Add LKL (Linux Kernel as a Library) backend.

Check out the LKL sources (https://github.com/lkl/linux) and compile
them by following the instructions in Documentation/lkl.txt.

Then add the following to the libguestfs configure command:

  ./configure --with-lkl=/path/to/linux

To use it, eg. from guestfish:

  export LIBGUESTFS_BACKEND=lkl
  export LIBGUESTFS_HV=$(pwd)/daemon/guestfsd-lkl
  ./run guestfish

To do:

 - Documentation.

 - Pass per-disk flags from library to daemon (on the command line).
   Currently all disks are opened for write, even if you specify
   the readonly flag.

 - Pass g->memsize from library to daemon.

 - Pass g->append from library to daemon.

 - Disable unsafe APIs.  Many APIs could never be supported by LKL,
   and are completely unsafe to use.  eg. guestfs_sh.  These must be
   disabled when HAVE_LKL=1 so the user cannot accidentally damage
   their host.

.gitignore

@@ -122,6 +122,7 @@ Makefile.in
 /daemon/guestfsd
 /daemon/guestfsd.8
 /daemon/guestfsd.exe
+/daemon/guestfsd-lkl
 /daemon/guestfs_protocol.c
 /daemon/guestfs_protocol.h
 /daemon/install-sh

configure.ac

@@ -108,6 +108,9 @@ m4_include([m4/guestfs_qemu.m4])
 dnl Miscellaneous libraries used by other programs.
 m4_include([m4/guestfs_misc_libraries.m4])
 
+dnl LKL (Linux Kernel Library)
+m4_include([m4/guestfs_lkl.m4])
+
 dnl Check for language bindings.
 m4_include([m4/guestfs_ocaml.m4])
 m4_include([m4/guestfs_perl.m4])

daemon/Makefile.am

@@ -218,6 +218,22 @@ guestfsd_CFLAGS = \
 	$(YAJL_CFLAGS) \
 	$(PCRE_CFLAGS)
 
+if HAVE_LKL
+
+# Compile guestfsd again, linked to liblkl.
+bin_PROGRAMS = guestfsd-lkl
+
+guestfsd_lkl_SOURCES = $(guestfsd_SOURCES)
+guestfsd_lkl_LDADD = \
+	-L$(LKL_PATH)/tools/lkl/lib -llkl -lrt $(guestfsd_LDADD)
+guestfsd_lkl_CPPFLAGS = \
+	$(guestfsd_CPPFLAGS) -DHAVE_LKL=1 -I$(LKL_PATH)/tools/lkl/include
+guestfsd_lkl_CFLAGS = \
+	-pthread \
+	$(guestfsd_CFLAGS)
+
+endif
+
 # Manual pages and HTML files for the website.
 if INSTALL_DAEMON
 man_MANS = guestfsd.8

daemon/daemon.h

@@ -64,6 +64,12 @@ extern int xread (int sock, void *buf, size_t len)
 
 extern char *mountable_to_string (const mountable_t *mountable);
 
+#if HAVE_LKL
+/* LKL disk IDs. */
+extern int *disk_id;
+extern size_t nr_disks;
+#endif
+
 /*-- in mount.c --*/
 
 extern int mount_vfs_nochroot (const char *options, const char *vfstype,

daemon/guestfsd.c

@@ -32,6 +32,11 @@
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#if HAVE_LKL /* Wut? XXX */
+#undef st_atime
+#undef st_mtime
+#undef st_ctime
+#endif
 #include <fcntl.h>
 #include <signal.h>
 #include <netdb.h>
@@ -47,6 +52,11 @@
 # include <printf.h>
 #endif
 
+#ifdef HAVE_LKL
+#include <lkl.h>
+#include <lkl_host.h>
+#endif
+
 #include <augeas.h>
 
 #include "sockets.h"
@@ -128,11 +138,21 @@ const char *program_name = "guestfsd";
 /* Name of the virtio-serial channel. */
 #define VIRTIO_SERIAL_CHANNEL "/dev/virtio-ports/org.libguestfs.channel.0"
 
+#if HAVE_LKL
+/* LKL disk IDs. */
+int *disk_id;
+size_t nr_disks;
+#endif
+
 static void
 usage (void)
 {
   fprintf (stderr,
-	   "guestfsd [-r] [-v|--verbose]\n");
+	   "guestfsd [-r] [-v|--verbose]"
+#if HAVE_LKL
+           " disk [disk ...]"
+#endif
+           "\n");
 }
 
 int
@@ -152,6 +172,15 @@ main (int argc, char *argv[])
   const char *channel = NULL;
   int listen_mode = 0;
 
