In preparation for asynchronous handling of raid6 operations move the
spare page to a percpu allocation to allow multiple simultaneous
synchronous raid6 recovery operations.

Make this allocation cpu hotplug aware to maximize allocation
efficiency.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

We currently update the metadata :
 1/ every 3Megabytes
 2/ When the place we will write new-layout data to is recorded in
    the metadata as still containing old-layout data.

Rule one exists to avoid having to re-do too much reshaping in the
face of a crash/restart.  So it should really be time based rather
than size based.  So change it to "every 10 seconds".

Rule two turns out to be too harsh when restriping an array
'in-place', as in that case the metadata much be updates for every
stripe.
For the in-place update, it can only possibly be safe from a crash if
some user-space program data a backup of every e.g. few hundred
stripes before allowing them to be reshaped.  In that case, the
constant metadata update is pointless.
So only update the metadata if the new metadata will report that the
end of the 'old-layout' data is beyond where we are currently
writing 'new-layout' data.
Signed-off-by: NNeilBrown <neilb@suse.de>

Add prev_algo to raid5_conf_t along the same lines as prev_chunk
and previous_raid_disks.
Signed-off-by: NNeilBrown <neilb@suse.de>

Add "prev_chunk" to raid5_conf_t, similar to "previous_raid_disks", to
remember what the chunk size was before the reshape that is currently
underway.

This seems like duplication with "chunk_size" and "new_chunk" in
mddev_t, and to some extent it is, but there are differences.
The values in mddev_t are always defined and often the same.
The prev* values are only defined if a reshape is underway.

Also (and more significantly) the raid5_conf_t values will be changed
at the same time (inside an appropriate lock) that the reshape is
started by setting reshape_position.  In contrast, the new_chunk value
is set when the sysfs file is written which could be well before the
reshape starts.
Signed-off-by: NNeilBrown <neilb@suse.de>

During a raid5 reshape, we have some stripes in the cache that are
'before' the reshape (and are still to be processed) and some that are
'after'.  They are currently differentiated by having different
->disks values as the only reshape current supported involves changing
the number of disks.

However we will soon support reshapes that do not change the number
of disks (chunk parity or chunk size).  So make the difference more
explicit with a 'generation' number.
Signed-off-by: NNeilBrown <neilb@suse.de>

When reducing the number of devices in a raid4/5/6, the reshape
process has to start at the end of the array and work down to the
beginning.  So we need to handle expand_progress and expand_lo
differently.

This patch renames "expand_progress" and "expand_lo" to avoid the
implication that anything is getting bigger (expand->reshape) and
every place they are used, we make sure that they are used the right
way depending on whether delta_disks is positive or negative.
Signed-off-by: NNeilBrown <neilb@suse.de>

We now have this value in stripe_head so we don't need to duplicate
it.
Signed-off-by: NNeilBrown <neilb@suse.de>

Move the raid6 data processing routines into a standalone module
(raid6_pq) to prepare them to be called from async_tx wrappers and other
non-md drivers/modules.  This precludes a circular dependency of raid456
needing the async modules for data processing while those modules in
turn depend on raid456 for the base level synchronous raid6 routines.

To support this move:
1/ The exportable definitions in raid6.h move to include/linux/raid/pq.h
2/ The raid6_call, recovery calls, and table symbols are exported
3/ Extra #ifdef __KERNEL__ statements to enable the userspace raid6test to
   compile
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeilBrown <neilb@suse.de>

.. so that the code to create the private data structures is separate.
This will help with future code to change the level of an active
array.
Signed-off-by: NNeilBrown <neilb@suse.de>

DDF requires RAID6 calculations over different devices in a different
order.
For md/raid6, we calculate over just the data devices, starting
immediately after the 'Q' block.
For ddf/raid6 we calculate over all devices, using zeros in place of
the P and Q blocks.

This requires unfortunately complex loops...
Signed-off-by: NNeilBrown <neilb@suse.de>

DDF uses different layouts for P and Q blocks than current md/raid6
so add those that are missing.
Also add support for RAID6 layouts that are identical to various
raid5 layouts with the simple addition of one device to hold all of
the 'Q' blocks.
Finally add 'raid5' layouts to match raid4.
These last to will allow online level conversion.

