct bpf_prog *prog;
+     void *callback_fn;
+     void *value;
+};
+
+/* the actual struct hidden inside uapi struct bpf_timer */
+struct bpf_timer_kern {
+     struct bpf_hrtimer *timer;
+     struct bpf_spin_lock lock;
+};

Looks like in 32bit system, sizeof(struct bpf_timer_kern) is 64
and sizeof(struct bpf_timer) is 128.

struct bpf_spin_lock {
          __u32   val;
};

struct bpf_timer {
         __u64 :64;
         __u64 :64;
};

Checking the code, we may not have issues as structure
"bpf_timer" is only used to reserve spaces and
map copy value routine handles that properly.

Maybe we can still make it consistent with
two fields in bpf_timer_kern mapping to
two fields in bpf_timer?

struct bpf_timer_kern {
         __bpf_md_ptr(struct bpf_hrtimer *, timer);
         struct bpf_spin_lock lock;
};

Such alignment of fields is not necessary,
since the fields are not accessible directly from bpf prog.
struct bpf_timer_kern needs to fit into struct bpf_timer and
alignof these two structs needs to be the same.
That's all. I'll add build_bug_on to make sure.

Sounds good to me. Thanks!