[PATCH] md: "Faulty" personality

The 'faulty' personality provides a layer over any block device in which
errors may be synthesised.

A variety of errors are possible including transient and persistent read
and write errors, and read errors that persist until the next write.

There error mode can be changed on a live array.

Accessing this personality requires mdadm 2.8.0 or later.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/Kconfig

@@ -164,6 +164,15 @@ config MD_MULTIPATH
 
 	  If unsure, say N.
 
+config MD_FAULTY
+	tristate "Faulty test module for MD"
+	depends on BLK_DEV_MD
+	help
+	  The "faulty" module allows for a block device that occasionally returns
+	  read or write errors.  It is useful for testing.
+
+	  In unsure, say N.
+
 config BLK_DEV_DM
 	tristate "Device mapper support"
 	depends on MD

drivers/md/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_MD_RAID10)		+= raid10.o
 obj-$(CONFIG_MD_RAID5)		+= raid5.o xor.o
 obj-$(CONFIG_MD_RAID6)		+= raid6.o xor.o
 obj-$(CONFIG_MD_MULTIPATH)	+= multipath.o
+obj-$(CONFIG_MD_FAULTY)		+= faulty.o
 obj-$(CONFIG_BLK_DEV_MD)	+= md.o
 obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o
 obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o

drivers/md/faulty.c

+/*
+ * faulty.c : Multiple Devices driver for Linux
+ *
+ * Copyright (C) 2004 Neil Brown
+ *
+ * fautly-device-simulator personality for md
+ *
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * You should have received a copy of the GNU General Public License
+ * (for example /usr/src/linux/COPYING); if not, write to the Free
+ * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+/*
+ * The "faulty" personality causes some requests to fail.
+ *
+ * Possible failure modes are:
+ *   reads fail "randomly" but succeed on retry
+ *   writes fail "randomly" but succeed on retry
+ *   reads for some address fail and then persist until a write
+ *   reads for some address fail and then persist irrespective of write
+ *   writes for some address fail and persist
+ *   all writes fail
+ *
+ * Different modes can be active at a time, but only
+ * one can be set at array creation.  Others can be added later.
+ * A mode can be one-shot or recurrent with the recurrance being
+ * once in every N requests.
+ * The bottom 5 bits of the "layout" indicate the mode.  The
+ * remainder indicate a period, or 0 for one-shot.
+ *
+ * There is an implementation limit on the number of concurrently
+ * persisting-faulty blocks. When a new fault is requested that would
+ * exceed the limit, it is ignored.
+ * All current faults can be clear using a layout of "0".
+ *
+ * Requests are always sent to the device.  If they are to fail,
+ * we clone the bio and insert a new b_end_io into the chain.
+ */
+
+#define	WriteTransient	0
+#define	ReadTransient	1
+#define	WritePersistent	2
+#define	ReadPersistent	3
+#define	WriteAll	4 /* doesn't go to device */
+#define	ReadFixable	5
+#define	Modes	6
+
+#define	ClearErrors	31
+#define	ClearFaults	30
+
+#define AllPersist	100 /* internal use only */
+#define	NoPersist	101
+
+#define	ModeMask	0x1f
+#define	ModeShift	5
+
+#define MaxFault	50
+#include <linux/raid/md.h>
+
+
+static int faulty_fail(struct bio *bio, unsigned int bytes_done, int error)
+{
+	struct bio *b = bio->bi_private;
+
+	b->bi_size = bio->bi_size;
+	b->bi_sector = bio->bi_sector;
+
+	if (bio->bi_size == 0)
+		bio_put(bio);
+
+	clear_bit(BIO_UPTODATE, &b->bi_flags);
+	return (b->bi_end_io)(b, bytes_done, -EIO);
+}
+
+typedef struct faulty_conf {
+	int period[Modes];
+	atomic_t counters[Modes];
+	sector_t faults[MaxFault];
+	int	modes[MaxFault];
+	int nfaults;
+	mdk_rdev_t *rdev;
+} conf_t;
+
+static int check_mode(conf_t *conf, int mode)
+{
+	if (conf->period[mode] == 0 &&
+	    atomic_read(&conf->counters[mode]) <= 0)
+		return 0; /* no failure, no decrement */
+
+
+	if (atomic_dec_and_test(&conf->counters[mode])) {
+		if (conf->period[mode])
+			atomic_set(&conf->counters[mode], conf->period[mode]);
+		return 1;
+	}
+	return 0;
+}
+
+static int check_sector(conf_t *conf, sector_t start, sector_t end, int dir)
+{
+	/* If we find a ReadFixable sector, we fix it ... */
+	int i;
+	for (i=0; i<conf->nfaults; i++)
+		if (conf->faults[i] >= start &&
+		    conf->faults[i] < end) {
+			/* found it ... */
+			switch (conf->modes[i] * 2 + dir) {
+			case WritePersistent*2+WRITE: return 1;
+			case ReadPersistent*2+READ: return 1;
+			case ReadFixable*2+READ: return 1;
+			case ReadFixable*2+WRITE:
+				conf->modes[i] = NoPersist;
+				return 0;
+			case AllPersist*2+READ:
+			case AllPersist*2+WRITE: return 1;
+			default:
+				return 0;
+			}
+		}
+	return 0;
+}
+
+static void add_sector(conf_t *conf, sector_t start, int mode)
+{
+	int i;
+	int n = conf->nfaults;
+	for (i=0; i<conf->nfaults; i++)
+		if (conf->faults[i] == start) {
+			switch(mode) {
+			case NoPersist: conf->modes[i] = mode; return;
+			case WritePersistent:
