linux: fix a hang if there are no reads from the tty

Makefile.am

@@ -35,6 +35,7 @@ endif
 check_LTLIBRARIES = libcrun_testing.la
 
 libcrun_SOURCES = src/libcrun/utils.c \
+		src/libcrun/ring_buffer.c \
 		src/libcrun/blake3/blake3.c \
 		src/libcrun/blake3/blake3_portable.c \
 		src/libcrun/cgroup-cgroupfs.c \
@@ -154,12 +155,12 @@ EXTRA_DIST = COPYING COPYING.libcrun README.md NEWS SECURITY.md rpm/crun.spec au
 	src/libcrun/handlers/handler-utils.h \
 	src/libcrun/linux.h src/libcrun/utils.h src/libcrun/error.h src/libcrun/criu.h \
 	src/libcrun/scheduler.h src/libcrun/status.h src/libcrun/terminal.h \
-	src/libcrun/mount_flags.h src/libcrun/intelrdt.h \
+	src/libcrun/mount_flags.h src/libcrun/intelrdt.h src/libcrun/ring_buffer.h \
 	crun.1.md crun.1 libcrun.lds \
 	krun.1.md krun.1 \
 	lua/luacrun.rockspec
 
-UNIT_TESTS = tests/tests_libcrun_utils tests/tests_libcrun_errors tests/tests_libcrun_intelrdt
+UNIT_TESTS = tests/tests_libcrun_utils tests/tests_libcrun_ring_buffer tests/tests_libcrun_errors tests/tests_libcrun_intelrdt
 
 if ENABLE_CRUN
 bin_PROGRAMS = crun
@@ -181,6 +182,11 @@ tests_tests_libcrun_utils_SOURCES = tests/tests_libcrun_utils.c
 tests_tests_libcrun_utils_LDADD = $(TESTS_LDADD)
 tests_tests_libcrun_utils_LDFLAGS = $(crun_LDFLAGS)
 
+tests_tests_libcrun_ring_buffer_CFLAGS = -I $(abs_top_builddir)/libocispec/src -I $(abs_top_srcdir)/libocispec/src -I $(abs_top_builddir)/src -I $(abs_top_srcdir)/src
+tests_tests_libcrun_ring_buffer_SOURCES = tests/tests_libcrun_ring_buffer.c
+tests_tests_libcrun_ring_buffer_LDADD = $(TESTS_LDADD)
+tests_tests_libcrun_ring_buffer_LDFLAGS = $(crun_LDFLAGS)
+
 tests_tests_libcrun_intelrdt_CFLAGS = -I $(abs_top_builddir)/libocispec/src -I $(abs_top_srcdir)/libocispec/src -I $(abs_top_builddir)/src -I $(abs_top_srcdir)/src
 tests_tests_libcrun_intelrdt_SOURCES = tests/tests_libcrun_intelrdt.c
 tests_tests_libcrun_intelrdt_LDADD = $(TESTS_LDADD)

src/libcrun/container.c

@@ -1968,21 +1968,34 @@ struct wait_for_process_args
 static int
 wait_for_process (struct wait_for_process_args *args, libcrun_error_t *err)
 {
+  cleanup_channel_fd_pair struct channel_fd_pair *from_terminal = NULL;
+  cleanup_channel_fd_pair struct channel_fd_pair *to_terminal = NULL;
+  int ret, container_exit_code = 0, last_process;
+  cleanup_close int terminal_fd_from = -1;
+  cleanup_close int terminal_fd_to = -1;
+  const size_t max_events = 10;
   cleanup_close int epollfd = -1;
   cleanup_close int signalfd = -1;
-  int ret, container_exit_code = 0, last_process;
   sigset_t mask;
-  int fds[10];
-  int levelfds[10];
-  int levelfds_len = 0;
-  int fds_len = 0;
+  int in_fds[max_events];
+  int in_fds_len = 0;
+  int out_fds[max_events];
+  int out_fds_len = 0;
+  size_t i;
+
   cleanup_seccomp_notify_context struct seccomp_notify_context_s *seccomp_notify_ctx = NULL;
 
   container_exit_code = 0;
 
   if (args == NULL || args->context == NULL)
     return crun_make_error (err, 0, "internal error: context is empty");
 
+  for (i = 0; i < max_events; i++)
+    {
+      in_fds[i] = -1;
+      out_fds[i] = -1;
+    }
+
   if (args->context->pid_file)
     {
       char buf[32];
@@ -2041,7 +2054,7 @@ wait_for_process (struct wait_for_process_args *args, libcrun_error_t *err)
       conf.bundle_path = args->context->bundle;
       conf.oci_config_path = oci_config_path;
 
-      ret = set_blocking_fd (args->seccomp_notify_fd, 0, err);
+      ret = set_blocking_fd (args->seccomp_notify_fd, false, err);
       if (UNLIKELY (ret < 0))
         return ret;
 
