[PATCH v2 bpf-next] libbpf: Ensure undefined bpf_attr field stays 0

[PATCH v2 bpf-next] libbpf: Ensure undefined bpf_attr field stays 0

[Martin KaFai Lau]

From: Martin KaFai Lau <martin.lau@kernel.org>

The commit 9e926acda0c2 ("libbpf: Find correct module BTFs for struct_ops maps and progs.")
sets a newly added field (value_type_btf_obj_fd) to -1 in libbpf when
the caller of the libbpf's bpf_map_create did not define this field by
passing a NULL "opts" or passing in a "opts" that does not cover this
new field. OPT_HAS(opts, field) is used to decide if the field is
defined or not:

	((opts) && opts->sz >= offsetofend(typeof(*(opts)), field))

Once OPTS_HAS decided the field is not defined, that field should
be set to 0. For this particular new field (value_type_btf_obj_fd),
its corresponding map_flags "BPF_F_VTYPE_BTF_OBJ_FD" is not set.
Thus, the kernel does not treat it as a fd field.

Cc: Kui-Feng Lee <thinker.li@gmail.com>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Fixes: 9e926acda0c2 ("libbpf: Find correct module BTFs for struct_ops maps and progs.")
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
v2: Improve the commit message

 tools/lib/bpf/bpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 3a35472a17c5..b133acfe08fb 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -192,7 +192,7 @@ int bpf_map_create(enum bpf_map_type map_type,
 	attr.btf_key_type_id = OPTS_GET(opts, btf_key_type_id, 0);
 	attr.btf_value_type_id = OPTS_GET(opts, btf_value_type_id, 0);
 	attr.btf_vmlinux_value_type_id = OPTS_GET(opts, btf_vmlinux_value_type_id, 0);
-	attr.value_type_btf_obj_fd = OPTS_GET(opts, value_type_btf_obj_fd, -1);
+	attr.value_type_btf_obj_fd = OPTS_GET(opts, value_type_btf_obj_fd, 0);
 
 	attr.inner_map_fd = OPTS_GET(opts, inner_map_fd, 0);
 	attr.map_flags = OPTS_GET(opts, map_flags, 0);
-- 
2.34.1

Re: [PATCH v2 bpf-next] libbpf: Ensure undefined bpf_attr field stays 0

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed, 24 Jan 2024 14:44:18 -0800 you wrote:
> From: Martin KaFai Lau <martin.lau@kernel.org>
> 
> The commit 9e926acda0c2 ("libbpf: Find correct module BTFs for struct_ops maps and progs.")
> sets a newly added field (value_type_btf_obj_fd) to -1 in libbpf when
> the caller of the libbpf's bpf_map_create did not define this field by
> passing a NULL "opts" or passing in a "opts" that does not cover this
> new field. OPT_HAS(opts, field) is used to decide if the field is
> defined or not:
> 
> [...]

Here is the summary with links:
  - [v2,bpf-next] libbpf: Ensure undefined bpf_attr field stays 0
    https://git.kernel.org/bpf/bpf-next/c/77c03cf314b4

You are awesome, thank you!
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