Merge branch 'for-2.6.33' of git://git.kernel.dk/linux-2.6-block

* 'for-2.6.33' of git://git.kernel.dk/linux-2.6-block: (113 commits)
  cfq-iosched: Do not access cfqq after freeing it
  block: include linux/err.h to use ERR_PTR
  cfq-iosched: use call_rcu() instead of doing grace period stall on queue exit
  blkio: Allow CFQ group IO scheduling even when CFQ is a module
  blkio: Implement dynamic io controlling policy registration
  blkio: Export some symbols from blkio as its user CFQ can be a module
  block: Fix io_context leak after failure of clone with CLONE_IO
  block: Fix io_context leak after clone with CLONE_IO
  cfq-iosched: make nonrot check logic consistent
  io controller: quick fix for blk-cgroup and modular CFQ
  cfq-iosched: move IO controller declerations to a header file
  cfq-iosched: fix compile problem with !CONFIG_CGROUP
  blkio: Documentation
  blkio: Wait on sync-noidle queue even if rq_noidle = 1
  blkio: Implement group_isolation tunable
  blkio: Determine async workload length based on total number of queues
  blkio: Wait for cfq queue to get backlogged if group is empty
  blkio: Propagate cgroup weight updation to cfq groups
  blkio: Drop the reference to queue once the task changes cgroup
  blkio: Provide some isolation between groups
  ...

15 files changed, 1085 insertions, 28 deletions

diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index ba4ec39a1131..57b5c3c82e86 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -13,6 +13,7 @@
 #define flush_cache_dup_mm(mm)			do { } while (0)
 #define flush_cache_range(vma, start, end)	do { } while (0)
 #define flush_cache_page(vma, vmaddr, pfn)	do { } while (0)
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
 #define flush_dcache_page(page)			do { } while (0)
 #define flush_dcache_mmap_lock(mapping)		do { } while (0)
 #define flush_dcache_mmap_unlock(mapping)	do { } while (0)
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b449e738533a..fcbc26af00e4 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -331,4 +331,17 @@ static inline int bdi_sched_wait(void *word)
 	return 0;
 }
 
+static inline void blk_run_backing_dev(struct backing_dev_info *bdi,
+				       struct page *page)
+{
+	if (bdi && bdi->unplug_io_fn)
+		bdi->unplug_io_fn(bdi, page);
+}
+
+static inline void blk_run_address_space(struct address_space *mapping)
+{
+	if (mapping)
+		blk_run_backing_dev(mapping->backing_dev_info, NULL);
+}
+
 #endif		/* _LINUX_BACKING_DEV_H */
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 5be93f18d842..7fc5606e6ea5 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -391,6 +391,18 @@ extern struct bio *bio_copy_kern(struct request_queue *, void *, unsigned int,
 				 gfp_t, int);
 extern void bio_set_pages_dirty(struct bio *bio);
 extern void bio_check_pages_dirty(struct bio *bio);
+
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+# error	"You should define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE for your platform"
+#endif
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+extern void bio_flush_dcache_pages(struct bio *bi);
+#else
+static inline void bio_flush_dcache_pages(struct bio *bi)
+{
+}
+#endif
+
 extern struct bio *bio_copy_user(struct request_queue *, struct rq_map_data *,
 				 unsigned long, unsigned int, int, gfp_t);
 extern struct bio *bio_copy_user_iov(struct request_queue *,
@@ -450,11 +462,8 @@ extern struct biovec_slab bvec_slabs[BIOVEC_NR_POOLS] __read_mostly;
 /*
  * remember never ever reenable interrupts between a bvec_kmap_irq and
  * bvec_kunmap_irq!
- *
- * This function MUST be inlined - it plays with the CPU interrupt flags.
  */
-static __always_inline char *bvec_kmap_irq(struct bio_vec *bvec,
-		unsigned long *flags)
+static inline char *bvec_kmap_irq(struct bio_vec *bvec, unsigned long *flags)
 {
 	unsigned long addr;
 
@@ -470,8 +479,7 @@ static __always_inline char *bvec_kmap_irq(struct bio_vec *bvec,
 	return (char *) addr + bvec->bv_offset;
 }
 
-static __always_inline void bvec_kunmap_irq(char *buffer,
-		unsigned long *flags)
+static inline void bvec_kunmap_irq(char *buffer, unsigned long *flags)
 {
 	unsigned long ptr = (unsigned long) buffer & PAGE_MASK;
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 221cecd86bd3..784a919aa0d0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -312,13 +312,17 @@ struct queue_limits {
 	unsigned int		io_min;
 	unsigned int		io_opt;
 	unsigned int		max_discard_sectors;
+	unsigned int		discard_granularity;
+	unsigned int		discard_alignment;
 
 	unsigned short		logical_block_size;
 	unsigned short		max_hw_segments;
 	unsigned short		max_phys_segments;
 
 	unsigned char		misaligned;
+	unsigned char		discard_misaligned;
 	unsigned char		no_cluster;
+	signed char		discard_zeroes_data;
 };
 
 struct request_queue
@@ -749,6 +753,17 @@ struct req_iterator {
 #define rq_iter_last(rq, _iter)					\
 		(_iter.bio->bi_next == NULL && _iter.i == _iter.bio->bi_vcnt-1)
 
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+# error	"You should define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE for your platform"
+#endif
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+extern void rq_flush_dcache_pages(struct request *rq);
+#else
+static inline void rq_flush_dcache_pages(struct request *rq)
+{
+}
+#endif
+
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
 extern void register_disk(struct gendisk *dev);
@@ -823,19 +838,6 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 	return bdev->bd_disk->queue;
 }
 
-static inline void blk_run_backing_dev(struct backing_dev_info *bdi,
-				       struct page *page)
-{
-	if (bdi && bdi->unplug_io_fn)
-		bdi->unplug_io_fn(bdi, page);
-}
-
-static inline void blk_run_address_space(struct address_space *mapping)
-{
-	if (mapping)
-		blk_run_backing_dev(mapping->backing_dev_info, NULL);
-}
-
 /*
  * blk_rq_pos()			: the current sector
  * blk_rq_bytes()		: bytes left in the entire request
@@ -1134,6 +1136,34 @@ static inline int bdev_alignment_offset(struct block_device *bdev)
 	return q->limits.alignment_offset;
 }
 
+static inline int queue_discard_alignment(struct request_queue *q)
+{
+	if (q->limits.discard_misaligned)
+		return -1;
+
+	return q->limits.discard_alignment;
+}
+
+static inline int queue_sector_discard_alignment(struct request_queue *q,
+						 sector_t sector)
+{
+	return ((sector << 9) - q->limits.discard_alignment)
+		& (q->limits.discard_granularity - 1);
+}
+
+static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
+{
+	if (q->limits.discard_zeroes_data == 1)
+		return 1;
+
+	return 0;
+}
+
+static inline unsigned int bdev_discard_zeroes_data(struct block_device *bdev)
+{
+	return queue_discard_zeroes_data(bdev_get_queue(bdev));
+}
+
 static inline int queue_dma_alignment(struct request_queue *q)
 {
 	return q ? q->dma_alignment : 511;
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index 9c8d31bacf46..ccefff02b6cb 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -60,3 +60,9 @@ SUBSYS(net_cls)
 #endif
 
