Add the documentation for debugging

Signed-off-by: utam0k <k0ma@utam0k.jp>

docs/src/SUMMARY.md

@@ -22,6 +22,7 @@
   - [Good places to start](./developer/good_places_to_start.md)
   - [This Documentation](./developer/documentation_mdbook.md)
   - [Repository Structure](./developer/repo_structure.md)
+  - [Debugging](./developer/debugging.md)
   - [Crate Specific Information](./developer/crate_specific_information.md)
     - [libcgroups](./developer/libcgroups.md)
     - [libcontainer](./developer/libcontainer.md)

docs/src/developer/debugging.md

@@ -0,0 +1,85 @@
+# Debugging
+
+Since Youki uses pipe and double-fork in the creating phase, it is hard to debug what happened.
+You might encounter the error message, "Broken pipe ..." Unfortunately, 
+this error message has only information that a child process exists with an error for some reason.
+
+This section will give some tips to debug youki to know what happens in the child processes.
+
+# bpftrace
+
+[bpftrace](https://github.com/iovisor/bpftrace) is an eBPF based tool.
+In the case of youki, you can catch the system calls youki issued.
+For example, if you catch a write system call, you can see the log output until the middle of process.
+It allows you to do something similar to print debugging.
+
+_How to debug_
+1. You need to install bpftrace, please refere to [the official documentation](https://github.com/iovisor/bpftrace/blob/master/INSTALL.md) to know how to install it.
+2. Before running the process or comannd you want to debug, run the following command in another terminal.
+
+    You need the root privilege to run it.
+    ```console
+    $ cd ${youki_repo}
+    $ just hack-bpftrace
+    ```
+3. Run the command you want to debug.
+
+_For example_
+
+1. Run the bpftrace script.
+
+    ```console
+    $ just hack-bpftrace
+    BPFTRACE_STRLEN=120 ./hack/debug.bt
+    Attaching 13 probes...
+    Tracing Youki syscalls... Hit Ctrl-C to end.
+    TIME                 COMMAND PID      EVENT     CONTENT
+    ```
+
+2. Run the Kubernetes cluster using kind with youki
+
+    ```console
+    $ cd ${youki_repo}
+    $ just test-kind
+    docker buildx build --output=bin/ -f tests/k8s/Dockerfile --target kind-bin .
+    ...
+    Creating cluster "youki" ...
+    ...
+    kubectl --context=kind-youki apply -f tests/k8s/deploy.yaml
+    runtimeclass.node.k8s.io/youki created
+    deployment.apps/nginx-deployment created
+    ...
+    kubectl --context=kind-youki delete -f tests/k8s/deploy.yaml
+    runtimeclass.node.k8s.io "youki" deleted
+    deployment.apps "nginx-deployment" deleted
+    ```
+
+3. Returning to the first command executed, the system calls youki issued are caught and logged.
+    
+    ```console
+    $ just hack-bpftrace
+    BPFTRACE_STRLEN=120 ./hack/debug.bt
+    Attaching 13 probes...
+    Tracing Youki syscalls... Hit Ctrl-C to end.
+    TIME                 COMMAND PID      EVENT     CONTENT
+    207033348942           youki 13743    open      errno=2, fd=-1, file=/opt/containerd/lib/glibc-hwcaps/x86-64-v3/libc.so.6
+    ...
+    207035462044           youki 13743    open      errno=0, fd=3, file=/proc/self/exe
+    207035478523           youki 13743    write     fd=4, ELF
+    207066996623               4 13743    open      errno=2, fd=-1, file=/opt/containerd/lib/glibc-hwcaps/x86-64-v3/libc.so.6
+    ...
+    207070130175               4 13743    clone3
+    207070418829 youki:[1:INTER] 13747    write     fd=4, {"timestamp":"2023-09-24T10:47:07.427846Z","level":"INFO","message":"cgroup manager V2 will be used","target":"libcgrou
+    ...
+    207084948440 youki:[1:INTER] 13747    clone3
+    207085058811 youki:[1:INTER] 13747    write     fd=4, {"timestamp":"2023-09-24T10:47:07.442502Z","level":"DEBUG","message":"sending init pid (Pid(1305))","target":"libcontai
+    207085343170  youki:[2:INIT] 13750    write     fd=4, {"timestamp":"2023-09-24T10:47:07.442746Z","level":"DEBUG","message":"unshare or setns: LinuxNamespace { typ: Uts, path
+    ...
+    207088256843  youki:[2:INIT] 13750    pivt_root new_root=/run/containerd/io.containerd.runtime.v2.task/k8s.io/0fea8cf5f8d1619a35ca67fd6fa73d8d7c8fc70ac2ed43ee2ac2f8610bb938f6/r, put_old=/run/containerd/io.containerd.runtime.v2.task/k8s.io/0fea8cf5f8d1619a35ca67fd6fa73d8d7c8fc70ac2ed43ee2ac2f8610bb938f6/r
+    ...
+    207097207551  youki:[2:INIT] 13750    write     fd=4, {"timestamp":"2023-09-24T10:47:07.454645Z","level":"DEBUG","message":"found executable in executor","executable":"\"/pa
+    ...
+    207139391811  youki:[2:INIT] 13750    write     fd=4, {"timestamp":"2023-09-24T10:47:07.496815Z","level":"DEBUG","message":"received: start container","target":"libcontainer
+    207139423243  youki:[2:INIT] 13750    write     fd=4, {"timestamp":"2023-09-24T10:47:07.496868Z","level":"DEBUG","message":"executing workload with default handler","target"
+
+    ```