Note that this does not provide correct support for DDF/raid6 yet
as the order in which data blocks are summed to produce the Q block
is significant and different between current md code and DDF
requirements.
Signed-off-by: NNeilBrown <neilb@suse.de>

Code currently assumes that the devices in a raid6 stripe are
  0 1 ... N-1 P Q
in some rotated order.  We will shortly add new layouts in which
this strict pattern is broken.
So remove this expectation.  We still assume that the data disks
are roughly in-order.  However P and Q can be inserted anywhere within
that order.
Signed-off-by: NNeilBrown <neilb@suse.de>

This makes the includes more explicit, and is preparation for moving
md_k.h to drivers/md/md.h

Remove include/raid/md.h as its only remaining use was to #include
other files.
Signed-off-by: NNeilBrown <neilb@suse.de>

Move the headers with the local structures for the disciplines and
bitmap.h into drivers/md/ so that they are more easily grepable for
hacking and not far away.  md.h is left where it is for now as there
are some uses from the outside.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NNeilBrown <neilb@suse.de>

From: Dan Williams <dan.j.williams@intel.com>

Currently ops_run_biodrain and other locations have extra logic to determine
which blocks are processed in the prexor and non-prexor cases.  This can be
eliminated if handle_write_operations5 flags the blocks to be processed in all
cases via R5_Wantdrain.  The presence of the prexor operation is tracked in
sh->reconstruct_state.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>

From: Dan Williams <dan.j.williams@intel.com>

Track the state of reconstruct operations (recalculating the parity block
usually due to incoming writes, or as part of array expansion)  Reduces the
scope of the STRIPE_OP_{BIODRAIN,PREXOR,POSTXOR} flags to only tracking whether
a reconstruct operation has been requested via the ops_request field of struct
stripe_head_state.

This is the final step in the removal of ops.{pending,ack,complete,count}, i.e.
the STRIPE_OP_{BIODRAIN,PREXOR,POSTXOR} flags only request an operation and do
not track the state of the operation.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>

From: Dan Williams <dan.j.williams@intel.com>

The STRIPE_OP_* flags record the state of stripe operations which are
performed outside the stripe lock.  Their use in indicating which
operations need to be run is straightforward; however, interpolating what
the next state of the stripe should be based on a given combination of
these flags is not straightforward, and has led to bugs.  An easier to read
implementation with minimal degrees of freedom is needed.

Towards this goal, this patch introduces explicit states to replace what was
previously interpolated from the STRIPE_OP_* flags.  For now this only converts
the handle_parity_checks5 path, removing a user of the
ops.{pending,ack,complete,count} fields of struct stripe_operations.

This conversion also found a remaining issue with the current code.  There is
a small window for a drive to fail between when we schedule a repair and when
the parity calculation for that repair completes.  When this happens we will
writeback to 'failed_num' when we really want to write back to 'pd_idx'.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>

From: Dan Williams <dan.j.williams@intel.com>

The R5_Want{Read,Write} flags already gate i/o.  So, this flag is
superfluous and we can unconditionally call ops_run_io().
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>

From: Dan Williams <dan.j.williams@intel.com>

This micro-optimization allowed the raid code to skip a re-read of the
parity block after checking parity.  It took advantage of the fact that
xor-offload-engines have their own internal result buffer and can check
parity without writing to memory.  Remove it for the following reasons:

1/ It is a layering violation for MD to need to manage the DMA and
   non-DMA paths within async_xor_zero_sum
2/ Bad precedent to toggle the 'ops' flags outside the lock
3/ Hard to realize a performance gain as reads will not need an updated
   parity block and writes will dirty it anyways.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>

Improve write performance by preventing the delayed_list from dumping all its
stripes onto the handle_list in one shot.  Delayed stripes are now further
delayed by being held on the 'hold_list'.  The 'hold_list' is bypassed when:

  * a STRIPE_IO_STARTED stripe is found at the head of 'handle_list'
  * 'handle_list' is empty and i/o is being done to satisfy full stripe-width
    write requests
  * 'bypass_count' is less than 'bypass_threshold'.  By default the threshold
    is 1, i.e. every other stripe handled is a preread stripe provided the
    top two conditions are false.

Benchmark data:
System: 2x Xeon 5150, 4x SATA, mem=1GB
Baseline: 2.6.24-rc7
Configuration: mdadm --create /dev/md0 /dev/sd[b-e] -n 4 -l 5 --assume-clean
Test1: dd if=/dev/zero of=/dev/md0 bs=1024k count=2048
  * patched:  +33% (stripe_cache_size = 256), +25% (stripe_cache_size = 512)

Test2: tiobench --size 2048 --numruns 5 --block 4096 --block 131072 (XFS)
  * patched: +13%
  * patched + preread_bypass_threshold = 0: +37%

