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@c  COPYRIGHT (c) 1988-2002.

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@c  eventlog.t,v 1.27 2002/01/17 21:47:45 joel Exp

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@chapter Event Logging Manager

@section Introduction

The event logging manager provides a portable method for logging

system and application events and subsequent processing of those

events.  The capabilities in this manager were defined in the POSIX

1003.1h/D3 proposed standard titled @b{Services for Reliable,

Available, and Serviceable Systems}.

The directives provided by the event logging manager are:

@itemize @bullet

@item @code{log_create} - Create a log file

@item @code{log_sys_create} - Create a system log file

@item @code{log_write} - Write to the system Log

@item @code{log_write_any} - Write to any log file

@item @code{log_write_entry} - Write entry to any log file

@item @code{log_open} - Open a log file

@item @code{log_read} - Read from a log file

@item @code{log_notify} - Notify Process of writes to the system log

@item @code{log_close} - Close log descriptor

@item @code{log_seek} - Reposition log file offset

@item @code{log_severity_before} - Compare event record severities

@item @code{log_facilityemptyset} - Manipulate log facility sets

@item @code{log_facilityfillset} - Manipulate log facility sets

@item @code{log_facilityaddset} - Manipulate log facility sets

@item @code{log_facilitydelset} - Manipulate log facility sets

@item @code{log_facilityismember} - Manipulate log facility sets

@item @code{log_facilityisvalid} - Manipulate log facility sets

@end itemize

@section Background

@subsection Log Files and Events

The operating system uses a special log file named @code{syslog}.

This log file is called the system log and is automatically created and

tracked by the operating system.  The system log is written with

the @code{log_write()} function.  An alternative log file may be written

using the @code{log_write_any()} function.  It is possible to use @code{log_read()}

to query the system log and and write the records to a non-system log file

using @code{log_write_entry()} to produce a filtered version of the

system log.  For example you could produce a log of all disk controller

faults that have occurred.

A non-system log may be a special log file created by an application to

describe application faults, or a subset of the system log created

by the application.

@subsection Facilities

A facility is an identification code for a subsystem, device, or

other object about which information is being written to

a log file.

A facility set is a collection of facilities.

@subsection Severity

Severity is a rating of the error that is being logged.

@subsection Queries

The facility identifier and the event severity are the basis for

subsequent log query.  A log query is used as a filter to

obtain a subset of a given log file.  The log file may be configured

to send out an event.

@section Operations

@subsection Creating and Writing a non-System Log

The following code fragment create a non-System log file at /temp/.

A real filename previously read entry and buffer @code{log_buf} of size

@code{readsize} are written into the log.  See the discussion on opening

and reading a log for how the entry is created.

@example

#include 

   :

  logd_t           *outlog = NULL;

  char             *path   = "/temp/";

  log_create( outlog, path );

   :

  log_write_entry( outlog, &entry, log_buf, readsize );

@end example

@subsection Reading a Log

Discuss opening and reading from a log.

@example

  build a query

  log_open

  log_read loop

@end example

@section Directives

This section details the event logging manager's directives.

A subsection is dedicated to each of this manager's directives

and describes the calling sequence, related constants, usage,

and status codes.

@page

@subsection log_write - Write to the system Log

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_write(

  const log_facility_t  facility,

  const int             event_id,

  const log_severity_t  severity,

  const void           *buf,

  const size_t          len

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_write()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item E2BIG

This error indicates an inconsistency in the implementation.

Report this as a bug.

@item EINVAL

The @code{facility} argument is not a valid log facility.

@item EINVAL

The @code{severity} argument exceeds @code{LOG_SEVERITY_MAX}.

@item EINVAL

The @code{len} argument exceeds @code{LOG_MAXIUM_BUFFER_SIZE}.

@item EINVAL

The @code{len} argument was non-zero and @code{buf} is @code{NULL}.

@item ENOSPC

The device which contains the log file has run out of space.

@item EIO

An I/O error occurred in writing to the log file.

@end table

@subheading DESCRIPTION:

The @code{log_write} function writes an event record to the

system log file.  The event record written consists of the

event attributes specified by the @code{facility}, @code{event_id},

and @code{severity} arguments as well as the data identified by the

@code{buf} and @code{len} arguments.  The fields of the event record

structure to be written are filled in as follows:

@table @b

@item log_recid

This is set to a monotonically increasing log record id

maintained by the system for this individual log file.

