pmFreeOptions (3) - Linux Manuals

pmFreeOptions: command line handling for PMAPI tools

NAME

pmgetopt_r, pmGetOptions, pmGetContextOptions, pmFreeOptions, pmUsageMessage - command line handling for PMAPI tools

C SYNOPSIS

#include <pcp/pmapi.h>

int pmgetopt_r(int argc, char *const *argv, pmOptions *opts);
int pmGetOptions(int argc, char *const *argv, pmOptions *opts);
int pmGetContextOptions(int ctx, pmOptions *opts);
void pmUsageMessage(pmOptions *opts);
void pmFreeOptions(pmOptions *opts);

cc ... -lpcp

DESCRIPTION

The pmGetOptions function provides command line option processing services for both monitor and collector PMAPI(3) tools. It is modelled on the thread-safe variants of the GNU getopt_long(3) API, and primarily differs in its focus on providing generalised processing for the (de-facto) standard PCP command line options described in PCPIntro(1). These common options include the host and archive specification, time windows, timezones, sample counts, time intervals, and so on.

The primary interface is pmGetOptions, which should be passed the argc argument count and argv array, as passed to the main() function on program invocation. The final opts argument describes the set of long and short options the tools is prepared to process, and other metadata regarding how those options should be processed.

The pmgetopt_r interface, used internally by pmGetOptions, behaves in a similar fashion, but it does not perform any common option processing. It is more suited to PCP collector processes, whereas PCP monitor tools tend to use pmGetOptions.

The opts argument consists of an array of pmLongOpts entries describing the arguments, as well as the enclosing pmOptions struct, which are defined as follows (internal fields are not presented, for brevity):

typedef struct {
    const char *        long_opt;
    int                 has_arg;
    int                 short_opt;
    const char *        argname;
    const char *        message;
} pmLongOptions;

typedef struct {
    int                 version;
    int                 flags;
    const char *        short_options;
    pmLongOptions *     long_options;
    const char *        short_usage;
    pmOptionOverride    override;

    int                 index;
    int                 optind;
    int                 opterr;
    int                 optopt;
    char                *optarg;
    /* [internal fields, undocumented] */

    int                 errors;
    int                 context; /* PM_CONTEXT_{HOST,ARCHIVE,LOCAL} */
    int                 nhosts;
    int                 narchives;
    char **             hosts;
    char **             archives;
    struct timeval      start;
    struct timeval      finish;
    struct timeval      origin;
    struct timeval      interval;
    char *              align_optarg;
    char *              start_optarg;
    char *              finish_optarg;
    char *              origin_optarg;
    char *              guiport_optarg;
    char *              timezone;
    int                 samples;
    int                 guiport;
    int                 padding;
    unsigned int        guiflag : 1;
    unsigned int        tzflag  : 1;
    unsigned int        nsflag  : 1;
    unsigned int        Lflag   : 1;
    unsigned int        zeroes  : 28;
} pmOptions;

The initial flags and version fields describe how the rest of the pmOptions structure is to be interpreted. These fields can be zeroed, specifying a default interpretation. Alternatively, the PMAPI_VERSION macro can be used to specify the API level to use (currently, values of 2 or less are allowed). The flags field can be used to modify option processing behaviour as described in the ``FLAGS VALUES'' section below.

The array of long_options pmLongOpts structures must be terminated by a sentinel and the PMAPI_OPTIONS_END macro can be used to effect this termination. Individual records within the long_options array can be of two types - options headers, or actual options. An options header is constructed using the PMAPI_OPTIONS_HEADER macro, and is used for usage message option grouping. Free form text can be inserted into the usage message at any point using the PMAPI_OPTIONS_TEXT macro - this is intended for additional explanatory text covering detailed usage that is beyond the scope of the individual headers or options. Otherwise, the array entry specifies an option. These should be named (long_opt) if a long-option form is allowed, specify whether or not they take an argument (has_arg), specify the single character variant argument (short_opt) if a short-option form is allowed, and finally specify how to present the option in the usage message. This latter component consists of a short, one-word description of the optional argument (argname) and a one-line description of what the command-line option does (message).

The short_usage string is also used only when constructing the usage message. It forms the component of the usage message that follows the program name (i.e. argv[0]).

The optional short_options string is the normal getopt command-line option specification string, using individual characters (those with arguments are designated as such using the ':' character) - as used by all getopt implementations.

A facility is provided to extend the existing set of common options with additional options, as well as to re-task the standard options into non-standard roles for individual tools. The latter is achieved using the override method, which allows a callback function to be provided which will be called on receipt of every argument, prior to common processing. If this callback returns a non-zero value the common processing will be short-circuited for that option, otherwise processing continues. Thus, aach client tool is free to choose exactly which of the standard options they wish to support - this can be all, some, or none, and no matter what they choose, each tool always has access to the long option parsing capability and the usage message generation facility.

The remaining pmOptions structure fields are filled in as a result of processing the arguments, and are largely self-explanatory. Further discussion of these is deferred to the ``FLAGS VALUES'' section below. The error field contains a count of errors detected during option processing. These can be either usage or runtime errors, as indicated by the flags field (set, and passed out to the caller). Typically, a command line tool will fail to start successfully and will produce an error message (e.g. via pmUsageMessage) if the error field is non-zero at the end of either pmGetOptions or pmGetContextOptions.

