partitions/ibm: Replace strncpy() and improve readability

strncpy() is deprecated and needs to be replaced. The volume label
information strings are not nul-terminated and strncpy() can simply be
replaced with memcpy().

To enhance the readability of find_label() alongside this change, the
following improvements are made:
- Introduce the array dasd_vollabels[] containing all information
  necessary for the label detection.
- Provide a helper function to obtain an index value corresponding to a
  volume label type. This allows the use of a switch statement to reduce
  indentation levels.
- The 'temp' variable is used to check against valid volume label types.
  In the good case, this variable already contains the volume label type
  making it unnecessary to copy the information again from e.g.
  label->vol.vollbl. Remove the 'temp' variable and the second copy as
  all information are already provided.
- Remove the 'found' variable and replace it with early returns
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://lore.kernel.org/r/20230915131001.697070-3-sth@linux.ibm.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/partitions/ibm.c

@@ -61,6 +61,43 @@ static sector_t cchhb2blk(struct vtoc_cchhb *ptr, struct hd_geometry *geo)
 		ptr->b;
 }
 
+/* Volume Label Types */
+#define DASD_VOLLBL_TYPE_VOL1 0
+#define DASD_VOLLBL_TYPE_LNX1 1
+#define DASD_VOLLBL_TYPE_CMS1 2
+
+struct dasd_vollabel {
+	char *type;
+	int idx;
+};
+
+static struct dasd_vollabel dasd_vollabels[] = {
+	[DASD_VOLLBL_TYPE_VOL1] = {
+		.type = "VOL1",
+		.idx = DASD_VOLLBL_TYPE_VOL1,
+	},
+	[DASD_VOLLBL_TYPE_LNX1] = {
+		.type = "LNX1",
+		.idx = DASD_VOLLBL_TYPE_LNX1,
+	},
+	[DASD_VOLLBL_TYPE_CMS1] = {
+		.type = "CMS1",
+		.idx = DASD_VOLLBL_TYPE_CMS1,
+	},
+};
+
+static int get_label_by_type(const char *type)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(dasd_vollabels); i++) {
+		if (!memcmp(type, dasd_vollabels[i].type, 4))
+			return dasd_vollabels[i].idx;
+	}
+
+	return -1;
+}
+
 static int find_label(struct parsed_partitions *state,
 		      dasd_information2_t *info,
 		      struct hd_geometry *geo,
@@ -70,12 +107,10 @@ static int find_label(struct parsed_partitions *state,
 		      char type[],
 		      union label_t *label)
 {
-	Sector sect;
-	unsigned char *data;
 	sector_t testsect[3];
-	unsigned char temp[5];
-	int found = 0;
 	int i, testcount;
+	Sector sect;
+	void *data;
 
 	/* There a three places where we may find a valid label:
 	 * - on an ECKD disk it's block 2
@@ -103,29 +138,27 @@ static int find_label(struct parsed_partitions *state,
 		if (data == NULL)
 			continue;
 		memcpy(label, data, sizeof(*label));
-		memcpy(temp, data, 4);
-		temp[4] = 0;
-		EBCASC(temp, 4);
+		memcpy(type, data, 4);
+		EBCASC(type, 4);
 		put_dev_sector(sect);
-		if (!strcmp(temp, "VOL1") ||
-		    !strcmp(temp, "LNX1") ||
-		    !strcmp(temp, "CMS1")) {
-			if (!strcmp(temp, "VOL1")) {
-				strncpy(type, label->vol.vollbl, 4);
-				strncpy(name, label->vol.volid, 6);
-			} else {
-				strncpy(type, label->lnx.vollbl, 4);
-				strncpy(name, label->lnx.volid, 6);
-			}
-			EBCASC(type, 4);
+		switch (get_label_by_type(type)) {
+		case DASD_VOLLBL_TYPE_VOL1:
+			memcpy(name, label->vol.volid, 6);
 			EBCASC(name, 6);
 			*labelsect = testsect[i];
-			found = 1;
+			return 1;
+		case DASD_VOLLBL_TYPE_LNX1:
+		case DASD_VOLLBL_TYPE_CMS1:
+			memcpy(name, label->lnx.volid, 6);
+			EBCASC(name, 6);
+			*labelsect = testsect[i];
+			return 1;
+		default:
 			break;
 		}
 	}
 
-	return found;
+	return 0;
 }
 
 static int find_vol1_partitions(struct parsed_partitions *state,
@@ -328,18 +361,21 @@ int ibm_partition(struct parsed_partitions *state)
 		info = NULL;
 	}
 
-	if (find_label(state, info, geo, blocksize, &labelsect, name, type,
-		       label)) {
-		if (!strncmp(type, "VOL1", 4)) {
+	if (find_label(state, info, geo, blocksize, &labelsect, name, type, label)) {
+		switch (get_label_by_type(type)) {
+		case DASD_VOLLBL_TYPE_VOL1:
 			res = find_vol1_partitions(state, geo, blocksize, name,
 						   label);
-		} else if (!strncmp(type, "LNX1", 4)) {
+			break;
+		case DASD_VOLLBL_TYPE_LNX1:
 			res = find_lnx1_partitions(state, geo, blocksize, name,
 						   label, labelsect, nr_sectors,
 						   info);
-		} else if (!strncmp(type, "CMS1", 4)) {
+			break;
+		case DASD_VOLLBL_TYPE_CMS1:
 			res = find_cms1_partitions(state, geo, blocksize, name,
 						   label, labelsect);
+			break;
 		}
 	} else if (info) {
 		/*