create_mddev: add support for /dev/md_XXX non-numeric names.

With the 'devnm' infrastructure fixed, it is quite easy to support
names like "md_home" for md arrays.
The currently defaults to "off" and can be enabled in mdadm.conf with
  CREATE names=yes
This is incase other tools get confused by the new names.

Signed-off-by: NeilBrown <neilb@suse.de>

Create.c

@@ -687,6 +687,7 @@ int Create(struct supertype *st, char *mddev,
 		/* base name on mddev */
 		/*  /dev/md0 -> 0
 		 *  /dev/md_d0 -> d0
+		 *  /dev/md_foo -> foo
 		 *  /dev/md/1 -> 1
 		 *  /dev/md/d1 -> d1
 		 *  /dev/md/home -> home
@@ -696,9 +697,8 @@ int Create(struct supertype *st, char *mddev,
 		name = strrchr(mddev, '/');
 		if (name) {
 			name++;
-			if (strncmp(name, "md_d", 4)==0 &&
-			    strlen(name) > 4 &&
-			    isdigit(name[4]) &&
+			if (strncmp(name, "md_", 3)==0 &&
+			    strlen(name) > 3 &&
 			    (name-mddev) == 5 /* /dev/ */)
 				name += 3;
 			else if (strncmp(name, "md", 2)==0 &&

config.c

@@ -219,6 +219,7 @@ struct mddev_dev *load_containers(void)
 struct createinfo createinfo = {
 	.autof = 2, /* by default, create devices with standard names */
 	.symlinks = 1,
+	.names = 0, /* By default, stick with numbered md devices. */
 #ifdef DEBIAN
 	.gid = 6, /* disk */
 	.mode = 0660,
@@ -334,6 +335,10 @@ static void createline(char *line)
 			createinfo.symlinks = 1;
 		else if  (strncasecmp(w, "symlinks=no", 11) == 0)
 			createinfo.symlinks = 0;
+		else if (strncasecmp(w, "names=yes", 12) == 0)
+			createinfo.names = 1;
+		else if  (strncasecmp(w, "names=no", 11) == 0)
+			createinfo.names = 0;
 		else {
 			pr_err("unrecognised word on CREATE line: %s\n",
 				w);

mdadm.8.in

@@ -2957,19 +2957,33 @@ exists or is listed in the config file.
 The standard names for non-partitioned arrays (the only sort of md
 array available in 2.4 and earlier) are of the form
 .IP
-/dev/mdNN
+.RB /dev/md NN
 .PP
 where NN is a number.
 The standard names for partitionable arrays (as available from 2.6
-onwards) are of the form
+onwards) are of the form:
 .IP
-/dev/md_dNN
+.RB /dev/md_d NN
 .PP
-Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
+Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
 .PP
-From kernel version, 2.6.28 the "non-partitioned array" can actually
-be partitioned.  So the "md_dNN" names are no longer needed, and
-partitions such as "/dev/mdNNpXX" are possible.
+From kernel version 2.6.28 the "non-partitioned array" can actually
+be partitioned.  So the "md_d\fBNN\fP"
+names are no longer needed, and
+partitions such as "/dev/md\fBNN\fPp\fBXX\fp"
+are possible.
+.PP
+From kernel version 2.6.29 standard names can be non-numeric following
+the form:
+.IP
+.RB /dev/md_ XXX
+.PP
+where
+.B XXX
+is any string.  These names are supported by
+.I mdadm
+since version 3.3 provided they are enabled in
+.IR mdadm.conf .
 