 /* */
+
+#ifdef CONFIG_BLK_CGROUP
+SUBSYS(blkio)
+#endif
+
+/* */
diff --git a/include/linux/connector.h b/include/linux/connector.h
index 3a14615fd35c..72ba63eb83c5 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -43,6 +43,8 @@
 #define CN_DST_VAL			0x1
 #define CN_IDX_DM			0x7	/* Device Mapper */
 #define CN_VAL_DM_USERSPACE_LOG		0x1
+#define CN_IDX_DRBD			0x8
+#define CN_VAL_DRBD			0x1
 
 #define CN_NETLINK_USERS		8
 
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
new file mode 100644
index 000000000000..e84f4733cb55
--- /dev/null
+++ b/include/linux/drbd.h
@@ -0,0 +1,343 @@
+/*
+  drbd.h
+  Kernel module for 2.6.x Kernels
+
+  This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+  Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
+  Copyright (C) 2001-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+  Copyright (C) 2001-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+  drbd 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.
+
+  drbd is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with drbd; see the file COPYING.  If not, write to
+  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+#ifndef DRBD_H
+#define DRBD_H
+#include <linux/connector.h>
+#include <asm/types.h>
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+#include <asm/byteorder.h>
+#else
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <limits.h>
+
+/* Altough the Linux source code makes a difference between
+   generic endianness and the bitfields' endianness, there is no
+   architecture as of Linux-2.6.24-rc4 where the bitfileds' endianness
+   does not match the generic endianness. */
+
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define __LITTLE_ENDIAN_BITFIELD
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#define __BIG_ENDIAN_BITFIELD
+#else
+# error "sorry, weird endianness on this box"
+#endif
+
+#endif
+
+
+extern const char *drbd_buildtag(void);
+#define REL_VERSION "8.3.6"
+#define API_VERSION 88
+#define PRO_VERSION_MIN 86
+#define PRO_VERSION_MAX 91
+
+
+enum drbd_io_error_p {
+	EP_PASS_ON, /* FIXME should the better be named "Ignore"? */
+	EP_CALL_HELPER,
+	EP_DETACH
+};
+
+enum drbd_fencing_p {
+	FP_DONT_CARE,
+	FP_RESOURCE,
+	FP_STONITH
+};
+
+enum drbd_disconnect_p {
+	DP_RECONNECT,
+	DP_DROP_NET_CONF,
+	DP_FREEZE_IO
+};
+
+enum drbd_after_sb_p {
+	ASB_DISCONNECT,
+	ASB_DISCARD_YOUNGER_PRI,
+	ASB_DISCARD_OLDER_PRI,
+	ASB_DISCARD_ZERO_CHG,
+	ASB_DISCARD_LEAST_CHG,
+	ASB_DISCARD_LOCAL,
+	ASB_DISCARD_REMOTE,
+	ASB_CONSENSUS,
+	ASB_DISCARD_SECONDARY,
+	ASB_CALL_HELPER,
+	ASB_VIOLENTLY
+};
+
+/* KEEP the order, do not delete or insert. Only append. */
+enum drbd_ret_codes {
+	ERR_CODE_BASE		= 100,
+	NO_ERROR		= 101,
+	ERR_LOCAL_ADDR		= 102,
+	ERR_PEER_ADDR		= 103,
+	ERR_OPEN_DISK		= 104,
+	ERR_OPEN_MD_DISK	= 105,
+	ERR_DISK_NOT_BDEV	= 107,
+	ERR_MD_NOT_BDEV		= 108,
+	ERR_DISK_TO_SMALL	= 111,
+	ERR_MD_DISK_TO_SMALL	= 112,
+	ERR_BDCLAIM_DISK	= 114,
+	ERR_BDCLAIM_MD_DISK	= 115,
+	ERR_MD_IDX_INVALID	= 116,
+	ERR_IO_MD_DISK		= 118,
+	ERR_MD_INVALID          = 119,
+	ERR_AUTH_ALG		= 120,
+	ERR_AUTH_ALG_ND		= 121,
+	ERR_NOMEM		= 122,
+	ERR_DISCARD		= 123,
+	ERR_DISK_CONFIGURED	= 124,
+	ERR_NET_CONFIGURED	= 125,
+	ERR_MANDATORY_TAG	= 126,
+	ERR_MINOR_INVALID	= 127,
+	ERR_INTR		= 129, /* EINTR */
+	ERR_RESIZE_RESYNC	= 130,
+	ERR_NO_PRIMARY		= 131,
+	ERR_SYNC_AFTER		= 132,
+	ERR_SYNC_AFTER_CYCLE	= 133,
+	ERR_PAUSE_IS_SET	= 134,
+	ERR_PAUSE_IS_CLEAR	= 135,
+	ERR_PACKET_NR		= 137,
+	ERR_NO_DISK		= 138,
+	ERR_NOT_PROTO_C		= 139,
+	ERR_NOMEM_BITMAP	= 140,
+	ERR_INTEGRITY_ALG	= 141, /* DRBD 8.2 only */
+	ERR_INTEGRITY_ALG_ND	= 142, /* DRBD 8.2 only */
+	ERR_CPU_MASK_PARSE	= 143, /* DRBD 8.2 only */
+	ERR_CSUMS_ALG		= 144, /* DRBD 8.2 only */
+	ERR_CSUMS_ALG_ND	= 145, /* DRBD 8.2 only */
+	ERR_VERIFY_ALG		= 146, /* DRBD 8.2 only */
+	ERR_VERIFY_ALG_ND	= 147, /* DRBD 8.2 only */
+	ERR_CSUMS_RESYNC_RUNNING= 148, /* DRBD 8.2 only */
+	ERR_VERIFY_RUNNING	= 149, /* DRBD 8.2 only */
+	ERR_DATA_NOT_CURRENT	= 150,
+	ERR_CONNECTED		= 151, /* DRBD 8.3 only */
+	ERR_PERM		= 152,
+
+	/* insert new ones above this line */
+	AFTER_LAST_ERR_CODE
+};
+
+#define DRBD_PROT_A   1
+#define DRBD_PROT_B   2
+#define DRBD_PROT_C   3
+
+enum drbd_role {
+	R_UNKNOWN = 0,
+	R_PRIMARY = 1,     /* role */
+	R_SECONDARY = 2,   /* role */
+	R_MASK = 3,
+};
+
+/* The order of these constants is important.
+ * The lower ones (<C_WF_REPORT_PARAMS) indicate
+ * that there is no socket!
+ * >=C_WF_REPORT_PARAMS ==> There is a socket
+ */
+enum drbd_conns {
+	C_STANDALONE,
+	C_DISCONNECTING,  /* Temporal state on the way to StandAlone. */
+	C_UNCONNECTED,    /* >= C_UNCONNECTED -> inc_net() succeeds */
+
+	/* These temporal states are all used on the way
