1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
244 lines
9.9 KiB
C
244 lines
9.9 KiB
C
#ifndef _RAID5_H
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#define _RAID5_H
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#include <linux/raid/md.h>
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#include <linux/raid/xor.h>
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/*
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*
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* Each stripe contains one buffer per disc. Each buffer can be in
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* one of a number of states stored in "flags". Changes between
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* these states happen *almost* exclusively under a per-stripe
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* spinlock. Some very specific changes can happen in bi_end_io, and
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* these are not protected by the spin lock.
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*
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* The flag bits that are used to represent these states are:
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* R5_UPTODATE and R5_LOCKED
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*
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* State Empty == !UPTODATE, !LOCK
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* We have no data, and there is no active request
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* State Want == !UPTODATE, LOCK
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* A read request is being submitted for this block
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* State Dirty == UPTODATE, LOCK
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* Some new data is in this buffer, and it is being written out
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* State Clean == UPTODATE, !LOCK
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* We have valid data which is the same as on disc
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*
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* The possible state transitions are:
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*
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* Empty -> Want - on read or write to get old data for parity calc
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* Empty -> Dirty - on compute_parity to satisfy write/sync request.(RECONSTRUCT_WRITE)
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* Empty -> Clean - on compute_block when computing a block for failed drive
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* Want -> Empty - on failed read
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* Want -> Clean - on successful completion of read request
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* Dirty -> Clean - on successful completion of write request
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* Dirty -> Clean - on failed write
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* Clean -> Dirty - on compute_parity to satisfy write/sync (RECONSTRUCT or RMW)
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*
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* The Want->Empty, Want->Clean, Dirty->Clean, transitions
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* all happen in b_end_io at interrupt time.
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* Each sets the Uptodate bit before releasing the Lock bit.
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* This leaves one multi-stage transition:
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* Want->Dirty->Clean
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* This is safe because thinking that a Clean buffer is actually dirty
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* will at worst delay some action, and the stripe will be scheduled
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* for attention after the transition is complete.
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*
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* There is one possibility that is not covered by these states. That
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* is if one drive has failed and there is a spare being rebuilt. We
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* can't distinguish between a clean block that has been generated
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* from parity calculations, and a clean block that has been
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* successfully written to the spare ( or to parity when resyncing).
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* To distingush these states we have a stripe bit STRIPE_INSYNC that
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* is set whenever a write is scheduled to the spare, or to the parity
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* disc if there is no spare. A sync request clears this bit, and
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* when we find it set with no buffers locked, we know the sync is
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* complete.
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*
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* Buffers for the md device that arrive via make_request are attached
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* to the appropriate stripe in one of two lists linked on b_reqnext.
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* One list (bh_read) for read requests, one (bh_write) for write.
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* There should never be more than one buffer on the two lists
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* together, but we are not guaranteed of that so we allow for more.
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*
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* If a buffer is on the read list when the associated cache buffer is
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* Uptodate, the data is copied into the read buffer and it's b_end_io
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* routine is called. This may happen in the end_request routine only
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* if the buffer has just successfully been read. end_request should
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* remove the buffers from the list and then set the Uptodate bit on
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* the buffer. Other threads may do this only if they first check
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* that the Uptodate bit is set. Once they have checked that they may
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* take buffers off the read queue.
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*
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* When a buffer on the write list is committed for write it is copied
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* into the cache buffer, which is then marked dirty, and moved onto a
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* third list, the written list (bh_written). Once both the parity
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* block and the cached buffer are successfully written, any buffer on
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* a written list can be returned with b_end_io.
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*
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* The write list and read list both act as fifos. The read list is
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* protected by the device_lock. The write and written lists are
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* protected by the stripe lock. The device_lock, which can be
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* claimed while the stipe lock is held, is only for list
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* manipulations and will only be held for a very short time. It can
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* be claimed from interrupts.
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*
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*
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* Stripes in the stripe cache can be on one of two lists (or on
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* neither). The "inactive_list" contains stripes which are not
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* currently being used for any request. They can freely be reused
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* for another stripe. The "handle_list" contains stripes that need
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* to be handled in some way. Both of these are fifo queues. Each
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* stripe is also (potentially) linked to a hash bucket in the hash
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* table so that it can be found by sector number. Stripes that are
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* not hashed must be on the inactive_list, and will normally be at
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* the front. All stripes start life this way.
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*
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* The inactive_list, handle_list and hash bucket lists are all protected by the
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* device_lock.
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* - stripes on the inactive_list never have their stripe_lock held.
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* - stripes have a reference counter. If count==0, they are on a list.
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* - If a stripe might need handling, STRIPE_HANDLE is set.
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* - When refcount reaches zero, then if STRIPE_HANDLE it is put on
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* handle_list else inactive_list
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*
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* This, combined with the fact that STRIPE_HANDLE is only ever
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* cleared while a stripe has a non-zero count means that if the
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* refcount is 0 and STRIPE_HANDLE is set, then it is on the
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* handle_list and if recount is 0 and STRIPE_HANDLE is not set, then
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* the stripe is on inactive_list.
