xattrs: Add a test case for previous commits

This is actually the first test case in libglnx 🙌; hopefully the
consumers are prepared for us injecting into `TESTS`.

Makefile-libglnx.am

@@ -51,3 +51,10 @@ libglnx_la_SOURCES = \
 libglnx_la_CFLAGS = $(AM_CFLAGS) $(libglnx_cflags)
 libglnx_la_LDFLAGS = -avoid-version -Bsymbolic-functions -export-symbols-regex "^glnx_" -no-undefined -export-dynamic 
 libglnx_la_LIBADD = $(libglnx_libs)
+
+TESTS += test-libglnx-xattrs
+
+check_PROGRAMS += test-libglnx-xattrs
+test_libglnx_xattrs_SOURCES = $(libglnx_srcpath)/tests/test-libglnx-xattrs.c
+test_libglnx_xattrs_CFLAGS = $(AM_CFLAGS) $(libglnx_cflags)
+test_libglnx_xattrs_LDADD = $(libglnx_libs) libglnx.la

tests/test-libglnx-xattrs.c

@@ -0,0 +1,282 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2017 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include "config.h"
+#include "libglnx.h"
+#include <glib.h>
+#include <stdlib.h>
+#include <gio/gio.h>
+#include <string.h>
+
+#define XATTR_THREAD_RUN_TIME_USECS (5 * G_USEC_PER_SEC)
+
+struct XattrWorker {
+  int dfd;
+  gboolean is_writer;
+  guint n_attrs_read;
+};
+
+typedef enum {
+  WRITE_RUN_MUTATE,
+  WRITE_RUN_CREATE,
+} WriteType;
+
+static gboolean
+set_random_xattr_value (int fd, const char *name, GError **error)
+{
+  const guint8 randxattrbyte = g_random_int_range (0, 256);
+  const guint32 randxattrvalue_len = g_random_int () % 256; /* Picked to be not too small or large */
+  g_autofree char *randxattrvalue = g_malloc (randxattrvalue_len);
+
+  memset (randxattrvalue, randxattrbyte, randxattrvalue_len);
+
+  if (fsetxattr (fd, name, randxattrvalue, randxattrvalue_len, 0) < 0)
+    {
+      glnx_set_error_from_errno (error);
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static gboolean
+add_random_xattrs (int fd, GError **error)
+{
+  const guint nattrs = MIN (2, g_random_int () % 16);
+
+  for (guint i = 0; i < nattrs; i++)
+    {
+      guint32 randxattrname_v = g_random_int ();
+      g_autofree char *randxattrname = g_strdup_printf ("user.test%u", randxattrname_v);
+
+      if (!set_random_xattr_value (fd, randxattrname, error))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
+static gboolean
+do_write_run (GLnxDirFdIterator *dfd_iter, GError **error)
+{
+  WriteType wtype = g_random_int () % 2;
+
+  if (wtype == WRITE_RUN_CREATE)
+    {
+      guint32 randname_v = g_random_int ();
+      g_autofree char *randname = g_strdup_printf ("file%u", randname_v);
+      glnx_fd_close int fd = -1;
+
+    again:
+      fd = openat (dfd_iter->fd, randname, O_CREAT | O_EXCL, 0644);
+      if (fd < 0)
+        {
+          if (errno == EEXIST)
+            {
+              g_printerr ("Congratulations!  I suggest purchasing a lottery ticket today!\n");
+              goto again;
+            }
+          else
+            {
+              glnx_set_error_from_errno (error);
+              return FALSE;
+            }
+        }
+
+      if (!add_random_xattrs (fd, error))
+        return FALSE;
+      }
+  else if (wtype == WRITE_RUN_MUTATE)
+    {
+      while (TRUE)
+        {
+          g_autoptr(GVariant) current_xattrs = NULL;
+          glnx_fd_close int fd = -1;
+
+          struct dirent *dent;
+          if (!glnx_dirfd_iterator_next_dent (dfd_iter, &dent, NULL, error))
+            return FALSE;
+          if (!dent)
+            break;
+
+          fd = openat (dfd_iter->fd, dent->d_name, O_RDONLY | O_CLOEXEC);
+          if (fd < 0)
+            {
+              glnx_set_error_from_errno (error);
+              return FALSE;
+            }
+
+          if (!glnx_fd_get_all_xattrs (fd, &current_xattrs, NULL, error))
+            return FALSE;
+
+          for (int i = 0; i < g_variant_n_children (current_xattrs); i++)
+            {
+              const char *name, *value;
