LLOG(3)

NAME
llog - library logging package

SYNOPSIS
ll_open  (loginfo)
    struct ll_struct *loginfo;
ll_hdinit (loginfo, pref)
    struct ll_struct *loginfo;
    char *pref;
ll_init  (lloginfo)
    struct ll_struct *loginfo;
ll_log   (loginfo, verbosity, printf args...)
    struct ll_struct *loginfo;
    char verbosity;
ll_err   (loginfo, verbosity, printf args...)
    char verbosity;
    struct ll_struct *loginfo;
ll_close (loginfo)
    struct ll_struct *loginfo;
struct  ll_struct
{
 char *ll_file;  /* path name to logging file        */
 char *ll_hdr;   /* text to put in opening line      */
 char  ll_level; /* max verbosity level              */
	LLOGFAT  /* Fatal error                      */
	LLOGTMP  /* Temporary (minor?) error         */
	LLOGGEN  /* General information              */
	LLOGBST  /* Basic statistics                 */
	LLOGFST  /* Full statistics                  */
	LLOGPTR  /* Trace of program phases          */
	LLOGBTR  /* Trace of more basic activities   */
	LLOGFTR  /* Full program trace               */
	LLOGMAX  /* Maximum possible value           */
 char  ll_msize; /* max log size, in 100's of blocks */
 char  ll_stat;  /* assorted switches                */
	LLOGCLS  /* Close after each write           */
	LLOGCYC  /* Cycle to beginning when log full */
	LLOGWAT  /* Wait, if log locked and LLOGCLS  */
	LLOGSOME /* CLS and WAT */
	LLOGTIMED /* Reopen periodically */
 char  ll_fd;    /* * CHAR * holds file descriptor   */
 int   ll_timmax;	/* how long can fd be in use before reopen? */
 time_t ll_timer;	/* time of last open of log file */
 FILE *ll_fp;		/* Standard IO stream pointer       */
};

DESCRIPTION

This package is intended to perform standardized information logging for programs. The time of an entry is recorded in addition to its text.

  Format of Entries

Depending on the mode of logging (whether the log is left open between ll_log() calls or is re-opened to make each entry, as indicated by the LLOGCLS flag) the date, hour and loginfo.llhdr string are recorded on a header line when the log is opened (if LLOGCLS and LLOGTIMED are off) or on the logging line (if LLOGCLS is on). In addition, the current minute and second are recorded, followed by the actual log text. Each log entry is started on a new line. The text of the entry is entered with a printf(), called with parameters passed to the ll_log() function.

  Access to Log Files

Multiple logs can be accessed simultaneously by the same process, since all of the state information for a single log is kept in the user-maintained structure, llogstruct, which is included as a parameter when calling llog functions. While opened by one process, a single log cannot be shared with another process, since logging files are opened with exclusive access (the specific locking mechanism depends on the version of Unix you are running). The LLOGCLS flag is intended to help circumvent this protection. Also, the LLOGWAT flag may be used to cause ll_open() to repeatedly retry opening the log, if the failure to open it was due to its being used by another process. Ll_open() will try up to five times, waiting five seconds between tries; after that, it will return. The failure is treated as temporary if LLOGCLS is used (implying infrequent logging expected); otherwise the failure is treated as permanent. In either case, the log is marked as "broken" and no further attempts are made to use it until either ll_close() or ll_open() is called. Exclusive opening of the log file is not currently used. As a result, the LLOGWAT flag does not have any effect. Exclusive opening could be re-added but seeking to the end of the log and flushing after writes works most of the time.

  Limiting Size of Log Files

The package can impose a size limit to log files. If lloginfo.llmsize is zero, size-limiting is NOT imposed, otherwise llog will not allow a log to grow larger (25 * lloginfo.llmsize) blocks. If the log is being held open between entries and cycling is allowed (i.e., LLOGCYC is set and LLOGCLS is not) then when ll_init() is called (by ll_open() or by the user) during successive uses, entries will be made starting from the beginning of the file. If the LLOGCLS bit is set or if the LLOGCYC bit is not set, then the log is marked as unusable. Ll_open() attempts to open the logging file. It returns the return value from its open() call. It does NOT attempt to create the file if the file does not exist. The result of the open() call is placed in the ll_fd member of the logstruct structure. The using program should ensure that ll_fd initially has the value zero. Ll_log() will simply return, if ll_fd is -1; therefore the caller can ignore failures to open the log. Also, the existence of the logging file can be used as a convenient external switch for turning logging on and off. Entries are appended to the end of any old entries in the file, except when cycling occurs. If the LLOGCLS bit is set in the loginfo.ll_stat field, then the file is opened only long enough to make an entry; this makes it more reasonable for multiple processes to share a log into which relatively few entries are made, such as when only error messages are recorded. Ll_init() is to be used when the logging file is already opened (e.g., when the file descriptor has been inherited from a parent process) instead of calling ll_open(). Ll_log() actually makes the log entries. If the log is not already opened and loginfo.ll_fd is 0, ll_log() will call ll_open(). (Note that this means that the calling program usually does not need to call ll_open(), unless there is a concern about locking the file.) The ll_level value indicates how much logging the caller desires. When called, ll_log() will not make the log entry if the value of the verbosity argument is GREATER than than the value of ll_level. This allows, for example, distinction between mandatory and debugging information, with many levels of (256) information possible. As a guide, the list shown in the synopsis can be used. Ll_log() uses printf() to make the entries. There is a limit of ten (10) arguments that may be passed to it. The third argument to ll_log() becomes the first argument to printf(). Flush() is then called so that the log is always up-to-date; this is deemed more important than fully minimizing write calls, and in any event, is required to allow ll_log() to use the printf() mechanism in a way that does not interfere with its use elsewhere in the process. Ll_close() closes the logging file and marks ll_fd as clear (i.e., resets it to be zero). Note that this normally need not be called, since the file will automatically be closed when the process exits. However, it is necessary to close the log, during execution, if a child or some other process is expected to open the same log independently. Calling ll_close() also always clears the file descriptor, making it possible for a new try at opening the log, if it failed previously.

DIAGNOSTICS

Ll_open() returns the value of its open call, if that fails; otherwise it returns the value of its call to ll_init(). Ll_log() returns the value of its flush() call, or zero if ll_fd is -1; if flush() returns less than zero, then ll_log() closes the log and returns NOTOK. Ll_close() returns the value of its close() call.

AUTHOR

Dave Crocker
    Dept. of E.E., Univ. of Delaware