krun/nitro: Redirect enclave VM output to stdout

Nitro enclaves print their output logs via vsock. As such, libkrun-nitro
spawns a listener thread to retrieve enclave application output from
vsock and forward it to a file.

Redirect all krun-nitro application output to stdout to allowing viewing
of logs from container applications launched within nitro enclaves.

Signed-off-by: Tyler Fanelli <tfanelli@redhat.com>

Author: tylerfanelli

src/libcrun/handlers/krun.c

@@ -311,6 +311,7 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
   int32_t (*krun_set_root) (uint32_t ctx_id, const char *root_path);
   int32_t (*krun_set_root_disk) (uint32_t ctx_id, const char *disk_path);
   int32_t (*krun_set_tee_config_file) (uint32_t ctx_id, const char *file_path);
+  int32_t (*krun_set_console_output) (uint32_t ctx_id, const char *c_filepath);
   struct krun_config *kconf = (struct krun_config *) cookie;
   void *handle;
   uint32_t num_vcpus, ram_mib;
@@ -370,6 +371,19 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
         error (EXIT_FAILURE, -ret, "could not set krun root");
     }
 
+  if (kconf->nitro)
+    {
+      // need krun_set_exec and krun_set_console_output.
+      krun_set_console_output = dlsym (handle, "krun_set_console_output");
+      if (krun_set_console_output == NULL)
+        error (EXIT_FAILURE, 0, "could not find symbol in `libkrun.so`");
+
+      // Redirect all enclave output (read from vsock) to stdout.
+      ret = krun_set_console_output (ctx_id, "/dev/stdout");
+      if (UNLIKELY (ret < 0))
+        error (EXIT_FAILURE, -ret, "could not redirect enclave output to stdout");
+    }
+
   ret = libkrun_configure_vm (ctx_id, handle, &configured, &config_tree, &err);
   if (UNLIKELY (ret))
     {