ebpf: Change error types to `c_long`

All helper functions and context methods are returning `c_long` as an
error. Before this change, aya-template and book examples were adjusting
the error type in `try_*` functionns return type of the program. For
example, for XDP programs programs, which return `u32`, the type
returned by `try_*` functions, was `Result<u32, u32>`.

This approach is forcing people to write boilerplate code for casting
errors from `c_long` to the expected type, like:

```rust
MY_MAP.insert(k, v, 0).map_err(|_| 1u32)?;
```

This change solves that problem by:

* Using `Result<i32, c_long>` as a type for `try_*` functions for
  SKB-based programs and then replacing errors with `TC_ACT_SHOT` or
  `0` once in the main program function.
* Using `Result<u32, c_long>` as a type for `try_*` functions in `try_*`
  funnctions for XDP programs and then replacing errors with `XDP_ABORT`.
* Using either `Result<u32, c_long>` or `Result<i32, c_long>` as types
  in `try_*` functions for all other program types where the return value
  matters (LSM, sysctl etc.) and replacing the error either with `0` or
  `1` (depending on which number means "block the action" for particular
  type of program).
* Using `Result<(), c_long` for all other program types where the
  return value doesn't matter (kprobe, uprobe etc.).

So errors can be handled without casting, like:

```rust
MY_MAP.insert(k, v, 0)?;
```

The other change is fixing return values of cgroup_skb, sockopt and
sysctl programs (1 means "allow", 0 means "deny").

Signed-off-by: Michal Rostecki <vadorovsky@gmail.com>

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

@@ -1,116 +1,112 @@
 #![no_std]
 #![no_main]
+
 {% case program_type -%}
 {%- when "kprobe" %}
-use aya_bpf::{macros::kprobe, programs::ProbeContext};
+use aya_bpf::{
+    cty::c_long,
+    macros::kprobe,
+    programs::ProbeContext,
+};
 use aya_log_ebpf::info;
 
 #[kprobe(name = "{{crate_name}}")]
-pub fn {{crate_name}}(ctx: ProbeContext) -> u32 {
+pub fn {{crate_name}}(ctx: ProbeContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: ProbeContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: ProbeContext) -> Result<(), c_long> {
     info!(&ctx, "function {{kprobe}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "kretprobe" %}
-use aya_bpf::{macros::kretprobe, programs::ProbeContext};
+use aya_bpf::{
+    cty::c_long,
+    macros::kretprobe,
+    programs::ProbeContext,
+};
 use aya_log_ebpf::info;
 
 #[kretprobe(name = "{{crate_name}}")]
-pub fn {{crate_name}}(ctx: ProbeContext) -> u32 {
+pub fn {{crate_name}}(ctx: ProbeContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: ProbeContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: ProbeContext) -> Result<(), c_long> {
     info!(&ctx, "function {{kprobe}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "fentry" %}
 use aya_bpf::{
+    cty::c_long,
     macros::fentry,
     programs::FEntryContext,
 };
 use aya_log_ebpf::info;
 
 #[fentry(name="{{crate_name}}")]
-pub fn {{crate_name}}(ctx: FEntryContext) -> u32 {
+pub fn {{crate_name}}(ctx: FEntryContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: FEntryContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: FEntryContext) -> Result<(), c_long> {
     info!(&ctx, "function {{fn_name}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "fexit" %}
 use aya_bpf::{
+    cty::c_long,
     macros::fexit,
     programs::FExitContext,
 };
 use aya_log_ebpf::info;
 
 #[fexit(name="{{crate_name}}")]
-pub fn {{crate_name}}(ctx: FExitContext) -> u32 {
+pub fn {{crate_name}}(ctx: FExitContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: FExitContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: FExitContext) -> Result<(), c_long> {
     info!(&ctx, "function {{fn_name}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "uprobe" %}
 use aya_bpf::{
+    cty::c_long,
     macros::uprobe,
     programs::ProbeContext,
 };
 use aya_log_ebpf::info;
 
 #[uprobe(name="{{crate_name}}")]
-pub fn {{crate_name}}(ctx: ProbeContext) -> u32 {
+pub fn {{crate_name}}(ctx: ProbeContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: ProbeContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: ProbeContext) -> Result<(), c_long> {
     info!(&ctx, "function {{uprobe_fn_name}} called by {{uprobe_target}}");
-    Ok(0)
+    Ok(())
 }
 {%- when "uretprobe" %}
 use aya_bpf::{
+    cty::c_long,
     macros::uretprobe,
     programs::ProbeContext,
 };
 use aya_log_ebpf::info;
 
 #[uretprobe(name="{{crate_name}}")]
-pub fn {{crate_name}}(ctx: ProbeContext) -> u32 {
+pub fn {{crate_name}}(ctx: ProbeContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: ProbeContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: ProbeContext) -> Result<(), c_long> {
     info!(&ctx, "function {{uprobe_fn_name}} called by {{uprobe_target}}");
-    Ok(0)
+    Ok(())
 }
 {%- when "sock_ops" %}
 use aya_bpf::{
+    cty::c_long,
     macros::sock_ops,
     programs::SockOpsContext,
 };
@@ -120,16 +116,17 @@ use aya_log_ebpf::info;
 pub fn {{crate_name}}(ctx: SockOpsContext) -> u32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => 1,
     }
 }
 
