Introduce devname2devnum

and use it instead of opencoding.

mdadm.h

@@ -775,6 +775,7 @@ extern int mdmon_running(int devnum);
 extern int signal_mdmon(int devnum);
 
 extern char *devnum2devname(int num);
+extern int devname2devnum(char *name);
 extern int fd2devnum(int fd);
 
 static inline int dev2major(int d)

mdstat.c

@@ -191,11 +191,7 @@ struct mdstat_ent *mdstat_read(int hold, int start)
 					 * there.
 					 */
 					struct mdstat_ent **ih;
-					int dn2;
+					int dn2 = devname2devnum(w);
-					if (strncmp(w, "md_d", 4)==0)
-						dn2 = -1-strtoul(w+4, &ep, 10);
-					else
-						dn2 = strtoul(w+2, &ep, 10);
 					ih = &all;
 					while (ih != insert_here && *ih &&
 					       (*ih)->devnum != dn2)

sysfs.c

@@ -59,15 +59,9 @@ void sysfs_free(struct mdinfo *sra)
 int sysfs_open(int devnum, char *devname, char *attr)
 {
 	char fname[50];
-	char sys_name[16];
 	int fd;
-	if (devnum >= 0)
-		sprintf(sys_name, "md%d", devnum);
-	else
-		sprintf(sys_name, "md_d%d",
-			-1-devnum);
 
-	sprintf(fname, "/sys/block/%s/md/", sys_name);
+	sprintf(fname, "/sys/block/%s/md/", devnum2devname(devnum));
 	if (devname) {
 		strcat(fname, devname);
 		strcat(fname, "/");

util.c

@@ -826,10 +826,7 @@ struct supertype *super_by_fd(int fd)
 		int devnum;
 		if (subarray)
 			*subarray++ = '\0';
-		if (strncmp(dev, "md_d", 4) == 0)
+		devnum = devname2devnum(dev);
-			devnum = -1-atoi(dev+4);
-		else
-			devnum = atoi(dev+2);
 		subarray = strdup(subarray);
 		if (sra)
 			sysfs_free(sra);
@@ -1013,6 +1010,17 @@ char *devnum2devname(int num)
 	return strdup(name);
 }
 
+int devname2devnum(char *name)
+{
+	char *ep;
+	int num;
+	if (strncmp(name, "md_d", 4)==0)
+		num = -1-strtoul(name+4, &ep, 10);
+	else
+		num = strtoul(name+2, &ep, 10);
+	return num;
+}
+
 int fd2devnum(int fd)
 {
 	struct stat stb;