mdadm: add --no-devices to avoid component devices detail information

When people assemble a md raid device with a large number of
component deivces (e.g. 1500 DASD disks), the raid device detail
information generated by 'mdadm --detail --export $devnode' is very
large. It is because the detail information contains information of
all the component disks (even the missing/failed ones).

In such condition, when udev-md-raid-arrays.rules is triggered and
internally calls "mdadm --detail --no-devices --export $devnode",
user may observe systemd error message ""invalid message length". It
is because the following on-stack raw message buffer in systemd code
is not big enough,
        systemd/src/libudev/libudev-monitor.c
        _public_ struct udev_device *udev_monito ...
                struct ucred *cred;
                union {
                        struct udev_monitor_netlink_header nlh;
                        char raw[8192];
                } buf;
Even change size of raw[] from 8KB to larger size, it may still be not
enough for detail message of a md raid device with much larger number of
component devices.

To fix this problem, an extra option '--no-devices' is added (the
original idea is proposed by Neil Brown). When printing detailed
information of a md raid device, if '--no-devices' is specified, then
all component devices information will not be printed, then the output
message size can be restricted to a small number, even with the systemd
only has 8KB on-disk raw buffer, the md raid array udev rules can work
correctly without failure message.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>

Detail.c

@@ -56,7 +56,7 @@ int Detail(char *dev, struct context *c)
 	 */
 	int fd = open(dev, O_RDONLY);
 	mdu_array_info_t array;
-	mdu_disk_info_t *disks;
+	mdu_disk_info_t *disks = NULL;
 	int next;
 	int d;
 	time_t atime;
@@ -280,7 +280,7 @@ int Detail(char *dev, struct context *c)
 			}
 			map_free(map);
 		}
-		if (sra) {
+		if (!c->no_devices && sra) {
 			struct mdinfo *mdi;
 			for (mdi  = sra->devs; mdi; mdi = mdi->next) {
 				char *path;
@@ -655,12 +655,17 @@ This is pretty boring
 			printf("\n\n");
 		}
 
-		if (array.raid_disks)
-			printf("    Number   Major   Minor   RaidDevice State\n");
-		else
-			printf("    Number   Major   Minor   RaidDevice\n");
+		if (!c->no_devices) {
+			if (array.raid_disks)
+				printf("    Number   Major   Minor   RaidDevice State\n");
+			else
+				printf("    Number   Major   Minor   RaidDevice\n");
+		}
 	}
-	free(info);
+
+	/* if --no_devices specified, not print component devices info */
+	if (c->no_devices)
+		goto skip_devices_state;
 
 	for (d = 0; d < max_disks * 2; d++) {
 		char *dv;
@@ -747,6 +752,8 @@ This is pretty boring
 		if (!c->brief)
 			printf("\n");
 	}
+
+skip_devices_state:
 	if (spares && c->brief && array.raid_disks)
 		printf(" spares=%d", spares);
 	if (c->brief && st && st->sb)
@@ -766,8 +773,9 @@ This is pretty boring
 	    !enough(array.level, array.raid_disks, array.layout, 1, avail))
 		rv = 2;
 
-	free(disks);
 out:
+	free(info);
+	free(disks);
 	close(fd);
 	free(subarray);
 	free(avail);

ReadMe.c

@@ -181,6 +181,7 @@ struct option long_options[] = {
 
     /* For Detail/Examine */
     {"brief",	  0, 0, Brief},
+    {"no-devices",0, 0, NoDevices},
     {"export",	  0, 0, 'Y'},
     {"sparc2.2",  0, 0, Sparc22},
     {"test",      0, 0, 't'},

mdadm.c

@@ -159,6 +159,10 @@ int main(int argc, char *argv[])
 			c.brief = 1;
 			continue;
 
+		case NoDevices:
+			c.no_devices = 1;
+			continue;
+
 		case 'Y': c.export++;
 			continue;
 

mdadm.h

@@ -440,6 +440,7 @@ enum special_options {
 	NoSharing,
 	HelpOptions,
 	Brief,
+	NoDevices,
 	ManageOpt,
 	Add,
 	AddSpare,
@@ -550,6 +551,7 @@ struct context {
 	int	runstop;
 	int	verbose;
 	int	brief;
+	int	no_devices;
 	int	force;
 	char	*homehost;
 	int	require_homehost;