Ubuntu Manpage: pmDiscoverServices, __pmDiscoverServicesWithOptions

NAME

       pmDiscoverServices, __pmDiscoverServicesWithOptions - discover PCP services on the network

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmDiscoverServices(const char *service, const char *mechanism, char ***urls);

       #include <pcp/libpcp.h>

       int __pmDiscoverServicesWithOptions(const char *service, const char *mechanism, const char *optionsString, const volatile unsigned *flags, char ***urls);

       cc ... -lpcp

CAVEAT

       This documentation is intended for internal Performance Co-Pilot (PCP) developer use.

       These  interfaces  are not part of the PCP APIs that are guaranteed to remain fixed across
       releases, and they may not work, or may provide different semantics at some point  in  the
       future.

DESCRIPTION

Given a PCP service name, as identified by service, and using the type of discovery
optionally specified in mechanism, pmDiscoverServices returns, via urls, a list of URLs
representing the services discovered on the network.

The internal function __pmDiscoverServicesWithOptions performs the same function and adds
arguments for global options and a mechanism for interrupting the discovery process.

The pmfind(1) utility provides command line access to both of these interfaces.

Calling

pmDiscoverServices(service, mechanism, urls)

is equivalent to calling

__pmDiscoverServicesWithOptions(service, mechanism, NULL, NULL, urls);

service specifies the PCP service to be discovered. Currently supported services are
PM_SERVER_SERVICE_SPEC and PM_PROXY_SERVICE_SPEC which search for pmcd(1), and pmproxy(1)
servers respectively.

mechanism specifies the style of discovery to be used.

The currently supported mechanisms are:

avahi This searches for services which are broadcasting using mDNS via avahi-daemon(8).
An optional suffix ",timeout=N" may be added to specify the discovery timeout in
floating-point multiples of one second. The default timeout is 0.5 seconds, which
may be overridden by the AVAHI_DISCOVERY_TIMEOUT environment variable, also
specified in floating-point multiples of one second. If both are specified, then
the value specified in the environment variable takes precedence.

probe=<net-address>/<mask-bits>
Actively probes the given subnet for the requested PCP service(s). <net-address>
is an inet or ipv6 network address and <mask-bits> is the number of bits used to
define the subnet. For example, 192.168.1.0/24 defines an 8 bit subnet consisting
of the addresses 192.168.1.0 through 192.168.1.255. An optional suffix
",maxThreads=N" may be added to limit the number of threads used while probing.
The default is the value of FD_SETSIZE (which is typically 1024) or the number of
addresses in the subnet, whichever is less. An optional suffix ",timeout=N" may be
added to specify the timeout for each connection attempt in floating-point
multiples of one second. The default is 0.02 seconds (20 milliseconds).

shell Probes the list of addresses provided by scripts for requested PCP service(s).
Several optional, comma-separated parameters can also be provided. Firstly, the
"path=DIR" option specifies the directory where commands like pcp-kube-pods(1) are
located (defaults to $PCP_BINADM_DIR/discover/). This setting can be further
restricted to an individual command using the command=CMD option, but the default
is to use all available commands from the path. The "maxThreads=N" option limits
the number of threads used while probing. The default is the value of FD_SETSIZE
(which is typically 1024) or the number of addresses returned by the scripts,
whichever is less. The "timeout=N" option may be added to limit the amount of time
spent waiting for each connection attempt. N is a floating point number specifying
the number of seconds to wait. The default is 0.02 seconds (20 milliseconds).

mechanism may also be NULL, which means to use all available discovery mechanisms.

For __pmDiscoverServicesWithOptions, optionsString specifies global options to be applied
to the discovery process. Options are comma-separated and may be one or more of the
following:

resolve
This requests that DNS name resolution be attempted for the addresses of any
discovered services.

timeout=N
This specifies a timeout period after which the discovery process will be
interrupted. N is a floating point number representing the number of seconds
before timing out.

optionsString may also be NULL, which means that no global options are specified.

For __pmDiscoverServicesWithOptions, flags specifies a pointer to an object of type
unsigned which is a bit mask of options/status flags for the discovery process. The
supported flags are:

PM_SERVICE_DISCOVERY_RESOLVE
Specifying this flag is equivalent to specifying resolve in the optionsString

PM_SERVICE_DISCOVERY_INTERRUPTED
This flag must be unset when calling __pmDiscoverServicesWithOptions but may be set
asynchronously (by an interrupt handler, for example) in order to interrupt the
service discovery process.

flags may also be NULL, which indicates that no flags are set.

pmDiscoverServices and __pmDiscoverServicesWithOptions will return the number of services
discovered, else a value less than zero for an error. The value zero indicates that no
services were discovered.

The resulting list of pointers, urls, and the values (the URLs) that the pointers
reference will have been allocated by pmDiscoverServices or
__pmDiscoverServicesWithOptions with a single call to malloc(3), and it is the
responsibility of the pmDiscoverServices or __pmDiscoverServicesWithOptions caller to
free(urls) to release the space when it is no longer required.

When an error occurs, or no services are discovered, urls is undefined (no space will have
been allocated, and so calling free(3) is a singularly bad idea).

PCP ENVIRONMENT

       Environment variables with the prefix PCP_ are used to parameterize the file and directory
       names used by PCP.  On each installation, the file /etc/pcp.conf contains the local values
       for  these  variables.   The  $PCP_CONF  variable  may  be  used to specify an alternative
       configuration file, as described in  pcp.conf(5).   Values  for  these  variables  may  be
       obtained programmatically using the pmGetConfig(3) function.

DIAGNOSTICS