+	 * from >= C_CONNECTED to Unconnected.
+	 * The 'disconnect reason' states
+	 * I do not allow to change beween them. */
+	C_TIMEOUT,
+	C_BROKEN_PIPE,
+	C_NETWORK_FAILURE,
+	C_PROTOCOL_ERROR,
+	C_TEAR_DOWN,
+
+	C_WF_CONNECTION,
+	C_WF_REPORT_PARAMS, /* we have a socket */
+	C_CONNECTED,      /* we have introduced each other */
+	C_STARTING_SYNC_S,  /* starting full sync by admin request. */
+	C_STARTING_SYNC_T,  /* stariing full sync by admin request. */
+	C_WF_BITMAP_S,
+	C_WF_BITMAP_T,
+	C_WF_SYNC_UUID,
+
+	/* All SyncStates are tested with this comparison
+	 * xx >= C_SYNC_SOURCE && xx <= C_PAUSED_SYNC_T */
+	C_SYNC_SOURCE,
+	C_SYNC_TARGET,
+	C_VERIFY_S,
+	C_VERIFY_T,
+	C_PAUSED_SYNC_S,
+	C_PAUSED_SYNC_T,
+	C_MASK = 31
+};
+
+enum drbd_disk_state {
+	D_DISKLESS,
+	D_ATTACHING,      /* In the process of reading the meta-data */
+	D_FAILED,         /* Becomes D_DISKLESS as soon as we told it the peer */
+			/* when >= D_FAILED it is legal to access mdev->bc */
+	D_NEGOTIATING,    /* Late attaching state, we need to talk to the peer */
+	D_INCONSISTENT,
+	D_OUTDATED,
+	D_UNKNOWN,       /* Only used for the peer, never for myself */
+	D_CONSISTENT,     /* Might be D_OUTDATED, might be D_UP_TO_DATE ... */
+	D_UP_TO_DATE,       /* Only this disk state allows applications' IO ! */
+	D_MASK = 15
+};
+
+union drbd_state {
+/* According to gcc's docs is the ...
+ * The order of allocation of bit-fields within a unit (C90 6.5.2.1, C99 6.7.2.1).
+ * Determined by ABI.
+ * pointed out by Maxim Uvarov q<muvarov@ru.mvista.com>
+ * even though we transmit as "cpu_to_be32(state)",
+ * the offsets of the bitfields still need to be swapped
+ * on different endianess.
+ */
+	struct {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+		unsigned role:2 ;   /* 3/4	 primary/secondary/unknown */
+		unsigned peer:2 ;   /* 3/4	 primary/secondary/unknown */
+		unsigned conn:5 ;   /* 17/32	 cstates */
+		unsigned disk:4 ;   /* 8/16	 from D_DISKLESS to D_UP_TO_DATE */
+		unsigned pdsk:4 ;   /* 8/16	 from D_DISKLESS to D_UP_TO_DATE */
+		unsigned susp:1 ;   /* 2/2	 IO suspended  no/yes */
+		unsigned aftr_isp:1 ; /* isp .. imposed sync pause */
+		unsigned peer_isp:1 ;
+		unsigned user_isp:1 ;
+		unsigned _pad:11;   /* 0	 unused */
+#elif defined(__BIG_ENDIAN_BITFIELD)
+		unsigned _pad:11;   /* 0	 unused */
+		unsigned user_isp:1 ;
+		unsigned peer_isp:1 ;
+		unsigned aftr_isp:1 ; /* isp .. imposed sync pause */
+		unsigned susp:1 ;   /* 2/2	 IO suspended  no/yes */
+		unsigned pdsk:4 ;   /* 8/16	 from D_DISKLESS to D_UP_TO_DATE */
+		unsigned disk:4 ;   /* 8/16	 from D_DISKLESS to D_UP_TO_DATE */
+		unsigned conn:5 ;   /* 17/32	 cstates */
+		unsigned peer:2 ;   /* 3/4	 primary/secondary/unknown */
+		unsigned role:2 ;   /* 3/4	 primary/secondary/unknown */
+#else
+# error "this endianess is not supported"
+#endif
+	};
+	unsigned int i;
+};
+
+enum drbd_state_ret_codes {
+	SS_CW_NO_NEED = 4,
+	SS_CW_SUCCESS = 3,
+	SS_NOTHING_TO_DO = 2,
+	SS_SUCCESS = 1,
+	SS_UNKNOWN_ERROR = 0, /* Used to sleep longer in _drbd_request_state */
+	SS_TWO_PRIMARIES = -1,
+	SS_NO_UP_TO_DATE_DISK = -2,
+	SS_NO_LOCAL_DISK = -4,
+	SS_NO_REMOTE_DISK = -5,
+	SS_CONNECTED_OUTDATES = -6,
+	SS_PRIMARY_NOP = -7,
+	SS_RESYNC_RUNNING = -8,
+	SS_ALREADY_STANDALONE = -9,
+	SS_CW_FAILED_BY_PEER = -10,
+	SS_IS_DISKLESS = -11,
+	SS_DEVICE_IN_USE = -12,
+	SS_NO_NET_CONFIG = -13,
+	SS_NO_VERIFY_ALG = -14,       /* drbd-8.2 only */
+	SS_NEED_CONNECTION = -15,    /* drbd-8.2 only */
+	SS_LOWER_THAN_OUTDATED = -16,
+	SS_NOT_SUPPORTED = -17,      /* drbd-8.2 only */
+	SS_IN_TRANSIENT_STATE = -18,  /* Retry after the next state change */
+	SS_CONCURRENT_ST_CHG = -19,   /* Concurrent cluster side state change! */
+	SS_AFTER_LAST_ERROR = -20,    /* Keep this at bottom */
+};
+
+/* from drbd_strings.c */
+extern const char *drbd_conn_str(enum drbd_conns);
+extern const char *drbd_role_str(enum drbd_role);
+extern const char *drbd_disk_str(enum drbd_disk_state);
+extern const char *drbd_set_st_err_str(enum drbd_state_ret_codes);
+
+#define SHARED_SECRET_MAX 64
+
+#define MDF_CONSISTENT		(1 << 0)
+#define MDF_PRIMARY_IND		(1 << 1)
+#define MDF_CONNECTED_IND	(1 << 2)
+#define MDF_FULL_SYNC		(1 << 3)
+#define MDF_WAS_UP_TO_DATE	(1 << 4)
+#define MDF_PEER_OUT_DATED	(1 << 5)
+#define MDF_CRASHED_PRIMARY     (1 << 6)
+
+enum drbd_uuid_index {
+	UI_CURRENT,
+	UI_BITMAP,
+	UI_HISTORY_START,
+	UI_HISTORY_END,
+	UI_SIZE,      /* nl-packet: number of dirty bits */
+	UI_FLAGS,     /* nl-packet: flags */
+	UI_EXTENDED_SIZE   /* Everything. */
+};
+
+enum drbd_timeout_flag {
+	UT_DEFAULT      = 0,
+	UT_DEGRADED     = 1,
+	UT_PEER_OUTDATED = 2,
+};
+
+#define UUID_JUST_CREATED ((__u64)4)
+
+#define DRBD_MAGIC 0x83740267
