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 since partitions may be reused that could result
in confusion and was decided against.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #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 +4170,23 @@ zpool_label_disk_check(char *path)
 	return (0);
 }
 
+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) {
+		read(fd, &id, sizeof (id));
+		close(fd);
+	} else {
+		id = (((uint64_t)rand()) << 32) | (uint64_t)rand();
+	}
+
+	sprintf(label_name, "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 +4277,13 @@ 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");
+
+	/*
+	 * Partions must have unique names so udev will be able to create
+	 * symlinks under /dev/disk/by-partlabel/ for all pool devices.
+	 * The partition names are of the form <pool>-<unique-id>.
+	 */
+	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;