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.

po/POTFILES

@@ -258,6 +258,7 @@ src/launch.c
 src/libvirt-auth.c
 src/libvirt-domain.c
 src/listfs.c
+src/lpj.c
 src/match.c
 src/private-data.c
 src/proto.c

src/Makefile.am

@@ -166,6 +166,7 @@ libguestfs_la_SOURCES = \
 	libvirt-auth.c \
 	libvirt-domain.c \
 	listfs.c \
+	lpj.c \
 	match.c \
 	private-data.c \
 	proto.c \

src/guestfs-internal.h

@@ -567,7 +567,8 @@ extern void guestfs___rollback_drives (guestfs_h *g, size_t);
 extern void guestfs___launch_failed_error (guestfs_h *g);
 extern void guestfs___add_dummy_appliance_drive (guestfs_h *g);
 extern void guestfs___free_drives (guestfs_h *g);
-extern char *guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev);
+extern char *guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev, int flags);
+#define APPLIANCE_COMMAND_LINE_IS_TCG 1
 
 /* launch-appliance.c */
 extern char *guestfs___drive_name (size_t index, char *ret);
@@ -606,6 +607,9 @@ extern int guestfs___check_installer_root (guestfs_h *g, struct inspect_fs *fs);
 typedef int (*guestfs___db_dump_callback) (guestfs_h *g, const unsigned char *key, size_t keylen, const unsigned char *value, size_t valuelen, void *opaque);
 extern int guestfs___read_db_dump (guestfs_h *g, const char *dumpfile, void *opaque, guestfs___db_dump_callback callback);
 
+/* lpj.c */
+extern int guestfs___get_lpj (guestfs_h *g);
+
 /* fuse.c */
 #if HAVE_FUSE
 extern void guestfs___free_fuse (guestfs_h *g);

src/launch-appliance.c

@@ -427,7 +427,7 @@ launch_appliance (guestfs_h *g, const char *arg)
     add_cmdline (g, initrd);
 
     add_cmdline (g, "-append");
-    char *cmdline = guestfs___appliance_command_line (g, appliance_dev);
+    char *cmdline = guestfs___appliance_command_line (g, appliance_dev, 0);
     add_cmdline (g, cmdline);
     free (cmdline);
 

src/launch-libvirt.c

@@ -642,9 +642,13 @@ construct_libvirt_xml_boot (guestfs_h *g,
                             xmlTextWriterPtr xo)
 {
   char *cmdline;
+  int flags;
 
   /* Linux kernel command line. */
-  cmdline = guestfs___appliance_command_line (g, params->appliance_dev);
+  flags = 0;
+  if (!params->is_kvm)
+    flags |= APPLIANCE_COMMAND_LINE_IS_TCG;
+  cmdline = guestfs___appliance_command_line (g, params->appliance_dev, flags);
 
   XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "os"));
 

src/launch.c

@@ -21,6 +21,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <stdbool.h>
 #include <inttypes.h>
 #include <unistd.h>
 #include <string.h>
@@ -794,6 +795,13 @@ guestfs__get_state (guestfs_h *g)
  * appliance disk and must have already been adjusted to take into
  * account virtio-blk or virtio-scsi; eg "/dev/sdb".
  *
+ * The 'flags' parameter can contain the following flags logically
+ * or'd together (or 0):
+ *
+ * GUESTFS___APPLIANCE_COMMAND_LINE_IS_TCG: If we are launching a qemu
+ * TCG guest (ie. KVM is known to be disabled or unavailable).  If you
+ * don't know, don't pass this flag.
+ *
  * Note that this returns a newly allocated buffer which must be freed
  * by the caller.
  */
@@ -804,10 +812,19 @@ guestfs__get_state (guestfs_h *g)
 #endif
 
 char *
-guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev)
+guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev,
+                                  int flags)
 {
   char *term = getenv ("TERM");
   char *ret;
+  bool tcg = flags & APPLIANCE_COMMAND_LINE_IS_TCG;
+  char lpj_s[64] = "";
+
+  if (tcg) {
+    int lpj = guestfs___get_lpj (g);
+    if (lpj > 0)
+      snprintf (lpj_s, sizeof lpj_s, " lpj=%d", lpj);
+  }
 
   ret = safe_asprintf
     (g,
@@ -815,6 +832,7 @@ guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev)
      " console=" SERIAL_CONSOLE /* serial console */
      " udevtimeout=600" /* good for very slow systems (RHBZ#480319) */
      " no_timer_check"  /* fix for RHBZ#502058 */
+     "%s"               /* lpj */
      " acpi=off"        /* we don't need ACPI, turn it off */
      " printk.time=1"   /* display timestamp before kernel messages */
      " cgroup_disable=memory"   /* saves us about 5 MB of RAM */
@@ -823,6 +841,7 @@ guestfs___appliance_command_line (guestfs_h *g, const char *appliance_dev)
      "%s"                       /* verbose */
      " TERM=%s"                 /* TERM environment variable */
      "%s%s",                    /* append */
+     lpj_s,
      appliance_dev,
      g->selinux ? "selinux=1 enforcing=0" : "selinux=0",
      g->verbose ? " guestfs_verbose=1" : "",

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;
+}