+#define BE_DRBD_MAGIC __constant_cpu_to_be32(DRBD_MAGIC)
+
+/* these are of type "int" */
+#define DRBD_MD_INDEX_INTERNAL -1
+#define DRBD_MD_INDEX_FLEX_EXT -2
+#define DRBD_MD_INDEX_FLEX_INT -3
+
+/* Start of the new netlink/connector stuff */
+
+#define DRBD_NL_CREATE_DEVICE 0x01
+#define DRBD_NL_SET_DEFAULTS  0x02
+
+
+/* For searching a vacant cn_idx value */
+#define CN_IDX_STEP			6977
+
+struct drbd_nl_cfg_req {
+	int packet_type;
+	unsigned int drbd_minor;
+	int flags;
+	unsigned short tag_list[];
+};
+
+struct drbd_nl_cfg_reply {
+	int packet_type;
+	unsigned int minor;
+	int ret_code; /* enum ret_code or set_st_err_t */
+	unsigned short tag_list[]; /* only used with get_* calls */
+};
+
+#endif
diff --git a/include/linux/drbd_limits.h b/include/linux/drbd_limits.h
new file mode 100644
index 000000000000..51f47a586ad8
--- /dev/null
+++ b/include/linux/drbd_limits.h
@@ -0,0 +1,137 @@
+/*
+  drbd_limits.h
+  This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+*/
+
+/*
+ * Our current limitations.
+ * Some of them are hard limits,
+ * some of them are arbitrary range limits, that make it easier to provide
+ * feedback about nonsense settings for certain configurable values.
+ */
+
+#ifndef DRBD_LIMITS_H
+#define DRBD_LIMITS_H 1
+
+#define DEBUG_RANGE_CHECK 0
+
+#define DRBD_MINOR_COUNT_MIN 1
+#define DRBD_MINOR_COUNT_MAX 255
+
+#define DRBD_DIALOG_REFRESH_MIN 0
+#define DRBD_DIALOG_REFRESH_MAX 600
+
+/* valid port number */
+#define DRBD_PORT_MIN 1
+#define DRBD_PORT_MAX 0xffff
+
+/* startup { */
+  /* if you want more than 3.4 days, disable */
+#define DRBD_WFC_TIMEOUT_MIN 0
+#define DRBD_WFC_TIMEOUT_MAX 300000
+#define DRBD_WFC_TIMEOUT_DEF 0
+
+#define DRBD_DEGR_WFC_TIMEOUT_MIN 0
+#define DRBD_DEGR_WFC_TIMEOUT_MAX 300000
+#define DRBD_DEGR_WFC_TIMEOUT_DEF 0
+
+#define DRBD_OUTDATED_WFC_TIMEOUT_MIN 0
+#define DRBD_OUTDATED_WFC_TIMEOUT_MAX 300000
+#define DRBD_OUTDATED_WFC_TIMEOUT_DEF 0
+/* }*/
+
+/* net { */
+  /* timeout, unit centi seconds
+   * more than one minute timeout is not usefull */
+#define DRBD_TIMEOUT_MIN 1
+#define DRBD_TIMEOUT_MAX 600
+#define DRBD_TIMEOUT_DEF 60       /* 6 seconds */
+
+  /* active connection retries when C_WF_CONNECTION */
+#define DRBD_CONNECT_INT_MIN 1
+#define DRBD_CONNECT_INT_MAX 120
+#define DRBD_CONNECT_INT_DEF 10   /* seconds */
+
+  /* keep-alive probes when idle */
+#define DRBD_PING_INT_MIN 1
+#define DRBD_PING_INT_MAX 120
+#define DRBD_PING_INT_DEF 10
+
+ /* timeout for the ping packets.*/
+#define DRBD_PING_TIMEO_MIN  1
+#define DRBD_PING_TIMEO_MAX  100
+#define DRBD_PING_TIMEO_DEF  5
+
+  /* max number of write requests between write barriers */
+#define DRBD_MAX_EPOCH_SIZE_MIN 1
+#define DRBD_MAX_EPOCH_SIZE_MAX 20000
+#define DRBD_MAX_EPOCH_SIZE_DEF 2048
+
+  /* I don't think that a tcp send buffer of more than 10M is usefull */
+#define DRBD_SNDBUF_SIZE_MIN  0
+#define DRBD_SNDBUF_SIZE_MAX  (10<<20)
+#define DRBD_SNDBUF_SIZE_DEF  0
+
+#define DRBD_RCVBUF_SIZE_MIN  0
+#define DRBD_RCVBUF_SIZE_MAX  (10<<20)
+#define DRBD_RCVBUF_SIZE_DEF  0
+
+  /* @4k PageSize -> 128kB - 512MB */
+#define DRBD_MAX_BUFFERS_MIN  32
+#define DRBD_MAX_BUFFERS_MAX  131072
+#define DRBD_MAX_BUFFERS_DEF  2048
+
+  /* @4k PageSize -> 4kB - 512MB */
+#define DRBD_UNPLUG_WATERMARK_MIN  1
+#define DRBD_UNPLUG_WATERMARK_MAX  131072
+#define DRBD_UNPLUG_WATERMARK_DEF (DRBD_MAX_BUFFERS_DEF/16)
+
+  /* 0 is disabled.
+   * 200 should be more than enough even for very short timeouts */
+#define DRBD_KO_COUNT_MIN  0
+#define DRBD_KO_COUNT_MAX  200
+#define DRBD_KO_COUNT_DEF  0
+/* } */
+
+/* syncer { */
+  /* FIXME allow rate to be zero? */
+#define DRBD_RATE_MIN 1
+/* channel bonding 10 GbE, or other hardware */
+#define DRBD_RATE_MAX (4 << 20)
+#define DRBD_RATE_DEF 250  /* kb/second */
+
+  /* less than 7 would hit performance unneccessarily.
+   * 3833 is the largest prime that still does fit
+   * into 64 sectors of activity log */
+#define DRBD_AL_EXTENTS_MIN  7
+#define DRBD_AL_EXTENTS_MAX  3833
+#define DRBD_AL_EXTENTS_DEF  127
+
+#define DRBD_AFTER_MIN  -1
+#define DRBD_AFTER_MAX  255
+#define DRBD_AFTER_DEF  -1
+
+/* } */
+
+/* drbdsetup XY resize -d Z
+ * you are free to reduce the device size to nothing, if you want to.
+ * the upper limit with 64bit kernel, enough ram and flexible meta data
+ * is 16 TB, currently. */
+/* DRBD_MAX_SECTORS */
+#define DRBD_DISK_SIZE_SECT_MIN  0
+#define DRBD_DISK_SIZE_SECT_MAX  (16 * (2LLU << 30))
+#define DRBD_DISK_SIZE_SECT_DEF  0 /* = disabled = no user size... */
+
+#define DRBD_ON_IO_ERROR_DEF EP_PASS_ON
+#define DRBD_FENCING_DEF FP_DONT_CARE
+#define DRBD_AFTER_SB_0P_DEF ASB_DISCONNECT
+#define DRBD_AFTER_SB_1P_DEF ASB_DISCONNECT
+#define DRBD_AFTER_SB_2P_DEF ASB_DISCONNECT
