Merge branch 'bpf-multi-prog-prep'

Jakub Sitnicki says:

====================
This patch set prepares ground for link-based multi-prog attachment for
future netns attach types, with BPF_SK_LOOKUP attach type in mind [0].

Two changes are needed in order to attach and run a series of BPF programs:

  1) an bpf_prog_array of programs to run (patch #2), and
  2) a list of attached links to keep track of attachments (patch #3).

Nothing changes for BPF flow_dissector. Just as before only one program can
be attached to netns.

In v3 I've simplified patch #2 that introduces bpf_prog_array to take
advantage of the fact that it will hold at most one program for now.

In particular, I'm no longer using bpf_prog_array_copy. It turned out to be
less suitable for link operations than I thought as it fails to append the
same BPF program.

bpf_prog_array_replace_item is also gone, because we know we always want to
replace the first element in prog_array.

Naturally the code that handles bpf_prog_array will need change once
more when there is a program type that allows multi-prog attachment. But I
feel it will be better to do it gradually and present it together with
tests that actually exercise multi-prog code paths.

[0] https://lore.kernel.org/bpf/20200511185218.1422406-1-jakub@cloudflare.com/

v2 -> v3:
- Don't check if run_array is null in link update callback. (Martin)
- Allow updating the link with the same BPF program. (Andrii)
- Add patch #4 with a test for the above case.
- Kill bpf_prog_array_replace_item. Access the run_array directly.
- Switch from bpf_prog_array_copy() to bpf_prog_array_alloc(1, ...).
- Replace rcu_deref_protected & RCU_INIT_POINTER with rcu_replace_pointer.
- Drop Andrii's Ack from patch #2. Code changed.

v1 -> v2:

- Show with a (void) cast that bpf_prog_array_replace_item() return value
  is ignored on purpose. (Andrii)
- Explain why bpf-cgroup cannot replace programs in bpf_prog_array based
  on bpf_prog pointer comparison in patch #2 description. (Andrii)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 7 insertions, 3 deletions

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index a7eba43fe4e4..4b6e36288ddd 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -372,7 +372,8 @@ flow_dissector_init_keys(struct flow_dissector_key_control *key_control,
 }
 
 #ifdef CONFIG_BPF_SYSCALL
-int flow_dissector_bpf_prog_attach(struct net *net, struct bpf_prog *prog);
+int flow_dissector_bpf_prog_attach_check(struct net *net,
+					 struct bpf_prog *prog);
 #endif /* CONFIG_BPF_SYSCALL */
 
 #endif
diff --git a/include/net/netns/bpf.h b/include/net/netns/bpf.h
index a8dce2a380c8..0ca6a1b87185 100644
--- a/include/net/netns/bpf.h
+++ b/include/net/netns/bpf.h
@@ -9,10 +9,13 @@
 #include <linux/bpf-netns.h>
 
 struct bpf_prog;
+struct bpf_prog_array;
 
 struct netns_bpf {
-	struct bpf_prog __rcu *progs[MAX_NETNS_BPF_ATTACH_TYPE];
-	struct bpf_link *links[MAX_NETNS_BPF_ATTACH_TYPE];
+	/* Array of programs to run compiled from progs or links */
+	struct bpf_prog_array __rcu *run_array[MAX_NETNS_BPF_ATTACH_TYPE];
+	struct bpf_prog *progs[MAX_NETNS_BPF_ATTACH_TYPE];
+	struct list_head links[MAX_NETNS_BPF_ATTACH_TYPE];
 };
 
 #endif /* __NETNS_BPF_H__ */