Some command line option post-processing can only be performed once the tool has established a PMAPI context via pmNewContext(3). This processing includes use of context-aware timezones (-z), and time window processing (-A, -O, -S, -T) that may be affected by the timezone, for example. The pmGetContextOptions function is available for such situations, and it completes any remaining processing of opts with respect to the ctx context identifier given.

The pmUsageMessage function generates a usage message for the tool, and included both standard PCP options and custom options for each tool, as specified by the pmLongOptions array. It supports grouping of options (via PMAPI_OPTIONS_HEADER) as well as neat formatting of all options - short and long - their arguments, and individual explanatory messages. It will build this usage message using pmprintf(3) upon which it will issue a single pmflush(3) before returning to the caller, provided the PM_OPTFLAG_USAGE_ERR flag is set in flags, which will happen automatically during option parsing, when usage errors are detected.

In certain situations, such as recording lists of host specifications or PCP archive paths, the pmGetOptions routine may allocate memory, and store pointers to it within opts. Should a program wish to free this memory before exiting, it can use the pmFreeOptions routine to do so. This is safe to call irrespective of whether memory was allocated dynamically, provided that opts was zeroed initially.

FLAGS VALUES

PM_OPTFLAG_INIT

Used internally within the library to indicate initialisation has been done, so that on subsequent calls it will not be done again.

PM_OPTFLAG_DONE

Used primarily internally within the library to indicate that the final option processing has been completed. This processing involves cross-referencing a number of the options, to check for mutual exclusion, for example. There may be other post-processing at this stage also, provided it does not require a PMAPI context.

PM_OPTFLAG_MULTI

Allow more than one host or set of archives to be specified. The default is to allow one source of metrics only, however some of the more sophisticated tools permit multiple metric sources, each of which is handled within a separate context. See also PM_OPTFLAG_MIXED.

PM_OPTFLAG_USAGE_ERR

Indicates that the library has detected a command-line usage error. This is an error such as when an option requires an argument but none is supplied, or conflicting options are specified (such as -s and -T).

PM_OPTFLAG_RUNTIME_ERR

Indicates that the library has detected an error at run time. This is an error such as failing to retrieve timezone information from pmcd (1) or failing to load an alternate metric namespace from a local file (via the -n option).

PM_OPTFLAG_EXIT

Indicates a suggestion from the library that the tool exit cleanly. This is used when the version number is requested, for example (the -V option and PMOPT_VERSION macro).

PM_OPTFLAG_POSIX

Use strict POSIX command line argument handling. This means options and following arguments will not be reordered, so additional options cannot follow command line arguments. This may be important for tools where the arguments can be negative numbers, for example, as these should not be treated as command line options in this case.

PM_OPTFLAG_MIXED

Allow both live and archive metric sources to be specified. The default is to allow one type of metric context only, however some of the more sophisticated tools permit multiple context types. See also PM_OPTFLAG_MULTI.

PM_OPTFLAG_ENV_ONLY

Many options can be specified through the either the command line or from similarly-named environment variables. This flag disables all argument parsing, and only changes opts based on the environment variables. This may be useful for tools wishing to ensure no command line option conflicts occur between their own set and the standard PCP option set (such as an existing tool, reimplemented using PMAPI services).

PM_OPTFLAG_LONG_ONLY

Only process long options, not short options.

PM_OPTFLAG_BOUNDARIES

The default pmGetOptions behaviour is to parse the time window options (namely, -A, -O, -S and -T), only if one of those options has been specified on the command line. However, this flag can be used (particularly with archive contexts) to find the start and finish times associated with the context(s) even if no time window options were specified. In the case of multiple archives, the time window is defined as the time window spanning all of the archives.

PM_OPTFLAG_STDOUT_TZ

The timezone being used will be reported on the standard output stream during option parsing. The default behaviour is to not report, but simply return timezone information via the timezone (-Z) and tzflag (-z) fields in the opts structure.

PM_OPTFLAG_NOFLUSH

The final pmflush call issued by pmUsageMessage will be skipped if this flag is set. This is useful in situations where the caller wishes to append additional test to the generated usage message before flushing.

PM_OPTFLAG_QUIET

Suppress messages from pmgetopt_r about unrecognised command line options. This is the equivalent to setting the opterr field in the opt parameter (which mimics the getopt variable of the same name).

RETURN VALUE

The pmGetOptions function returns either when it detects a command-line option that is not one of the standard PCP set, or when the end of the command line options has been reached (at which point -1 is returned). Both the pmgetopt_r and pmGetOptions routines return control to the caller in the same way that a regular getopt call would, with the return value indicating either the end of all processing (-1), or the single character form of the option currently being processed, or zero for the special long-option-only case. For all option-processing cases, the opts structure is returned containing filled out optarg, opterr, optopt, optind, and index fields as normal (do NOT use the global optarg or optind from your platform C library, these will NOT be modified).

pmGetOptions does not return to the caller when any of the standard PCP options are being processed (although the override mechanism can be used to still detect such options if needed).

The pmGetContextOptions function returns zero on success, or a negative PCP error code on failure. The error field within the opts parameter will also be non-zero in the latter case.

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 pmGetOptions(3) function.