-fn try_{{crate_name}}(ctx: SockOpsContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: SockOpsContext) -> Result<u32, c_long> {
     info!(&ctx, "received TCP connection");
     Ok(0)
 }
 {%- when "sk_msg" %}
 use aya_bpf::{
+    cty::c_long,
     macros::{map, sk_msg},
     maps::SockHash,
     programs::SkMsgContext,
@@ -145,16 +142,21 @@ static {{sock_map}}: SockHash<SockKey> = SockHash::<SockKey>::with_max_entries(1
 pub fn {{crate_name}}(ctx: SkMsgContext) -> u32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => 1,
     }
 }
 
-fn try_{{crate_name}}(ctx: SkMsgContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: SkMsgContext) -> Result<u32, c_long> {
     info!(&ctx, "received a message on the socket");
     Ok(0)
 }
 {%- when "xdp" %}
-use aya_bpf::{bindings::xdp_action, macros::xdp, programs::XdpContext};
+use aya_bpf::{
+    bindings::xdp_action,
+    cty::c_long,
+    macros::xdp,
+    programs::XdpContext,
+};
 use aya_log_ebpf::info;
 
 #[xdp(name = "{{crate_name}}")]
@@ -165,28 +167,34 @@ pub fn {{crate_name}}(ctx: XdpContext) -> u32 {
     }
 }
 
-fn try_{{crate_name}}(ctx: XdpContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: XdpContext) -> Result<u32, c_long> {
     info!(&ctx, "received a packet");
     Ok(xdp_action::XDP_PASS)
 }
 {%- when "classifier" %}
-use aya_bpf::{macros::classifier, programs::TcContext};
+use aya_bpf::{
+    bindings::{TC_ACT_PIPE, TC_ACT_SHOT},
+    cty::c_long,
+    macros::classifier,
+    programs::TcContext,
+};
 use aya_log_ebpf::info;
 
 #[classifier(name = "{{crate_name}}")]
 pub fn {{crate_name}}(ctx: TcContext) -> i32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => TC_ACT_SHOT,
     }
 }
 
-fn try_{{crate_name}}(ctx: TcContext) -> Result<i32, i32> {
+fn try_{{crate_name}}(ctx: TcContext) -> Result<i32, c_long> {
     info!(&ctx, "received a packet");
-    Ok(0)
+    Ok(TC_ACT_PIPE)
 }
 {%- when "cgroup_skb" %}
 use aya_bpf::{
+    cty::c_long,
     macros::cgroup_skb,
     programs::SkBuffContext,
 };
@@ -196,35 +204,34 @@ use aya_log_ebpf::info;
 pub fn {{crate_name}}(ctx: SkBuffContext) -> i32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => 0,
     }
 }
 
-fn try_{{crate_name}}(ctx: SkBuffContext) -> Result<i32, i32> {
+fn try_{{crate_name}}(ctx: SkBuffContext) -> Result<i32, c_long> {
     info!(&ctx, "received a packet");
-    Ok(0)
+    Ok(1)
 }
 {%- when "tracepoint" %}
 use aya_bpf::{
+    cty::c_long,
     macros::tracepoint,
     programs::TracePointContext,
 };
 use aya_log_ebpf::info;
 
 #[tracepoint(name = "{{crate_name}}")]
-pub fn {{crate_name}}(ctx: TracePointContext) -> u32 {
+pub fn {{crate_name}}(ctx: TracePointContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: TracePointContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: TracePointContext) -> Result<(), c_long> {
     info!(&ctx, "tracepoint {{tracepoint_name}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "lsm" %}
 use aya_bpf::{
+    cty::c_long,
     macros::lsm,
     programs::LsmContext,
 };
@@ -234,45 +241,52 @@ use aya_log_ebpf::info;
 pub fn {{lsm_hook}}(ctx: LsmContext) -> i32 {
     match try_{{lsm_hook}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(ret) => 1,
     }
 }
 
-fn try_{{lsm_hook}}(ctx: LsmContext) -> Result<i32, i32> {
+fn try_{{lsm_hook}}(ctx: LsmContext) -> Result<i32, c_long> {
     info!(&ctx, "lsm hook {{lsm_hook}} called");
     Ok(0)
 }
 {%- when "tp_btf" %}
 use aya_bpf::{
+    cty::c_long,
     macros::btf_tracepoint,
     programs::BtfTracePointContext,
 };
 use aya_log_ebpf::info;
 