@@ -2051,65 +2064,81 @@ wait_for_process (struct wait_for_process_args *args, libcrun_error_t *err)
       if (UNLIKELY (ret < 0))
         return ret;
 
-      fds[fds_len++] = args->seccomp_notify_fd;
+      in_fds[in_fds_len++] = args->seccomp_notify_fd;
+    }
+
+  if (args->terminal_fd >= 0)
+    {
+      /* The terminal_fd is dup()ed so that it can be registered with
+         epoll multiple times using different masks.  */
+      terminal_fd_from = dup (args->terminal_fd);
+      if (UNLIKELY (terminal_fd_from < 0))
+        return crun_make_error (err, errno, "dup terminal fd");
+      terminal_fd_to = dup (args->terminal_fd);
+      if (UNLIKELY (terminal_fd_to < 0))
+        return crun_make_error (err, errno, "dup terminal fd");
+
+      int i, non_blocking_fds[] = { terminal_fd_from, terminal_fd_to, 0, 1, -1 };
+      for (i = 0; non_blocking_fds[i] >= 0; i++)
+        {
+          ret = set_blocking_fd (non_blocking_fds[i], false, err);
+          if (UNLIKELY (ret < 0))
+            return ret;
+        }
+
+      from_terminal = channel_fd_pair_new (terminal_fd_from, 1, BUFSIZ);
+      to_terminal = channel_fd_pair_new (0, terminal_fd_to, BUFSIZ);
     }
 
-  fds[fds_len++] = signalfd;
+  in_fds[in_fds_len++] = signalfd;
   if (args->notify_socket >= 0)
-    fds[fds_len++] = args->notify_socket;
+    in_fds[in_fds_len++] = args->notify_socket;
   if (args->terminal_fd >= 0)
     {
-      fds[fds_len++] = 0;
-      levelfds[levelfds_len++] = args->terminal_fd;
+      in_fds[in_fds_len++] = 0;
+      out_fds[out_fds_len++] = terminal_fd_to;
+
+      in_fds[in_fds_len++] = terminal_fd_from;
+      out_fds[out_fds_len++] = 1;
     }
-  fds[fds_len++] = -1;
-  levelfds[levelfds_len++] = -1;
 
-  epollfd = epoll_helper (fds, levelfds, err);
+  epollfd = epoll_helper (in_fds, NULL, out_fds, NULL, err);
   if (UNLIKELY (epollfd < 0))
     return epollfd;
 
   while (1)
     {
+      struct epoll_event events[max_events];
       struct signalfd_siginfo si;
       struct winsize ws;
-      ssize_t res;
-      struct epoll_event events[10];
       int i, nr_events;
+      ssize_t res;
 
-      nr_events = TEMP_FAILURE_RETRY (epoll_wait (epollfd, events, 10, -1));
+      nr_events = TEMP_FAILURE_RETRY (epoll_wait (epollfd, events, max_events, -1));
       if (UNLIKELY (nr_events < 0))
         return crun_make_error (err, errno, "epoll_wait");
 
       for (i = 0; i < nr_events; i++)
         {
-          if (events[i].data.fd == 0)
+          if (events[i].data.fd == 0 || events[i].data.fd == terminal_fd_to)
             {
-              ret = copy_from_fd_to_fd (0, args->terminal_fd, 0, err);
+              ret = channel_fd_pair_process (to_terminal, epollfd, err);
               if (UNLIKELY (ret < 0))
                 return crun_error_wrap (err, "copy to terminal fd");
             }
+          else if (events[i].data.fd == 1 || events[i].data.fd == terminal_fd_from)
+            {
+              ret = channel_fd_pair_process (from_terminal, epollfd, err);
+              if (UNLIKELY (ret < 0))
+                return crun_error_wrap (err, "copy from terminal fd");
+            }
           else if (events[i].data.fd == args->seccomp_notify_fd)
             {
               ret = libcrun_seccomp_notify_plugins (seccomp_notify_ctx,
                                                     args->seccomp_notify_fd, err);
               if (UNLIKELY (ret < 0))
                 return ret;
             }
-          else if (events[i].data.fd == args->terminal_fd)
-            {
-              ret = set_blocking_fd (args->terminal_fd, 0, err);
-              if (UNLIKELY (ret < 0))
-                return crun_error_wrap (err, "set terminal fd not blocking");
-
-              ret = copy_from_fd_to_fd (args->terminal_fd, 1, 1, err);
-              if (UNLIKELY (ret < 0))
-                return crun_error_wrap (err, "copy from terminal fd");
-
-              ret = set_blocking_fd (args->terminal_fd, 1, err);
-              if (UNLIKELY (ret < 0))
-                return crun_error_wrap (err, "set terminal fd blocking");
-            }
           else if (events[i].data.fd == args->notify_socket)
             {
               ret = handle_notify_socket (args->notify_socket, err);