+#define DRBD_RR_CONFLICT_DEF ASB_DISCONNECT
+
+#define DRBD_MAX_BIO_BVECS_MIN 0
+#define DRBD_MAX_BIO_BVECS_MAX 128
+#define DRBD_MAX_BIO_BVECS_DEF 0
+
+#undef RANGE
+#endif
diff --git a/include/linux/drbd_nl.h b/include/linux/drbd_nl.h
new file mode 100644
index 000000000000..db5721ad50d1
--- /dev/null
+++ b/include/linux/drbd_nl.h
@@ -0,0 +1,137 @@
+/*
+   PAKET( name,
+	  TYPE ( pn, pr, member )
+	  ...
+   )
+
+   You may never reissue one of the pn arguments
+*/
+
+#if !defined(NL_PACKET) || !defined(NL_STRING) || !defined(NL_INTEGER) || !defined(NL_BIT) || !defined(NL_INT64)
+#error "The macros NL_PACKET, NL_STRING, NL_INTEGER, NL_INT64 and NL_BIT needs to be defined"
+#endif
+
+NL_PACKET(primary, 1,
+       NL_BIT(		1,	T_MAY_IGNORE,	overwrite_peer)
+)
+
+NL_PACKET(secondary, 2, )
+
+NL_PACKET(disk_conf, 3,
+	NL_INT64(	2,	T_MAY_IGNORE,	disk_size)
+	NL_STRING(	3,	T_MANDATORY,	backing_dev,	128)
+	NL_STRING(	4,	T_MANDATORY,	meta_dev,	128)
+	NL_INTEGER(	5,	T_MANDATORY,	meta_dev_idx)
+	NL_INTEGER(	6,	T_MAY_IGNORE,	on_io_error)
+	NL_INTEGER(	7,	T_MAY_IGNORE,	fencing)
+	NL_BIT(		37,	T_MAY_IGNORE,	use_bmbv)
+	NL_BIT(		53,	T_MAY_IGNORE,	no_disk_flush)
+	NL_BIT(		54,	T_MAY_IGNORE,	no_md_flush)
+	  /*  55 max_bio_size was available in 8.2.6rc2 */
+	NL_INTEGER(	56,	T_MAY_IGNORE,	max_bio_bvecs)
+	NL_BIT(		57,	T_MAY_IGNORE,	no_disk_barrier)
+	NL_BIT(		58,	T_MAY_IGNORE,	no_disk_drain)
+)
+
+NL_PACKET(detach, 4, )
+
+NL_PACKET(net_conf, 5,
+	NL_STRING(	8,	T_MANDATORY,	my_addr,	128)
+	NL_STRING(	9,	T_MANDATORY,	peer_addr,	128)
+	NL_STRING(	10,	T_MAY_IGNORE,	shared_secret,	SHARED_SECRET_MAX)
+	NL_STRING(	11,	T_MAY_IGNORE,	cram_hmac_alg,	SHARED_SECRET_MAX)
+	NL_STRING(	44,	T_MAY_IGNORE,	integrity_alg,	SHARED_SECRET_MAX)
+	NL_INTEGER(	14,	T_MAY_IGNORE,	timeout)
+	NL_INTEGER(	15,	T_MANDATORY,	wire_protocol)
+	NL_INTEGER(	16,	T_MAY_IGNORE,	try_connect_int)
+	NL_INTEGER(	17,	T_MAY_IGNORE,	ping_int)
+	NL_INTEGER(	18,	T_MAY_IGNORE,	max_epoch_size)
+	NL_INTEGER(	19,	T_MAY_IGNORE,	max_buffers)
+	NL_INTEGER(	20,	T_MAY_IGNORE,	unplug_watermark)
+	NL_INTEGER(	21,	T_MAY_IGNORE,	sndbuf_size)
+	NL_INTEGER(	22,	T_MAY_IGNORE,	ko_count)
+	NL_INTEGER(	24,	T_MAY_IGNORE,	after_sb_0p)
+	NL_INTEGER(	25,	T_MAY_IGNORE,	after_sb_1p)
+	NL_INTEGER(	26,	T_MAY_IGNORE,	after_sb_2p)
+	NL_INTEGER(	39,	T_MAY_IGNORE,	rr_conflict)
+	NL_INTEGER(	40,	T_MAY_IGNORE,	ping_timeo)
+	NL_INTEGER(	67,	T_MAY_IGNORE,	rcvbuf_size)
+	  /* 59 addr_family was available in GIT, never released */
+	NL_BIT(		60,	T_MANDATORY,	mind_af)
+	NL_BIT(		27,	T_MAY_IGNORE,	want_lose)
+	NL_BIT(		28,	T_MAY_IGNORE,	two_primaries)
+	NL_BIT(		41,	T_MAY_IGNORE,	always_asbp)
+	NL_BIT(		61,	T_MAY_IGNORE,	no_cork)
+	NL_BIT(		62,	T_MANDATORY,	auto_sndbuf_size)
+)
+
+NL_PACKET(disconnect, 6, )
+
+NL_PACKET(resize, 7,
+	NL_INT64(		29,	T_MAY_IGNORE,	resize_size)
+)
+
+NL_PACKET(syncer_conf, 8,
+	NL_INTEGER(	30,	T_MAY_IGNORE,	rate)
+	NL_INTEGER(	31,	T_MAY_IGNORE,	after)
+	NL_INTEGER(	32,	T_MAY_IGNORE,	al_extents)
+	NL_STRING(      52,     T_MAY_IGNORE,   verify_alg,     SHARED_SECRET_MAX)
+	NL_STRING(      51,     T_MAY_IGNORE,   cpu_mask,       32)
+	NL_STRING(	64,	T_MAY_IGNORE,	csums_alg,	SHARED_SECRET_MAX)
+	NL_BIT(         65,     T_MAY_IGNORE,   use_rle)
+)
+
+NL_PACKET(invalidate, 9, )
+NL_PACKET(invalidate_peer, 10, )
+NL_PACKET(pause_sync, 11, )
+NL_PACKET(resume_sync, 12, )
+NL_PACKET(suspend_io, 13, )
+NL_PACKET(resume_io, 14, )
+NL_PACKET(outdate, 15, )
+NL_PACKET(get_config, 16, )
+NL_PACKET(get_state, 17,
+	NL_INTEGER(	33,	T_MAY_IGNORE,	state_i)
+)
+
+NL_PACKET(get_uuids, 18,
+	NL_STRING(	34,	T_MAY_IGNORE,	uuids,	(UI_SIZE*sizeof(__u64)))
+	NL_INTEGER(	35,	T_MAY_IGNORE,	uuids_flags)
+)
+
+NL_PACKET(get_timeout_flag, 19,
+	NL_BIT(		36,	T_MAY_IGNORE,	use_degraded)
+)
+
+NL_PACKET(call_helper, 20,
+	NL_STRING(	38,	T_MAY_IGNORE,	helper,		32)
+)
+
+/* Tag nr 42 already allocated in drbd-8.1 development. */
+
+NL_PACKET(sync_progress, 23,
+	NL_INTEGER(	43,	T_MAY_IGNORE,	sync_progress)
+)
+
+NL_PACKET(dump_ee, 24,
+	NL_STRING(	45,	T_MAY_IGNORE,	dump_ee_reason, 32)
+	NL_STRING(	46,	T_MAY_IGNORE,	seen_digest, SHARED_SECRET_MAX)
+	NL_STRING(	47,	T_MAY_IGNORE,	calc_digest, SHARED_SECRET_MAX)
+	NL_INT64(	48,	T_MAY_IGNORE,	ee_sector)
+	NL_INT64(	49,	T_MAY_IGNORE,	ee_block_id)
+	NL_STRING(	50,	T_MAY_IGNORE,	ee_data,	32 << 10)
+)
+
+NL_PACKET(start_ov, 25,
+	NL_INT64(	66,	T_MAY_IGNORE,	start_sector)
+)
+
+NL_PACKET(new_c_uuid, 26,
+       NL_BIT(		63,	T_MANDATORY,	clear_bm)
+)
+
+#undef NL_PACKET
+#undef NL_INTEGER
+#undef NL_INT64
+#undef NL_BIT
+#undef NL_STRING
+
diff --git a/include/linux/drbd_tag_magic.h b/include/linux/drbd_tag_magic.h
new file mode 100644
index 000000000000..fcdff8410e99
--- /dev/null