+#if HAVE_LKL
+  /* XXX Safety check.  Because large parts of the daemon haven't been
+   * ported to use LKL, refuse to run as root in case someone ends up
+   * trashing their host system by using some unported command.
+   */
+  if (geteuid () == 0)
+    error (EXIT_FAILURE, 0, "refusing to run as root");
+#endif
+
   ignore_value (chdir ("/"));
 
   if (winsock_init () == -1)
@@ -230,6 +259,32 @@ main (int argc, char *argv[])
     }
   }
 
+#if HAVE_LKL
+  nr_disks = argc - optind;
+  disk_id = malloc (nr_disks * sizeof (int));
+  if (disk_id == NULL)
+    error (EXIT_FAILURE, errno, "malloc");
+
+  for (size_t i = 0; i < nr_disks; ++i, ++optind) {
+    union lkl_disk_backstore disk;
+
+    /* XXX Pass through readonly and other per-disk flags from library side. */
+
+    disk.fd = open (argv[optind], O_RDWR);
+    if (disk.fd == -1)
+      error (EXIT_FAILURE, errno, "open: %s", argv[optind]);
+    disk_id[i] = lkl_disk_add (disk);
+    if (disk_id[i] < 0)
+      error (EXIT_FAILURE, 0, "lkl_disk_add: %s: %s",
+             argv[optind], lkl_strerror (disk_id[i]));
+  }
+
+  /* XXX I assume the second parameter is memory size.  Pass
+   * g->memsize setting through to the daemon.
+   */
+  lkl_start_kernel (&lkl_host_ops, 100 * 1024 * 1024, "");
+#endif
+
   if (optind < argc) {
     usage ();
     exit (EXIT_FAILURE);
@@ -269,11 +324,13 @@ main (int argc, char *argv[])
   _umask (0);
 #endif
 
+#ifndef HAVE_LKL
   /* Make a private copy of /etc/lvm so we can change the config (see
    * daemon/lvm-filter.c).
    */
   if (!test_mode)
     copy_lvm ();
+#endif
 
   /* Connect to virtio-serial channel. */
   if (!channel)

m4/guestfs_lkl.m4

@@ -0,0 +1,49 @@
+# libguestfs
+# Copyright (C) 2009-2015 Red Hat Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+dnl LKL (Linux Kernel compiled as a Library).
+dnl
+dnl You have to use --with-lkl=/path/to/linux
+dnl
+dnl where '/path/to/linux' is the absolute path to the Linux sources
+dnl (https://github.com/lkl/linux), compiled.  See Documentation/lkl.txt
+dnl for how to build LKL.
+
+AC_MSG_CHECKING([for LKL (Linux Kernel Library)])
+AC_ARG_WITH([lkl],
+    [AS_HELP_STRING([--with-lkl=/path/to/linux],
+        [build the LKL (Linux Kernel Library) backend])],
+    [
+    LKL_PATH="$withval"
+
+    # Does it contain the compiled static library?
+    if ! test -f "$LKL_PATH/tools/lkl/lib/liblkl.a"; then
+        AC_MSG_FAILURE([--with-lkl parameter does not point to compiled LKL])
+    fi
+
+    # Does it contain the header file?
+    if ! test -f "$LKL_PATH/tools/lkl/include/lkl.h"; then
+        AC_MSG_FAILURE([--with-lkl parameter does not point to LKL header file])
+    fi
+
+    ],
+    [LKL_PATH=no])
+AC_MSG_RESULT([$LKL_PATH])
+
+AC_SUBST([LKL_PATH])
+
+AM_CONDITIONAL([HAVE_LKL], [test "x$LKL_PATH" != "xno"])

po/POTFILES

@@ -331,6 +331,7 @@ src/inspect.c
 src/journal.c
 src/launch-direct.c
 src/launch-libvirt.c
+src/launch-lkl.c
 src/launch-uml.c
 src/launch-unix.c
 src/launch.c

src/Makefile.am

@@ -112,6 +112,7 @@ libguestfs_la_SOURCES = \
 	launch.c \
 	launch-direct.c \
 	launch-libvirt.c \
+	launch-lkl.c \
 	launch-uml.c \
 	launch-unix.c \
 	libvirt-auth.c \

src/guestfs-internal.h

@@ -915,6 +915,7 @@ void guestfs_int_init_direct_backend (void) __attribute__((constructor));
 void guestfs_int_init_libvirt_backend (void) __attribute__((constructor));
 #endif
 void guestfs_int_init_uml_backend (void) __attribute__((constructor));
+void guestfs_int_init_lkl_backend (void) __attribute__((constructor));
 void guestfs_int_init_unix_backend (void) __attribute__((constructor));
 
 /* guid.c */