RFC: Canonicalize block device paths

There are many naming conventions for partitions associated with a
block device.  Some of the major ones are:

/dev/foo -> /dev/foo1
/dev/foo1 -> /dev/foo1p1
/dev/mapper/foo -> /dev/mapper/foop1
/dev/disk/by-path/foo -> /dev/disk/by-path/foo-part1

The universe of possible conventions isn't clear.  Rather than trying
to understand all possible conventions, this patch divides devices
into two groups, device mapper devices and everything else.  Device
mapper devices seem always to follow the convention of device ->
devicep1; everything else is canonicalized.

src/Makefile.am

@@ -1037,8 +1037,13 @@ libexec_PROGRAMS += libvirt_parthelper
 
 libvirt_parthelper_SOURCES = $(STORAGE_HELPER_DISK_SOURCES)
 libvirt_parthelper_LDFLAGS = $(WARN_LDFLAGS) $(COVERAGE_LDFLAGS)
-libvirt_parthelper_LDADD = $(LIBPARTED_LIBS) ../gnulib/lib/libgnu.la
-libvirt_parthelper_CFLAGS = $(LIBPARTED_CFLAGS)
+libvirt_parthelper_LDADD =		\
+		$(LIBPARTED_LIBS)	\
+		$(DEVMAPPER_LIBS)	\
+		libvirt_util.la		\
+		../gnulib/lib/libgnu.la
+
+libvirt_parthelper_CFLAGS = $(LIBPARTED_CFLAGS) $(DEVMAPPER_CFLAGS)
 endif
 endif
 EXTRA_DIST += $(STORAGE_HELPER_DISK_SOURCES)

src/storage/parthelper.c

@@ -35,7 +35,12 @@
 #include <parted/parted.h>
 #include <stdio.h>
 #include <string.h>
+#include <libdevmapper.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
+#include "util.h"
 #include "c-ctype.h"
 
 /* we don't need to include the full internal.h just for this */
@@ -52,6 +57,18 @@ enum diskCommand {
     DISK_GEOMETRY
 };
 
+static int
+is_dm_device(const char *devname)
+{
+    struct stat buf;
+
+    if (devname && !stat(devname, &buf) && dm_is_dm_major(major(buf.st_rdev))) {
+        return 1;
+    }
+
+    return 0;
+}
+
 int main(int argc, char **argv)
 {
     PedDevice *dev;
@@ -59,6 +76,7 @@ int main(int argc, char **argv)
     PedPartition *part;
     int cmd = DISK_LAYOUT;
     const char *path;
+    char *canonical_path;
     const char *partsep;
 
     if (argc == 3 && STREQ(argv[2], "-g")) {
@@ -69,7 +87,20 @@ int main(int argc, char **argv)
     }
 
     path = argv[1];
-    partsep = *path && c_isdigit(path[strlen(path)-1]) ? "p" : "";
+    if (is_dm_device(path)) {
+        partsep = "p";
+        canonical_path = strdup(path);
+        if (canonical_path == NULL) {
+            return 2;
+        }
+    } else {
+        if (virFileResolveLink(path, &canonical_path) != 0) {
+            return 2;
+        }
+
+        partsep = *canonical_path &&
+            c_isdigit(canonical_path[strlen(canonical_path)-1]) ? "p" : "";
+    }
 
     if ((dev = ped_device_get(path)) == NULL) {
         fprintf(stderr, "unable to access device %s\n", path);
@@ -125,7 +156,7 @@ int main(int argc, char **argv)
          */
         if (part->num != -1) {
             printf("%s%s%d%c%s%c%s%c%llu%c%llu%c%llu%c",
-                   path, partsep,
+                   canonical_path, partsep,
                    part->num, '\0',
                    type, '\0',
                    content, '\0',