Create unique partition labels

When partitioning a device a name may be specified for each partion.
Internally zfs doesn't use this partition name for anything so it
has always just been set to "zfs".

However this isn't optimal because udev will create symlinks using
this name in /dev/disk/by-partlabel/.  If the name isn't unique
then all the links cannot be created.

Therefore a random 64-bit value has been added to the partition
label, i.e "zfs-1234567890abcdef".  Additional information could
be encoded here but since partitions may be reused that could
result in confusion and it was decided against.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue openzfs#4517

cmd/zpool/zpool_main.c

@@ -6055,6 +6055,7 @@ main(int argc, char **argv)
 
 	(void) setlocale(LC_ALL, "");
 	(void) textdomain(TEXT_DOMAIN);
+	srand(time(NULL));
 
 	dprintf_setup(&argc, argv);
 

lib/libzfs/libzfs_pool.c

@@ -4170,6 +4170,32 @@ zpool_label_disk_check(char *path)
 	return (0);
 }
 
+/*
+ * Generate a unique partition name for the ZFS member.  Partitions must
+ * have unique names to ensure udev will be able to create symlinks under
+ * /dev/disk/by-partlabel/ for all pool members.  The partition names are
+ * of the form <pool>-<unique-id>.
+ */
+static void
+zpool_label_name(char *label_name, int label_size)
+{
+	uint64_t id = 0;
+	int fd;
+
+	fd = open("/dev/urandom", O_RDONLY);
+	if (fd > 0) {
+		if (read(fd, &id, sizeof (id)) != sizeof (id))
+			id = 0;
+
+		close(fd);
+	}
+
+	if (id == 0)
+		id = (((uint64_t)rand()) << 32) | (uint64_t)rand();
+
+	snprintf(label_name, label_size, "zfs-%016llx", (u_longlong_t) id);
+}
+
 /*
  * Label an individual disk.  The name provided is the short name,
  * stripped of any leading /dev path.
@@ -4260,7 +4286,7 @@ zpool_label_disk(libzfs_handle_t *hdl, zpool_handle_t *zhp, char *name)
 	 * can get, in the absence of V_OTHER.
 	 */
 	vtoc->efi_parts[0].p_tag = V_USR;
-	(void) strcpy(vtoc->efi_parts[0].p_name, "zfs");
+	zpool_label_name(vtoc->efi_parts[0].p_name, EFI_PART_NAME_LEN);
 
 	vtoc->efi_parts[8].p_start = slice_size + start_block;
 	vtoc->efi_parts[8].p_size = resv;