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dm-integrity stores checksums of the data written to an
LV, and returns an error if data read from the LV does
not match the previously saved checksum. When used on
raid images, dm-raid will correct the error by reading
the block from another image, and the device user sees
no error. The integrity metadata (checksums) are stored
on an internal LV allocated by lvm for each linear image.
The internal LV is allocated on the same PV as the image.
Create a raid LV with an integrity layer over each
raid image (for raid levels 1,4,5,6,10):
lvcreate --type raidN --raidintegrity y [options]
Add an integrity layer to images of an existing raid LV:
lvconvert --raidintegrity y LV
Remove the integrity layer from images of a raid LV:
lvconvert --raidintegrity n LV
Settings
Use --raidintegritymode journal|bitmap (journal is default)
to configure the method used by dm-integrity to ensure
crash consistency.
Initialization
When integrity is added to an LV, the kernel needs to
initialize the integrity metadata/checksums for all blocks
in the LV. The data corruption checking performed by
dm-integrity will only operate on areas of the LV that
are already initialized. The progress of integrity
initialization is reported by the "syncpercent" LV
reporting field (and under the Cpy%Sync lvs column.)
Example: create a raid1 LV with integrity:
$ lvcreate --type raid1 -m1 --raidintegrity y -n rr -L1G foo
Creating integrity metadata LV rr_rimage_0_imeta with size 12.00 MiB.
Logical volume "rr_rimage_0_imeta" created.
Creating integrity metadata LV rr_rimage_1_imeta with size 12.00 MiB.
Logical volume "rr_rimage_1_imeta" created.
Logical volume "rr" created.
$ lvs -a foo
LV VG Attr LSize Origin Cpy%Sync
rr foo rwi-a-r--- 1.00g 4.93
[rr_rimage_0] foo gwi-aor--- 1.00g [rr_rimage_0_iorig] 41.02
[rr_rimage_0_imeta] foo ewi-ao---- 12.00m
[rr_rimage_0_iorig] foo -wi-ao---- 1.00g
[rr_rimage_1] foo gwi-aor--- 1.00g [rr_rimage_1_iorig] 39.45
[rr_rimage_1_imeta] foo ewi-ao---- 12.00m
[rr_rimage_1_iorig] foo -wi-ao---- 1.00g
[rr_rmeta_0] foo ewi-aor--- 4.00m
[rr_rmeta_1] foo ewi-aor--- 4.00m
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. Define a prototype for every lvm command.
. Match every user command with one definition.
. Generate help text and man pages from them.
The new file command-lines.in defines a prototype for every
unique lvm command. A unique lvm command is a unique
combination of: command name + required option args +
required positional args. Each of these prototypes also
includes the optional option args and optional positional
args that the command will accept, a description, and a
unique string ID for the definition. Any valid command
will match one of the prototypes.
Here's an example of the lvresize command definitions from
command-lines.in, there are three unique lvresize commands:
lvresize --size SizeMB LV
OO: --alloc Alloc, --autobackup Bool, --force,
--nofsck, --nosync, --noudevsync, --reportformat String, --resizefs,
--stripes Number, --stripesize SizeKB, --poolmetadatasize SizeMB
OP: PV ...
ID: lvresize_by_size
DESC: Resize an LV by a specified size.
lvresize LV PV ...
OO: --alloc Alloc, --autobackup Bool, --force,
--nofsck, --nosync, --noudevsync,
--reportformat String, --resizefs, --stripes Number, --stripesize SizeKB
ID: lvresize_by_pv
DESC: Resize an LV by specified PV extents.
FLAGS: SECONDARY_SYNTAX
lvresize --poolmetadatasize SizeMB LV_thinpool
OO: --alloc Alloc, --autobackup Bool, --force,
--nofsck, --nosync, --noudevsync,
--reportformat String, --stripes Number, --stripesize SizeKB
OP: PV ...
ID: lvresize_pool_metadata_by_size
DESC: Resize a pool metadata SubLV by a specified size.
The three commands have separate definitions because they have
different required parameters. Required parameters are specified
on the first line of the definition. Optional options are
listed after OO, and optional positional args are listed after OP.
This data is used to generate corresponding command definition
structures for lvm in command-lines.h. usage/help output is also
auto generated, so it is always in sync with the definitions.
Every user-entered command is compared against the set of
command structures, and matched with one. An error is
reported if an entered command does not have the required
parameters for any definition. The closest match is printed
as a suggestion, and running lvresize --help will display
the usage for each possible lvresize command.
The prototype syntax used for help/man output includes
required --option and positional args on the first line,
and optional --option and positional args enclosed in [ ]
on subsequent lines.
command_name <required_opt_args> <required_pos_args>
[ <optional_opt_args> ]
[ <optional_pos_args> ]
Command definitions that are not to be advertised/suggested
have the flag SECONDARY_SYNTAX. These commands will not be
printed in the normal help output.
Man page prototypes are also generated from the same original
command definitions, and are always in sync with the code
and help text.
Very early in command execution, a matching command definition
is found. lvm then knows the operation being done, and that
the provided args conform to the definition. This will allow
lots of ad hoc checking/validation to be removed throughout
the code.
Each command definition can also be routed to a specific
function to implement it. The function is associated with
an enum value for the command definition (generated from
the ID string.) These per-command-definition implementation
functions have not yet been created, so all commands
currently fall back to the existing per-command-name
implementation functions.
Using per-command-definition functions will allow lots of
code to be removed which tries to figure out what the
command is meant to do. This is currently based on ad hoc
and complicated option analysis. When using the new
functions, what the command is doing is already known
from the associated command definition.
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