examples: Add virt-dhcp-address program.

This is like the mythical 'virt-ifconfig'.  There is not enough
certainty around the right way to be doing this for us to make
a full virt tool for this.  Therefore the code is just an example.

1 files changed, 342 insertions, 0 deletions

diff --git a/examples/virt-dhcp-address.c b/examples/virt-dhcp-address.c
new file mode 100644
index 00000000..c075a473
--- /dev/null
+++ b/examples/virt-dhcp-address.c
@@ -0,0 +1,342 @@
+/* This is a more significant example of a tool which can grab the
+ * DHCP address from some types of virtual machine.  Since there are
+ * so many possible ways to do this, without clarity on which is the
+ * best way, I don't want to make this into an official virt tool.
+ *
+ * For more information, see:
+ *
+ * https://rwmj.wordpress.com/2010/10/26/tip-find-the-ip-address-of-a-virtual-machine/
+ * https://rwmj.wordpress.com/2011/03/30/tip-another-way-to-get-the-ip-address-of-a-virtual-machine/
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <assert.h>
+
+#include <guestfs.h>
+#include <hivex.h>
+
+static int compare_keys_len (const void *p1, const void *p2);
+static size_t count_strings (char *const *argv);
+static void free_strings (char **argv);
+static void mount_disks (guestfs_h *g, char *root);
+static void print_dhcp_address (guestfs_h *g, char *root);
+static void print_dhcp_address_linux (guestfs_h *g, char *root, const char *logfile);
+static void print_dhcp_address_windows (guestfs_h *g, char *root);
+
+int
+main (int argc, char *argv[])
+{
+  guestfs_h *g;
+  size_t i;
+  char **roots, *root;
+
+  if (argc < 2) {
+    fprintf (stderr,
+             "Usage: virt-dhcp-address disk.img [disk.img [...]]\n"
+             "Note that all disks must come from a single virtual machine.\n");
+    exit (EXIT_FAILURE);
+  }
+
+  g = guestfs_create ();
+  if (g == NULL) {
+    perror ("failed to create libguestfs handle");
+    exit (EXIT_FAILURE);
+  }
+
+  for (i = 1; i < (size_t) argc; ++i) {
+    /* Attach the disk image(s) read-only to libguestfs. */
+    if (guestfs_add_drive_opts (g, argv[i],
+                                /* GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw", */
+                                GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+                                -1) /* this marks end of optional arguments */
+        == -1)
+      exit (EXIT_FAILURE);
+  }
+
+  /* Run the libguestfs back-end. */
+  if (guestfs_launch (g) == -1)
+    exit (EXIT_FAILURE);
+
+  /* Ask libguestfs to inspect for operating systems. */
+  roots = guestfs_inspect_os (g);
+  if (roots == NULL)
+    exit (EXIT_FAILURE);
+  if (roots[0] == NULL) {
+    fprintf (stderr, "virt-dhcp-address: no operating systems found\n");
+    exit (EXIT_FAILURE);
+  }
+  if (count_strings (roots) > 1) {
+    fprintf (stderr, "virt-dhcp-address: multi-boot operating system\n");
+    exit (EXIT_FAILURE);
+  }
+
+  root = roots[0];
+
+  /* Mount up the guest's disks. */
+  mount_disks (g, root);
+
+  /* Print DHCP address. */
+  print_dhcp_address (g, root);
+
+  /* Close handle and exit. */
+  guestfs_close (g);
+  free_strings (roots);
+
+  exit (EXIT_SUCCESS);
+}
+
+static void
+mount_disks (guestfs_h *g, char *root)
+{
+  char **mountpoints;
+  size_t i;
+
+  /* Mount up the disks, like guestfish -i.
+   *
+   * Sort keys by length, shortest first, so that we end up
+   * mounting the filesystems in the correct order.
