Add -fail support to --incremental

This can be used for hot-unplug.  When a device has been remove,
udev can call
   mdadm --incremental --fail sda

and mdadm will find the array holding sda and remove sda from
the array.

Based on code from  Doug Ledford <dledford@redhat.com>

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

Incremental.c

@@ -849,3 +849,42 @@ int Incremental_container(struct supertype *st, char *devname, int verbose,
 	map_unlock(&map);
 	return 0;
 }
+
+/*
+ * IncrementalRemove - Attempt to see if the passed in device belongs to any
+ * raid arrays, and if so first fail (if needed) and then remove the device.
+ *
+ * @devname - The device we want to remove
+ *
+ * Note: the device name must be a kernel name like "sda", so
+ * that we can find it in /proc/mdstat
+ */
+int IncrementalRemove(char *devname, int verbose)
+{
+	int mdfd;
+	struct mdstat_ent *ent;
+	struct mddev_dev_s devlist;
+
+	if (strchr(devname, '/')) {
+		fprintf(stderr, Name ": incremental removal requires a "
+			"kernel device name, not a file: %s\n", devname);
+		return 1;
+	}
+	ent = mdstat_by_component(devname);
+	if (!ent) {
+		fprintf(stderr, Name ": %s does not appear to be a component "
+			"of any array\n", devname);
+		return 1;
+	}
+	mdfd = open_dev(ent->devnum);
+	if (mdfd < 0) {
+		fprintf(stderr, Name ": Cannot open array %s!!\n", ent->dev);
+		return 1;
+	}
+	memset(&devlist, 0, sizeof(devlist));
+	devlist.devname = devname;
+	devlist.disposition = 'f';
+	Manage_subdevs(ent->dev, mdfd, &devlist, verbose);
+	devlist.disposition = 'r';
+	return Manage_subdevs(ent->dev, mdfd, &devlist, verbose);
+}

Manage.c

@@ -892,8 +892,8 @@ int Manage_subdevs(char *devname, int fd,
 			if (lfd >= 0)
 				close(lfd);
 			if (verbose >= 0)
-				fprintf(stderr, Name ": hot removed %s\n",
-					dnprintable);
+				fprintf(stderr, Name ": hot removed %s from %s\n",
+					dnprintable, devname);
 			break;
 
 		case 'f': /* set faulty */

ReadMe.c

@@ -213,7 +213,7 @@ char Help[] =
 "       mdadm --grow options device\n"
 "            resize/reshape an active array\n"
 "       mdadm --incremental device\n"
-"            add a device to an array as appropriate\n"
+"            add/remove a device to/from an array as appropriate\n"
 "       mdadm --monitor options...\n"
 "            Monitor one or more array for significant changes.\n"
 "       mdadm device options...\n"
@@ -256,7 +256,7 @@ char OptionHelp[] =
 "  --examine-bitmap -X: Display the detail of a bitmap file\n"
 "  --monitor     -F   : monitor (follow) some arrays\n"
 "  --grow        -G   : resize/ reshape and array\n"
-"  --incremental -I   : add a single device to an array as appropriate\n"
+"  --incremental -I   : add/remove a single device to/from an array as appropriate\n"
 "  --query       -Q   : Display general information about how a\n"
 "                       device relates to the md driver\n"
 "  --auto-detect      : Start arrays auto-detected by the kernel\n"
@@ -535,20 +535,26 @@ char Help_grow[] =
 ;
 
 char Help_incr[] =
-"Usage: mdadm --incremental [-Rqrs] device\n"
+"Usage: mdadm --incremental [-Rqrsf] device\n"
 "\n"
 "This usage allows for incremental assembly of md arrays.  Devices can be\n"
 "added one at a time as they are discovered.  Once an array has all expected\n"
 "devices, it will be started.\n"
 "\n"
-"Options that are valid with incremental assembly (-I --incremental) more are:\n"
-"  --run         -R : run arrays as soon as a minimal number of devices are\n"
+"Optionally, the process can be reversed by using the fail option.\n"
+"When fail mode is invoked, mdadm will see if the device belongs to an array\n"
+"and then both fail (if needed) and remove the device from that array.\n"
+"\n"
+"Options that are valid with incremental assembly (-I --incremental) are:\n"
+"  --run         -R : Run arrays as soon as a minimal number of devices are\n"
 "                   : present rather than waiting for all expected.\n"
 "  --quiet       -q : Don't print any information messages, just errors.\n"
 "  --rebuild-map -r : Rebuild the 'map' file that mdadm uses for tracking\n"
 "                   : partial arrays.\n"
 "  --scan        -s : Use with -R to start any arrays that have the minimal\n"
 "                   : required number of devices, but are not yet started.\n"
+"  --fail      -f  : First fail (if needed) and then remove device from\n"
+"                  : any array that it is a member of.\n"
 ;
 
