On 1/7/25 8:21 PM, Jason Xing wrote:
Hi Martin,
- bpf_skops_tx_timestamping(sk, skb, op, 2, args);
+ if (sk_is_tcp(sk))
+ args[2] = skb_shinfo(skb)->tskey;
Instead of only passing one info "skb_shinfo(skb)->tskey" of a skb, pass the
whole skb ptr to the bpf prog. Take a look at bpf_skops_init_skb. Lets start
with end_offset = 0 for now so that the bpf prog won't use it to read the
skb->data. It can be revisited later.
bpf_skops_init_skb(&sock_ops, skb, 0);
The bpf prog can use bpf_cast_to_kern_ctx() and bpf_core_cast() to get to the
skb_shinfo(skb). Take a look at the md_skb example in type_cast.c.
In recent days, I've been working on this part. It turns out to be
infeasible to pass "struct __sk_buff *skb" as the second parameter in
skops_sockopt() in patch [11/11]. I cannot find a way to acquire the
skb itself
I didn't mean to pass skb in sock_ops_kern->args[] or pass skb to the bpf prog
"SEC("sockops") skops_sockopt(struct bpf_sock_ops *skops, struct sk_buff *skb)".
The bpf prog can only take one ctx argument which is
"struct bpf_sock_ops *skops" here.
I meant to have kernel initializing the sock_ops_kern->skb by doing
"bpf_skops_init_skb(&sock_ops, skb, 0);" before running the bpf prog.
The bpf prog can read the skb by using bpf_cast_to_kern_ctx() and bpf_core_cast().
Something like the following. I directly change the existing test_tcp_hdr_options.c.
It has not been changed to use the vmlinux.h, so I need to redefine some parts of
the sk_buff, skb_shared_info, and bpf_sock_ops_kern. Your new test should directly
include <vmlinux.h> and no need to redefine them.
Untested code:
diff --git i/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c w/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c
index 5f4e87ee949a..c98ebe71f6ba 100644
--- i/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c
+++ w/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c
@@ -12,8 +12,10 @@
#include <linux/types.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
+#include <bpf/bpf_core_read.h>
#define BPF_PROG_TEST_TCP_HDR_OPTIONS
#include "test_tcp_hdr_options.h"
+#include "bpf_kfuncs.h"
#ifndef sizeof_field
#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
@@ -348,9 +350,63 @@ static int current_mss_opt_len(struct bpf_sock_ops *skops)
return CG_OK;
}
+struct sk_buff {
+ unsigned int end;
+ unsigned char *head;
+} __attribute__((preserve_access_index));
+
+struct skb_shared_info {
+ __u8 flags;
+ __u8 meta_len;
+ __u8 nr_frags;
+ __u8 tx_flags;
+ unsigned short gso_size;
+ unsigned short gso_segs;
+ unsigned int gso_type;
+ __u32 tskey;
+} __attribute__((preserve_access_index));
+
+struct bpf_sock_ops_kern {
+ struct sock *sk;
+ union {
+ __u32 args[4];
+ __u32 reply;
+ __u32 replylong[4];
+ };
+ struct sk_buff *syn_skb;
+ struct sk_buff *skb;
+ void *skb_data_end;
+ __u8 op;
+ __u8 is_fullsock;
+ __u8 remaining_opt_len;
+ __u64 temp; /* temp and everything after is not
+ * initialized to 0 before calling
+ * the BPF program. New fields that
+ * should be initialized to 0 should
+ * be inserted before temp.
+ * temp is scratch storage used by
+ * sock_ops_convert_ctx_access
+ * as temporary storage of a register.
+ */
+} __attribute__((preserve_access_index));
+
static int handle_hdr_opt_len(struct bpf_sock_ops *skops)
{
__u8 tcp_flags = skops_tcp_flags(skops);
+ struct bpf_sock_ops_kern *skops_kern;
+ struct skb_shared_info *shared_info;
+ struct sk_buff *skb;
+
+ skops_kern = bpf_cast_to_kern_ctx(skops);
+ skb = skops_kern->skb;
+
+ if (skb) {
+ shared_info = bpf_core_cast(skb->head + skb->end, struct skb_shared_info);
+ /* printk as an example. don't do that in selftests. */
+ bpf_printk("tskey %u gso_size %u gso_segs %u gso_type %u flags %x\n",
+ shared_info->tskey, shared_info->gso_size,
+ shared_info->gso_segs, shared_info->gso_type, shared_info->flags);
+ }
if ((tcp_flags & TCPHDR_SYNACK) == TCPHDR_SYNACK)
return synack_opt_len(skops);