+   */
+  mountpoints = guestfs_inspect_get_mountpoints (g, root);
+  if (mountpoints == NULL)
+    exit (EXIT_FAILURE);
+
+  qsort (mountpoints, count_strings (mountpoints) / 2, 2 * sizeof (char *),
+         compare_keys_len);
+
+  for (i = 0; mountpoints[i] != NULL; i += 2) {
+    /* Ignore failures from this call, since bogus entries can
+     * appear in the guest's /etc/fstab.
+     */
+    guestfs_mount_ro (g, mountpoints[i+1], mountpoints[i]);
+  }
+
+  free_strings (mountpoints);
+}
+
+static void
+print_dhcp_address (guestfs_h *g, char *root)
+{
+  char *guest_type, *guest_distro;
+
+  /* Depending on the guest type, try to get the DHCP address. */
+  guest_type = guestfs_inspect_get_type (g, root);
+
+  if (strcmp (guest_type, "linux") == 0) {
+    guest_distro = guestfs_inspect_get_distro (g, root);
+
+    if (strcmp (guest_distro, "fedora") == 0 ||
+        strcmp (guest_distro, "rhel") == 0 ||
+        strcmp (guest_distro, "redhat-based") == 0) {
+      print_dhcp_address_linux (g, root, "/var/log/messages");
+    }
+    else if (strcmp (guest_distro, "debian") == 0 ||
+             strcmp (guest_distro, "ubuntu") == 0) {
+      print_dhcp_address_linux (g, root, "/var/log/syslog");
+    }
+    else {
+      fprintf (stderr, "virt-dhcp-address: don't know how to get DHCP address from '%s'\n",
+               guest_distro);
+      exit (EXIT_FAILURE);
+    }
+
+    free (guest_distro);
+  }
+  else if (strcmp (guest_type, "windows") == 0) {
+    print_dhcp_address_windows (g, root);
+  }
+  else {
+    fprintf (stderr, "virt-dhcp-address: don't know how to get DHCP address from '%s'\n",
+             guest_type);
+    exit (EXIT_FAILURE);
+  }
+
+  free (guest_type);
+}
+
+/* Look for dhclient messages in logfile.
+ */
+static void
+print_dhcp_address_linux (guestfs_h *g, char *root, const char *logfile)
+{
+  char **lines, *p;
+  size_t len;
+
+  lines = guestfs_egrep (g, "dhclient.*: bound to ", logfile);
+  if (lines == NULL)
+    exit (EXIT_FAILURE);
+
+  len = count_strings (lines);
+  if (len == 0) {
+    fprintf (stderr, "virt-dhcp-address: cannot find DHCP address for this guest.\n");
+    exit (EXIT_FAILURE);
+  }
+
+  /* Only want the last message. */
+  p = strstr (lines[len-1], "bound to ");
+  assert (p);
+  p += 9;
+  len = strcspn (p, " ");
+  p[len] = '\0';
+
+  printf ("%s\n", p);
+
+  free_strings (lines);
+}
+
+/* Download the Windows SYSTEM hive and find DHCP configuration in there. */
+static void
+print_dhcp_address_windows (guestfs_h *g, char *root_unused)
+{
+  char *system_path;
+  char tmpfile[] = "/tmp/systemXXXXXX";
+  int fd, err;
+  hive_h *h;
+  hive_node_h root, node, *nodes;
+  hive_value_h value;
+  int32_t dword;
+  char controlset[] = "ControlSetXXX";
+  size_t i;
+  char *p;
+
+  /* Locate the SYSTEM hive case-sensitive path. */
+  system_path =
+    guestfs_case_sensitive_path (g, "/windows/system32/config/system");
+  if (!system_path) {
+    fprintf (stderr, "virt-dhcp-address: HKLM\\System not found in this guest.");
+    exit (EXIT_FAILURE);
+  }
+
+  fd = mkstemp (tmpfile);
+  if (fd == -1) {
+    perror ("mkstemp");
+    exit (EXIT_FAILURE);
+  }
+