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*
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* The possible transitions are:
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* activate an unhashed/inactive stripe (get_active_stripe())
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* lockdev check-hash unlink-stripe cnt++ clean-stripe hash-stripe unlockdev
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* activate a hashed, possibly active stripe (get_active_stripe())
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* lockdev check-hash if(!cnt++)unlink-stripe unlockdev
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* attach a request to an active stripe (add_stripe_bh())
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* lockdev attach-buffer unlockdev
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* handle a stripe (handle_stripe())
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* lockstripe clrSTRIPE_HANDLE ... (lockdev check-buffers unlockdev) .. change-state .. record io needed unlockstripe schedule io
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* release an active stripe (release_stripe())
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* lockdev if (!--cnt) { if STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
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*
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* The refcount counts each thread that have activated the stripe,
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* plus raid5d if it is handling it, plus one for each active request
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* on a cached buffer.
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*/
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struct stripe_head {
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struct stripe_head *hash_next, **hash_pprev; /* hash pointers */
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struct list_head lru; /* inactive_list or handle_list */
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struct raid5_private_data *raid_conf;
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sector_t sector; /* sector of this row */
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int pd_idx; /* parity disk index */
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unsigned long state; /* state flags */
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atomic_t count; /* nr of active thread/requests */
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spinlock_t lock;
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struct r5dev {
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struct bio req;
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struct bio_vec vec;
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struct page *page;
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struct bio *toread, *towrite, *written;
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sector_t sector; /* sector of this page */
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unsigned long flags;
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} dev[1]; /* allocated with extra space depending of RAID geometry */
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};
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/* Flags */
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#define R5_UPTODATE 0 /* page contains current data */
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#define R5_LOCKED 1 /* IO has been submitted on "req" */
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#define R5_OVERWRITE 2 /* towrite covers whole page */
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/* and some that are internal to handle_stripe */
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#define R5_Insync 3 /* rdev && rdev->in_sync at start */
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#define R5_Wantread 4 /* want to schedule a read */
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#define R5_Wantwrite 5
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#define R5_Syncio 6 /* this io need to be accounted as resync io */
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#define R5_Overlap 7 /* There is a pending overlapping request on this block */
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/*
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* Write method
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*/
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#define RECONSTRUCT_WRITE 1
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#define READ_MODIFY_WRITE 2
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/* not a write method, but a compute_parity mode */
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#define CHECK_PARITY 3
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/*
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* Stripe state
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*/
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#define STRIPE_ERROR 1
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#define STRIPE_HANDLE 2
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#define STRIPE_SYNCING 3
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#define STRIPE_INSYNC 4
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#define STRIPE_PREREAD_ACTIVE 5
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#define STRIPE_DELAYED 6
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/*
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* Plugging:
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*
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* To improve write throughput, we need to delay the handling of some
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* stripes until there has been a chance that several write requests
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* for the one stripe have all been collected.
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* In particular, any write request that would require pre-reading
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* is put on a "delayed" queue until there are no stripes currently
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* in a pre-read phase. Further, if the "delayed" queue is empty when
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* a stripe is put on it then we "plug" the queue and do not process it
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* until an unplug call is made. (the unplug_io_fn() is called).
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*
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* When preread is initiated on a stripe, we set PREREAD_ACTIVE and add
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* it to the count of prereading stripes.
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* When write is initiated, or the stripe refcnt == 0 (just in case) we
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* clear the PREREAD_ACTIVE flag and decrement the count
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* Whenever the delayed queue is empty and the device is not plugged, we
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* move any strips from delayed to handle and clear the DELAYED flag and set PREREAD_ACTIVE.
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* In stripe_handle, if we find pre-reading is necessary, we do it if
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* PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
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* HANDLE gets cleared if stripe_handle leave nothing locked.
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*/
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struct disk_info {
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mdk_rdev_t *rdev;
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};
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struct raid5_private_data {
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struct stripe_head **stripe_hashtbl;
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mddev_t *mddev;
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struct disk_info *spare;
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int chunk_size, level, algorithm;
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int raid_disks, working_disks, failed_disks;
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int max_nr_stripes;
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struct list_head handle_list; /* stripes needing handling */
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struct list_head delayed_list; /* stripes that have plugged requests */
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atomic_t preread_active_stripes; /* stripes with scheduled io */
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char cache_name[20];
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kmem_cache_t *slab_cache; /* for allocating stripes */
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/*
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* Free stripes pool
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*/
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atomic_t active_stripes;
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struct list_head inactive_list;
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wait_queue_head_t wait_for_stripe;
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wait_queue_head_t wait_for_overlap;
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int inactive_blocked; /* release of inactive stripes blocked,
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* waiting for 25% to be free
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*/
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spinlock_t device_lock;
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struct disk_info disks[0];
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};
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typedef struct raid5_private_data raid5_conf_t;
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#define mddev_to_conf(mddev) ((raid5_conf_t *) mddev->private)
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/*
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* Our supported algorithms
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*/
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#define ALGORITHM_LEFT_ASYMMETRIC 0
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#define ALGORITHM_RIGHT_ASYMMETRIC 1
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#define ALGORITHM_LEFT_SYMMETRIC 2
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#define ALGORITHM_RIGHT_SYMMETRIC 3
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#endif
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