appliance: Pass lpj=... on the appliance command line (thanks Marcelo Tosatti).

Try to get the host's loops_per_jiffy value and pass this on the
command line to the guest.  In theory this should avoid the appliance
having to recalculate this value in a VM with TCG (which is generally
error-prone).  This should avoid timing issues.

We only do this when we are certain that the guest will be TCG.
Currently we only have enough information to do this from the libvirt
attach-method.  So mostly this will only affect people using Fedora in
a VM.

The host loops_per_jiffy value is not exported by the kernel.  It is
only printed by the kernel early during boot, so if boot messages have
"scrolled off" the kernel ring buffer, it won't be available.  Some
operating systems save early kernel messages in /var/log/dmesg but (a)
Fedora 18+ seem to have abandoned this file and (b) on Ubuntu this
file is unreadable for spurious "security" reasons.

I have submitted a patch to make lpj available through /proc/cpuinfo.

1 files changed, 139 insertions, 0 deletions

diff --git a/src/lpj.c b/src/lpj.c
new file mode 100644
index 00000000..9c1acce9
--- /dev/null
+++ b/src/lpj.c
@@ -0,0 +1,139 @@
+/* libguestfs
+ * Copyright (C) 2012 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#include "glthread/lock.h"
+
+#include "guestfs.h"
+#include "guestfs-internal.h"
+
+/* Calculate host kernel loops_per_jiffy, so that this can be passed
+ * to TCG guests (only) using the lpj= kernel parameter, which avoids
+ * have to compute this at kernel boot time in a VM.
+ *
+ * Currently this is only available in the boot messages, but I have
+ * posted a patch asking for this to be added to /proc/cpuinfo too.
+ *
+ * Notes:
+ * - We only try to calculate lpj once.
+ * - Trying to calculate lpj must not fail.  If the return value is
+ *   <= 0, it is ignored by the caller.
+ *
+ * (Suggested by Marcelo Tosatti)
+ */
+
+gl_lock_define_initialized (static, lpj_lock);
+static int lpj = 0;
+static int read_lpj_from_var_log_dmesg (guestfs_h *g);
+static int read_lpj_from_dmesg (guestfs_h *g);
+static int read_lpj_common (guestfs_h *g, const char *func, const char *command);
+
+int
+guestfs___get_lpj (guestfs_h *g)
+{
+  int r;
+
+  gl_lock_lock (lpj_lock);
+  if (lpj != 0)
+    goto out;
+
+  /* Try reading lpj from these sources:
+   * - /proc/cpuinfo [in future]
+   * - dmesg
+   * - /var/log/dmesg
+   */
+  r = read_lpj_from_dmesg (g);
+  if (r > 0) {
+    lpj = r;
+    goto out;
+  }
+  lpj = read_lpj_from_var_log_dmesg (g);
+
+ out:
+  gl_lock_unlock (lpj_lock);
+  return lpj;
+}
+
+static int
+read_lpj_from_dmesg (guestfs_h *g)
+{
+  return read_lpj_common (g, __func__,
+                          "dmesg | grep -Eo 'lpj=[[:digit:]]+'");
+}
+
+static int
+read_lpj_from_var_log_dmesg (guestfs_h *g)
+{
+  return read_lpj_common (g, __func__,
+                          "grep -Eo 'lpj=[[:digit:]]+' /var/log/dmesg");
+}
+
+static void
+read_all (guestfs_h *g, void *retv, const char *buf, size_t len)
+{
+  char **ret = retv;
+
+  *ret = safe_strndup (g, buf, len);
+}
+
+static int
+read_lpj_common (guestfs_h *g, const char *func, const char *command)
+{
+  struct command *cmd;
+  int r;
+  char *buf = NULL;
+
+  cmd = guestfs___new_command (g);
+  guestfs___cmd_add_string_unquoted (cmd, command);
+  guestfs___cmd_set_stdout_callback (cmd, read_all, &buf,
+                                     CMD_STDOUT_FLAG_WHOLE_BUFFER);
+  r = guestfs___cmd_run (cmd);
+  guestfs___cmd_close (cmd);
+
+  if (r == -1 || !WIFEXITED (r) || WEXITSTATUS (r) != 0) {
+    debug (g, "%s: command failed with code %d: %s", func, r, command);
+    free (buf);
+    return -1;
+  }
+
+  if (buf == NULL) {
+    debug (g, "%s: callback not called", func);
+    return -1;
+  }
+
+  if (strlen (buf) < 4 || sscanf (&buf[4], "%d", &r) != 1) {
+    debug (g, "%s: invalid buffer returned by grep: %s", func, buf);
+    free (buf);
+    return -1;
+  }
+
+  free (buf);
+
+  debug (g, "%s: calculated lpj=%d", func, r);
+
+  return r;
+}