+  /* Download the SYSTEM hive. */
+  if (guestfs_download (g, system_path, tmpfile) == -1)
+    exit (EXIT_FAILURE);
+
+  free (system_path);
+
+  /* Open the hive to parse it. */
+  h = hivex_open (tmpfile, 0);
+  err = errno;
+  close (fd);
+  unlink (tmpfile);
+
+  if (h == NULL) {
+    errno = err;
+    perror ("hivex_open");
+    exit (EXIT_FAILURE);
+  }
+
+  /* Navigate to the Select key so we know which ControlSet is in use. */
+  root = hivex_root (h);
+  if (root == 0) {
+    perror ("hivex_root");
+    exit (EXIT_FAILURE);
+  }
+  node = hivex_node_get_child (h, root, "Select");
+  if (node == 0) {
+    if (errno != 0)
+      perror ("hivex_node_get_child");
+    else
+      fprintf (stderr, "virt-dhcp-address: HKLM\\System\\Select key not found.");
+    exit (EXIT_FAILURE);
+  }
+  value = hivex_node_get_value (h, node, "Current");
+  if (value == 0) {
+    if (errno != 0)
+      perror ("hivex_node_get_value");
+    else
+      fprintf (stderr, "virt-dhcp-address: HKLM\\System\\Select Default entry not found.");
+    exit (EXIT_FAILURE);
+  }
+  /* XXX Should check the type. */
+  dword = hivex_value_dword (h, value);
+  snprintf (controlset, sizeof controlset, "ControlSet%03d", dword);
+
+  /* Get ControlSetXXX\Services\Tcpip\Parameters\Interfaces. */
+  const char *path[] = { controlset, "Services", "Tcpip", "Parameters",
+                         "Interfaces" };
+  node = root;
+  errno = 0;
+  for (i = 0; node != 0 && i < sizeof path / sizeof path[0]; ++i)
+    node = hivex_node_get_child (h, node, path[i]);
+
+  if (node == 0) {
+    if (errno != 0)
+      perror ("hivex_node_get_child");
+    else
+      fprintf (stderr, "virt-dhcp-address: HKLM\\System\\%s\\Services\\Tcpip\\Parameters\\Interfaces not found.", controlset);
+    exit (EXIT_FAILURE);
+  }
+
+  /* Look for a node under here which has a "DhcpIPAddress" entry in it. */
+  nodes = hivex_node_children (h, node);
+  if (nodes == NULL) {
+    perror ("hivex_node_children");
+    exit (EXIT_FAILURE);
+  }
+
+  value = 0;
+  for (i = 0; value == 0 && nodes[i] != 0; ++i) {
+    errno = 0;
+    value = hivex_node_get_value (h, nodes[i], "DhcpIPAddress");
+    if (value == 0 && errno != 0) {
+      perror ("hivex_node_get_value");
+      exit (EXIT_FAILURE);
+    }
+  }
+
+  if (value == 0) {
+    fprintf (stderr, "virt-dhcp-address: cannot find DHCP address for this guest.\n");
+    exit (EXIT_FAILURE);
+  }
+
+  /* Get the string and use hivex's auto-conversion to convert it to UTF-8
+   * for output.
+   */
+  p = hivex_value_string (h, value);
+  if (!p) {
+    perror ("hivex_value_string");
+    exit (EXIT_FAILURE);
+  }
+
+  printf ("%s\n", p);
+
+  /* Close the hive handle. */
+  hivex_close (h);
+}
+
+static int
+compare_keys_len (const void *p1, const void *p2)
+{
+  const char *key1 = * (char * const *) p1;
+  const char *key2 = * (char * const *) p2;
+  return strlen (key1) - strlen (key2);
+}
+
+static size_t
+count_strings (char *const *argv)
+{
+  size_t c;
+
+  for (c = 0; argv[c]; ++c)
+    ;
+  return c;
+}
+
+static void
+free_strings (char **argv)
+{
+  size_t i;
+
+  for (i = 0; argv[i]; ++i)
+    free (argv[i]);
+  free (argv);
+}