+              g_variant_get_child (current_xattrs, i, "(^&ay^&ay)", &name, &value);
+
+              /* We don't want to potentially test/change xattrs like security.selinux
+               * that were injected by the system.
+               */
+              if (!g_str_has_prefix (name, "user.test"))
+                continue;
+
+              if (!set_random_xattr_value (fd, name, error))
+                return FALSE;
+            }
+        }
+    }
+  else
+    g_assert_not_reached ();
+
+  return TRUE;
+}
+
+static gboolean
+do_read_run (GLnxDirFdIterator *dfd_iter,
+             guint *out_n_read,
+             GError **error)
+{
+  guint nattrs = 0;
+  while (TRUE)
+    {
+      g_autoptr(GVariant) current_xattrs = NULL;
+      glnx_fd_close int fd = -1;
+
+      struct dirent *dent;
+      if (!glnx_dirfd_iterator_next_dent (dfd_iter, &dent, NULL, error))
+        return FALSE;
+      if (!dent)
+        break;
+
+      fd = openat (dfd_iter->fd, dent->d_name, O_RDONLY | O_CLOEXEC);
+      if (fd < 0)
+        {
+          glnx_set_error_from_errno (error);
+          return FALSE;
+        }
+
+      if (!glnx_fd_get_all_xattrs (fd, &current_xattrs, NULL, error))
+        return FALSE;
+
+      /* We don't actually care about the values, just use the variable
+       * to avoid compiler warnings.
+       */
+      nattrs += g_variant_n_children (current_xattrs);
+    }
+
+  *out_n_read = nattrs;
+  return TRUE;
+}
+
+static gpointer
+xattr_thread (gpointer data)
+{
+  g_autoptr(GError) local_error = NULL;
+  GError **error = &local_error;
+  struct XattrWorker *worker = data;
+  guint64 end_time = g_get_monotonic_time () + XATTR_THREAD_RUN_TIME_USECS;
+  guint n_read;
+
+  while (g_get_monotonic_time () < end_time)
+    {
+      g_auto(GLnxDirFdIterator) dfd_iter = { 0, };
+
+      if (!glnx_dirfd_iterator_init_at (worker->dfd, ".", TRUE, &dfd_iter, error))
+        goto out;
+
+      if (worker->is_writer)
+        {
+          if (!do_write_run (&dfd_iter, error))
+            goto out;
+        }
+      else
+        {
+          if (!do_read_run (&dfd_iter, &n_read, error))
+            goto out;
+        }
+    }
+
+ out:
+  g_assert_no_error (local_error);
+
+  return GINT_TO_POINTER (n_read);
+}
+
+static void
+test_xattr_races (void)
+{
+  /* If for some reason we're built in a VM which only has one vcpu, let's still
+   * at least make the test do something.
+   */
+  /* FIXME - this deadlocks for me on 4.9.4-201.fc25.x86_64, whether
+   * using overlayfs or xfs as source/dest.
+   */
+  const guint nprocs = MAX (4, g_get_num_processors ());
+  struct XattrWorker wdata[nprocs];
+  GThread *threads[nprocs];
+  g_autoptr(GError) local_error = NULL;
+  GError **error = &local_error;
+  glnx_fd_close int dfd = -1;
+  g_autofree char *tmpdir = g_strdup_printf ("%s/libglnx-xattrs-XXXXXX",
+                                             getenv ("TMPDIR") ?: "/var/tmp");
+  guint nread = 0;
+
+  if (!glnx_mkdtempat (AT_FDCWD, tmpdir, 0700, error))
+    goto out;
+
+  if (!glnx_opendirat (AT_FDCWD, tmpdir, TRUE, &dfd, error))
+    goto out;
+
+  for (guint i = 0; i < nprocs; i++)
+    {
+      struct XattrWorker *worker = &wdata[i];
+      worker->dfd = dfd;
+      worker->is_writer = i % 2 == 0;
+      threads[i] = g_thread_new (NULL, xattr_thread, worker);
+    }
+
+  for (guint i = 0; i < nprocs; i++)
+    {
+      if (wdata[i].is_writer)
+        (void) g_thread_join (threads[i]);
+      else
+        nread += GPOINTER_TO_UINT (g_thread_join (threads[i]));
+    }
+
+  g_print ("Read %u xattrs race free!\n", nread);
+
+  (void) glnx_shutil_rm_rf_at (AT_FDCWD, tmpdir, NULL, NULL);
+
+ out:
+  g_assert_no_error (local_error);
+}
+
+int main (int argc, char **argv)
+{
+  int ret;
+
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/xattr-races", test_xattr_races);
+
+  ret = g_test_run();
+
+  return ret;
+}