On 2/28/24 4:30 PM, Andrii Nakryiko wrote:
On Wed, Feb 28, 2024 at 4:25 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
On 2/28/24 3:55 PM, Andrii Nakryiko wrote:
On Tue, Feb 27, 2024 at 6:11 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
On 2/27/24 12:45 PM, Eduard Zingerman wrote:
Make bpf_map__set_autocreate() for struct_ops maps toggle autoload
state for referenced programs.
E.g. for the BPF code below:
SEC("struct_ops/test_1") int BPF_PROG(foo) { ... }
SEC("struct_ops/test_2") int BPF_PROG(bar) { ... }
SEC(".struct_ops.link")
struct test_ops___v1 A = {
.foo = (void *)foo
};
SEC(".struct_ops.link")
struct test_ops___v2 B = {
.foo = (void *)foo,
.bar = (void *)bar,
};
And the following libbpf API calls:
bpf_map__set_autocreate(skel->maps.A, true);
bpf_map__set_autocreate(skel->maps.B, false);
The autoload would be enabled for program 'foo' and disabled for
program 'bar'.
Do not apply such toggling if program autoload state is set by a call
to bpf_program__set_autoload().
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b39d3f2898a1..1ea3046724f8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -446,13 +446,18 @@ struct bpf_program {
struct bpf_object *obj;
int fd;
- bool autoload;
+ bool autoload:1;
+ bool autoload_user_set:1;
bool autoattach;
bool sym_global;
bool mark_btf_static;
enum bpf_prog_type type;
enum bpf_attach_type expected_attach_type;
int exception_cb_idx;
+ /* total number of struct_ops maps with autocreate == true
+ * that reference this program
+ */
+ __u32 struct_ops_refs;
Instead of adding struct_ops_refs and autoload_user_set,
for BPF_PROG_TYPE_STRUCT_OPS, how about deciding to load it or not by checking
prog->attach_btf_id (non zero) alone. The prog->attach_btf_id is now decided at
load time and is only set if it is used by at least one autocreate map, if I
read patch 2 & 3 correctly.
Meaning ignore prog->autoload*. Load the struct_ops prog as long as it is used
by one struct_ops map with autocreate == true.
If the struct_ops prog is not used in any struct_ops map, the bpf prog cannot be
loaded even the autoload is set. If bpf prog is used in a struct_ops map and its
autoload is set to false, the struct_ops map will be in broken state. Thus,
We can easily detect this condition and report meaningful error.
prog->autoload does not fit very well with struct_ops prog and may as well
depend on whether the struct_ops prog is used by a struct_ops map alone?
I think it's probably fine from a usability standpoint to disable
loading the BPF program if its struct_ops map was explicitly set to
not auto-create. It's a bit of deviation from other program types, but
in practice this logic will make it easier for users.
One question I have, though, is whether we should report as an error a
stand-alone struct_ops BPF program that is not used from any
struct_ops map? Or should we load it nevertheless? Or should we
silently not load it?
I think the libbpf could report an error if the prog is not used in any
struct_ops map at the source code level, not sure if it is useful.
However, it probably should not report error if that struct_ops map (where the
prog is resided) does not have autocreate set to true.
If a BPF program is not used in any struct_ops map, it cannot be loaded anyway
because the prog->attach_btf_id is not set. If libbpf tries to load the prog,
the kernel will reject it also. I think it may be a question on whether it is
the user intention of not loading the prog if the prog is not used in any
struct_ops map. I tend to think it is the user intention of not loading it in
this case.
SEC("struct_ops/test1")
int BPF_PROG(test1) { ... }
SEC("struct_ops/test2")
int BPF_PROG(test2) { ... }
SEC("?.struct_ops.link") struct some_ops___v1 a = { .test1 = test1 }
SEC("?.struct_ops.link") struct some_ops___v2 b = { .test1 = test1,
.test2 = test2, }
In the above, the userspace may try to load with a newer some_ops___v2 first,
failed and then try a lower version some_ops___v1 and then succeeded. The test2
prog will not be used and not expected to be loaded.
Yes, it's all sane in the above example. But imagine a stand-alone
struct_ops program with no SEC(".struct_ops") at all:
SEC("struct_ops/test1")
int BPF_PROG(test1) { ... }
/* nothing else */
Currently this will fail, right?
And with your proposal it will succeed without actually even
attempting to load the BPF program. Or am I misunderstanding?
Yep, currently it should fail.
Agree that we need to distinguish this case and prog->attach_btf_id is not
enough. This probably can be tracked in collect_st_ops_relos at the open phase.
