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[dconf/wip/nfs-client] wip: NFS on the library side

commit 81521e8c1fef4911901278bff90746d2b3cc6ebf
Author: Ryan Lortie <desrt desrt ca>
Date:   Tue Oct 23 10:14:43 2012 +0200

    wip: NFS on the library side

 engine/Makefile.am                    |    1 +
 engine/dconf-engine-source-private.h  |    1 +
 engine/dconf-engine-source-user-nfs.c |   93 +++++++++++++++++
 engine/dconf-engine-source.c          |   17 +++-
 service/dconf-nfs-writer.c            |  182 +++++++++++++++++++++++++++++++++
 shm/Makefile.am                       |    3 +-
 shm/dconf-shm-nfs-check.c             |   63 +++++++++++
 shm/dconf-shm.c                       |    2 +-
 shm/dconf-shm.h                       |    6 +
 tests/dconf-mock-shm.c                |   12 ++
 10 files changed, 375 insertions(+), 5 deletions(-)
---
diff --git a/engine/Makefile.am b/engine/Makefile.am
index b69c70c..8eda5f1 100644
--- a/engine/Makefile.am
+++ b/engine/Makefile.am
@@ -9,6 +9,7 @@ libdconf_engine_a_SOURCES = \
 	dconf-engine-source-private.h	\
 	dconf-engine-source.h		\
 	dconf-engine-source-user.c	\
+	dconf-engine-source-user-nfs.c	\
 	dconf-engine-source-system.c	\
 	dconf-engine-source.c		\
 	dconf-engine.h			\
diff --git a/engine/dconf-engine-source-private.h b/engine/dconf-engine-source-private.h
index 822354a..57840dc 100644
--- a/engine/dconf-engine-source-private.h
+++ b/engine/dconf-engine-source-private.h
@@ -26,6 +26,7 @@
 #include "dconf-engine-source.h"
 
 G_GNUC_INTERNAL extern const DConfEngineSourceVTable dconf_engine_source_user_vtable;
+G_GNUC_INTERNAL extern const DConfEngineSourceVTable dconf_engine_source_user_nfs_vtable;
 G_GNUC_INTERNAL extern const DConfEngineSourceVTable dconf_engine_source_system_vtable;
 
 #endif /* __dconf_engine_source_private_h__ */
diff --git a/engine/dconf-engine-source-user-nfs.c b/engine/dconf-engine-source-user-nfs.c
new file mode 100644
index 0000000..336fa04
--- /dev/null
+++ b/engine/dconf-engine-source-user-nfs.c
@@ -0,0 +1,93 @@
+/*
+ * Copyright  2010 Codethink Limited
+ * Copyright  2012 Canonical Limited
+ *
+ * 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 licence, 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.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#include "dconf-engine-source-private.h"
+
+#include "../shm/dconf-shm.h"
+#include "dconf-engine.h"
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <errno.h>
+
+static void
+dconf_engine_source_user_nfs_init (DConfEngineSource *source)
+{
+  GError *error = NULL;
+  GVariant *reply;
+
+  source->bus_type = G_BUS_TYPE_SESSION;
+  source->bus_name = g_strdup ("ca.desrt.dconf");
+  source->object_path = g_strdup_printf ("/ca/desrt/dconf/Writer/%s", source->name);
+  source->writable = TRUE;
+
+  /* We need to get the dconf-service to come online and notice that
+   * we're on an NFS home directory.  In that case it will copy the
+   * given database into the XDG_RUNTIME_DIR which is where we will
+   * access it.
+   *
+   * This prevents us from doing mmap() on a file on NFS (which often
+   * results in us seeing SIGBUS).
+   */
+  reply = dconf_engine_dbus_call_sync_func (G_BUS_TYPE_SESSION, source->bus_name, source->object_path,
+                                            "ca.desrt.dconf.Writer", "Init", NULL, G_VARIANT_TYPE_UNIT, &error);
+
+  if (reply)
+    g_variant_unref (reply);
+  else
+    {
+      g_warning ("Trying to start the dconf service failed: %s.  Expect problems.", error->message);
+      g_error_free (error);
+    }
+}
+
+static gboolean
+dconf_engine_source_user_nfs_needs_reopen (DConfEngineSource *source)
+{
+  return !source->values || !gvdb_table_is_valid (source->values);
+}
+
+static GvdbTable *
+dconf_engine_source_user_nfs_reopen (DConfEngineSource *source)
+{
+  GvdbTable *table;
+  gchar *filename;
+
+  filename = g_build_filename (dconf_shm_get_shmdir (), source->name, NULL);
+  table = gvdb_table_new (filename, FALSE, NULL);
+  g_free (filename);
+
+  return table;
+}
+
+static void
+dconf_engine_source_user_nfs_finalize (DConfEngineSource *source)
+{
+}
+
+G_GNUC_INTERNAL
+const DConfEngineSourceVTable dconf_engine_source_user_nfs_vtable = {
+  .instance_size    = sizeof (DConfEngineSource),
+  .init             = dconf_engine_source_user_nfs_init,
+  .finalize         = dconf_engine_source_user_nfs_finalize,
+  .needs_reopen     = dconf_engine_source_user_nfs_needs_reopen,
+  .reopen           = dconf_engine_source_user_nfs_reopen
+};
diff --git a/engine/dconf-engine-source.c b/engine/dconf-engine-source.c
index 4eb7faa..68b10de 100644
--- a/engine/dconf-engine-source.c
+++ b/engine/dconf-engine-source.c
@@ -71,6 +71,15 @@ dconf_engine_source_refresh (DConfEngineSource *source)
   return FALSE;
 }
 