+++ b/include/linux/drbd_tag_magic.h
@@ -0,0 +1,83 @@
+#ifndef DRBD_TAG_MAGIC_H
+#define DRBD_TAG_MAGIC_H
+
+#define TT_END     0
+#define TT_REMOVED 0xE000
+
+/* declare packet_type enums */
+enum packet_types {
+#define NL_PACKET(name, number, fields) P_ ## name = number,
+#define NL_INTEGER(pn, pr, member)
+#define NL_INT64(pn, pr, member)
+#define NL_BIT(pn, pr, member)
+#define NL_STRING(pn, pr, member, len)
+#include "drbd_nl.h"
+	P_nl_after_last_packet,
+};
+
+/* These struct are used to deduce the size of the tag lists: */
+#define NL_PACKET(name, number, fields)	\
+	struct name ## _tag_len_struct { fields };
+#define NL_INTEGER(pn, pr, member)		\
+	int member; int tag_and_len ## member;
+#define NL_INT64(pn, pr, member)		\
+	__u64 member; int tag_and_len ## member;
+#define NL_BIT(pn, pr, member)		\
+	unsigned char member:1; int tag_and_len ## member;
+#define NL_STRING(pn, pr, member, len)	\
+	unsigned char member[len]; int member ## _len; \
+	int tag_and_len ## member;
+#include "linux/drbd_nl.h"
+
+/* declate tag-list-sizes */
+static const int tag_list_sizes[] = {
+#define NL_PACKET(name, number, fields) 2 fields ,
+#define NL_INTEGER(pn, pr, member)      + 4 + 4
+#define NL_INT64(pn, pr, member)        + 4 + 8
+#define NL_BIT(pn, pr, member)          + 4 + 1
+#define NL_STRING(pn, pr, member, len)  + 4 + (len)
+#include "drbd_nl.h"
+};
+
+/* The two highest bits are used for the tag type */
+#define TT_MASK      0xC000
+#define TT_INTEGER   0x0000
+#define TT_INT64     0x4000
+#define TT_BIT       0x8000
+#define TT_STRING    0xC000
+/* The next bit indicates if processing of the tag is mandatory */
+#define T_MANDATORY  0x2000
+#define T_MAY_IGNORE 0x0000
+#define TN_MASK      0x1fff
+/* The remaining 13 bits are used to enumerate the tags */
+
+#define tag_type(T)   ((T) & TT_MASK)
+#define tag_number(T) ((T) & TN_MASK)
+
+/* declare tag enums */
+#define NL_PACKET(name, number, fields) fields
+enum drbd_tags {
+#define NL_INTEGER(pn, pr, member)     T_ ## member = pn | TT_INTEGER | pr ,
+#define NL_INT64(pn, pr, member)       T_ ## member = pn | TT_INT64   | pr ,
+#define NL_BIT(pn, pr, member)         T_ ## member = pn | TT_BIT     | pr ,
+#define NL_STRING(pn, pr, member, len) T_ ## member = pn | TT_STRING  | pr ,
+#include "drbd_nl.h"
+};
+
+struct tag {
+	const char *name;
+	int type_n_flags;
+	int max_len;
+};
+
+/* declare tag names */
+#define NL_PACKET(name, number, fields) fields
+static const struct tag tag_descriptions[] = {
+#define NL_INTEGER(pn, pr, member)     [ pn ] = { #member, TT_INTEGER | pr, sizeof(int)   },
+#define NL_INT64(pn, pr, member)       [ pn ] = { #member, TT_INT64   | pr, sizeof(__u64) },
+#define NL_BIT(pn, pr, member)         [ pn ] = { #member, TT_BIT     | pr, sizeof(int)   },
+#define NL_STRING(pn, pr, member, len) [ pn ] = { #member, TT_STRING  | pr, (len)         },
+#include "drbd_nl.h"
+};
+
+#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2620a8c63571..891f7d642e5c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -129,7 +129,7 @@ struct inodes_stat_t {
  * WRITE_SYNC		Like WRITE_SYNC_PLUG, but also unplugs the device
  *			immediately after submission. The write equivalent
  *			of READ_SYNC.
- * WRITE_ODIRECT	Special case write for O_DIRECT only.
+ * WRITE_ODIRECT_PLUG	Special case write for O_DIRECT only.
  * SWRITE_SYNC
  * SWRITE_SYNC_PLUG	Like WRITE_SYNC/WRITE_SYNC_PLUG, but locks the buffer.
  *			See SWRITE.
@@ -151,7 +151,7 @@ struct inodes_stat_t {
 #define READ_META	(READ | (1 << BIO_RW_META))
 #define WRITE_SYNC_PLUG	(WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
 #define WRITE_SYNC	(WRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
-#define WRITE_ODIRECT	(WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
+#define WRITE_ODIRECT_PLUG	(WRITE | (1 << BIO_RW_SYNCIO))
 #define SWRITE_SYNC_PLUG	\
 			(SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
 #define SWRITE_SYNC	(SWRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
@@ -304,6 +304,7 @@ struct inodes_stat_t {
 #define BLKIOOPT _IO(0x12,121)
 #define BLKALIGNOFF _IO(0x12,122)
 #define BLKPBSZGET _IO(0x12,123)
+#define BLKDISCARDZEROES _IO(0x12,124)
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 297df45ffd0a..c6c0c41af35f 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -91,6 +91,7 @@ struct hd_struct {
 	sector_t start_sect;
 	sector_t nr_sects;
 	sector_t alignment_offset;
+	unsigned int discard_alignment;
 	struct device __dev;
 	struct kobject *holder_dir;
 	int policy, partno;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 4da4a75c3f1e..a63235996309 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -40,16 +40,11 @@ struct cfq_io_context {
 	struct io_context *ioc;
 
