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libcfg(3)
NAME
libcfg - introduction to the Configuration Management Library
DESCRIPTION
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 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.
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)();
}str;
struct {
caddr_t val;
ulong min_size;
ulong max_size;
void (*disposal)();
ulong val_size;
}bin;
struct {
ulong val;
ulong min_val;
ulong max_val;
}num;
}attr;
}cfg_attr_t;
The following list describes the elements of the cfg_attr_t data type:
· 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 Name Description
________________________________________________________
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 Code Meaning
_________________________________________________________
CFG_ATTR_EEXISTS Attribute does not exist
CFG_ATTR_EINDEX Invalid attribute index
CFG_ATTR_ELARGE
Attribute value or size is too
large
CFG_ATTR_EMEM
No memory available for the
attribute
CFG_ATTR_EOP
Attribute does not support the
requested operation
CFG_ATTR_ESMALL
Attribute 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_SUCCESS Successful operation
CFG_ATTR_ENOTNUMBER
Attribute value cannot be converted
to a number
_________________________________________________________
· The operation field contains one of the operation codes listed in the
following table:
__________________________________________________________
Request Code Meaning
__________________________________________________________
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:
break;
case CFG_FRAME_EEXISTS:
printf("framework error: subsystem not loaded/found\n");
break
.
.
.
case CFG_FRAM_EATTRLIST:
printf("framework error: bad attribute list\n");
break;
default:
printf("framework error: unknown %d\n" \
CFG_STATUS_FRAME(status))
break;
}
/****************************************************************/
/* 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"
,sys_errlist[subsys_status]);
else
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.
SEE ALSO
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
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