+static const DConfEngineSourceVTable *
+dconf_engine_source_get_user_vtable (void)
+{
+  if (dconf_shm_homedir_is_native ())
+    return &dconf_engine_source_user_vtable;
+  else
+    return &dconf_engine_source_user_nfs_vtable;
+}
+
 DConfEngineSource *
 dconf_engine_source_new (const gchar *description)
 {
@@ -94,7 +103,7 @@ dconf_engine_source_new (const gchar *description)
 
   /* Check if the part before the colon is "user-db"... */
   if ((colon == description + 7) && memcmp (description, "user-db", 7) == 0)
-    vtable = &dconf_engine_source_user_vtable;
+    vtable = dconf_engine_source_get_user_vtable ();
 
   /* ...or "system-db" */
   else if ((colon == description + 9) && memcmp (description, "system-db", 9) == 0)
@@ -122,10 +131,12 @@ dconf_engine_source_new (const gchar *description)
 DConfEngineSource *
 dconf_engine_source_new_default (void)
 {
+  const DConfEngineSourceVTable *vtable;
   DConfEngineSource *source;
 
-  source = g_malloc0 (dconf_engine_source_user_vtable.instance_size);
-  source->vtable = &dconf_engine_source_user_vtable;
+  vtable = dconf_engine_source_get_user_vtable ();
+  source = g_malloc0 (vtable->instance_size);
+  source->vtable = vtable;
   source->name = g_strdup ("user");
   source->vtable->init (source);
 
