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There is a problem with the way mirrors have been designed to handle
failures that is resulting in stuck LVM processes and hung I/O. When
mirrors encounter a write failure, they block I/O and notify userspace
to reconfigure the mirror to remove failed devices. This process is
open to a couple races:
1) Any LVM process other than the one that is meant to deal with the
mirror failure can attempt to read the mirror, fail, and block other
LVM commands (including the repair command) from proceeding due to
holding a lock on the volume group.
2) If there are multiple mirrors that suffer a failure in the same
volume group, a repair can block while attempting to read the LVM
label from one mirror while trying to repair the other.
Mitigation of these races has been attempted by disallowing label reading
of mirrors that are either suspended or are indicated as blocking by
the kernel. While this has closed the window of opportunity for hitting
the above problems considerably, it hasn't closed it completely. This is
because it is still possible to start an LVM command, read the status of
the mirror as healthy, and then perform the read for the label at the
moment after a the failure is discovered by the kernel.
I can see two solutions to this problem:
1) Allow users to configure whether mirrors can be candidates for LVM
labels (i.e. whether PVs can be created on mirror LVs). If the user
chooses to allow label scanning of mirror LVs, it will be at the expense
of a possible hang in I/O or LVM processes.
2) Instrument a way to allow asynchronous label reading - allowing
blocked label reads to be ignored while continuing to process the LVM
command. This would action would allow LVM commands to continue even
though they would have otherwise blocked trying to read a mirror. They
can then release their lock and allow a repair command to commence. In
the event of #2 above, the repair command already in progress can continue
and repair the failed mirror.
This patch brings solution #1. If solution #2 is developed later on, the
configuration option created in #1 can be negated - allowing mirrors to
be scanned for labels by default once again.
Add allocation/thin_pool_chunk_size_calculation lvm.conf
option to select a method for calculating thin pool chunk
sizes and define two possible values - "default" and "performance".
Add internal devtypes reporting command to display built-in recognised
block device types. (The output does not include any additional
types added by a configuration file.)
> lvm devtypes -o help
Device Types Fields
-------------------
devtype_all - All fields in this section.
devtype_name - Name of Device Type exactly as it appears in /proc/devices.
devtype_max_partitions - Maximum number of partitions. (How many device minor numbers get reserved for each device.)
devtype_description - Description of Device Type.
> lvm devtypes
DevType MaxParts Description
aoe 16 ATA over Ethernet
ataraid 16 ATA Raid
bcache 1 bcache block device cache
blkext 1 Extended device partitions
...
Add new configure lvm.conf options for binaries thin_repair
and thin_dump.
Those are part of device-mapper-persistent-data package
and will be used for recovery of thin_pool.
cfg_def_get_path uses a global static var to store the result (for efficiency).
So we need to apply the profile first and then get the path for the config item
when calling find_config_tree_* fns.
Also activation/auto_set_activation is not profilable (at least not now,
maybe later if we need that).
The activation/auto_set_activation_skip enables/disables automatic
adding of the ACTIVATION_SKIP LV flag. By default thin snapshots
are flagged to be skipped during activation.
And by default, the auto_set_activation_skip is enabled.
These settins are customizable by profiles:
allocation/thin_pool_zero
allocation/thin_pool_discards
allocation/thin_pool_chunk_size
activation/thin_pool_autoextend_threshold
activation/thin_pool_autoextend_percent
Besides the classical configuration checks (type checking and
checking whether the item is recognized by lvm tools) for profiles,
do an extra check whether the configuration setting is customizable
by a profile at all. Give a warning message if not.
This patch adds --profile arg to lvm cmds and adds config/profile_dir
configuration setting to select the directory where profiles are stored
By default it's /etc/lvm/profile.
The profiles are added by using new "add_profile" fn and then loaded
using the "load_profile" fn. All profiles are stored in a cmd context
within the new "struct profile_params":
struct profile_params {
const char *dir;
struct profile *global_profile;
struct dm_list profiles_to_load;
struct dm_list profiles;
};
...where "dir" is the directory with profiles, "global_profile" is
the profile that is set globally via the --profile arg (IOW, not
set per VG/LV basis based on metadata record) and the "profiles"
is the list with loaded profiles.
Configuration checking is initiated during config load/processing
(_process_config fn) which is part of the command context
creation/refresh.
This patch also defines 5 types of trees that could be created from
the configuration definition (config_settings.h), the cfg_def_tree_t:
- CFG_DEF_TREE_CURRENT that denotes a tree of all the configuration
nodes that are explicitly defined in lvm.conf/--config
- CFG_DEF_TREE_MISSING that denotes a tree of all missing
configuration nodes for which default valus are used since they're
not explicitly used in lvm.conf/--config
- CFG_DEF_TREE_DEFAULT that denotes a tree of all possible
configuration nodes with default values assigned, no matter what
the actual lvm.conf/--config is
- CFG_DEF_TREE_NEW that denotes a tree of all new configuration nodes
that appeared in given version
- CFG_DEF_TREE_COMPLETE that denotes a tree of the whole configuration
tree that is used in LVM2 (a combination of CFG_DEF_TREE_CURRENT +
CFG_DEF_TREE_MISSING). This is not implemented yet, it will be added
later...
The function that creates the definition tree of given type:
struct dm_config_tree *config_def_create_tree(struct config_def_tree_spec *spec);
Where the "spec" specifies the tree type to be created:
struct config_def_tree_spec {
cfg_def_tree_t type; /* tree type */
uint16_t version; /* tree at this LVM2 version */
int ignoreadvanced; /* do not include advanced configs */
int ignoreunsupported; /* do not include unsupported configs */
};
This tree can be passed to already existing functions that write
the tree on output (like we already do with cmd->cft).
There is a new lvm.conf section called "config" with two new options:
- config/checks which enables/disables checking (enabled by default)
- config/abort_on_errors which enables/disables aborts on any type of
mismatch found in the config (disabled by default)
This file centrally defines all recognized LVM2 configuration
sections and settings. Each item here has its parent, set of
allowed types, default value, brief comment, version the setting
first appeared in and flags that further define the nature of
the configuration setting and its use.