 #[btf_tracepoint(name = "{{tracepoint_name}}")]
-pub fn {{tracepoint_name}}(ctx: BtfTracePointContext) -> i32 {
+pub fn {{tracepoint_name}}(ctx: BtfTracePointContext) {
-    match try_{{tracepoint_name}}(ctx) {
+    let _ = try_{{tracepoint_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{tracepoint_name}}(ctx: BtfTracePointContext) -> Result<i32, i32> {
+fn try_{{tracepoint_name}}(ctx: BtfTracePointContext) -> Result<(), c_long> {
     info!(&ctx, "tracepoint {{tracepoint_name}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "socket_filter" %}
 use aya_bpf::{
+    cty::c_long,
     macros::socket_filter,
     programs::SkBuffContext,
 };
 
 #[socket_filter(name = "{{crate_name}}")]
-pub fn {{crate_name}}(_ctx: SkBuffContext) -> i64 {
+pub fn {{crate_name}}(ctx: SkBuffContext) -> i64 {
-    return 0
+    match try_{{crate_name}}(ctx) {
+        Ok(ret) => ret,
+        Err(_) => 0,
+    }
+}
+
+fn try_{{crate_name}}(ctx: SkBuffContext) -> Result<i64, c_long> {
+    Ok(0)
 }
 {%- when "cgroup_sysctl" %}
 use aya_bpf::{
+    cty::c_long,
     macros::cgroup_sysctl,
     programs::SysctlContext,
 };
@@ -282,61 +296,70 @@ use aya_log_ebpf::info;
 pub fn {{crate_name}}(ctx: SysctlContext) -> i32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => 0,
     }
 }
 
-fn try_{{crate_name}}(ctx: SysctlContext) -> Result<i32, i32> {
+fn try_{{crate_name}}(ctx: SysctlContext) -> Result<i32, c_long> {
     info!(&ctx, "sysctl operation called");
-    Ok(0)
+    Ok(1)
 }
 {%- when "cgroup_sockopt" %}
-use aya_bpf::{macros::cgroup_sockopt, programs::SockoptContext};
+use aya_bpf::{
+    cty::c_long,
+    macros::cgroup_sockopt,
+    programs::SockoptContext,
+};
 use aya_log_ebpf::info;
 
 #[cgroup_sockopt({{sockopt_target}}, name = "{{crate_name}}")]
 pub fn {{crate_name}}(ctx: SockoptContext) -> i32 {
     match try_{{crate_name}}(ctx) {
         Ok(ret) => ret,
-        Err(ret) => ret,
+        Err(_) => 0,
     }
 }
 
-fn try_{{crate_name}}(ctx: SockoptContext) -> Result<i32, i32> {
+fn try_{{crate_name}}(ctx: SockoptContext) -> Result<i32, c_long> {
     info!(&ctx, "{{sockopt_target}} called");
-    Ok(0)
+    Ok(1)
 }
 {%- when "raw_tracepoint" %}
-use aya_bpf::{macros::raw_tracepoint, programs::RawTracePointContext};
+use aya_bpf::{
+    cty::c_long,
+    macros::raw_tracepoint,
+    programs::RawTracePointContext,
+};
 use aya_log_ebpf::info;
 
 #[raw_tracepoint(name = "{{crate_name}}")]
-pub fn {{crate_name}}(ctx: RawTracePointContext) -> i32 {
+pub fn {{crate_name}}(ctx: RawTracePointContext) {
-    match try_{{crate_name}}(ctx) {
+    let _ = try_{{crate_name}}(ctx);
-        Ok(ret) => ret,
-        Err(ret) => ret,
-    }
 }
 
-fn try_{{crate_name}}(ctx: RawTracePointContext) -> Result<i32, i32> {
+fn try_{{crate_name}}(ctx: RawTracePointContext) -> Result<(), c_long> {
     info!(&ctx, "tracepoint {{tracepoint_name}} called");
-    Ok(0)
+    Ok(())
 }
 {%- when "perf_event" %}
 use aya_bpf::{
-    helpers::bpf_get_smp_processor_id, macros::perf_event, programs::PerfEventContext, BpfContext,
+    cty::c_long,
+    helpers::bpf_get_smp_processor_id,
+    macros::perf_event,
+    programs::PerfEventContext,
+    BpfContext,
 };
 use aya_log_ebpf::info;
 
 #[perf_event]
 pub fn {{crate_name}}(ctx: PerfEventContext) -> u32 {
     match try_{{crate_name}}(ctx) {
-        Ok(ret) => ret,
+        Ok(_) => 0,
-        Err(ret) => ret,
+        Err(_) => 1,
     }
 }
 
-fn try_{{crate_name}}(ctx: PerfEventContext) -> Result<u32, u32> {
+fn try_{{crate_name}}(ctx: PerfEventContext) -> Result<(), c_long> {
     let cpu = unsafe { bpf_get_smp_processor_id() };
     match ctx.pid() {
         0 => info!(
@@ -349,7 +372,7 @@ fn try_{{crate_name}}(ctx: PerfEventContext) -> Result<u32, u32> {
         ),
     }
 
-    Ok(0)
+    Ok(())
 }
 {%- endcase %}