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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _RAID5_H
#define _RAID5_H
#include <linux/raid/xor.h>
#include <linux/dmaengine.h>
* Each stripe contains one buffer per device. Each buffer can be in
* one of a number of states stored in "flags". Changes between
* these states happen *almost* exclusively under the protection of the
* STRIPE_ACTIVE flag. Some very specific changes can happen in bi_end_io, and
* these are not protected by STRIPE_ACTIVE.
* The flag bits that are used to represent these states are:
* State Empty == !UPTODATE, !LOCK
* We have no data, and there is no active request
* State Want == !UPTODATE, LOCK
* A read request is being submitted for this block
* State Dirty == UPTODATE, LOCK
* Some new data is in this buffer, and it is being written out
* State Clean == UPTODATE, !LOCK
* We have valid data which is the same as on disc
* The possible state transitions are:
* Empty -> Want - on read or write to get old data for parity calc
* Empty -> Dirty - on compute_parity to satisfy write/sync request.
* Empty -> Clean - on compute_block when computing a block for failed drive
* Want -> Empty - on failed read
* Want -> Clean - on successful completion of read request
* Dirty -> Clean - on successful completion of write request
* Dirty -> Clean - on failed write
* Clean -> Dirty - on compute_parity to satisfy write/sync (RECONSTRUCT or RMW)
* The Want->Empty, Want->Clean, Dirty->Clean, transitions
* all happen in b_end_io at interrupt time.
* Each sets the Uptodate bit before releasing the Lock bit.
* This leaves one multi-stage transition:
* Want->Dirty->Clean
* This is safe because thinking that a Clean buffer is actually dirty
* will at worst delay some action, and the stripe will be scheduled
* for attention after the transition is complete.
* There is one possibility that is not covered by these states. That
* is if one drive has failed and there is a spare being rebuilt. We
* can't distinguish between a clean block that has been generated
* from parity calculations, and a clean block that has been
* successfully written to the spare ( or to parity when resyncing).
* To distinguish these states we have a stripe bit STRIPE_INSYNC that
* is set whenever a write is scheduled to the spare, or to the parity
* disc if there is no spare. A sync request clears this bit, and
* when we find it set with no buffers locked, we know the sync is
* complete.
* Buffers for the md device that arrive via make_request are attached
* to the appropriate stripe in one of two lists linked on b_reqnext.
* One list (bh_read) for read requests, one (bh_write) for write.
* There should never be more than one buffer on the two lists
* together, but we are not guaranteed of that so we allow for more.
* If a buffer is on the read list when the associated cache buffer is
* Uptodate, the data is copied into the read buffer and it's b_end_io
* routine is called. This may happen in the end_request routine only
* if the buffer has just successfully been read. end_request should
* remove the buffers from the list and then set the Uptodate bit on
* the buffer. Other threads may do this only if they first check
* that the Uptodate bit is set. Once they have checked that they may
* take buffers off the read queue.
* When a buffer on the write list is committed for write it is copied
* into the cache buffer, which is then marked dirty, and moved onto a
* third list, the written list (bh_written). Once both the parity
* block and the cached buffer are successfully written, any buffer on
* a written list can be returned with b_end_io.
* The write list and read list both act as fifos. The read list,
* write list and written list are protected by the device_lock.
* The device_lock is only for list manipulations and will only be
* held for a very short time. It can be claimed from interrupts.
* Stripes in the stripe cache can be on one of two lists (or on
* neither). The "inactive_list" contains stripes which are not
* currently being used for any request. They can freely be reused
* for another stripe. The "handle_list" contains stripes that need
* to be handled in some way. Both of these are fifo queues. Each
* stripe is also (potentially) linked to a hash bucket in the hash
* table so that it can be found by sector number. Stripes that are
* not hashed must be on the inactive_list, and will normally be at
* the front. All stripes start life this way.
* The inactive_list, handle_list and hash bucket lists are all protected by the
* device_lock.
* - stripes have a reference counter. If count==0, they are on a list.
* - If a stripe might need handling, STRIPE_HANDLE is set.
