janitor.cpp

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#include <chrono>
#include <cstdlib>
#include <thread>
#include <filesystem>
#include <csignal>
 
#include "../std/expected.hpp"
#include "../lib/log.hpp"
#include "../lib/fuse.hpp"
#include "../macro.hpp"
 
// https://stackoverflow.com/questions/24931456/how-does-sig-atomic-t-actually-work
// https://en.cppreference.com/w/cpp/utility/program/sig_atomic_t.html
// https://man7.org/linux/man-pages/man7/signal-safety.7.html
// https://www.cs.wm.edu/~smherwig/courses/csci415-common/signals/sig_atomic/index.html
volatile std::sig_atomic_t G_PARENT_OK = 0;

void cleanup([[maybe_unused]] int sig)
{
  G_PARENT_OK = 1;
}
 

[[nodiscard]] Value<void> boot(int argc, char** argv)
{
  // Register signal handlers
  signal(SIGTERM, cleanup);
  // Ignore SIGPIPE - when parent dies and pipe readers close, we can still cleanup
  signal(SIGPIPE, SIG_IGN);
  // Check argc
  return_if(argc < 3, Error("E::Incorrect usage: fim_janitor <parent_pid> <log_path>"));
  // Get pid to wait for
  pid_t pid_parent = Try(std::stoi(argv[1]));
  // Get log path from parent
  std::string path_log_file = argv[2];
  // Create a novel session for the child process
  pid_t pid_session = setsid();
  return_if(pid_session < 0, Error("E::Failed to create a novel session for janitor"));
  // Enable logger to write INFO messages to stdout (for pipe capture)
  ns_log::set_level(ns_log::Level::DEBUG);
  ns_log::set_as_fork();
  // Configure logger sink to write directly to file (fallback if pipe readers die)
  ns_log::set_sink_file(path_log_file);
  logger("I::Session id is '{}'", pid_session);
  // Wait for parent process to exit
  while (not G_PARENT_OK and kill(pid_parent, 0) == 0)
  {
    std::this_thread::sleep_for(std::chrono::milliseconds{100});
  }
  // Check if should skip clean
  if(G_PARENT_OK)
  {
    logger("I::Parent process with pid '{}' finished", pid_parent);
    return {};
  }
  // Log that parent exited abnormally
  logger("E::Parent process with pid '{}' failed to send skip signal", pid_parent);
  // Cleanup of mountpoints
  for (auto&& path_dir_mountpoint : std::vector<std::filesystem::path>(argv+2, argv+argc))
  {
    logger("I::Un-mount '{}'", path_dir_mountpoint);
    ns_fuse::unmount(path_dir_mountpoint).discard("E::Could not un-mount '{}'", path_dir_mountpoint);
  }
  return {};
}

int main(int argc, char** argv)
{
  auto __expected_fn = [](auto&&){ return 1; };
  Pop(boot(argc, argv), "C::Failure to start janitor");
  return EXIT_SUCCESS;
} // main
 
/* vim: set expandtab fdm=marker ts=2 sw=2 tw=100 et :*/