Changes since v1:
* reduce bypass_threshold from (chunk_size / sectors_per_chunk) to (1) and
  make it configurable.  This defaults to fairness and modest performance
  gains out of the box.
Changes since v2:
* [neilb@suse.de]: kill STRIPE_PRIO_HI and preread_needed as they are not
  necessary, the important change was clearing STRIPE_DELAYED in
  add_stripe_bio and this has been moved out to make_request for the hang
  fix.
* [neilb@suse.de]: simplify get_priority_stripe
* [dan.j.williams@intel.com]: reset the bypass_count when ->hold_list is
  sampled empty (+11%)
* [dan.j.williams@intel.com]: decrement the bypass_count at the detection
  of stripes being naturally promoted off of hold_list +2%.  Note, resetting
  bypass_count instead of decrementing on these events yields +4% but that is
  probably too aggressive.
Changes since v3:
* cosmetic fixups
Tested-by: NJames W. Laferriere <babydr@baby-dragons.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

When a read bio is attached to the stripe and the corresponding block is
marked R5_UPTODATE, then a read (biofill) operation is scheduled to copy
the data from the stripe cache to the bio buffer.  handle_stripe flags the
blocks to be operated on with the R5_Wantfill flag.  If new read requests
arrive while raid5_run_ops is running they will not be handled until
handle_stripe is scheduled to run again.

Changelog:
* cleanup to_read and to_fill accounting
* do not fail reads that have reached the cache
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-By: NNeilBrown <neilb@suse.de>

handle_stripe will compute a block when a backing disk has failed, or when
it determines it can save a disk read by computing the block from all the
other up-to-date blocks.

Previously a block would be computed under the lock and subsequent logic in
handle_stripe could use the newly up-to-date block.  With the raid5_run_ops
implementation the compute operation is carried out a later time outside
the lock.  To preserve the old functionality we take advantage of the
dependency chain feature of async_tx to flag the block as R5_Wantcompute
and then let other parts of handle_stripe operate on the block as if it
were up-to-date.  raid5_run_ops guarantees that the block will be ready
before it is used in another operation.

However, this only works in cases where the compute and the dependent
operation are scheduled at the same time.  If a previous call to
handle_stripe sets the R5_Wantcompute flag there is no facility to pass the
async_tx dependency chain across successive calls to raid5_run_ops.  The
req_compute variable protects against this case.

Changelog:
* remove the req_compute BUG_ON
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-By: NNeilBrown <neilb@suse.de>

When the raid acceleration work was proposed, Neil laid out the following
attack plan:

1/ move the xor and copy operations outside spin_lock(&sh->lock)
2/ find/implement an asynchronous offload api

The raid5_run_ops routine uses the asynchronous offload api (async_tx) and
the stripe_operations member of a stripe_head to carry out xor+copy
operations asynchronously, outside the lock.

To perform operations outside the lock a new set of state flags is needed
to track new requests, in-flight requests, and completed requests.  In this
new model handle_stripe is tasked with scanning the stripe_head for work,
updating the stripe_operations structure, and finally dropping the lock and
calling raid5_run_ops for processing.  The following flags outline the
requests that handle_stripe can make of raid5_run_ops:

STRIPE_OP_BIOFILL
 - copy data into request buffers to satisfy a read request
STRIPE_OP_COMPUTE_BLK
 - generate a missing block in the cache from the other blocks
STRIPE_OP_PREXOR
 - subtract existing data as part of the read-modify-write process
STRIPE_OP_BIODRAIN
 - copy data out of request buffers to satisfy a write request
STRIPE_OP_POSTXOR
 - recalculate parity for new data that has entered the cache
STRIPE_OP_CHECK
 - verify that the parity is correct
STRIPE_OP_IO
 - submit i/o to the member disks (note this was already performed outside
   the stripe lock, but it made sense to add it as an operation type

The flow is:
1/ handle_stripe sets STRIPE_OP_* in sh->ops.pending
2/ raid5_run_ops reads sh->ops.pending, sets sh->ops.ack, and submits the
   operation to the async_tx api
3/ async_tx triggers the completion callback routine to set
   sh->ops.complete and release the stripe
4/ handle_stripe runs again to finish the operation and optionally submit
   new operations that were previously blocked

Note this patch just defines raid5_run_ops, subsequent commits (one per
major operation type) modify handle_stripe to take advantage of this
routine.