* - When refcount reaches zero, then if STRIPE_HANDLE it is put on
* handle_list else inactive_list
* This, combined with the fact that STRIPE_HANDLE is only ever
* cleared while a stripe has a non-zero count means that if the
* refcount is 0 and STRIPE_HANDLE is set, then it is on the
* handle_list and if recount is 0 and STRIPE_HANDLE is not set, then
* the stripe is on inactive_list.
* The possible transitions are:
* activate an unhashed/inactive stripe (get_active_stripe())
* lockdev check-hash unlink-stripe cnt++ clean-stripe hash-stripe unlockdev
* activate a hashed, possibly active stripe (get_active_stripe())
* lockdev check-hash if(!cnt++)unlink-stripe unlockdev
* attach a request to an active stripe (add_stripe_bh())
* lockdev attach-buffer unlockdev
* handle a stripe (handle_stripe())
* (lockdev check-buffers unlockdev) ..
* change-state ..
* record io/ops needed clearSTRIPE_ACTIVE schedule io/ops
* release an active stripe (release_stripe())
* lockdev if (!--cnt) { if STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
* The refcount counts each thread that have activated the stripe,
* plus raid5d if it is handling it, plus one for each active request
* on a cached buffer, and plus one if the stripe is undergoing stripe
* operations.
* The stripe operations are:
* -copying data between the stripe cache and user application buffers
* -computing blocks to save a disk access, or to recover a missing block
* -updating the parity on a write operation (reconstruct write and
* read-modify-write)
* -checking parity correctness
* -running i/o to disk
* These operations are carried out by raid5_run_ops which uses the async_tx
* api to (optionally) offload operations to dedicated hardware engines.
* When requesting an operation handle_stripe sets the pending bit for the
* operation and increments the count. raid5_run_ops is then run whenever
* the count is non-zero.
* There are some critical dependencies between the operations that prevent some
* from being requested while another is in flight.
* 1/ Parity check operations destroy the in cache version of the parity block,
* so we prevent parity dependent operations like writes and compute_blocks
* from starting while a check is in progress. Some dma engines can perform
* the check without damaging the parity block, in these cases the parity
* block is re-marked up to date (assuming the check was successful) and is
* not re-read from disk.
* 2/ When a write operation is requested we immediately lock the affected
* blocks, and mark them as not up to date. This causes new read requests
* to be held off, as well as parity checks and compute block operations.
* 3/ Once a compute block operation has been requested handle_stripe treats
* that block as if it is up to date. raid5_run_ops guaruntees that any
* operation that is dependent on the compute block result is initiated after
* the compute block completes.
* Operations state - intermediate states that are visible outside of
* In general _idle indicates nothing is running, _run indicates a data
* processing operation is active, and _result means the data processing result
* is stable and can be acted upon. For simple operations like biofill and
* compute that only have an _idle and _run state they are indicated with
* enum check_states - handles syncing / repairing a stripe
* @check_state_idle - check operations are quiesced
* @check_state_run - check operation is running
* @check_state_result - set outside lock when check result is valid
* @check_state_compute_run - check failed and we are repairing
* @check_state_compute_result - set outside lock when compute result is valid
enum check_states {
check_state_idle = 0,
check_state_run, /* xor parity check */
check_state_run_q, /* q-parity check */
check_state_run_pq, /* pq dual parity check */
check_state_compute_run, /* parity repair */
* enum reconstruct_states - handles writing or expanding a stripe
enum reconstruct_states {
reconstruct_state_idle = 0,
reconstruct_state_prexor_drain_run, /* prexor-write */
reconstruct_state_drain_run, /* write */
reconstruct_state_run, /* expand */
struct stripe_head {
struct hlist_node hash;
struct list_head lru; /* inactive_list or handle_list */
struct llist_node release_list;
struct r5conf *raid_conf;
short generation; /* increments with every
* reshape */
sector_t sector; /* sector of this row */
short pd_idx; /* parity disk index */
short qd_idx; /* 'Q' disk index for raid6 */
short ddf_layout;/* use DDF ordering to calculate Q */
short hash_lock_index;
unsigned long state; /* state flags */
atomic_t count; /* nr of active thread/requests */
int bm_seq; /* sequence number for bitmap flushes */
int disks; /* disks in stripe */
int overwrite_disks; /* total overwrite disks in stripe,
* this is only checked when stripe
enum check_states check_state;
enum reconstruct_states reconstruct_state;
spinlock_t stripe_lock;
int cpu;
struct r5worker_group *group;
struct stripe_head *batch_head; /* protected by stripe lock */
spinlock_t batch_lock; /* only header's lock is useful */
struct list_head batch_list; /* protected by head's batch lock*/
union {
struct r5l_io_unit *log_io;
struct ppl_io_unit *ppl_io;
struct list_head log_list;
sector_t log_start; /* first meta block on the journal */
struct list_head r5c; /* for r5c_cache->stripe_in_journal */
struct page *ppl_page; /* partial parity of this stripe */
* struct stripe_operations
* @target - STRIPE_OP_COMPUTE_BLK target
* @target2 - 2nd compute target in the raid6 case
* @zero_sum_result - P and Q verification flags
* @request - async service request flags for raid_run_ops
struct stripe_operations {
int target, target2;
enum sum_check_flags zero_sum_result;
} ops;
/* These pages will be used by bios in dev[i] */
struct page **pages;
int nr_pages; /* page array size */
int stripes_per_page;
struct r5dev {
/* rreq and rvec are used for the replacement device when
* writing data to both devices.