 .SH NOTE
 .I mdadm

mdadm.conf.5

@@ -148,7 +148,7 @@ created as /dev/mdX, then the minor number X is stored.
 The value is a comma separated list of device names or device name
 patterns.
 Only devices with names which match one entry in the list will be used
-to assemble the array.  Note that the devices 
+to assemble the array.  Note that the devices
 listed there must also be listed on a DEVICE line.
 .TP
 .B level=
@@ -339,6 +339,32 @@ or
 Give
 .B symlinks=no
 to suppress this symlink creation.
+
+.TP
+.B names=yes
+Since Linux 2.6.29 it has been possible to create
+.B md
+devices with a name like
+.B md_home
+rather than just a number, like
+.BR md3 .
+.I mdadm
+will use the numeric alternative by default as other tools that interact
+with md arrays may expect only numbers.
+If
+.B names=yes
+is given in
+.I mdadm.conf
+then
+.I mdadm
+will use a name when appropriate.
+If
+.B names=no
+is given, then non-numeric
+.I md
+device names will not be used even if the default changes in a future
+release of
+.IR mdadm .
 .RE
 
 .TP
@@ -437,7 +463,7 @@ The known metadata types are
 
 .TP
 .B POLICY
-This is used to specify what automatic behavior is allowed on devices 
+This is used to specify what automatic behavior is allowed on devices
 newly appearing in the system and provides a way of marking spares that can
 be moved to other arrays as well as the migration domains.
 .I Domain
@@ -475,7 +501,7 @@ file glob matching anything from
 .B /dev/disk/by-path
 .TP
 .B type=
-either 
+either
 .B disk
 or
 .BR part .

mdadm.h

@@ -257,6 +257,7 @@ struct createinfo {
 	int	autof;
 	int	mode;
 	int	symlinks;
+	int	names;
 	struct supertype *supertype;
 };
 

mdopen.c

@@ -126,7 +126,7 @@ void make_parts(char *dev, int cnt)
  *
  * If udev is configured, we create a temporary device, open it, and
  * unlink it.
- * If not, we create the /dev/mdXX device, and is name is usable,
+ * If not, we create the /dev/mdXX device, and if name is usable,
  * /dev/md/name
  * In any case we return /dev/md/name or (if that isn't available)
  * /dev/mdXX in 'chosen'.
@@ -260,25 +260,6 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy,
 		}
 	}
 
-	if (num < 0) {
-		/* need to choose a free number. */
-		char *_devnm = find_free_devnm(use_mdp);
-		if (devnm == NULL) {
-			pr_err("No avail md devices - aborting\n");
-			return -1;
-		}
-		strcpy(devnm, _devnm);
-	} else {
-		sprintf(devnm, "%s%d", use_mdp?"md_d":"md", num);
-		if (mddev_busy(devnm)) {
-			pr_err("%s is already in use.\n",
-				dev);
-			return -1;
-		}
-	}
-
-	sprintf(devname, "/dev/%s", devnm);
-
 	if (cname[0] == 0 && name) {
 		/* Need to find a name if we can
 		 * We don't completely trust 'name'.  Truncate to
@@ -323,6 +304,40 @@ int create_mddev(char *dev, char *name, int autof, int trustworthy,
 		}
 	}
 
+	devnm[0] = 0;
+	if (num < 0 && cname && ci->names) {
+		int fd;
+		int n = -1;
+		sprintf(devnm, "md_%s", cname);
+		fd = open("/sys/module/md_mod/parameters/new_array", O_WRONLY);
+		if (fd >= 0) {
+			n = write(fd, devnm, strlen(devnm));
+			close(fd);
+		}
+		if (n < 0)
+			devnm[0] = 0;
+	}
+	if (devnm[0])
+		;
+	else if (num < 0) {
+		/* need to choose a free number. */
+		char *_devnm = find_free_devnm(use_mdp);
+		if (devnm == NULL) {
+			pr_err("No avail md devices - aborting\n");
+			return -1;
+		}
+		strcpy(devnm, _devnm);
+	} else {
+		sprintf(devnm, "%s%d", use_mdp?"md_d":"md", num);
+		if (mddev_busy(devnm)) {
+			pr_err("%s is already in use.\n",
+				dev);
+			return -1;
+		}
+	}
+
+	sprintf(devname, "/dev/%s", devnm);
+
 	if (dev && dev[0] == '/')
 		strcpy(chosen, dev);
 	else if (cname[0] == 0)