diff --git a/service/dconf-nfs-writer.c b/service/dconf-nfs-writer.c
new file mode 100644
index 0000000..69675ef
--- /dev/null
+++ b/service/dconf-nfs-writer.c
@@ -0,0 +1,182 @@
+/*
+ * Copyright  2010 Codethink Limited
+ *
+ * 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 licence, 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.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#include "dconf-writer.h"
+
+#include "../gvdb/gvdb-reader.h"
+
+#include <sys/fcntl.h>
+#include <errno.h>
+
+typedef DConfWriterClass DConfNfsWriterClass;
+
+typedef struct
+{
+  DConfWriter parent_instance;
+
+  gchar *lockfile;
+  gchar *filename;
+  gint lock_fd;
+} DConfNfsWriter;
+
+G_DEFINE_TYPE (DConfNfsWriter, dconf_nfs_writer, DCONF_TYPE_WRITER)
+
+static void
+dconf_nfs_writer_constructed (GObject *object)
+{
+  DConfNfsWriter *nfs = (DConfNfsWriter *) object;
+  DConfWriter *writer = DCONF_WRITER (object);
+
+  G_OBJECT_CLASS (dconf_nfs_writer_parent_class)->constructed (object);
+
+  nfs->filename = g_build_filename (g_get_user_config_dir (), "dconf", writer->name, NULL);
+}
+
+static DConfChangeset *
+dconf_nfs_writer_diff (DConfNfsWriter  *nfs,
+                       GHashTable      *old,
+                       GError         **error)
+{
+  DConfChangeset *changeset;
+  GvdbTable *new;
+  GBytes *bytes;
+
+  {
+    gchar *contents;
+    gsize size;
+
+    if (!g_file_get_contents (nfs->filename, &contents, &size, error))
+      return NULL;
+
+    bytes = g_bytes_new_take (contents, size);
+  }
+
+  new = gvdb_table_new (bytes, FALSE, error);
+
+  g_bytes_unref (bytes);
+
+  if (new == NULL)
+    return NULL;
+}
+
+static gboolean
+dconf_nfs_writer_begin (DConfWriter  *writer,
+                        GError      **error)
+{
+  DConfNfsWriter *nfs = (DConfNfsWriter *) writer;
+  DConfChangeset *changeset;
+  struct flock lock;
+  gint fd;
+
+  nfs->lock_fd = open (nfs->lockfile, O_CREAT | O_WRONLY, 0600);
+
+  if (nfs->lock_fd == -1)
+    {
+      gint saved_errno = errno;
+
+      g_set_error (error, G_FILE_ERROR, g_file_error_from_errno (saved_errno),
+                   "Cannot open dconf lockfile %s: %s", nfs->lockfile, g_strerror (saved_errno));
+      goto out;
+    }
+
+  lock.l_whence = SEEK_SET;
+  lock.l_type = F_WRLCK;
+  lock.l_start = 0;
+  lock.l_len = 0;
+
+  if (fcntl (nfs->lock_fd, F_SETLKW, &lock) != 0)
+    {
+      gint saved_errno = errno;
+
+      g_set_error (error, G_FILE_ERROR, g_file_error_from_errno (saved_errno),
+                   "Unable to lock dconf lockfile %s: %s", nfs->lockfile, g_strerror (saved_errno));
+      goto out;
+    }
+
+  if (!DCONF_WRITER_CLASS (dconf_nfs_writer_parent_class)->begin (writer, error))
+    goto out;
+
+  changeset = dconf_nfs_writer_diff (nfs, writer->uncommited_values, error);
+  if (changeset == NULL)
+    goto out;
+
+  if (!dconf_changeset_is_empty (changeset))
+    dconf_writer_change (writer, changeset, "(updated from nfs home directory)");
+
+  dconf_changeset_unref (changeset);
+
+  return TRUE;
+
+out:
+  if (writer->uncommited_values)
+    DCONF_WRITER_CLASS (dconf_nfs_writer_parent_class)->end (writer);
+
+  if (nfs->lock_fd != -1)
+    {
+      close (nfs->lock_fd);
+      nfs->lock_fd = -1;
+    }
+
+  return FALSE;
+}
+
+static gboolean
+dconf_nfs_writer_commit (DConfWriter  *writer,
+                         GError      **error)
+{
+  return DCONF_WRITER_CLASS (dconf_nfs_writer_parent_class)->commit (writer, error);
+}
+
+static void
+dconf_nfs_writer_end (DConfWriter *writer)
+{
+  DConfNfsWriter *nfs = (DConfNfsWriter *) writer;
+
+  DCONF_WRITER_CLASS (dconf_nfs_writer_parent_class)->end (writer);
+
+  if (nfs->lock_fd != -1)
+    {
+      close (nfs->lock_fd);
+      nfs->lock_fd = -1;
+    }
+}
+
+static void
+dconf_nfs_writer_init (DConfNfsWriter *nfs)
+{
+  dconf_writer_set_native (DCONF_WRITER (nfs), FALSE);
+
+  nfs->lock_fd = -1;
+}
+
+static void
+dconf_nfs_writer_class_init (DConfNfsWriterClass *class)
+{
+  class->begin = dconf_nfs_writer_begin;
+  class->commit = dconf_nfs_writer_commit;
+  class->end = dconf_nfs_writer_end;
+}
+
+DConfWriter *
+dconf_nfs_writer_new (const gchar *name)
+{
+  return g_object_new (dconf_nfs_writer_get_type (), NULL);
+}
diff --git a/shm/Makefile.am b/shm/Makefile.am
index ffa2fd3..2417500 100644
--- a/shm/Makefile.am
+++ b/shm/Makefile.am
@@ -5,7 +5,8 @@ noinst_LIBRARIES = libdconf-shm.a libdconf-shm-shared.a
 libdconf_shm_a_CFLAGS = $(glib_CFLAGS)
 libdconf_shm_a_SOURCES = \
 	dconf-shm.h		\
-	dconf-shm.c
+	dconf-shm.c		\
+	dconf-shm-nfs-check.c
 
