fateshare: a plugin for managing child processes

For the reasons of modularity and security, it is useful
to have various functionality split into processes different from VPP.
However, this approach presents the challenges of managing those processes,
and is markedly different from simply running everything within VPP process.

This plugin is an experiment in having the VPP itself start off a monitor
process which in turn starts the child processes, and restarts them if they
quit.

If the VPP process ceases to exist, the monitor process terminates all
the descendant processes and quits itself.

This allows to preserve the "single entity to manage" approach of
simply running a barebones VPP.

An example of running it:

export DPDK_CONFIG=""
export DISABLED_PLUGINS=dpdk
export EXTRA_VPP_CONFIG="fateshare { monitor ./build-root/install-vpp_debug-native/vpp/bin/vpp_fateshare_monitor command ./test1 }"
make run

Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Change-Id: I66221fd7403f220d9652fe76958ca499cfd070a7
Type: feature

1 files changed, 287 insertions, 0 deletions

diff --git a/src/plugins/fateshare/fateshare.c b/src/plugins/fateshare/fateshare.c
new file mode 100644
index 00000000000..33ee167bce3
--- /dev/null
+++ b/src/plugins/fateshare/fateshare.c
@@ -0,0 +1,287 @@
+/*
+ * fateshare.c - skeleton vpp engine plug-in
+ *
+ * Copyright (c) 2022 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vnet/vnet.h>
+#include <vnet/plugin/plugin.h>
+#include <fateshare/fateshare.h>
+
+#include <vlibapi/api.h>
+#include <vlibmemory/api.h>
+#include <vpp/app/version.h>
+#include <stdbool.h>
+
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/prctl.h> // prctl(), PR_SET_PDEATHSIG
+#include <limits.h>
+
+fateshare_main_t fateshare_main;
+
+/* Action function shared between message handler and debug CLI */
+
+static void
+child_handler (int sig)
+{
+  pid_t pid;
+  int status;
+  fateshare_main_t *kmp = &fateshare_main;
+
+  while ((pid = waitpid (-1, &status, WNOHANG)) > 0)
+    {
+      if (pid == kmp->monitor_pid)
+	{
+	  clib_warning ("Monitor child %d exited with status %d!", pid,
+			status);
+	  kmp->vlib_main->main_loop_exit_now = 1;
+	}
+      else
+	{
+	  clib_warning ("child %d exited with status %d!", pid, status);
+	}
+    }
+}
+
+clib_error_t *
+launch_monitor (fateshare_main_t *kmp)
+{
+  clib_error_t *error = 0;
+  pid_t ppid_before_fork = getpid ();
+  pid_t cpid = fork ();
+  if (cpid == -1)
+    {
+      perror (0);
+      error = clib_error_return (0, "can not fork");
+      goto done;
+    }
+  clib_warning ("fateshare about to launch monitor %v.", kmp->monitor_cmd);
+  int logfd =
+    open ((char *) kmp->monitor_logfile, O_APPEND | O_RDWR | O_CREAT, 0777);
+  if (logfd < 0)
+    {
+      error = clib_error_return (0, "can not open log file");
+      goto done;
+    }
+  if (cpid)
+    {
+      /* parent */
+      kmp->monitor_pid = cpid;
+      close (logfd);
+      return 0;
+    }
+  else
+    {
+      dup2 (logfd, 1);
+      dup2 (logfd, 2);
+      int r = prctl (PR_SET_PDEATHSIG, SIGTERM);
+      if (r == -1)
+	{
+	  perror (0);
+	  exit (1);
+	}
+      pid_t current_ppid = getppid ();
+      if (current_ppid != ppid_before_fork)
+	{
+	  fprintf (stderr, "parent pid changed while starting (%d => %d)\n",
+		   ppid_before_fork, current_ppid);
+	  if (current_ppid == 1)
+	    {
+	      fprintf (stderr, "exiting.\n");
+	      exit (1);
+	    }
+	}
+
+      int r1 = setpgid (getpid (), 0);
+      if (r1 != 0)
+	{
+	  perror ("setpgid error");
+	  exit (1);
+	}
+
+      u8 *scmd = format (0, "%v\0", kmp->monitor_cmd);
+      u8 *logfile_base = format (0, "%v\0", kmp->monitor_logfile);
+      int fd = logfd - 1;
+      while (fd > 2)
+	{
+	  close (fd);
+	  fd--;
+	}
+
+      fd = open ("/dev/null", O_RDONLY);
+      if (fd < 0)
+	{
+	  exit (1);
+	}
+      dup2 (fd, 0);
