Commit 6995f0b (md: takeover should clear unrelated bits) clear
unrelated bits, but it's quite fragile. To avoid error in the future,
define a macro for unsupported mddev flags for each raid type and use it
to clear unsupported mddev flags. This should be less error-prone.

Suggested-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

Refactor raid1_make_request to make read and write code in their own
functions to clean up the code.

Signed-off-by: Robert LeBlanc <robert@leblancnet.us>
Signed-off-by: Shaohua Li <shli@fb.com>

The mddev->flags are used for different purposes. There are a lot of
places we check/change the flags without masking unrelated flags, we
could check/change unrelated flags. These usage are most for superblock
write, so spearate superblock related flags. This should make the code
clearer and also fix real bugs.

Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

When we change level from raid1 to raid5, the MD_FAILFAST_SUPPORTED bit
will be accidentally set, but raid5 doesn't support it. The same is true
for the MD_HAS_JOURNAL bit.

Fix: 46533ff (md: Use REQ_FAILFAST_* on metadata writes where appropriate)
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

When writing to a fastfail device we use MD_FASTFAIL unless
it is the only device being written to.

For resync/recovery, assume there was a working device to
read from so always use REQ_FASTFAIL_DEV.

If a write for resync/recovery fails, we just fail the
device - there is not much else to do.

If a normal failfast write fails, but the device cannot be
failed (must be only one left), we queue for write error
handling.  This will call narrow_write_error() to retry the
write synchronously and without any FAILFAST flags.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

If a device is marked FailFast and it is not the only device
we can read from, we mark the bio with REQ_FAILFAST_* flags.

If this does fail, we don't try read repair but just allow
failure.  If it was the last device it doesn't fail of
course, so the retry happens on the same device - this time
without FAILFAST.  A subsequent failure will not retry but
will just pass up the error.

During resync we may use FAILFAST requests and on a failure
we will simply use the other device(s).

During recovery we will only use FAILFAST in the unusual
case were there are multiple places to read from - i.e. if
there are > 2 devices.  If we get a failure we will fail the
device and complete the resync/recovery with remaining
devices.

The new R1BIO_FailFast flag is set on read reqest to suggest
the a FAILFAST request might be acceptable.  The rdev needs
to have FailFast set as well for the read to actually use
REQ_FAILFAST_*.

We need to know there are at least two working devices
before we can set R1BIO_FailFast, so we mustn't stop looking
at the first device we find.  So the "min_pending == 0"
handling to not exit early, but too always choose the
best_pending_disk if min_pending == 0.

The spinlocked region in raid1_error() in enlarged to ensure
that if two bios, reading from two different devices, fail
at the same time, then there is no risk that both devices
will be marked faulty, leaving zero "In_sync" devices.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

This can only be supported on personalities which ensure
that md_error() never causes an array to enter the 'failed'
state.  i.e. if marking a device Faulty would cause some
data to be inaccessible, the device is status is left as
non-Faulty.  This is true for RAID1 and RAID10.

If we get a failure writing metadata but the device doesn't
fail, it must be the last device so we re-write without
FAILFAST to improve chance of success.  We also flag the
device as LastDev so that future metadata updates don't
waste time on failfast writes.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

Both raid1 and raid10 will sometimes delay handling an IO request,
such as when resync is happening or there are too many requests queued.

Add some blktrace messsages so we can see when that is happening when
looking for performance artefacts.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

The block tracing infrastructure (accessed with blktrace/blkparse)
supports the tracing of mapping bios from one device to another.
This is currently used when a bio in a partition is mapped to the
whole device, when bios are mapped by dm, and for mapping in md/raid5.
Other md personalities do not include this tracing yet, so add it.

When a read-error is detected we redirect the request to a different device.
This could justifiably be seen as a new mapping for the originial bio,
or a secondary mapping for the bio that errors.  This patch uses
the second option.

When md is used under dm-raid, the mappings are not traced as we do
not have access to the block device number of the parent.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

While performing a resync/recovery, raid1 divides the
array space into three regions:
 - before the resync
 - at or shortly after the resync point
 - much further ahead of the resync point.

Write requests to the first or third do not need to wait.  Write
requests to the middle region do need to wait if resync requests are
pending.

If there are any active write requests in the middle region, resync
will wait for them.

Due to an accounting error, there is a small range of addresses,
between conf->next_resync and conf->start_next_window, where write
requests will *not* be blocked, but *will* be counted in the middle
region.  This can effectively block resync indefinitely if filesystem
writes happen repeatedly to this region.

As ->next_window_requests is incremented when the sector is after
  conf->start_next_window + NEXT_NORMALIO_DISTANCE
the same boundary should be used for determining when write requests
should wait.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>