+				if (conf->modes[i] == ReadPersistent ||
+				    conf->modes[i] == ReadFixable)
+					conf->modes[i] = AllPersist;
+				else
+					conf->modes[i] = WritePersistent;
+				return;
+			case ReadPersistent:
+				if (conf->modes[i] == WritePersistent)
+					conf->modes[i] = AllPersist;
+				else
+					conf->modes[i] = ReadPersistent;
+				return;
+			case ReadFixable:
+				if (conf->modes[i] == WritePersistent ||
+				    conf->modes[i] == ReadPersistent)
+					conf->modes[i] = AllPersist;
+				else
+					conf->modes[i] = ReadFixable;
+				return;
+			}
+		} else if (conf->modes[i] == NoPersist)
+			n = i;
+
+	if (n >= MaxFault)
+		return;
+	conf->faults[n] = start;
+	conf->modes[n] = mode;
+	if (conf->nfaults == n)
+		conf->nfaults = n+1;
+}
+
+static int make_request(request_queue_t *q, struct bio *bio)
+{
+	mddev_t *mddev = q->queuedata;
+	conf_t *conf = (conf_t*)mddev->private;
+	int failit = 0;
+
+	if (bio->bi_rw & 1) {
+		/* write request */
+		if (atomic_read(&conf->counters[WriteAll])) {
+			/* special case - don't decrement, don't generic_make_request,
+			 * just fail immediately
+			 */
+			bio_endio(bio, bio->bi_size, -EIO);
+			return 0;
+		}
+
+		if (check_sector(conf, bio->bi_sector, bio->bi_sector+(bio->bi_size>>9),
+				 WRITE))
+			failit = 1;
+		if (check_mode(conf, WritePersistent)) {
+			add_sector(conf, bio->bi_sector, WritePersistent);
+			failit = 1;
+		}
+		if (check_mode(conf, WriteTransient))
+			failit = 1;
+	} else {
+		/* read request */
+		if (check_sector(conf, bio->bi_sector, bio->bi_sector + (bio->bi_size>>9),
+				 READ))
+			failit = 1;
+		if (check_mode(conf, ReadTransient))
+			failit = 1;
+		if (check_mode(conf, ReadPersistent)) {
+			add_sector(conf, bio->bi_sector, ReadPersistent);
+			failit = 1;
+		}
+		if (check_mode(conf, ReadFixable)) {
+			add_sector(conf, bio->bi_sector, ReadFixable);
+			failit = 1;
+		}
+	}
+	if (failit) {
+		struct bio *b = bio_clone(bio, GFP_NOIO);
+		b->bi_bdev = conf->rdev->bdev;
+		b->bi_private = bio;
+		b->bi_end_io = faulty_fail;
+		generic_make_request(b);
+		return 0;
+	} else {
+		bio->bi_bdev = conf->rdev->bdev;
+		return 1;
+	}
+}
+
+static void status(struct seq_file *seq, mddev_t *mddev)
+{
+	conf_t *conf = (conf_t*)mddev->private;
+	int n;
+
+	if ((n=atomic_read(&conf->counters[WriteTransient])) != 0)
+		seq_printf(seq, " WriteTransient=%d(%d)",
+			   n, conf->period[WriteTransient]);
+
+	if ((n=atomic_read(&conf->counters[ReadTransient])) != 0)
+		seq_printf(seq, " ReadTransient=%d(%d)",
+			   n, conf->period[ReadTransient]);
+
+	if ((n=atomic_read(&conf->counters[WritePersistent])) != 0)
+		seq_printf(seq, " WritePersistent=%d(%d)",
+			   n, conf->period[WritePersistent]);
+
+	if ((n=atomic_read(&conf->counters[ReadPersistent])) != 0)
+		seq_printf(seq, " ReadPersistent=%d(%d)",
+			   n, conf->period[ReadPersistent]);
+
+
+	if ((n=atomic_read(&conf->counters[ReadFixable])) != 0)
+		seq_printf(seq, " ReadFixable=%d(%d)",
+			   n, conf->period[ReadFixable]);
+
+	if ((n=atomic_read(&conf->counters[WriteAll])) != 0)
+		seq_printf(seq, " WriteAll");
+
+	seq_printf(seq, " nfaults=%d", conf->nfaults);
+}
+
+
+static int reconfig(mddev_t *mddev, int layout, int chunk_size)
+{
+	int mode = layout & ModeMask;
+	int count = layout >> ModeShift;
+	conf_t *conf = mddev->private;
+
+	if (chunk_size != -1)
+		return -EINVAL;
+
+	/* new layout */
+	if (mode == ClearFaults)
+		conf->nfaults = 0;
+	else if (mode == ClearErrors) {
+		int i;
+		for (i=0 ; i < Modes ; i++) {
+			conf->period[i] = 0;
+			atomic_set(&conf->counters[i], 0);
+		}
+	} else if (mode < Modes) {
+		conf->period[mode] = count;
+		if (!count) count++;
+		atomic_set(&conf->counters[mode], count);
+	} else
+		return -EINVAL;
+	mddev->layout = -1; /* makes sure further changes come through */
+	return 0;
+}
+
+static int run(mddev_t *mddev)
+{
+	mdk_rdev_t *rdev;
+	struct list_head *tmp;
+	int i;
+
+	conf_t *conf = kmalloc(sizeof(*conf), GFP_KERNEL);
+
+	for (i=0; i<Modes; i++) {
+		atomic_set(&conf->counters[i], 0);
+		conf->period[i] = 0;
+	}
+	conf->nfaults = 0;
+
+	ITERATE_RDEV(mddev, rdev, tmp)
+		conf->rdev = rdev;
+
+	mddev->array_size = mddev->size;
+	mddev->private = conf;
+
+	reconfig(mddev, mddev->layout, -1);
+
+	return 0;
+}
+
+static int stop(mddev_t *mddev)
+{
+	conf_t *conf = (conf_t *)mddev->private;
+
+	kfree(conf);
+	mddev->private = NULL;
+	return 0;
+}
+
+static mdk_personality_t faulty_personality =
+{
+	.name		= "faulty",
+	.owner		= THIS_MODULE,
+	.make_request	= make_request,
+	.run		= run,
+	.stop		= stop,
+	.status		= status,
+	.reconfig	= reconfig,
+};
+
+static int __init raid_init(void)
+{
+	return register_md_personality(FAULTY, &faulty_personality);
+}
+
+static void raid_exit(void)
+{
+	unregister_md_personality(FAULTY);
+}
+
+module_init(raid_init);
+module_exit(raid_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("md-personality-10"); /* faulty */