struct bio req, rreq;
struct bio_vec vec, rvec;
struct page *page, *orig_page;
unsigned int offset; /* offset of the page */
struct bio *toread, *read, *towrite, *written;
sector_t sector; /* sector of this page */
unsigned long flags;
u32 log_checksum;
unsigned short write_hint;
} dev[1]; /* allocated with extra space depending of RAID geometry */
/* stripe_head_state - collects and tracks the dynamic state of a stripe_head
* for handle_stripe.
struct stripe_head_state {
/* 'syncing' means that we need to read all devices, either
* to check/correct parity, or to reconstruct a missing device.
* 'replacing' means we are replacing one or more drives and
* the source is valid at this point so we don't need to
* read all devices, just the replacement targets.
int syncing, expanding, expanded, replacing;
int locked, uptodate, to_read, to_write, failed, written;
int to_fill, compute, req_compute, non_overwrite;
int injournal, just_cached;
int failed_num[2];
int p_failed, q_failed;
int dec_preread_active;
unsigned long ops_request;
struct md_rdev *blocked_rdev;
int handle_bad_blocks;
int log_failed;
int waiting_extra_page;
/* Flags for struct r5dev.flags */
enum r5dev_flags {
R5_UPTODATE, /* page contains current data */
R5_LOCKED, /* IO has been submitted on "req" */
R5_DOUBLE_LOCKED,/* Cannot clear R5_LOCKED until 2 writes complete */
R5_OVERWRITE, /* towrite covers whole page */
/* and some that are internal to handle_stripe */
R5_Insync, /* rdev && rdev->in_sync at start */
R5_Wantread, /* want to schedule a read */
R5_Overlap, /* There is a pending overlapping request
* on this block */
R5_ReadNoMerge, /* prevent bio from merging in block-layer */
R5_ReadError, /* seen a read error here recently */
R5_ReWrite, /* have tried to over-write the readerror */
R5_Expanded, /* This block now has post-expand data */
R5_Wantcompute, /* compute_block in progress treat as
* uptodate
R5_Wantfill, /* dev->toread contains a bio that needs
* filling
R5_Wantdrain, /* dev->towrite needs to be drained */
R5_WantFUA, /* Write should be FUA */
R5_SyncIO, /* The IO is sync */
R5_WriteError, /* got a write error - need to record it */
R5_MadeGood, /* A bad block has been fixed by writing to it */
R5_ReadRepl, /* Will/did read from replacement rather than orig */
R5_MadeGoodRepl,/* A bad block on the replacement device has been
* fixed by writing to it */
R5_NeedReplace, /* This device has a replacement which is not
* up-to-date at this stripe. */
R5_WantReplace, /* We need to update the replacement, we have read
* data in, and now is a good time to write it out.
R5_Discard, /* Discard the stripe */
R5_SkipCopy, /* Don't copy data from bio to stripe cache */
R5_InJournal, /* data being written is in the journal device.
* if R5_InJournal is set for parity pd_idx, all the
* data and parity being written are in the journal
* device
R5_OrigPageUPTDODATE, /* with write back cache, we read old data into
* dev->orig_page for prexor. When this flag is
* set, orig_page contains latest data in the
* raid disk.
