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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.
To be able to detect lvm2 command is not leaking some
'unexpected' device - remove all devices before
test exits by its own command so test teardown
now can check what was 'left' unexpectedly.
Add 'can_use_16T' to detect systems where we could
safely use 16T devices without causing system deadlocks.
16T size leads on those to endless loops in udevd
- it calls blkid which tries cached read from such device
- this ends in endless loop.
Related problems:
https://bugzilla.redhat.com/show_bug.cgi?id=1015028
The same corner cases that exist for snapshots on mirrors exist for
any logical volume layered on top of mirror. (One example is when
a mirror image fails and a non-repair LVM command is the first to
detect it via label reading. In this case, the LVM command will hang
and prevent the necessary LVM repair command from running.) When
a better alternative exists, it makes no sense to allow a new target
to stack on mirrors as a new feature. Since, RAID is now capable of
running EX in a cluster and thin is not active-active aware, it makes
sense to pair these two rather than mirror+thinpool.
As further background, here are some additional comments that I made
when addressing a bug related to mirror+thinpool:
(https://bugzilla.redhat.com/show_bug.cgi?id=919604#c9)
I am going to disallow thin* on top of mirror logical volumes.
Users will have to use the "raid1" segment type if they want this.
This bug has come down to a choice between:
1) Disallowing thin-LVs from being used as PVs.
2) Disallowing thinpools on top of mirrors.
The problem is that the code in dev_manager.c:device_is_usable() is unable
to tell whether there is a mirror device lower in the stack from the device
being checked. Pretty much anything layered on top of a mirror will suffer
from this problem. (Snapshots are a good example of this; and option #1
above has been chosen to deal with them. This can also be seen in
dev_manager.c:device_is_usable().) When a mirror failure occurs, the
kernel blocks all I/O to it. If there is an LVM command that comes along
to do the repair (or a different operation that requires label reading), it
would normally avoid the mirror when it sees that it is blocked. However,
if there is a snapshot or a thin-LV that is on a mirror, the above code
will not detect the mirror underneath and will issue label reading I/O.
This causes the command to hang.
Choosing #1 would mean that thin-LVs could never be used as PVs - even if
they are stacked on something other than mirrors.
Choosing #2 means that thinpools can never be placed on mirrors. This is
probably better than we think, since it is preferred that people use the
"raid1" segment type in the first place. However, RAID* cannot currently
be used in a cluster volume group - even in EX-only mode. Thus, a complete
solution for option #2 must include the ability to activate RAID logical
volumes (and perform RAID operations) in a cluster volume group. I've
already begun working on this.
In those places where mirrors were being created while assuming
a default segment type of "mirror", we include the '--type mirror'
argument to explicitly set the segment type. This will preserve
the mirror testing that is performed even though the default
mirroring segment type is now "raid1".
Suggest to use _tdata and _tmeta devices for that.
This fixes regression from too relaxed change in
f1d5f6ae81
Without this patch there are some empty LVs created before
mirror code recognizes it cannot continue.
(in release fix)