+
+      char *ppid_str = (char *) format (0, "%lld\0", current_ppid);
+
+      char **argv = 0;
+      vec_validate (argv, vec_len (kmp->commands) + 3 - 1);
+      argv[0] = (void *) scmd;
+      argv[1] = ppid_str;
+      argv[2] = (char *) logfile_base;
+      int i;
+      vec_foreach_index (i, kmp->commands)
+	{
+	  argv[3 + i] = (char *) kmp->commands[i];
+	}
+
+      int res = execv (argv[0], argv);
+      clib_warning ("ERROR during execve: %d", res);
+      perror ("execve");
+
+      exit (0);
+    }
+done:
+
+  return error;
+}
+
+static clib_error_t *
+fateshare_config (vlib_main_t *vm, unformat_input_t *input)
+{
+  fateshare_main_t *fmp = &fateshare_main;
+  u8 *command = 0;
+  u8 **new_command = 0;
+  clib_error_t *error = 0;
+
+  /* unix config may make vpp fork, we want to run after that. */
+  if ((error = vlib_call_config_function (vm, unix_config)))
+    return error;
+
+  /* Defaults */
+  while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
+    {
+      if (unformat (input, "monitor %s", &fmp->monitor_cmd))
+	{
+	  clib_warning ("setting monitor to %v", fmp->monitor_cmd);
+	}
+      else if (unformat (input, "logfile %s", &fmp->monitor_logfile))
+	{
+	  clib_warning ("setting logfile to %v", fmp->monitor_logfile);
+	}
+      else if (unformat (input, "command %s", &command))
+	{
+	  vec_add2 (fmp->commands, new_command, 1);
+	  *new_command = command;
+	}
+      else
+	return clib_error_return (0, "unknown input `%U'",
+				  format_unformat_error, input);
+    }
+
+  vec_add2 (fmp->commands, new_command, 1);
+  *new_command = 0;
+
+  /* Establish handler. */
+  struct sigaction sa;
+  sigemptyset (&sa.sa_mask);
+  sa.sa_flags = 0;
+  sa.sa_handler = child_handler;
+
+  sigaction (SIGCHLD, &sa, NULL);
+
+  if (fmp->monitor_cmd == 0)
+    {
+      char *p, path[PATH_MAX];
+      int rv;
+
+      /* find executable path */
+      if ((rv = readlink ("/proc/self/exe", path, PATH_MAX - 1)) == -1)
+	return clib_error_return (
+	  0, "could not stat /proc/self/exe - set monitor manually");
+
+      /* readlink doesn't provide null termination */
+      path[rv] = 0;
+
+      /* strip filename */
+      if ((p = strrchr (path, '/')) == 0)
+	return clib_error_return (
+	  0, "could not determine vpp directory - set monitor manually");
+      *p = 0;
+
+      fmp->monitor_cmd = format (0, "%s/vpp_fateshare_monitor\0", path);
+    }
+  if (fmp->monitor_logfile == 0)
+    {
+      fmp->monitor_logfile =
+	format (0, "/tmp/vpp-fateshare-monitor-log.txt\0");
+    }
+  error = launch_monitor (fmp);
+
+  return error;
+}
+
+clib_error_t *
+fateshare_init (vlib_main_t *vm)
+{
+  fateshare_main_t *kmp = &fateshare_main;
+  clib_error_t *error = 0;
+
+  kmp->vlib_main = vm;
+
+  return error;
+}
+
+static clib_error_t *
+fateshare_send_hup_fn (vlib_main_t *vm, unformat_input_t *input,
+		       vlib_cli_command_t *cmd)
+{
+  clib_error_t *error = 0;
+  fateshare_main_t *kmp = &fateshare_main;
+
+  if (kmp->monitor_pid)
+    {
+      int rc = kill (kmp->monitor_pid, SIGHUP);
+      if (rc)
+	{
+	  error = clib_error_return (
+	    0, "can not send signal to monitor process: %s", strerror (errno));
+	}
+    }
+  else
+    {
+      error = clib_error_return (0, "can not find monitor process");
+    }
+
+  return error;
+}
+
+VLIB_EARLY_CONFIG_FUNCTION (fateshare_config, "fateshare");
+
+VLIB_INIT_FUNCTION (fateshare_init);
+
+VLIB_CLI_COMMAND (fateshare_restart_process_command, static) = {
+  .path = "fateshare restart-processes",
+  .short_help = "restart dependent processes",
+  .function = fateshare_send_hup_fn,
+};
+
+VLIB_PLUGIN_REGISTER () = {
+  .version = VPP_BUILD_VER,
+  .description = "Run child processes which will share fate with VPP, restart "
+		 "them if they quit",
+  .default_disabled = 1,
+};
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */