Re: [PATCH bpf-next v4 1/5] bpf: Add bpf_link support for sk_msg and sk_skb progs

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On 4/5/24 12:43 PM, John Fastabend wrote:
Yonghong Song wrote:
On 4/5/24 9:23 AM, John Fastabend wrote:
Yonghong Song wrote:
On 4/5/24 8:19 AM, John Fastabend wrote:
Yonghong Song wrote:
Add bpf_link support for sk_msg and sk_skb programs. We have an
internal request to support bpf_link for sk_msg programs so user
space can have a uniform handling with bpf_link based libbpf
APIs. Using bpf_link based libbpf API also has a benefit which
makes system robust by decoupling prog life cycle and
attachment life cycle.

Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
    include/linux/bpf.h            |   6 +
    include/linux/skmsg.h          |   4 +
    include/uapi/linux/bpf.h       |   5 +
    kernel/bpf/syscall.c           |   4 +
    net/core/sock_map.c            | 268 ++++++++++++++++++++++++++++++++-
    tools/include/uapi/linux/bpf.h |   5 +
    6 files changed, 284 insertions(+), 8 deletions(-)

LGTM one question below.

+/* Handle the following two cases:
+ * case 1: link != NULL, prog != NULL, old != NULL
+ * case 2: link != NULL, prog != NULL, old == NULL
+ */
+static int sock_map_link_update_prog(struct bpf_link *link,
+				     struct bpf_prog *prog,
+				     struct bpf_prog *old)
+{
+	const struct sockmap_link *sockmap_link = container_of(link, struct sockmap_link, link);
+	struct bpf_prog **pprog;
+	struct bpf_link **plink;
+	int ret = 0;
+
+	mutex_lock(&sockmap_mutex);
+
+	/* If old prog is not NULL, ensure old prog is the same as link->prog. */
+	if (old && link->prog != old) {
+		ret = -EINVAL;
+		goto out;
+	}
+	/* Ensure link->prog has the same type/attach_type as the new prog. */
+	if (link->prog->type != prog->type ||
+	    link->prog->expected_attach_type != prog->expected_attach_type) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = sock_map_prog_lookup(sockmap_link->map, &pprog,
+				   sockmap_link->attach_type);
+	if (ret)
+		goto out;
+
+	/* Ensure the same link between the one in map and the passed-in. */
+	ret = sock_map_link_lookup(sockmap_link->map, &plink, link, false,
+				   sockmap_link->attach_type);
+	if (ret)
+		goto out;
+
+	if (old) {
+		ret = psock_replace_prog(pprog, prog, old);
+		goto out;
+	}
+
+	psock_set_prog(pprog, prog);
+
+out:
+	if (!ret) {
+		bpf_prog_inc(prog);
+		old = xchg(&link->prog, prog);
+		bpf_prog_put(old);
Need to check old? I don't think we can clal bpf_prog_put on null?

     if (old)
        bpf_prog_put(old)
The 'old' here represents the *old* link->prog program and
link->prog should not be NULL at this point.
Ah ok. Maybe instead of using the input old var make it
explicit?

      if (!ret) {
         struct bpf_prog *old_link;

         bpf_prog_inc(prog);
         old_link = xchg(&link->prog, prog);
         bpf_prog_put(old)
      }

Is a bit more obious to me at least. Up to you I have a slight preference
for the explicit more verbose above.
Regarding naming convention, yes, it is hard. My above code similar to
kernel/bpf/net_namespace.c:

static int bpf_netns_link_update_prog(struct bpf_link *link,
                                        struct bpf_prog *new_prog,
                                        struct bpf_prog *old_prog)
{
          struct bpf_netns_link *net_link =
                  container_of(link, struct bpf_netns_link, link);
          enum netns_bpf_attach_type type = net_link->netns_type;
          struct bpf_prog_array *run_array;
          struct net *net;
          int idx, ret;
if (old_prog && old_prog != link->prog)
                  return -EPERM;
	...
	old_prog = xchg(&link->prog, new_prog);
          bpf_prog_put(old_prog);
	...
}

The 'old_prog' is reused in the above.

I am okay to change
	old = xchg(&link->prog, prog);
to
	old_link_prog = xchg(&link->prog, prog);

in next revision (if requested or additional changes needed)
or as a followup.
I'm good with this series as is LGTM. We can do a follow up if we want.

Thanks! Sounds good to me.

Although the xchg is exactly one line above so I'm not sure its even necessary.

the xchg inpsock_set_prog() is used to set prog in pprog. The xchg I added is for &link->prog. I didn't make a change to psock_set_prog() since it is used in different places and I do not want to polute it with extra link parameter.


Otherwise for the series.

Reviewed-by: John Fastabend <john.fastabend@xxxxxxxxx>





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