Changelog:
* removed ops_complete_biodrain in favor of ops_complete_postxor and
  ops_complete_write.
* removed the raid5_run_ops workqueue
* call bi_end_io for reads in ops_complete_biofill, saves a call to
  handle_stripe
* explicitly handle the 2-disk raid5 case (xor becomes memcpy), Neil Brown
* fix race between async engines and bi_end_io call for reads, Neil Brown
* remove unnecessary spin_lock from ops_complete_biofill
* remove test_and_set/test_and_clear BUG_ONs, Neil Brown
* remove explicit interrupt handling for channel switching, this feature
  was absorbed (i.e. it is now implicit) by the async_tx api
* use return_io in ops_complete_biofill
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-By: NNeilBrown <neilb@suse.de>

handle_stripe5 and handle_stripe6 have very deep logic paths handling the
various states of a stripe_head.  By introducing the 'stripe_head_state'
and 'r6_state' objects, large portions of the logic can be moved to
sub-routines.

'struct stripe_head_state' consumes all of the automatic variables that previously
stood alone in handle_stripe5,6.  'struct r6_state' contains the handle_stripe6
specific variables like p_failed and q_failed.

One of the nice side effects of the 'stripe_head_state' change is that it
allows for further reductions in code duplication between raid5 and raid6.
The following new routines are shared between raid5 and raid6:

	handle_completed_write_requests
	handle_requests_to_failed_array
	handle_stripe_expansion

Changes:
* v2: fixed 'conf->raid_disk-1' for the raid6 'handle_stripe_expansion' path
* v3: removed the unused 'dirty' field from struct stripe_head_state
* v3: coalesced open coded bi_end_io routines into return_io()
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-By: NNeilBrown <neilb@suse.de>

If a bypass-the-cache read fails, we simply try again through the cache.  If
it fails again it will trigger normal recovery precedures.

update 1:

From: NeilBrown <neilb@suse.de>

1/
  chunk_aligned_read and retry_aligned_read assume that
      data_disks == raid_disks - 1
  which is not true for raid6.
  So when an aligned read request bypasses the cache, we can get the wrong data.

2/ The cloned bio is being used-after-free in raid5_align_endio
   (to test BIO_UPTODATE).

3/ We forgot to add rdev->data_offset when submitting
   a bio for aligned-read

4/ clone_bio calls blk_recount_segments and then we change bi_bdev,
   so we need to invalidate the segment counts.

5/ We don't de-reference the rdev when the read completes.
   This means we need to record the rdev to so it is still
   available in the end_io routine.  Fortunately
   bi_next in the original bio is unused at this point so
   we can stuff it in there.

6/ We leak a cloned bio if the target rdev is not usable.

From: NeilBrown <neilb@suse.de>

update 2:

1/ When aligned requests fail (read error) they need to be retried
   via the normal method (stripe cache).  As we cannot be sure that
   we can process a single read in one go (we may not be able to
   allocate all the stripes needed) we store a bio-being-retried
   and a list of bioes-that-still-need-to-be-retried.
   When find a bio that needs to be retried, we should add it to
   the list, not to single-bio...

2/ We were never incrementing 'scnt' when resubmitting failed
   aligned requests.

[akpm@osdl.org: build fix]
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Replace all uses of kmem_cache_t with struct kmem_cache.

The patch was generated using the following script:

	#!/bin/sh
	#
	# Replace one string by another in all the kernel sources.
	#

	set -e

	for file in `find * -name "*.c" -o -name "*.h"|xargs grep -l $1`; do
		quilt add $file
		sed -e "1,\$s/$1/$2/g" $file >/tmp/$$
		mv /tmp/$$ $file
		quilt refresh
	done

The script was run like this

	sh replace kmem_cache_t "struct kmem_cache"
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

They are not needed.  conf->failed_disks is the same as mddev->degraded and
conf->working_disks is conf->raid_disks - mddev->degraded.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

There is a lot of commonality between raid5.c and raid6main.c.  This patches
merges both into one module called raid456.  This saves a lot of code, and
paves the way for online raid5->raid6 migrations.

There is still duplication, e.g.  between handle_stripe5 and handle_stripe6.
This will probably be cleaned up later.

Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Instead of checkpointing at each stripe, only checkpoint when a new write
would overwrite uncheckpointed data.  Block any write to the uncheckpointed
area.  Arbitrarily checkpoint at least every 3Meg.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

We allow the superblock to record an 'old' and a 'new' geometry, and a
position where any conversion is up to.  The geometry allows for changing
chunksize, layout and level as well as number of devices.

When using verion-0.90 superblock, we convert the version to 0.91 while the
conversion is happening so that an old kernel will refuse the assemble the
array.  For version-1, we use a feature bit for the same effect.

When starting an array we check for an incomplete reshape and restart the
reshape process if needed.  If the reshape stopped at an awkward time (like
when updating the first stripe) we refuse to assemble the array, and let
user-space worry about it.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

This patch provides the core of the resize/expand process.

sync_request notices if a 'reshape' is happening and acts accordingly.

