Libguestfs - Feb 2016 - [PATCH v3] inspect: get windows drive letters for GPT disks.

This patch updates the guestfs_inspect_get_drive_mappings API call to
also return drive letters for GPT paritions. Previously this worked
only for MBR partitions. This is achieved by matching the GPT partition
GUID with the info stored in the blob from
HKLM\SYSTEM\MountedDevices\DosDevices keys. For GPT partions this blob
contains a "DMIO:ID:" prefix followed by a 16 byte binary GUID.
---

changes since v2:
 * added code review changes as per rjones

 src/inspect-fs-windows.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 94 insertions(+), 2 deletions(-)

diff --git a/src/inspect-fs-windows.c b/src/inspect-fs-windows.c
index ccf5cba..ba72727 100644
--- a/src/inspect-fs-windows.c
+++ b/src/inspect-fs-windows.c
@@ -25,6 +25,7 @@
 #include <string.h>
 #include <errno.h>
 #include <iconv.h>
+#include <inttypes.h>
 
 #ifdef HAVE_ENDIAN_H
 #include <endian.h>
@@ -57,6 +58,8 @@ static int check_windows_arch (guestfs_h *g, struct inspect_fs
*fs);
 static int check_windows_software_registry (guestfs_h *g, struct inspect_fs
*fs);
 static int check_windows_system_registry (guestfs_h *g, struct inspect_fs *fs);
 static char *map_registry_disk_blob (guestfs_h *g, const void *blob);
+static char *map_registry_disk_blob_gpt (guestfs_h *g, const void *blob);
+static char *extract_guid_from_registry_blob (guestfs_h *g, const void *blob);
 
 /* XXX Handling of boot.ini in the Perl version was pretty broken.  It
  * essentially didn't do anything for modern Windows guests.
@@ -386,6 +389,7 @@ check_windows_system_registry (guestfs_h *g, struct
inspect_fs *fs)
   int r;
   size_t len = strlen (fs->windows_systemroot) + 64;
   char system[len];
+  char gpt_prefix[] = "DMIO:ID:";
   snprintf (system, len, "%s/system32/config/system",
             fs->windows_systemroot);
 
@@ -490,12 +494,18 @@ check_windows_system_registry (guestfs_h *g, struct
inspect_fs *fs)
       CLEANUP_FREE char *blob = NULL;
       char *device;
       int64_t type;
+      bool is_gpt;
 
       type = guestfs_hivex_value_type (g, v);
       blob = guestfs_hivex_value_value (g, v, &len);
-      if (blob != NULL && type == 3 && len == 12) {
+      is_gpt = memcmp (blob, gpt_prefix, 8) == 0;
+      if (blob != NULL && type == 3 && (len == 12 || is_gpt)) {
         /* Try to map the blob to a known disk and partition. */
-        device = map_registry_disk_blob (g, blob);
+        if (is_gpt)
+          device = map_registry_disk_blob_gpt (g, blob);
+        else
+          device = map_registry_disk_blob (g, blob);
+
         if (device != NULL) {
           fs->drive_mappings[count++] = safe_strndup (g, &key[12], 1);
           fs->drive_mappings[count++] = device;
@@ -605,6 +615,88 @@ map_registry_disk_blob (guestfs_h *g, const void *blob)
   return safe_asprintf (g, "%s%d", devices[i],
partitions->val[j].part_num);
 }
 
+/* Matches Windows registry HKLM\SYSYTEM\MountedDevices\DosDevices blob to
+ * to libguestfs GPT partition device. For GPT disks, the blob is made of
+ * "DMIO:ID:" prefix followed by the GPT partition GUID.
+ */
+static char *
+map_registry_disk_blob_gpt (guestfs_h *g, const void *blob)
+{
+  CLEANUP_FREE_STRING_LIST char **parts = NULL;
+  CLEANUP_FREE char *blob_guid = extract_guid_from_registry_blob (g, blob);
+  size_t i;
+
+  parts = guestfs_list_partitions (g);
+  if (parts == NULL)
+    return NULL;
+
+  for (i = 0; parts[i] != NULL; ++i) {
+    CLEANUP_FREE char *fs_guid = NULL;
+    int partnum;
+    CLEANUP_FREE char *device = NULL;
+    CLEANUP_FREE char *type = NULL;
+
+    partnum = guestfs_part_to_partnum (g, parts[i]);
+    if (partnum == -1)
+      continue;
+
+    device = guestfs_part_to_dev (g, parts[i]);
+    if (device == NULL)
+      continue;
+
+    type = guestfs_part_get_parttype (g, device);
+    if (type == NULL)
+      continue;
+
+    if (STRCASENEQ (type, "gpt"))
+      continue;
+
+    /* get the GPT parition GUID from the partition block device */
+    fs_guid = guestfs_part_get_gpt_guid (g, device, partnum);
+    if (fs_guid == NULL)
+      continue;
+
+    /* if both GUIDs match, we have found the mapping for our device */
+    if (STRCASEEQ (fs_guid, blob_guid))
+      return safe_strdup (g, parts[i]);
+  }
+
+  return NULL;
+}
+
+/* Extracts the binary GUID stored in blob from Windows registry
+ * HKLM\SYSTYEM\MountedDevices\DosDevices value and converts it to a
+ * GUID string so that it can be matched against libguestfs partition
+ * device GPT GUID.
+ */
+static char *
+extract_guid_from_registry_blob (guestfs_h *g, const void *blob)
+{
+  char guid_bytes[16];
+  uint32_t data1;
+  uint16_t data2, data3;
+  uint64_t data4;
+
+  /* get the GUID bytes from blob (skip 8 byte "DMIO:ID:" prefix) */
+  memcpy (&guid_bytes, (char *) blob + 8, sizeof (guid_bytes));
+
+  /* copy relevant sections from blob to respective ints */
+  memcpy (&data1, guid_bytes, sizeof (data1));
+  memcpy (&data2, guid_bytes + 4, sizeof (data2));
+  memcpy (&data3, guid_bytes + 6, sizeof (data3));
+  memcpy (&data4, guid_bytes + 8, sizeof (data4));
+
+  /* ensure proper endianness */
+  data1 = le32toh (data1);
+  data2 = le16toh (data2);
+  data3 = le16toh (data3);
+  data4 = be64toh (data4);
+
+  return safe_asprintf (g,
+           "%08" PRIX32 "-%04" PRIX16 "-%04"
PRIX16 "-%04" PRIX64 "-%012" PRIX64,
+           data1, data2, data3, data4 >> 48, data4 & 0xffffffffffff);
+}
+
 /* NB: This function DOES NOT test for the existence of the file.  It
  * will return non-NULL even if the file/directory does not exist.
  * You have to call guestfs_is_file{,_opts} etc.
-- 
2.5.0

On Sat, Feb 06, 2016 at 11:50:05AM -0500, Dawid Zamirski
wrote:
> This patch updates the guestfs_inspect_get_drive_mappings API call to
> also return drive letters for GPT paritions. Previously this worked
> only for MBR partitions. This is achieved by matching the GPT partition
> GUID with the info stored in the blob from
> HKLM\SYSTEM\MountedDevices\DosDevices keys. For GPT partions this blob
> contains a "DMIO:ID:" prefix followed by a 16 byte binary GUID.
I've pushed this upstream.

Thanks for your contribution.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW