Update Linux to v5.4.2
Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
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+=======
+dm-raid
+=======
+
+The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
+It allows the MD RAID drivers to be accessed using a device-mapper
+interface.
+
+
+Mapping Table Interface
+-----------------------
+The target is named "raid" and it accepts the following parameters::
+
+ <raid_type> <#raid_params> <raid_params> \
+ <#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
+
+<raid_type>:
+
+ ============= ===============================================================
+ raid0 RAID0 striping (no resilience)
+ raid1 RAID1 mirroring
+ raid4 RAID4 with dedicated last parity disk
+ raid5_n RAID5 with dedicated last parity disk supporting takeover
+ Same as raid4
+
+ - Transitory layout
+ raid5_la RAID5 left asymmetric
+
+ - rotating parity 0 with data continuation
+ raid5_ra RAID5 right asymmetric
+
+ - rotating parity N with data continuation
+ raid5_ls RAID5 left symmetric
+
+ - rotating parity 0 with data restart
+ raid5_rs RAID5 right symmetric
+
+ - rotating parity N with data restart
+ raid6_zr RAID6 zero restart
+
+ - rotating parity zero (left-to-right) with data restart
+ raid6_nr RAID6 N restart
+
+ - rotating parity N (right-to-left) with data restart
+ raid6_nc RAID6 N continue
+
+ - rotating parity N (right-to-left) with data continuation
+ raid6_n_6 RAID6 with dedicate parity disks
+
+ - parity and Q-syndrome on the last 2 disks;
+ layout for takeover from/to raid4/raid5_n
+ raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk
+
+ - layout for takeover from raid5_la from/to raid6
+ raid6_ra_6 Same as "raid5_ra" dedicated last Q-syndrome disk
+
+ - layout for takeover from raid5_ra from/to raid6
+ raid6_ls_6 Same as "raid5_ls" dedicated last Q-syndrome disk
+
+ - layout for takeover from raid5_ls from/to raid6
+ raid6_rs_6 Same as "raid5_rs" dedicated last Q-syndrome disk
+
+ - layout for takeover from raid5_rs from/to raid6
+ raid10 Various RAID10 inspired algorithms chosen by additional params
+ (see raid10_format and raid10_copies below)
+
+ - RAID10: Striped Mirrors (aka 'Striping on top of mirrors')
+ - RAID1E: Integrated Adjacent Stripe Mirroring
+ - RAID1E: Integrated Offset Stripe Mirroring
+ - and other similar RAID10 variants
+ ============= ===============================================================
+
+ Reference: Chapter 4 of
+ http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
+
+<#raid_params>: The number of parameters that follow.
+
+<raid_params> consists of
+
+ Mandatory parameters:
+ <chunk_size>:
+ Chunk size in sectors. This parameter is often known as
+ "stripe size". It is the only mandatory parameter and
+ is placed first.
+
+ followed by optional parameters (in any order):
+ [sync|nosync]
+ Force or prevent RAID initialization.
+
+ [rebuild <idx>]
+ Rebuild drive number 'idx' (first drive is 0).
+
+ [daemon_sleep <ms>]
+ Interval between runs of the bitmap daemon that
+ clear bits. A longer interval means less bitmap I/O but
+ resyncing after a failure is likely to take longer.
+
+ [min_recovery_rate <kB/sec/disk>]
+ Throttle RAID initialization
+ [max_recovery_rate <kB/sec/disk>]
+ Throttle RAID initialization
+ [write_mostly <idx>]
+ Mark drive index 'idx' write-mostly.
+ [max_write_behind <sectors>]
+ See '--write-behind=' (man mdadm)
+ [stripe_cache <sectors>]
+ Stripe cache size (RAID 4/5/6 only)
+ [region_size <sectors>]
+ The region_size multiplied by the number of regions is the
+ logical size of the array. The bitmap records the device
+ synchronisation state for each region.
+
+ [raid10_copies <# copies>], [raid10_format <near|far|offset>]
+ These two options are used to alter the default layout of
+ a RAID10 configuration. The number of copies is can be
+ specified, but the default is 2. There are also three
+ variations to how the copies are laid down - the default
+ is "near". Near copies are what most people think of with
+ respect to mirroring. If these options are left unspecified,
+ or 'raid10_copies 2' and/or 'raid10_format near' are given,
+ then the layouts for 2, 3 and 4 devices are:
+
+ ======== ========== ==============
+ 2 drives 3 drives 4 drives
+ ======== ========== ==============
+ A1 A1 A1 A1 A2 A1 A1 A2 A2
+ A2 A2 A2 A3 A3 A3 A3 A4 A4
+ A3 A3 A4 A4 A5 A5 A5 A6 A6
+ A4 A4 A5 A6 A6 A7 A7 A8 A8
+ .. .. .. .. .. .. .. .. ..
+ ======== ========== ==============
+
+ The 2-device layout is equivalent 2-way RAID1. The 4-device
+ layout is what a traditional RAID10 would look like. The
+ 3-device layout is what might be called a 'RAID1E - Integrated
+ Adjacent Stripe Mirroring'.
+
+ If 'raid10_copies 2' and 'raid10_format far', then the layouts
+ for 2, 3 and 4 devices are:
+
+ ======== ============ ===================
+ 2 drives 3 drives 4 drives
+ ======== ============ ===================
+ A1 A2 A1 A2 A3 A1 A2 A3 A4
+ A3 A4 A4 A5 A6 A5 A6 A7 A8
+ A5 A6 A7 A8 A9 A9 A10 A11 A12
+ .. .. .. .. .. .. .. .. ..
+ A2 A1 A3 A1 A2 A2 A1 A4 A3
+ A4 A3 A6 A4 A5 A6 A5 A8 A7
+ A6 A5 A9 A7 A8 A10 A9 A12 A11
+ .. .. .. .. .. .. .. .. ..
+ ======== ============ ===================
+
+ If 'raid10_copies 2' and 'raid10_format offset', then the
+ layouts for 2, 3 and 4 devices are:
+
+ ======== ========== ================
+ 2 drives 3 drives 4 drives
+ ======== ========== ================
+ A1 A2 A1 A2 A3 A1 A2 A3 A4
+ A2 A1 A3 A1 A2 A2 A1 A4 A3
+ A3 A4 A4 A5 A6 A5 A6 A7 A8
+ A4 A3 A6 A4 A5 A6 A5 A8 A7
+ A5 A6 A7 A8 A9 A9 A10 A11 A12
+ A6 A5 A9 A7 A8 A10 A9 A12 A11
+ .. .. .. .. .. .. .. .. ..
+ ======== ========== ================
+
+ Here we see layouts closely akin to 'RAID1E - Integrated
+ Offset Stripe Mirroring'.
+
+ [delta_disks <N>]
+ The delta_disks option value (-251 < N < +251) triggers
+ device removal (negative value) or device addition (positive
+ value) to any reshape supporting raid levels 4/5/6 and 10.
+ RAID levels 4/5/6 allow for addition of devices (metadata
+ and data device tuple), raid10_near and raid10_offset only
+ allow for device addition. raid10_far does not support any
+ reshaping at all.
+ A minimum of devices have to be kept to enforce resilience,
+ which is 3 devices for raid4/5 and 4 devices for raid6.
+
+ [data_offset <sectors>]
+ This option value defines the offset into each data device
+ where the data starts. This is used to provide out-of-place
+ reshaping space to avoid writing over data while
+ changing the layout of stripes, hence an interruption/crash
+ may happen at any time without the risk of losing data.
+ E.g. when adding devices to an existing raid set during
+ forward reshaping, the out-of-place space will be allocated
+ at the beginning of each raid device. The kernel raid4/5/6/10
+ MD personalities supporting such device addition will read the data from
+ the existing first stripes (those with smaller number of stripes)
+ starting at data_offset to fill up a new stripe with the larger
+ number of stripes, calculate the redundancy blocks (CRC/Q-syndrome)
+ and write that new stripe to offset 0. Same will be applied to all
+ N-1 other new stripes. This out-of-place scheme is used to change
+ the RAID type (i.e. the allocation algorithm) as well, e.g.
+ changing from raid5_ls to raid5_n.
+
+ [journal_dev <dev>]
+ This option adds a journal device to raid4/5/6 raid sets and
+ uses it to close the 'write hole' caused by the non-atomic updates
+ to the component devices which can cause data loss during recovery.
+ The journal device is used as writethrough thus causing writes to
+ be throttled versus non-journaled raid4/5/6 sets.
+ Takeover/reshape is not possible with a raid4/5/6 journal device;
+ it has to be deconfigured before requesting these.
+
+ [journal_mode <mode>]
+ This option sets the caching mode on journaled raid4/5/6 raid sets
+ (see 'journal_dev <dev>' above) to 'writethrough' or 'writeback'.
+ If 'writeback' is selected the journal device has to be resilient
+ and must not suffer from the 'write hole' problem itself (e.g. use
+ raid1 or raid10) to avoid a single point of failure.
+
+<#raid_devs>: The number of devices composing the array.
+ Each device consists of two entries. The first is the device
+ containing the metadata (if any); the second is the one containing the
+ data. A Maximum of 64 metadata/data device entries are supported
+ up to target version 1.8.0.
+ 1.9.0 supports up to 253 which is enforced by the used MD kernel runtime.
+
+ If a drive has failed or is missing at creation time, a '-' can be
+ given for both the metadata and data drives for a given position.
+
+
+Example Tables
+--------------
+
+::
+
+ # RAID4 - 4 data drives, 1 parity (no metadata devices)
+ # No metadata devices specified to hold superblock/bitmap info
+ # Chunk size of 1MiB
+ # (Lines separated for easy reading)
+
+ 0 1960893648 raid \
+ raid4 1 2048 \
+ 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
+
+ # RAID4 - 4 data drives, 1 parity (with metadata devices)
+ # Chunk size of 1MiB, force RAID initialization,
+ # min recovery rate at 20 kiB/sec/disk
+
+ 0 1960893648 raid \
+ raid4 4 2048 sync min_recovery_rate 20 \
+ 5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82
+
+
+Status Output
+-------------
+'dmsetup table' displays the table used to construct the mapping.
+The optional parameters are always printed in the order listed
+above with "sync" or "nosync" always output ahead of the other
+arguments, regardless of the order used when originally loading the table.
+Arguments that can be repeated are ordered by value.
+
+
+'dmsetup status' yields information on the state and health of the array.
+The output is as follows (normally a single line, but expanded here for
+clarity)::
+
+ 1: <s> <l> raid \
+ 2: <raid_type> <#devices> <health_chars> \
+ 3: <sync_ratio> <sync_action> <mismatch_cnt>
+
+Line 1 is the standard output produced by device-mapper.
+
+Line 2 & 3 are produced by the raid target and are best explained by example::
+
+ 0 1960893648 raid raid4 5 AAAAA 2/490221568 init 0
+
+Here we can see the RAID type is raid4, there are 5 devices - all of
+which are 'A'live, and the array is 2/490221568 complete with its initial
+recovery. Here is a fuller description of the individual fields:
+
+ =============== =========================================================
+ <raid_type> Same as the <raid_type> used to create the array.
+ <health_chars> One char for each device, indicating:
+
+ - 'A' = alive and in-sync
+ - 'a' = alive but not in-sync
+ - 'D' = dead/failed.
+ <sync_ratio> The ratio indicating how much of the array has undergone
+ the process described by 'sync_action'. If the
+ 'sync_action' is "check" or "repair", then the process
+ of "resync" or "recover" can be considered complete.
+ <sync_action> One of the following possible states:
+
+ idle
+ - No synchronization action is being performed.
+ frozen
+ - The current action has been halted.
+ resync
+ - Array is undergoing its initial synchronization
+ or is resynchronizing after an unclean shutdown
+ (possibly aided by a bitmap).
+ recover
+ - A device in the array is being rebuilt or
+ replaced.
+ check
+ - A user-initiated full check of the array is
+ being performed. All blocks are read and
+ checked for consistency. The number of
+ discrepancies found are recorded in
+ <mismatch_cnt>. No changes are made to the
+ array by this action.
+ repair
+ - The same as "check", but discrepancies are
+ corrected.
+ reshape
+ - The array is undergoing a reshape.
+ <mismatch_cnt> The number of discrepancies found between mirror copies
+ in RAID1/10 or wrong parity values found in RAID4/5/6.
+ This value is valid only after a "check" of the array
+ is performed. A healthy array has a 'mismatch_cnt' of 0.
+ <data_offset> The current data offset to the start of the user data on
+ each component device of a raid set (see the respective
+ raid parameter to support out-of-place reshaping).
+ <journal_char> - 'A' - active write-through journal device.
+ - 'a' - active write-back journal device.
+ - 'D' - dead journal device.
+ - '-' - no journal device.
+ =============== =========================================================
+
+
+Message Interface
+-----------------
+The dm-raid target will accept certain actions through the 'message' interface.
+('man dmsetup' for more information on the message interface.) These actions
+include:
+
+ ========= ================================================
+ "idle" Halt the current sync action.