* Stripe state
enum {
STRIPE_IO_STARTED, /* do not count towards 'bypass_count' */
STRIPE_FULL_WRITE, /* all blocks are set to be overwritten */
STRIPE_BITMAP_PENDING, /* Being added to bitmap, don't add
* to batch yet.
STRIPE_LOG_TRAPPED, /* trapped into log (see raid5-cache.c)
* this bit is used in two scenarios:
* 1. write-out phase
* set in first entry of r5l_write_stripe
* clear in second entry of r5l_write_stripe
* used to bypass logic in handle_stripe
* 2. caching phase
* set in r5c_try_caching_write()
* clear when journal write is done
* used to initiate r5c_cache_data()
* also used to bypass logic in handle_stripe
STRIPE_R5C_CACHING, /* the stripe is in caching phase
* see more detail in the raid5-cache.c
STRIPE_R5C_PARTIAL_STRIPE, /* in r5c cache (to-be/being handled or
* in conf->r5c_partial_stripe_list)
STRIPE_R5C_FULL_STRIPE, /* in r5c cache (to-be/being handled or
* in conf->r5c_full_stripe_list)
STRIPE_R5C_PREFLUSH, /* need to flush journal device */
* Operation request flags
enum {
* RAID parity calculation preferences
enum {
* Pages requested from set_syndrome_sources()
enum {
* Plugging:
* To improve write throughput, we need to delay the handling of some
* stripes until there has been a chance that several write requests
* for the one stripe have all been collected.
* In particular, any write request that would require pre-reading
* is put on a "delayed" queue until there are no stripes currently
* in a pre-read phase. Further, if the "delayed" queue is empty when
* a stripe is put on it then we "plug" the queue and do not process it
* until an unplug call is made. (the unplug_io_fn() is called).
* When preread is initiated on a stripe, we set PREREAD_ACTIVE and add
* it to the count of prereading stripes.
* When write is initiated, or the stripe refcnt == 0 (just in case) we
* clear the PREREAD_ACTIVE flag and decrement the count
* Whenever the 'handle' queue is empty and the device is not plugged, we
* move any strips from delayed to handle and clear the DELAYED flag and set
* In stripe_handle, if we find pre-reading is necessary, we do it if
* PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
* HANDLE gets cleared if stripe_handle leaves nothing locked.
/* Note: disk_info.rdev can be set to NULL asynchronously by raid5_remove_disk.
* There are three safe ways to access disk_info.rdev.
* 1/ when holding mddev->reconfig_mutex
* 2/ when resync/recovery/reshape is known to be happening - i.e. in code that
* is called as part of performing resync/recovery/reshape.
* 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer
* and if it is non-NULL, increment rdev->nr_pending before dropping the RCU
* lock.
* When .rdev is set to NULL, the nr_pending count checked again and if
* it has been incremented, the pointer is put back in .rdev.
struct disk_info {
struct md_rdev *rdev, *replacement;
struct page *extra_page; /* extra page to use in prexor */
* Stripe cache
#define NR_STRIPES 256
#define IO_THRESHOLD 1
#define NR_HASH (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK (NR_HASH - 1)
/* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.
* This is because we sometimes take all the spinlocks
* and creating that much locking depth can cause
* problems.
struct r5worker {
struct work_struct work;
struct r5worker_group *group;
struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
bool working;
struct r5worker_group {
struct list_head handle_list;
struct list_head loprio_list;
struct r5conf *conf;
struct r5worker *workers;
int stripes_cnt;
* r5c journal modes of the array: write-back or write-through.
* write-through mode has identical behavior as existing log only
* implementation.
enum r5c_journal_mode {
enum r5_cache_state {
R5_INACTIVE_BLOCKED, /* release of inactive stripes blocked,
* waiting for 25% to be free
R5_ALLOC_MORE, /* It might help to allocate another
* stripe.
R5_DID_ALLOC, /* A stripe was allocated, don't allocate
* more until at least one has been
* released. This avoids flooding
* the cache.
R5C_LOG_TIGHT, /* log device space tight, need to
* prioritize stripes at last_checkpoint
R5C_LOG_CRITICAL, /* log device is running out of space,
* only process stripes that are already
* occupying the log
R5C_EXTRA_PAGE_IN_USE, /* a stripe is using disk_info.extra_page
* for prexor
#define PENDING_IO_MAX 512
struct r5pending_data {
struct list_head sibling;
sector_t sector; /* stripe sector */
struct bio_list bios;
struct r5conf {
struct hlist_head *stripe_hashtbl;
/* only protect corresponding hash list and inactive_list */
spinlock_t hash_locks[NR_STRIPE_HASH_LOCKS];
struct mddev *mddev;
int chunk_sectors;
int level, algorithm, rmw_level;
int max_degraded;
int raid_disks;
int max_nr_stripes;
int min_nr_stripes;
unsigned long stripe_size;
unsigned int stripe_shift;
unsigned long stripe_sectors;
/* reshape_progress is the leading edge of a 'reshape'
* It has value MaxSector when no reshape is happening
* If delta_disks < 0, it is the last sector we started work on,
* else is it the next sector to work on.
sector_t reshape_progress;
/* reshape_safe is the trailing edge of a reshape. We know that
* before (or after) this address, all reshape has completed.
sector_t reshape_safe;
int previous_raid_disks;
int prev_chunk_sectors;
int prev_algo;
short generation; /* increments with every reshape */
seqcount_spinlock_t gen_lock; /* lock against generation changes */
unsigned long reshape_checkpoint; /* Time we last updated
* metadata */
long long min_offset_diff; /* minimum difference between
* data_offset and
* new_data_offset across all
* devices. May be negative,
* but is closest to zero.
struct list_head handle_list; /* stripes needing handling */
struct list_head loprio_list; /* low priority stripes */
struct list_head hold_list; /* preread ready stripes */
struct list_head delayed_list; /* stripes that have plugged requests */
struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */
struct bio *retry_read_aligned; /* currently retrying aligned bios */
unsigned int retry_read_offset; /* sector offset into retry_read_aligned */
struct bio *retry_read_aligned_list; /* aligned bios retry list */
atomic_t preread_active_stripes; /* stripes with scheduled io */
atomic_t active_aligned_reads;
atomic_t pending_full_writes; /* full write backlog */
int bypass_count; /* bypassed prereads */
int bypass_threshold; /* preread nice */
int skip_copy; /* Don't copy data from bio to stripe cache */
struct list_head *last_hold; /* detect hold_list promotions */
atomic_t reshape_stripes; /* stripes with pending writes for reshape */
/* unfortunately we need two cache names as we temporarily have
* two caches.
int active_name;
char cache_name[2][32];
struct kmem_cache *slab_cache; /* for allocating stripes */
struct mutex cache_size_mutex; /* Protect changes to cache size */
int seq_flush, seq_write;
int quiesce;
int fullsync; /* set to 1 if a full sync is needed,
* (fresh device added).
* Cleared when a sync completes.
int recovery_disabled;
/* per cpu variables */
struct raid5_percpu {
struct page *spare_page; /* Used when checking P/Q in raid6 */
void *scribble; /* space for constructing buffer
* lists and performing address
* conversions
int scribble_obj_size;
} __percpu *percpu;
int scribble_disks;
int scribble_sectors;
struct hlist_node node;
* Free stripes pool
atomic_t active_stripes;
struct list_head inactive_list[NR_STRIPE_HASH_LOCKS];
atomic_t r5c_cached_full_stripes;
struct list_head r5c_full_stripe_list;
atomic_t r5c_cached_partial_stripes;
struct list_head r5c_partial_stripe_list;
atomic_t r5c_flushing_full_stripes;
atomic_t r5c_flushing_partial_stripes;
atomic_t empty_inactive_list_nr;
struct llist_head released_stripes;
wait_queue_head_t wait_for_quiescent;
wait_queue_head_t wait_for_stripe;
wait_queue_head_t wait_for_overlap;
unsigned long cache_state;
struct shrinker shrinker;
int pool_size; /* number of disks in stripeheads in pool */
spinlock_t device_lock;
struct disk_info *disks;
struct bio_set bio_split;
/* When taking over an array from a different personality, we store
* the new thread here until we fully activate the array.