 char Help_config[] =

mdadm.8.in

@@ -136,6 +136,10 @@ This provides a convenient interface to a
 system.  As each device is detected,
 .I mdadm
 has a chance to include it in some array as appropriate.
+Optionally, when the
+.I \-\-fail
+flag is passed in we will remove the device from any active array
+instead of adding it.
 
 If a
 .B CONTAINER
@@ -189,7 +193,7 @@ Change the size or shape of an active array.
 
 .TP
 .BR \-I ", " \-\-incremental
-Add a single device into an appropriate array, and possibly start the array.
+Add/remove a single device to/from an appropriate array, and possibly start the array.
 
 .TP
 .B \-\-auto-detect
@@ -1239,6 +1243,15 @@ in
 .B mdadm.conf
 as requiring an external bitmap, that bitmap will be attached first.
 
+.TP
+.BR \-\-fail ", " \-f
+This allows the hot-plug system to remove devices that have fully disappeared
+from the kernel.  It will first fail and then remove the device from any
+array it belongs to.
+The device name given should be a kernel device name such as "sda",
+not a name in
+.IR /dev .
+
 .SH For Monitor mode:
 .TP
 .BR \-m ", " \-\-mail
@@ -2145,6 +2158,10 @@ Usage:
 .I component-device
 .HP 12
 Usage:
+.B mdadm \-\-incremental \-\-fail
+.I component-device
+.HP 12
+Usage:
 .B mdadm \-\-incremental \-\-rebuild\-map
 .HP 12
 Usage:
@@ -2157,6 +2174,11 @@ passed to
 .B "mdadm \-\-incremental"
 to be conditionally added to an appropriate array.
 
+Conversely, it can also be used with the
+.B \-\-fail
+flag to do just the opposite and find whatever array a particular device
+is part of and remove the device from that array.
+
 If the device passed is a
 .B CONTAINER
 device created by a previous call to

mdadm.c

@@ -773,6 +773,9 @@ int main(int argc, char *argv[])
 			devmode = 'r';
 			continue;
 		case O(MANAGE,'f'): /* set faulty */
+		case O(INCREMENTAL,'f'): /* r for incremental is taken, use f
+					  * even though we will both fail and
+					  * remove the device */
 			devmode = 'f';
 			continue;
 		case O(INCREMENTAL,'R'):
@@ -1516,6 +1519,11 @@ int main(int argc, char *argv[])
 			 ": --incremental --scan meaningless without --run.\n");
 				break;
 			}
+			if (devmode == 'f') {
+				fprintf(stderr, Name
+			 ": --incremental --scan --fail not supported.\n");
+				break;
+			}
 			rv = IncrementalScan(verbose);
 		}
 		if (!devlist) {
@@ -1532,6 +1540,10 @@ int main(int argc, char *argv[])
 			rv = 1;
 			break;
 		}
+		if (devmode == 'f') {
+			rv = IncrementalRemove(devlist->devname, verbose-quiet);
+			break;
+		}
 		rv = Incremental(devlist->devname, verbose-quiet, runstop,
 				 ss, homehost, require_homehost, autof);
 		break;

mdadm.h

@@ -823,7 +823,7 @@ extern int Incremental_container(struct supertype *st, char *devname,
 				 int trustworthy);
 extern void RebuildMap(void);
 extern int IncrementalScan(int verbose);
-
+extern int IncrementalRemove(char *devname, int verbose);
 extern int CreateBitmap(char *filename, int force, char uuid[16],
 			unsigned long chunksize, unsigned long daemon_sleep,
 			unsigned long write_behind,