It allocated new stripe_heads for the next chunk-wide-stripe in the target
geometry, marking them STRIPE_EXPANDING.

Then it finds which stripe heads in the old geometry can provide data needed
by these and marks them STRIPE_EXPAND_SOURCE.  This causes stripe_handle to
read all blocks on those stripes.

Once all blocks on a STRIPE_EXPAND_SOURCE stripe_head are read, any that are
needed are copied into the corresponding STRIPE_EXPANDING stripe_head.  Once a
STRIPE_EXPANDING stripe_head is full, it is marks STRIPE_EXPAND_READY and then
is written out and released.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

We need to allow that different stripes are of different effective sizes, and
use the appropriate size.  Also, when a stripe is being expanded, we must
block any IO attempts until the stripe is stable again.

Key elements in this change are:
 - each stripe_head gets a 'disk' field which is part of the key,
   thus there can sometimes be two stripe heads of the same area of
   the array, but covering different numbers of devices.  One of these
   will be marked STRIPE_EXPANDING and so won't accept new requests.
 - conf->expand_progress tracks how the expansion is progressing and
   is used to determine whether the target part of the array has been
   expanded yet or not.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Before a RAID-5 can be expanded, we need to be able to expand the stripe-cache
data structure.

This requires allocating new stripes in a new kmem_cache.  If this succeeds,
we copy cache pages over and release the old stripes and kmem_cache.

We then allocate new pages.  If that fails, we leave the stripe cache at it's
new size.  It isn't worth the effort to shrink it back again.

Unfortuanately this means we need two kmem_cache names as we, for a short
period of time, we have two kmem_caches.  So they are raid5/%s and
raid5/%s-alt
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

The remainder of this batch implements raid5 reshaping.  Currently the only
shape change that is supported is added a device, but it is envisioned that
changing the chunksize and layout will also be supported, as well as changing
the level (e.g.  1->5, 5->6).

The reshape process naturally has to move all of the data in the array, and so
should be used with caution.  It is believed to work, and some testing does
support this, but wider testing would be great for increasing my confidence.

You will need a version of mdadm newer than 2.3.1 to make use of raid5 growth.
 This is because mdadm need to take a copy of a 'critical section' at the
start of the array incase there is a crash at an awkward moment.  On restart,
mdadm will restore the critical section and allow reshape to continue.

I hope to release a 2.4-pre by early next week - it still needs a little more
polishing.

This patch:

Previously the array of disk information was included in the raid5 'conf'
structure which was allocated to an appropriate size.  This makes it awkward
to change the size of that array.  So we split it off into a separate
kmalloced array which will require a little extra indexing, but is much easier
to grow.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

- replace open-coded hash chain with hlist macros

- Fix hash-table size at one page - it is already quite generous, so there
  will never be a need to use multiple pages, so no need for __get_free_pages

No functional change.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

There is this "FIXME" comment with a typo in it!!  that been annoying me for
days, so I just had to remove it.

conf->disks[i].rdev should only be accessed if
  - we know we hold a reference or
  - the mddev->reconfig_sem is down or
  - we have a rcu_readlock

handle_stripe was referencing rdev in three places without any of these.  For
the first two, get an rcu_readlock.  For the last, the same access
(md_sync_acct call) is made a little later after the rdev has been claimed
under and rcu_readlock, if R5_Syncio is set.  So just use that access...
However R5_Syncio isn't really needed as the 'syncing' variable contains the
same information.  So use that instead.

Issues, comment, and fix are identical in raid5 and raid6.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

raid6 currently does not check the P/Q syndromes when doing a resync, it just
calculates the correct value and writes it.  Doing the check can reduce writes
(often to 0) for a resync, and it is needed to properly implement the

  echo check > sync_action

operation.

This patch implements the appropriate checks and tidies up some related code.

It also allows raid6 user-requested resync to bypass the intent bitmap.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

There isn't really a need for raid5 attributes to be an a subdirectory,
so this patch moves them from
  /sys/block/mdX/md/raid5/attribute
to
  /sys/block/mdX/md/attribute

This suggests that all md personalities should co-operate about
namespace usage, but that shouldn't be a problem.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

/sys/block/mdX/md/raid5/
contains raid5-related attributes.
Currently
  stripe_cache_size
is number of entries in stripe cache, and is settable.
  stripe_cache_active
is number of active entries, and in only readable.
Signed-off-by: NNeil Brown <neilb@suse.de>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>