 libdconf_shm_shared_a_CFLAGS = $(libdconf_shm_a_CFLAGS) -fPIC -DPIC
 libdconf_shm_shared_a_SOURCES = $(libdconf_shm_a_SOURCES)
diff --git a/shm/dconf-shm-nfs-check.c b/shm/dconf-shm-nfs-check.c
new file mode 100644
index 0000000..7f1b199
--- /dev/null
+++ b/shm/dconf-shm-nfs-check.c
@@ -0,0 +1,63 @@
+/*
+ * Copyright  2012 Canonical Limited
+ *
+ * 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 licence, 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.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#include "dconf-shm.h"
+
+#include <glib.h>
+
+#include <sys/statfs.h>
+
+#ifndef ECRYPTFS_SUPER_MAGIC
+#define ECRYPTFS_SUPER_MAGIC 0xf15f
+#endif
+
+#ifndef NFS_SUPER_MAGIC
+#define NFS_SUPER_MAGIC 0x6969
+#endif
+
+/* returns TRUE if the filesystem is capable */
+static gboolean
+dconf_shm_check (const gchar *filename)
+{
+  struct statfs buf;
+
+  if (statfs (filename, &buf) != 0)
+    return FALSE;
+
+  return buf.f_type != NFS_SUPER_MAGIC && buf.f_type != ECRYPTFS_SUPER_MAGIC;
+}
+
+gboolean
+dconf_shm_homedir_is_native (void)
+{
+  static gsize homedir_is_native;
+
+  if (g_once_init_enter (&homedir_is_native))
+    {
+      gboolean is_native;
+
+      is_native = dconf_shm_check (g_get_home_dir ());
+
+      g_once_init_leave (&homedir_is_native, is_native + 1);
+    }
+
+  return homedir_is_native - 1;
+}
diff --git a/shm/dconf-shm.c b/shm/dconf-shm.c
index d291305..84bcc33 100644
--- a/shm/dconf-shm.c
+++ b/shm/dconf-shm.c
@@ -27,7 +27,7 @@
 #include <fcntl.h>
 #include <errno.h>
 
-static gchar *
+const gchar *
 dconf_shm_get_shmdir (void)
 {
   static gchar *shmdir;
diff --git a/shm/dconf-shm.h b/shm/dconf-shm.h
index c1f136c..3d77f16 100644
--- a/shm/dconf-shm.h
+++ b/shm/dconf-shm.h
@@ -25,6 +25,9 @@
 #include <glib.h>
 
 G_GNUC_INTERNAL
+const gchar *           dconf_shm_get_shmdir                            (void);
+
+G_GNUC_INTERNAL
 guint8 *                dconf_shm_open                                  (const gchar *name);
 G_GNUC_INTERNAL
 void                    dconf_shm_close                                 (guint8      *shm);
@@ -37,4 +40,7 @@ dconf_shm_is_flagged (const guint8 *shm)
   return shm == NULL || *shm != 0;
 }
 
+G_GNUC_INTERNAL
+gboolean                dconf_shm_homedir_is_native                     (void);
+
 #endif /* __dconf_shm_h__ */
diff --git a/tests/dconf-mock-shm.c b/tests/dconf-mock-shm.c
index 588667e..33384ac 100644
--- a/tests/dconf-mock-shm.c
+++ b/tests/dconf-mock-shm.c
@@ -122,3 +122,15 @@ dconf_mock_shm_assert_log (const gchar *expected_log)
   g_string_truncate (dconf_mock_shm_log, 0);
   g_mutex_unlock (&dconf_mock_shm_lock);
 }
+
+const gchar *
+dconf_shm_get_shmdir (void)
+{
+  g_assert_not_reached ();
+}
+
+gboolean
+dconf_shm_homedir_is_native (void)
+{
+  return TRUE;
+}
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