linux-toradex.git/Documentation/device-mapper, branch v4.19-rc5

dm raid: bump target version, update comments and documentation

2018-09-06T21:07:58+00:00

Bump target version to reflect the documented fixes are available.
Also fix some code comments (typos and clarity).

Signed-off-by: Heinz Mauelshagen 
Signed-off-by: Mike Snitzer

dm thin: include metadata_low_watermark threshold in pool status

2018-07-30T15:49:08+00:00

The metadata low watermark threshold is set by the kernel.  But the
kernel depends on userspace to extend the thinpool metadata device when
the threshold is crossed.

Since the metadata low watermark threshold is not visible to userspace,
upon receiving an event, userspace cannot tell that the kernel wants the
metadata device extended, instead of some other eventing condition.
Making it visible (but not settable) enables userspace to affirmatively
know the kernel is asking for a metadata device extension, by comparing
metadata_low_watermark against nr_free_blocks_metadata, also reported in
status.

Current solutions like dmeventd have their own thresholds for extending
the data and metadata devices, and both devices are checked against
their thresholds on each event.  This lessens the value of the kernel-set
threshold, since userspace will either extend the metadata device sooner,
when receiving another event; or will receive the metadata lowater event
and do nothing, if dmeventd's threshold is less than the kernel's.
(This second case is dangerous. The metadata lowater event will not be
re-sent, so no further event will be generated before the metadata
device is out if space, unless some other event causes userspace to
recheck its thresholds.)

Signed-off-by: Andy Grover 
Signed-off-by: Mike Snitzer

dm integrity: recalculate checksums on creation

2018-07-27T19:24:27+00:00

When using external metadata device and internal hash, recalculate the
checksums when the device is created - so that dm-integrity doesn't
have to overwrite the device.  The superblock stores the last position
when the recalculation ended, so that it is properly restarted.

Integrity tags that haven't been recalculated yet are ignored.

Also bump the target version.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Mike Snitzer

dm delay: add flush as a third class of IO

2018-07-27T19:24:19+00:00

Add a new class for dm-delay that delays flush requests.  Previously,
flushes were delayed as writes, but it caused problems if the user
needed to create a device with one or a few slow sectors for the purpose
of testing - all flushes would be forwarded to this device and delayed,
and that skews the test results.  Fix this by allowing to select 0 delay
for flushes.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Mike Snitzer

dm thin: update stale "Status" Documentation

2018-07-27T19:24:03+00:00

Documentation/device-mapper-/thin-provisioning.txt's "Status" section no
longer reflected the current fitness level of DM thin-provisioning.
That is, DM thinp is no longer "EXPERIMENTAL".  It has since seen
considerable improvement, has been fairly widely deployed and has
performed in a robust manner.

Update Documentation to dispel concern raised by potential DM thinp
users.

Reported-by: Drew Hastings 
Signed-off-by: Mike Snitzer

dm writecache: support optional offset for start of device

2018-07-02T20:14:02+00:00

Add an optional parameter "start_sector" to allow the start of the
device to be offset by the specified number of 512-byte sectors.  The
sectors below this offset are not used by the writecache device and are
left to be used for disk labels and/or userspace metadata (e.g. lvm).

Signed-off-by: Mikulas Patocka 
Signed-off-by: Mike Snitzer

dm: add writecache target

2018-06-08T15:59:51+00:00

The writecache target caches writes on persistent memory or SSD.
It is intended for databases or other programs that need extremely low
commit latency.

The writecache target doesn't cache reads because reads are supposed to
be cached in page cache in normal RAM.

If persistent memory isn't available this target can still be used in
SSD mode.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Colin Ian King  # fix missing goto
Signed-off-by: Ross Zwisler  # fix compilation issue with !DAX
Signed-off-by: Dan Carpenter  # use msecs_to_jiffies
Acked-by: Dan Williams  # reworks to unify ARM and x86 flushing
Signed-off-by: Mike Snitzer

dm thin: update Documentation to clarify when "read_only" is valid

2018-05-10T15:18:49+00:00

Due to user confusion, clarify that it doesn't make sense to try to
create a thin-pool with "read_only" mode enabled.

Signed-off-by: Mike Snitzer

dm verity: add 'check_at_most_once' option to only validate hashes once

2018-04-03T19:04:29+00:00

This allows platforms that are CPU/memory contrained to verify data
blocks only the first time they are read from the data device, rather
than every time.  As such, it provides a reduced level of security
because only offline tampering of the data device's content will be
detected, not online tampering.

Hash blocks are still verified each time they are read from the hash
device, since verification of hash blocks is less performance critical
than data blocks, and a hash block will not be verified any more after
all the data blocks it covers have been verified anyway.

This option introduces a bitset that is used to check if a block has
been validated before or not.  A block can be validated more than once
as there is no thread protection for the bitset.

These changes were developed and tested on entry-level Android Go
devices.

Signed-off-by: Patrik Torstensson 
Signed-off-by: Mike Snitzer

dm cache: Documentation: update default migration_throttling value

2018-01-30T21:55:47+00:00

In commit f8350daf7af0 ("dm cache: tune migration throttling") the
value for DEFAULT_MIGRATION_THRESHOLD was decreased from 204800 to
2048.  Edit device-mapper/cache.txt to reflect the correct default
value for migration_threshold.

Signed-off-by: John Pittman 
Signed-off-by: Mike Snitzer