drivers/md/md.c

@@ -2351,16 +2351,27 @@ static int update_array_info(mddev_t *mddev, mdu_array_info_t *info)
 /*	    mddev->patch_version != info->patch_version || */
 	    mddev->ctime         != info->ctime         ||
 	    mddev->level         != info->level         ||
-	    mddev->layout        != info->layout        ||
+/*	    mddev->layout        != info->layout        || */
 	    !mddev->persistent	 != info->not_persistent||
 	    mddev->chunk_size    != info->chunk_size    )
 		return -EINVAL;
 	/* Check there is only one change */
 	if (mddev->size != info->size) cnt++;
 	if (mddev->raid_disks != info->raid_disks) cnt++;
+	if (mddev->layout != info->layout) cnt++;
 	if (cnt == 0) return 0;
 	if (cnt > 1) return -EINVAL;
 
+	if (mddev->layout != info->layout) {
+		/* Change layout
+		 * we don't need to do anything at the md level, the
+		 * personality will take care of it all.
+		 */
+		if (mddev->pers->reconfig == NULL)
+			return -EINVAL;
+		else
+			return mddev->pers->reconfig(mddev, info->layout, -1);
+	}
 	if (mddev->size != info->size) {
 		mdk_rdev_t * rdev;
 		struct list_head *tmp;

include/linux/raid/md_k.h

@@ -25,10 +25,12 @@
 #define MULTIPATH         7UL
 #define RAID6		  8UL
 #define	RAID10		  9UL
-#define MAX_PERSONALITY   10UL
+#define FAULTY		  10UL
+#define MAX_PERSONALITY   11UL
 
 #define	LEVEL_MULTIPATH		(-4)
 #define	LEVEL_LINEAR		(-1)
+#define	LEVEL_FAULTY		(-5)
 
 #define MaxSector (~(sector_t)0)
 #define MD_THREAD_NAME_MAX 14
@@ -36,6 +38,7 @@
 static inline int pers_to_level (int pers)
 {
 	switch (pers) {
+		case FAULTY:		return LEVEL_FAULTY;
 		case MULTIPATH:		return LEVEL_MULTIPATH;
 		case HSM:		return -3;
 		case TRANSLUCENT:	return -2;
@@ -53,6 +56,7 @@ static inline int pers_to_level (int pers)
 static inline int level_to_pers (int level)
 {
 	switch (level) {
+		case LEVEL_FAULTY: return FAULTY;
 		case LEVEL_MULTIPATH: return MULTIPATH;
 		case -3: return HSM;
 		case -2: return TRANSLUCENT;
@@ -290,6 +294,7 @@ struct mdk_personality_s
 	int (*sync_request)(mddev_t *mddev, sector_t sector_nr, int go_faster);
 	int (*resize) (mddev_t *mddev, sector_t sectors);
 	int (*reshape) (mddev_t *mddev, int raid_disks);
+	int (*reconfig) (mddev_t *mddev, int layout, int chunk_size);
 };