bad block list management for md and RAID1

In the spirit of "release early" I thought I would post some patches that I have been working on lately.

Please don't try these on a system with valuable data - they are very early code and will probably do the wrong thing.

The goal of these patches is to add a 'bad block list' to each device and use it to allow us to fail single blocks rather than whole devices.

This is particularly useful in arrays will multiple redundancy (e.g. RAID6 or 3-device RAID1). In such cases, bad blocks in different places on different devices can leave an array that still has at-least single redundancy on all stripes. Without this support, such arrays could become non-fuinctional.

This is also a necessary preparation to being able to support 'hot-replace' where we build a new device while the old device is still in service. Such a process is only really needed if the old device is potentially faulty, and having the bad-block-list in place allows it to continue to provide the best service it can even when it cannot provide 100% service.

These patches have only seen limited testing, and are posted primarily for review rather than testing, though testing is always valuable, especially if you use the md/faulty module to simulate errors, or have a drive that provides you with real errors...

This series provides infrastructure and integration into raid1.c only. raid5.c and raid10.c support are still to be written.

NeilBrown

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NeilBrown (16):
md: beginnings of bad block management. md/bad-block-log: add sysfs interface for accessing bad-block-log.
md: don't allow arrays to contain devices with bad blocks.
md: load/store badblock list from v1.x metadata
md: reject devices with bad blocks and v0.90 metadata. md/raid1: clean up read_balance.
md: simplify raid10 read_balance
md/raid1: avoid reading from known bad blocks. md/raid1: avoid reading known bad blocks during resync
md: add 'write_error' flag to component devices. md/multipath: discard ->working_disks in favour of ->degraded
md: make error_handler functions more uniform and correct.
md: make it easier to wait for bad blocks to be acknowledged. md/raid1: avoid writing to known-bad blocks on known-bad drives. md/raid1: clear bad-block record when write succeeds. md/raid1: Handle write errors by updating badblock log.

 drivers/md/dm-raid456.c   |    6 
 drivers/md/md.c           |  725 +++++++++++++++++++++++++++++++++++++++++++--
 drivers/md/md.h           |   76 ++++-
 drivers/md/multipath.c    |   60 ++--
 drivers/md/multipath.h    |    1 
 drivers/md/raid1.c        |  714 +++++++++++++++++++++++++++++++++++---------
 drivers/md/raid1.h        |   14 +
 drivers/md/raid10.c       |  123 ++++----
 drivers/md/raid5.c        |   48 ++-
 include/linux/raid/md_p.h |   13 +
 10 files changed, 1475 insertions(+), 305 deletions(-)

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