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Section: C Library Functions (3)
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libcfg - Introduction to the Configuration Management Library  


The configuration management library (libcfg.a) provides routines that allow applications to manage static and dynamic kernel subsystems. Applications use the libcfg routines to communicate with the configuration management server (cfgmgr) and kernel subsystems. The configuration management library provides the following services: Adding and removing configurable subsystems from the kernel Displaying or modifying the value of kernel subsystem parameters Displaying information about the available subsystems and their states Accessing system_specific entries in the kernel, such as performing subsystem-defined operations

For example, you might use the library to create an application that manages a loadable device driver. Another example that uses the routines in libcfg is the sysconfig command. This command calls libcfg routines to allow system administrators to manage dynamically configurable kernel subsystems. (For more information, see the sysconfig(8))

This reference page introduces the library and provides information about the following topics: The purpose of the routines in the library The cfg_attr_t data type, which you need to understand in order to use the library How to handle error codes returned from the library

For information about creating configurable kernel subsystems, see the Programmer's Guide and Writing Device Drivers: Tutorial.  

Routines in the Configuration Management Library

The library includes routines that allow you to perform the following tasks on local and remote systems: Connect to the configuration management server on a remote host (cfg_connect()) Determine the state of a subsystem (cfg_subsys_state()) Obtain a list of subsystems and their states (cfg_subsys_list()) Configure the specified subsystem for use (cfg_subsys_config()) Determine the value of all attributes for a specified subsystem (cfg_subsys_query_all()) Determine the value of a specified subsystem attribute or list of attributes (cfg_subsys_query()) Modify the value of a specified subsystem attribute or list of attributes (cfg_subsys_reconfig()) Determine the /etc/sysconfigtab value for all attributes of a subsystem (cfg_subsys_defaults_all()) Determine the /etc/sysconfigtab value for selected attributes of a subsystem (cfg_subsys_defaults()) Perform an operation that is specific to and defined by the subsystem (cfg_subsys_op()) Unconfigure the specified subsystem (cfg_subsys_unconfig()) Remove the connection to the remote host (cfg_disconnect())


Sending and Receiving Subsystem Attribute Data

When you call one of the routines that manipulate subsystem attributes you communicate with the system using an attribute list. The <sys/sysconfig.h> header file declares the cfg_attr_t data type specifically for passing information about attributes. As shown in the example that follows, each element of this list carries information about one subsystem attribute: typedef struct cfg_attr {
        char         name[CFG_ATTR_NAME_SZ];
        uchar       type;
        uchar       operation;
        uint          status;
        long         index;
        union {
          struct {
                   caddr_t val;
                   ulong   min_len;
                   ulong   max_len;
                   void    (*disposal)();
          struct {
                   caddr_t val;
                   ulong   min_size;
                   ulong   max_size;
                   void    (*disposal)();
                   ulong   val_size;
          struct {
                   ulong   val;
                   ulong   min_val;
                   ulong   max_val;
               }attr; }cfg_attr_t; The following list describes the elements of the cfg_attr_t datatype: The name field specifies the name of the attribute. The name is defined by the subsystem and is a string of alphabetic characters, at least two characters long and no longer than the value stored in the CFG_ATTR_NAME_SZ constant. This constant is defined in the <sys/sysconfig.h> header file. The type field specifies the data type of the attribute, as shown in the following table:

Data Type NameDescription

CFG_ATTR_STRTYPE Null terminated array of characters (char*)
CFG_ATTR_INTTYPE 32 bit signed number (int)
CFG_ATTR_UINTTYPE 32 bit unsigned number (unsigned int)
CFG_ATTR_LONGTYPE 64 bit signed number (long)
CFG_ATTR_ULONGTYPE 64 bit unsigned number (unsigned long)
CFG_ATTR_BINTYPE Array of bytes

The status field contains one of the predefined status codes listed in the following table:

Status CodeMeaning

CFG_ATTR_EEXISTSAttribute does not exist
CFG_ATTR_EINDEXInvalid attribute index
CFG_ATTR_ELARGEAttribute value or size is too large
CFG_ATTR_EMEMNo memory available for the attribute
CFG_ATTR_EOP Attribute does not support the requested operation
CFG_ATTR_ESMALLAttribute value or size is too small
CFG_ATTR_ESUBSYS Subsystem failure (Code within the subsystem returned an error)
CFG_ATTR_ETYPE Invalid attribute type or mismatched attribute type
CFG_ATTR_SUCCESSSuccessful operation
CFG_ATTR_ENOTNUMBERAttribute value cannot be converted to a number

The operation field contains one of the operation codes listed in the following table:

Request CodeMeaning

CFG_OP_QUERY The application requests a query of the current value of the attribute
CFG_OP_RECONFIGURE The application requests a change to the value of the current value of the attribute

The index field is an index into a structured attribute. The attr union contains the value of the attribute and its maximum and minimum values.

For attributes with the CFG_ATTR_STRTYPE data type, the val variable contains the pointer to the string data. The minimum and maximum values are the minimum and maximum lengths allowed for the string. The disposal variable is used internally by subsystems.

For attributes with the CFG_ATTR_BINTYPE data type, the val field contains a pointer to the binary value. The minimum and maximum values are the minimum number of bytes allowed for the binary data. The disposal variable is used internally by subsystems.

For numerical data types, the val variable contains an integer value. The minimum and maximum values specify the range of values that is allowed for the attribute.  

Handling Error Return Values

All configuration management library routines return a status of type cfg_status_t. To determine whether a call was successful, you compare this status to the CFG_SUCCESS constant.

If a routine returns an error, the error might have occurred during the execution of kernel subsystem code, configuration management code, or both. You can use the CFG_STATUS_SUBSYS() and CFG_STATUS_FRAME() macros to extract the subsystem status and framework status, respectively, from the return value. All framework errors are defined in the <sys/sysconfig.h> header file as CFG_FRAME_???

The following example shows an error handler that determines and reports errors that occur during the execution of a configuration management library routine:

#include <errno.h> #include <sys/sysconfig.h> void print_error(
             cfg_status_t  status)

             int          subsys_status=CFG_STATUS_SUBSYS(status);

  /*   Report the status of configuration management software      */
  /*                                                               */

             switch (CFG_STATUS_FRAME(status)){
             case CFG_FRAME_SUCCESS:
             case CFG_FRAME_EEXISTS:
               printf("framework error: subsystem not loaded/found\n");
            case CFG_FRAM_EATTRLIST:
              printf("framework error: bad attribute list\n");
              printf("framework error: unknown %d\n" CFG_STATUS_FRAME(status))

  /*    Report the status of the kernel subsystem                 */
  /*                                                              */
            if (subsys_status != ESUCCESS) {
              if (subsys_status > 0 && subsys_status < sys_nerr && sys_errlist [subsys_status])
                 printf("subsystem error: %s\n"
                 printf("subsystem error %d: unknown status\n" subsys_status);
            } } In this example, the configuration manager status is supplied as the controlling expression for the switch statement. The various status constants shown are defined in the <sys/sysconfig.h> file. The example omits some constants, but you should include them all in your error handling routine. To see an example routine for displaying errors, refer to the /usr/examples/cfgmgr/sample_app.c file.

The subsystem status is included in an if statement and the body of the if statement is executed for error returns. If the subsystem status is equal to a system status defined in <sys/errno.h>, the message associated with that status is displayed. Otherwise, the unknown status message is displayed. If the subsystem defines its own error codes, those error codes should be included. Note that the absolute value of a subsystem error must be less than 2^15-1 or 32767.  


Commands: cfgmgr(8), sysconfig(8)

Routines: cfg_connect(3), cfg_disconnect(3), cfg_subsys_config(3), cfg_subsys_defaults(3), cfg_subsys_defaults_all(3), cfg_subsys_list(3), cfg_subsys_op(3), cfg_subsys_query(3), cfg_subsys_query_all(3), cfg_subsys_reconfig(3), cfg_subsys_state(3), cfg_subsys_unconfig(3), knlist(3)

Files: sysconfigtab(4)

Programmer's Guide
Writing Device Drivers: Tutorial delim off delim off



Routines in the Configuration Management Library
Sending and Receiving Subsystem Attribute Data
Handling Error Return Values

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Time: 02:42:16 GMT, October 02, 2010