 	unsigned long last_end_request;
-	sector_t last_request_pos;
 
 	unsigned long ttime_total;
 	unsigned long ttime_samples;
 	unsigned long ttime_mean;
 
-	unsigned int seek_samples;
-	u64 seek_total;
-	sector_t seek_mean;
-
 	struct list_head queue_list;
 	struct hlist_node cic_list;
 
@@ -73,6 +68,10 @@ struct io_context {
 	unsigned short ioprio;
 	unsigned short ioprio_changed;
 
+#ifdef CONFIG_BLK_CGROUP
+	unsigned short cgroup_changed;
+#endif
+
 	/*
 	 * For request batching
 	 */
@@ -99,14 +98,15 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc)
 	return NULL;
 }
 
+struct task_struct;
 #ifdef CONFIG_BLOCK
 int put_io_context(struct io_context *ioc);
-void exit_io_context(void);
+void exit_io_context(struct task_struct *task);
 struct io_context *get_io_context(gfp_t gfp_flags, int node);
 struct io_context *alloc_io_context(gfp_t gfp_flags, int node);
 void copy_io_context(struct io_context **pdst, struct io_context **psrc);
 #else
-static inline void exit_io_context(void)
+static inline void exit_io_context(struct task_struct *task)
 {
 }
 
diff --git a/include/linux/lru_cache.h b/include/linux/lru_cache.h
new file mode 100644
index 000000000000..3a2b2d9b0472
--- /dev/null
+++ b/include/linux/lru_cache.h
@@ -0,0 +1,294 @@
+/*
+   lru_cache.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+   drbd 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.
+
+   drbd is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with drbd; see the file COPYING.  If not, write to
+   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+ */
+
+#ifndef LRU_CACHE_H
+#define LRU_CACHE_H
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/string.h> /* for memset */
+#include <linux/seq_file.h>
+
+/*
+This header file (and its .c file; kernel-doc of functions see there)
+  define a helper framework to easily keep track of index:label associations,
+  and changes to an "active set" of objects, as well as pending transactions,
+  to persistently record those changes.
+
+  We use an LRU policy if it is necessary to "cool down" a region currently in
+  the active set before we can "heat" a previously unused region.
+
+  Because of this later property, it is called "lru_cache".
+  As it actually Tracks Objects in an Active SeT, we could also call it
+  toast (incidentally that is what may happen to the data on the
+  backend storage uppon next resync, if we don't get it right).
+
+What for?
+
+We replicate IO (more or less synchronously) to local and remote disk.
+
+For crash recovery after replication node failure,
+  we need to resync all regions that have been target of in-flight WRITE IO
+  (in use, or "hot", regions), as we don't know wether or not those WRITEs have
+  made it to stable storage.
+
+  To avoid a "full resync", we need to persistently track these regions.
+
+  This is known as "write intent log", and can be implemented as on-disk
+  (coarse or fine grained) bitmap, or other meta data.
+
+  To avoid the overhead of frequent extra writes to this meta data area,
+  usually the condition is softened to regions that _may_ have been target of
+  in-flight WRITE IO, e.g. by only lazily clearing the on-disk write-intent
+  bitmap, trading frequency of meta data transactions against amount of
+  (possibly unneccessary) resync traffic.
+
+  If we set a hard limit on the area that may be "hot" at any given time, we
+  limit the amount of resync traffic needed for crash recovery.
+
+For recovery after replication link failure,
+  we need to resync all blocks that have been changed on the other replica
+  in the mean time, or, if both replica have been changed independently [*],
+  all blocks that have been changed on either replica in the mean time.
+  [*] usually as a result of a cluster split-brain and insufficient protection.
+      but there are valid use cases to do this on purpose.
+
+  Tracking those blocks can be implemented as "dirty bitmap".
+  Having it fine-grained reduces the amount of resync traffic.
+  It should also be persistent, to allow for reboots (or crashes)
+  while the replication link is down.
+
+There are various possible implementations for persistently storing
+write intent log information, three of which are mentioned here.
+
+"Chunk dirtying"
+  The on-disk "dirty bitmap" may be re-used as "write-intent" bitmap as well.
+  To reduce the frequency of bitmap updates for write-intent log purposes,
+  one could dirty "chunks" (of some size) at a time of the (fine grained)
+  on-disk bitmap, while keeping the in-memory "dirty" bitmap as clean as
+  possible, flushing it to disk again when a previously "hot" (and on-disk
+  dirtied as full chunk) area "cools down" again (no IO in flight anymore,
+  and none expected in the near future either).
+
+"Explicit (coarse) write intent bitmap"
+  An other implementation could chose a (probably coarse) explicit bitmap,
+  for write-intent log purposes, additionally to the fine grained dirty bitmap.
+
+"Activity log"
+  Yet an other implementation may keep track of the hot regions, by starting
+  with an empty set, and writing down a journal of region numbers that have
+  become "hot", or have "cooled down" again.
+
+  To be able to use a ring buffer for this journal of changes to the active
+  set, we not only record the actual changes to that set, but also record the
+  not changing members of the set in a round robin fashion. To do so, we use a
+  fixed (but configurable) number of slots which we can identify by index, and
+  associate region numbers (labels) with these indices.
+  For each transaction recording a change to the active set, we record the
+  change itself (index: -old_label, +new_label), and which index is associated
+  with which label (index: current_label) within a certain sliding window that
+  is moved further over the available indices with each such transaction.
+
+  Thus, for crash recovery, if the ringbuffer is sufficiently large, we can
+  accurately reconstruct the active set.
+
+  Sufficiently large depends only on maximum number of active objects, and the
+  size of the sliding window recording "index: current_label" associations within
+  each transaction.
+
+  This is what we call the "activity log".
+
+  Currently we need one activity log transaction per single label change, which
+  does not give much benefit over the "dirty chunks of bitmap" approach, other
+  than potentially less seeks.
+
+  We plan to change the transaction format to support multiple changes per
+  transaction, which then would reduce several (disjoint, "random") updates to