struct md_thread *thread;
struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
struct r5worker_group *worker_groups;
int group_cnt;
int worker_cnt_per_group;
struct r5l_log *log;
void *log_private;
spinlock_t pending_bios_lock;
bool batch_bio_dispatch;
struct r5pending_data *pending_data;
struct list_head free_list;
struct list_head pending_list;
int pending_data_cnt;
struct r5pending_data *next_pending_data;
#define RAID5_STRIPE_SIZE(conf) ((conf)->stripe_size)
#define RAID5_STRIPE_SHIFT(conf) ((conf)->stripe_shift)
#define RAID5_STRIPE_SECTORS(conf) ((conf)->stripe_sectors)
/* bio's attached to a stripe+device for I/O are linked together in bi_sector
* order without overlap. There may be several bio's per stripe+device, and
* a bio could span several devices.
* When walking this list for a particular stripe+device, we must never proceed
* beyond a bio that extends past this device, as the next bio might no longer
* be valid.
* This function is used to determine the 'next' bio in the list, given the
* sector of the current stripe+device
static inline struct bio *r5_next_bio(struct r5conf *conf, struct bio *bio, sector_t sector)
if (bio_end_sector(bio) < sector + RAID5_STRIPE_SECTORS(conf))
return bio->bi_next;
return NULL;
* Our supported algorithms
#define ALGORITHM_LEFT_ASYMMETRIC 0 /* Rotating Parity N with Data Restart */
#define ALGORITHM_RIGHT_ASYMMETRIC 1 /* Rotating Parity 0 with Data Restart */
#define ALGORITHM_LEFT_SYMMETRIC 2 /* Rotating Parity N with Data Continuation */
#define ALGORITHM_RIGHT_SYMMETRIC 3 /* Rotating Parity 0 with Data Continuation */
/* Define non-rotating (raid4) algorithms. These allow
* conversion of raid4 to raid5.
#define ALGORITHM_PARITY_0 4 /* P or P,Q are initial devices */
#define ALGORITHM_PARITY_N 5 /* P or P,Q are final devices. */
/* DDF RAID6 layouts differ from md/raid6 layouts in two ways.
* Firstly, the exact positioning of the parity block is slightly
* different between the 'LEFT_*' modes of md and the "_N_*" modes
* of DDF.
* Secondly, or order of datablocks over which the Q syndrome is computed
* is different.
* Consequently we have different layouts for DDF/raid6 than md/raid6.
* These layouts are from the DDFv1.2 spec.
* Interestingly DDFv1.2-Errata-A does not specify N_CONTINUE but
* leaves RLQ=3 as 'Vendor Specific'
/* For every RAID5 algorithm we define a RAID6 algorithm
* with exactly the same layout for data and parity, and
* with the Q block always on the last device (N-1).
* This allows trivial conversion from RAID5 to RAID6
#define ALGORITHM_PARITY_0_6 20
static inline int algorithm_valid_raid5(int layout)
return (layout >= 0) &&
(layout <= 5);
static inline int algorithm_valid_raid6(int layout)
return (layout >= 0 && layout <= 5)
(layout >= 8 && layout <= 10)
(layout >= 16 && layout <= 20);
static inline int algorithm_is_DDF(int layout)
return layout >= 8 && layout <= 10;
* Return offset of the corresponding page for r5dev.
static inline int raid5_get_page_offset(struct stripe_head *sh, int disk_idx)
return (disk_idx % sh->stripes_per_page) * RAID5_STRIPE_SIZE(sh->raid_conf);
* Return corresponding page address for r5dev.
static inline struct page *
raid5_get_dev_page(struct stripe_head *sh, int disk_idx)
return sh->pages[disk_idx / sh->stripes_per_page];
extern void md_raid5_kick_device(struct r5conf *conf);
extern int raid5_set_cache_size(struct mddev *mddev, int size);
extern sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous);
extern void raid5_release_stripe(struct stripe_head *sh);
extern sector_t raid5_compute_sector(struct r5conf *conf, sector_t r_sector,
int previous, int *dd_idx,
struct stripe_head *sh);
extern struct stripe_head *
raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
int previous, int noblock, int noquiesce);
extern int raid5_calc_degraded(struct r5conf *conf);
extern int r5c_journal_mode_set(struct mddev *mddev, int journal_mode);