fix: make maps compatible with kernel <= 4.14

In kernel 4.15 and additional parameter was added to allow maps to have
names but using this breaks on older kernels.

This change makes it so the name is only added on kernels 4.15 and
newer.

aya/src/sys/bpf.rs

@@ -14,7 +14,7 @@ use crate::{
     generated::{bpf_attach_type, bpf_attr, bpf_cmd, bpf_insn, bpf_prog_info, bpf_prog_type},
     maps::PerCpuValues,
     programs::VerifierLog,
-    sys::SysResult,
+    sys::{kernel_version, SysResult},
     Pod, BPF_OBJ_NAME_LEN,
 };
 
@@ -30,10 +30,16 @@ pub(crate) fn bpf_create_map(name: &CStr, def: &bpf_map_def) -> SysResult {
     u.max_entries = def.max_entries;
     u.map_flags = def.map_flags;
 
-    // u.map_name is 16 bytes max and must be NULL terminated
-    let name_len = cmp::min(name.to_bytes().len(), BPF_OBJ_NAME_LEN - 1);
-    u.map_name[..name_len]
-        .copy_from_slice(unsafe { slice::from_raw_parts(name.as_ptr(), name_len) });
+    // https://github.com/torvalds/linux/commit/ad5b177bd73f5107d97c36f56395c4281fb6f089
+    // The map name was added as a parameter in kernel 4.15+ so we skip adding it on
+    // older kernels for compatibility 
+    let k_ver = kernel_version().unwrap();
+    if k_ver >= (4, 15, 0) {
+        // u.map_name is 16 bytes max and must be NULL terminated
+        let name_len = cmp::min(name.to_bytes().len(), BPF_OBJ_NAME_LEN - 1);
+        u.map_name[..name_len]
+            .copy_from_slice(unsafe { slice::from_raw_parts(name.as_ptr(), name_len) });
+    }
 
     sys_bpf(bpf_cmd::BPF_MAP_CREATE, &attr)
 }