Add cgroup_sysctl template for BPF_PROG_TYPE_CGROUP_SYSCTL

Since https://github.com/aya-rs/aya/pull/256 supports `BPF_PROG_TYPE_CGROUP_SYSCTL`,
this patch adds cgroup_sysctl template.

cargo-generate.toml

@@ -18,6 +18,7 @@ choices = [
     "xdp",
     "classifier",
     "cgroup_skb",
+    "cgroup_sysctl",
     "tracepoint",
     "lsm",
     "tp_btf"

{{project-name}}-ebpf/src/main.rs

@@ -284,6 +284,25 @@ use aya_bpf::{
 pub fn {{crate_name}}(_ctx: SkBuffContext) -> i64 {
     return 0
 }
+{%- when "cgroup_sysctl" %}
+use aya_bpf::{
+    macros::cgroup_sysctl,
+    programs::SysctlContext,
+};
+use aya_log_ebpf::info;
+
+#[cgroup_sysctl(name="{{crate_name}}")]
+pub fn {{crate_name}}(ctx: SysctlContext) -> i32 {
+    match unsafe { try_{{crate_name}}(ctx) } {
+        Ok(ret) => ret,
+        Err(ret) => ret,
+    }
+}
+
+unsafe fn try_{{crate_name}}(ctx: SysctlContext) -> Result<i32, i32> {
+    info!(&ctx, "sysctl operation called");
+    Ok(0)
+}
 {%- endcase %}
 
 #[panic_handler]

{{project-name}}/src/main.rs

@@ -21,6 +21,8 @@ use aya::programs::{Xdp, XdpFlags};
 use aya::programs::{tc, SchedClassifier, TcAttachType};
 {%- when "cgroup_skb" -%}
 use aya::programs::{CgroupSkb, CgroupSkbAttachType};
+{%- when "cgroup_sysctl" -%}
+use aya::programs::{CgroupSysctl};
 {%- when "tracepoint" -%}
 use aya::programs::TracePoint;
 {%- when "lsm" -%}
@@ -43,7 +45,7 @@ struct Opt {
     {% if program_type == "xdp" or program_type == "classifier" -%}
     #[clap(short, long, default_value = "eth0")]
     iface: String,
-    {%- elsif program_type == "sock_ops" or program_type == "cgroup_skb" -%}
+    {%- elsif program_type == "sock_ops" or program_type == "cgroup_skb" or program_type == "cgroup_sysctl" -%}
     #[clap(short, long, default_value = "/sys/fs/cgroup/unified")]
     cgroup_path: String,
     {%- elsif program_type == "uprobe" or program_type == "uretprobe" -%}
@@ -145,6 +147,11 @@ async fn main() -> Result<(), anyhow::Error> {
     let prog: &mut SocketFilter = bpf.program_mut("{{crate_name}}").unwrap().try_into()?;
     prog.load()?;
     prog.attach(client.as_raw_fd())?;
+    {%- when "cgroup_sysctl" -%}
+    let program: &mut CgroupSysctl = bpf.program_mut("{{crate_name}}").unwrap().try_into()?;
+    let cgroup = std::fs::File::open(opt.cgroup_path)?;
+    program.load()?;
+    program.attach(cgroup)?;
     {%- endcase %}
 
     info!("Waiting for Ctrl-C...");