NAME¶

ctl – interface for examination and modification of the library's internal state.

DESCRIPTION¶

The CTL namespace is organized in a tree structure. Starting from the root, each node can be either internal, containing other elements, or a leaf. Internal nodes themselves can only contain other nodes and cannot be entry points. There are two types of those nodes: named and indexed. Named nodes have string identifiers. Indexed nodes represent an abstract array index and have an associated string identifier. The index itself is provided by the user. A collection of indexes present on the path of an entry point is provided to the handler functions as name and index pairs.

The name argument specifies an entry point as defined in the CTL namespace specification. The entry point description specifies whether the extra arg is required. Those two parameters together create a CTL query. The functions and the entry points are thread-safe unless indicated otherwise below. If there are special conditions for calling an entry point, they are explicitly stated in its description. The functions propagate the return value of the entry point. If either name or arg is invalid, -1 is returned.

Entry points are the leaves of the CTL namespace structure. Each entry point can read from the internal state, write to the internal state, exec a function or a combination of these operations.

The entry points are listed in the following format:

name | r(ead)w(rite)x(ecute) | global/- | read argument type | write argument type | exec argument type | config argument type

A description of pmem_ctl functions can be found on the following manual pages: libpmemblk_ctl_get(3), libpmemlog_ctl_get(3), libpmemobj_ctl_get(3)

CTL EXTERNAL CONFIGURATION¶

In addition to direct function call, each write entry point can also be set using two alternative methods.

The first method is to load a configuration directly from the PMEMBLK_CONF/ PMEMLOG_CONF/ PMEMOBJ_CONF environment variable. A properly formatted ctl config string is a single-line sequence of queries separated by `;':

query0;query1;...;queryN

A single query is constructed from the name of the ctl write entry point and the argument, separated by `=':

entry_point=entry_point_argument

The entry point argument type is defined by the entry point itself, but there are three predefined primitives:

*) integer: represented by a sequence of [0-9] characters that form
    a single number.
*) boolean: represented by a single character: y/n/Y/N/0/1, each
    corresponds to true or false. If the argument contains any
    trailing characters, they are ignored.
*) string: a simple sequence of characters.

There are also complex argument types that are formed from the primitives separated by a `,':

first_arg,second_arg

In summary, a full configuration sequence looks like this:

(first_entry_point)=(arguments, ...);...;(last_entry_point)=(arguments, ...);

As an example, to set both prefault at_open and at_create variables:

PMEMBLK_CONF="prefault.at_open=1;prefault.at_create=1"

The second method of loading an external configuration is to set the PMEMBLK_CONF_FILE/ PMEMLOG_CONF_FILE/ PMEMOBJ_CONF_FILE environment variable to point to a file that contains a sequence of ctl queries. The parsing rules are all the same, but the file can also contain white-spaces and comments.

To create a comment, simply use `#' anywhere in a line and everything afterwards, until a new line, will be ignored.

An example configuration file:

#########################
# My pmemblk configuration
#########################
#
# Global settings:
prefault. # modify the behavior of pre-faulting
    at_open = 1; # prefault when the pool is opened
prefault.
    at_create = 0; # but don't prefault when it's created
# Per-pool settings:
# ...

SEE ALSO¶

libpmemblk_ctl_get(3), libpmemlog_ctl_get(3), libpmemobj_ctl_get(3) and <http://pmem.io>