On 7/30/2020 2:03 PM, Cong Wang wrote:
> On Wed, Jul 29, 2020 at 3:41 AM <we...@ucloud.cn> wrote:
>> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
>> index c510b03..45401d5 100644
>> --- a/include/net/sch_generic.h
>> +++ b/include/net/sch_generic.h
>> @@ -384,6 +384,7 @@ struct qdisc_skb_cb {
>> };
>> #define QDISC_CB_PRIV_LEN 20
>> unsigned char data[QDISC_CB_PRIV_LEN];
>> + u16 mru;
>> };
> Hmm, can you put it in the anonymous struct before 'data'?
>
> We validate this cb size and data size like blow:
>
> static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int
> sz)
> {
> struct qdisc_skb_cb *qcb;
>
> BUILD_BUG_ON(sizeof(skb->cb) < offsetof(struct qdisc_skb_cb,
> data) + sz);
> BUILD_BUG_ON(sizeof(qcb->data) < sz);
> }
>
> It _kinda_ expects ->data at the end.
It seems the data offsetof data should be align with szieof(u64)?
If I modify it as following
@@ -383,6 +383,9 @@ struct qdisc_skb_cb {
unsigned int pkt_len;
u16 slave_dev_queue_mapping;
u16 tc_classid;
+ u16 mru;
};
#define QDISC_CB_PRIV_LEN 20
unsigned char data[QDISC_CB_PRIV_LEN];
compile fail:
net/core/filter.c:7625:3: note: in expansion of macro ‘BUILD_BUG_ON’
BUILD_BUG_ON((offsetof(struct sk_buff, cb) +
inn the file: net/core/filter.c
case offsetof(struct __sk_buff, cb[0]) ...
offsetofend(struct __sk_buff, cb[4]) - 1:
BUILD_BUG_ON(sizeof_field(struct qdisc_skb_cb, data) < 20);
BUILD_BUG_ON((offsetof(struct sk_buff, cb) +
offsetof(struct qdisc_skb_cb, data)) %
sizeof(__u64));
If I modify it as following
@@ -383,6 +383,9 @@ struct qdisc_skb_cb {
unsigned int pkt_len;
u16 slave_dev_queue_mapping;
u16 tc_classid;
+ u16 mru;
+ u16 _pad1;
+ u32 _pad2;
};
#define QDISC_CB_PRIV_LEN 20
unsigned char data[QDISC_CB_PRIV_LEN];
compile fail:
./include/linux/filter.h:633:2: note: in expansion of macro ‘BUILD_BUG_ON’
BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));
static inline void bpf_compute_data_pointers(struct sk_buff *skb)
{
struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;
BUILD_BUG_ON(sizeof(*cb) > sizeof_field(struct sk_buff, cb));
cb->data_meta = skb->data - skb_metadata_len(skb);
cb->data_end = skb->data + skb_headlen(skb);
}
It seems no space for new value add before 'data'?
BR
wenxu
