netdev - [PATCH bpf-next v2] bpf: libbpf: retry map creation without the name

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Date:   Mon, 19 Nov 2018 14:49:01 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     vladum@...gle.com, Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf-next v2] bpf: libbpf: retry map creation without the name

Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
for maps. Pre v4.14 kernels don't know about map names and return an
error about unexpected non-zero data. Retry sys_bpf without a map
name to cover older kernels.

v2 changes:
* check for errno == EINVAL as suggested by Daniel Borkmann

Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
 tools/lib/bpf/bpf.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 03f9bcc4ef50..961e1b9fc592 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,7 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 {
 	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
 	union bpf_attr attr;
+	int ret;
 
 	memset(&attr, '\0', sizeof(attr));
 
@@ -86,7 +87,15 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 	attr.map_ifindex = create_attr->map_ifindex;
 	attr.inner_map_fd = create_attr->inner_map_fd;
 
-	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	ret = sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	if (ret < 0 && errno == EINVAL && create_attr->name) {
+		/* Retry the same syscall, but without the name.
+		 * Pre v4.14 kernels don't support map names.
+		 */
+		memset(attr.map_name, 0, sizeof(attr.map_name));
+		return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	}
+	return ret;
 }
 
 int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
-- 
2.19.1.1215.g8438c0b245-goog