+ "frozen" Freeze the current sync action.
+ "resync" Initiate/continue a resync.
+ "recover" Initiate/continue a recover process.
+ "check" Initiate a check (i.e. a "scrub") of the array.
+ "repair" Initiate a repair of the array.
+ ========= ================================================
+
+
+Discard Support
+---------------
+The implementation of discard support among hardware vendors varies.
+When a block is discarded, some storage devices will return zeroes when
+the block is read. These devices set the 'discard_zeroes_data'
+attribute. Other devices will return random data. Confusingly, some
+devices that advertise 'discard_zeroes_data' will not reliably return
+zeroes when discarded blocks are read! Since RAID 4/5/6 uses blocks
+from a number of devices to calculate parity blocks and (for performance
+reasons) relies on 'discard_zeroes_data' being reliable, it is important
+that the devices be consistent. Blocks may be discarded in the middle
+of a RAID 4/5/6 stripe and if subsequent read results are not
+consistent, the parity blocks may be calculated differently at any time;
+making the parity blocks useless for redundancy. It is important to
+understand how your hardware behaves with discards if you are going to
+enable discards with RAID 4/5/6.
+
+Since the behavior of storage devices is unreliable in this respect,
+even when reporting 'discard_zeroes_data', by default RAID 4/5/6
+discard support is disabled -- this ensures data integrity at the
+expense of losing some performance.
+
+Storage devices that properly support 'discard_zeroes_data' are
+increasingly whitelisted in the kernel and can thus be trusted.
+
+For trusted devices, the following dm-raid module parameter can be set
+to safely enable discard support for RAID 4/5/6:
+
+ 'devices_handle_discards_safely'
+
+
+Version History
+---------------
+
+::
+
+ 1.0.0 Initial version. Support for RAID 4/5/6
+ 1.1.0 Added support for RAID 1
+ 1.2.0 Handle creation of arrays that contain failed devices.
+ 1.3.0 Added support for RAID 10
+ 1.3.1 Allow device replacement/rebuild for RAID 10
+ 1.3.2 Fix/improve redundancy checking for RAID10
+ 1.4.0 Non-functional change. Removes arg from mapping function.
+ 1.4.1 RAID10 fix redundancy validation checks (commit 55ebbb5).
+ 1.4.2 Add RAID10 "far" and "offset" algorithm support.
+ 1.5.0 Add message interface to allow manipulation of the sync_action.
+ New status (STATUSTYPE_INFO) fields: sync_action and mismatch_cnt.
+ 1.5.1 Add ability to restore transiently failed devices on resume.
+ 1.5.2 'mismatch_cnt' is zero unless [last_]sync_action is "check".
+ 1.6.0 Add discard support (and devices_handle_discard_safely module param).
+ 1.7.0 Add support for MD RAID0 mappings.
+ 1.8.0 Explicitly check for compatible flags in the superblock metadata
+ and reject to start the raid set if any are set by a newer
+ target version, thus avoiding data corruption on a raid set
+ with a reshape in progress.
+ 1.9.0 Add support for RAID level takeover/reshape/region size
+ and set size reduction.
+ 1.9.1 Fix activation of existing RAID 4/10 mapped devices
+ 1.9.2 Don't emit '- -' on the status table line in case the constructor
+ fails reading a superblock. Correctly emit 'maj:min1 maj:min2' and
+ 'D' on the status line. If '- -' is passed into the constructor, emit
+ '- -' on the table line and '-' as the status line health character.
+ 1.10.0 Add support for raid4/5/6 journal device
+ 1.10.1 Fix data corruption on reshape request
+ 1.11.0 Fix table line argument order
+ (wrong raid10_copies/raid10_format sequence)
+ 1.11.1 Add raid4/5/6 journal write-back support via journal_mode option
+ 1.12.1 Fix for MD deadlock between mddev_suspend() and md_write_start() available
+ 1.13.0 Fix dev_health status at end of "recover" (was 'a', now 'A')
+ 1.13.1 Fix deadlock caused by early md_stop_writes(). Also fix size an
+ state races.
+ 1.13.2 Fix raid redundancy validation and avoid keeping raid set frozen
+ 1.14.0 Fix reshape race on small devices. Fix stripe adding reshape
+ deadlock/potential data corruption. Update superblock when
+ specific devices are requested via rebuild. Fix RAID leg
+ rebuild errors.