+  the bitmap into one transaction to the activity log ring buffer.
+*/
+
+/* this defines an element in a tracked set
+ * .colision is for hash table lookup.
+ * When we process a new IO request, we know its sector, thus can deduce the
+ * region number (label) easily.  To do the label -> object lookup without a
+ * full list walk, we use a simple hash table.
+ *
+ * .list is on one of three lists:
+ *  in_use: currently in use (refcnt > 0, lc_number != LC_FREE)
+ *     lru: unused but ready to be reused or recycled
+ *          (ts_refcnt == 0, lc_number != LC_FREE),
+ *    free: unused but ready to be recycled
+ *          (ts_refcnt == 0, lc_number == LC_FREE),
+ *
+ * an element is said to be "in the active set",
+ * if either on "in_use" or "lru", i.e. lc_number != LC_FREE.
+ *
+ * DRBD currently (May 2009) only uses 61 elements on the resync lru_cache
+ * (total memory usage 2 pages), and up to 3833 elements on the act_log
+ * lru_cache, totalling ~215 kB for 64bit architechture, ~53 pages.
+ *
+ * We usually do not actually free these objects again, but only "recycle"
+ * them, as the change "index: -old_label, +LC_FREE" would need a transaction
+ * as well.  Which also means that using a kmem_cache to allocate the objects
+ * from wastes some resources.
+ * But it avoids high order page allocations in kmalloc.
+ */
+struct lc_element {
+	struct hlist_node colision;
+	struct list_head list;		 /* LRU list or free list */
+	unsigned refcnt;
+	/* back "pointer" into ts_cache->element[index],
+	 * for paranoia, and for "ts_element_to_index" */
+	unsigned lc_index;
+	/* if we want to track a larger set of objects,
+	 * it needs to become arch independend u64 */
+	unsigned lc_number;
+
+	/* special label when on free list */
+#define LC_FREE (~0U)
+};
+
+struct lru_cache {
+	/* the least recently used item is kept at lru->prev */
+	struct list_head lru;
+	struct list_head free;
+	struct list_head in_use;
+
+	/* the pre-created kmem cache to allocate the objects from */
+	struct kmem_cache *lc_cache;
+
+	/* size of tracked objects, used to memset(,0,) them in lc_reset */
+	size_t element_size;
+	/* offset of struct lc_element member in the tracked object */
+	size_t element_off;
+
+	/* number of elements (indices) */
+	unsigned int  nr_elements;
+	/* Arbitrary limit on maximum tracked objects. Practical limit is much
+	 * lower due to allocation failures, probably. For typical use cases,
+	 * nr_elements should be a few thousand at most.
+	 * This also limits the maximum value of ts_element.ts_index, allowing the
+	 * 8 high bits of .ts_index to be overloaded with flags in the future. */
+#define LC_MAX_ACTIVE	(1<<24)
+
+	/* statistics */
+	unsigned used; /* number of lelements currently on in_use list */
+	unsigned long hits, misses, starving, dirty, changed;
+
+	/* see below: flag-bits for lru_cache */
+	unsigned long flags;
+
+	/* when changing the label of an index element */
+	unsigned int  new_number;
+
+	/* for paranoia when changing the label of an index element */
+	struct lc_element *changing_element;
+
+	void  *lc_private;
+	const char *name;
+
+	/* nr_elements there */
+	struct hlist_head *lc_slot;
+	struct lc_element **lc_element;
+};
+
+
+/* flag-bits for lru_cache */
+enum {
+	/* debugging aid, to catch concurrent access early.
+	 * user needs to guarantee exclusive access by proper locking! */
+	__LC_PARANOIA,
+	/* if we need to change the set, but currently there is a changing
+	 * transaction pending, we are "dirty", and must deferr further
+	 * changing requests */
+	__LC_DIRTY,
+	/* if we need to change the set, but currently there is no free nor
+	 * unused element available, we are "starving", and must not give out
+	 * further references, to guarantee that eventually some refcnt will
+	 * drop to zero and we will be able to make progress again, changing
+	 * the set, writing the transaction.
+	 * if the statistics say we are frequently starving,
+	 * nr_elements is too small. */
+	__LC_STARVING,
+};
+#define LC_PARANOIA (1<<__LC_PARANOIA)
+#define LC_DIRTY    (1<<__LC_DIRTY)
+#define LC_STARVING (1<<__LC_STARVING)
+
+extern struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
+		unsigned e_count, size_t e_size, size_t e_off);
+extern void lc_reset(struct lru_cache *lc);
+extern void lc_destroy(struct lru_cache *lc);
+extern void lc_set(struct lru_cache *lc, unsigned int enr, int index);
+extern void lc_del(struct lru_cache *lc, struct lc_element *element);
+
+extern struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr);
+extern struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr);
+extern struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr);
+extern unsigned int lc_put(struct lru_cache *lc, struct lc_element *e);
+extern void lc_changed(struct lru_cache *lc, struct lc_element *e);
+
+struct seq_file;
+extern size_t lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc);
+
+extern void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
+				void (*detail) (struct seq_file *, struct lc_element *));
+
+/**
+ * lc_try_lock - can be used to stop lc_get() from changing the tracked set
+ * @lc: the lru cache to operate on
+ *
+ * Note that the reference counts and order on the active and lru lists may
+ * still change.  Returns true if we aquired the lock.
+ */
+static inline int lc_try_lock(struct lru_cache *lc)
+{
+	return !test_and_set_bit(__LC_DIRTY, &lc->flags);
+}
+
+/**
+ * lc_unlock - unlock @lc, allow lc_get() to change the set again
+ * @lc: the lru cache to operate on
+ */
+static inline void lc_unlock(struct lru_cache *lc)
+{
+	clear_bit(__LC_DIRTY, &lc->flags);
+	smp_mb__after_clear_bit();
+}
+
+static inline int lc_is_used(struct lru_cache *lc, unsigned int enr)
+{
+	struct lc_element *e = lc_find(lc, enr);
+	return e && e->refcnt;
+}
+
+#define lc_entry(ptr, type, member) \
+	container_of(ptr, type, member)
+
+extern struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i);
+extern unsigned int lc_index_of(struct lru_cache *lc, struct lc_element *e);
+
+#endif
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 66ebddcff664..705f01fe413a 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -49,6 +49,7 @@ struct writeback_control {
 	unsigned nonblocking:1;		/* Don't get stuck on request queues */
 	unsigned encountered_congestion:1; /* An output: a queue is full */
 	unsigned for_kupdate:1;		/* A kupdate writeback */
+	unsigned for_background:1;	/* A background writeback */
 	unsigned for_reclaim:1;		/* Invoked from the page allocator */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned more_io:1;		/* more io to be dispatched */