@item log_size

This is set to the value of the @code{len} argument.

@item log_event_id

This is set to the value of the @code{event_id} argument.

@item log_facility

This is set to the value of the @code{facility} argument.

@item log_severity

This is set to the value of the @code{severity} argument.

@item log_uid

This is set to the value returned by @code{geteuid()}.

@item log_gid

This is set to the value returned by @code{getegid()}.

@item log_pid

This is set to the value returned by @code{getpid()}.

@item log_pgrp

This is set to the value returned by @code{getpgrp()}.

@item log_time

This is set to the value returned by @code{clock_gettime()} for the

@code{CLOCK_REALTIME clock} source.

@end table

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

This implementation can not return the @code{EPERM} error.

@page

@subsection log_write_any - Write to the any log file

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_write_any(

  const logd_t          logdes,

  const log_facility_t  facility,

  const int             event_id,

  const log_severity_t  severity,

  const void           *buf,

  const size_t          len

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_write_any()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item E2BIG

This error indicates an inconsistency in the implementation.

Report this as a bug.

@item EBADF

The @code{logdes} argument is not a valid log descriptor.

@item EINVAL

The @code{facility} argument is not a valid log facility.

@item EINVAL

The @code{severity} argument exceeds @code{LOG_SEVERITY_MAX}.

@item EINVAL

The @code{len} argument exceeds @code{LOG_MAXIMUM_BUFFER_SIZE}.

@item EINVAL

The @code{len} argument was non-zero and @code{buf} is @code{NULL}.

@item ENOSPC

The device which contains the log file has run out of space.

@item EIO

An I/O error occurred in writing to the log file.

@end table

@subheading DESCRIPTION:

The @code{log_write_any()} function writes an event record to the log file

specified by @code{logdes}.  The event record written consists of the

event attributes specified by the @code{facility}, @code{event_id},

and @code{severity} arguments as well as the data identified by the

@code{buf} and @code{len} arguments.  The fields of the event record

structure to be written are filled in as follows:

@table @b

@item log_recid

This is set to a monotonically increasing log record id

maintained by the system for this individual log file.

@item log_size

This is set to the value of the @code{len} argument.

@item log_event_id

This is set to the value of the @code{event_id} argument.

@item log_facility

This is set to the value of the @code{facility} argument.

@item log_severity

This is set to the value of the @code{severity} argument.

@item log_uid

This is set to the value returned by @code{geteuid()}.

@item log_gid

This is set to the value returned by @code{getegid()}.

@item log_pid

This is set to the value returned by @code{getpid()}.

@item log_pgrp

This is set to the value returned by @code{getpgrp()}.

@item log_time

This is set to the value returned by @code{clock_gettime()} for the

@code{CLOCK_REALTIME} clock source.

@end table

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

This implementation can not return the @code{EPERM} error.

This function is not defined in the POSIX specification.  It is

an extension provided by this implementation.

@page

@subsection log_write_entry - Write entry to any log file

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_write_entry(

  const logd_t      logdes,

  struct log_entry *entry,

  const void       *buf,

  const size_t      len

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_write_entry()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item E2BIG

This error indicates an inconsistency in the implementation.

Report this as a bug.

@item EBADF

The @code{logdes} argument is not a valid log descriptor.

@item EFAULT

The @code{entry} argument is not a valid pointer to a log entry.

@item EINVAL

The @code{facility} field in @code{entry} is not a valid log facility.

@item EINVAL

The @code{severity} field in @code{entry} exceeds @code{LOG_SEVERITY_MAX}.

@item EINVAL

The @code{len} argument exceeds @code{LOG_MAXIMUM_BUFFER_SIZE}.

@item EINVAL

The @code{len} argument was non-zero and @code{buf} is NULL.

@item ENOSPC

The device which contains the log file has run out of space.

@item EIO

An I/O error occurred in writing to the log file.

@end table

@subheading DESCRIPTION:

The @code{log_write_entry()} function writes an event record

specified by the @code{entry}, @code{buf}, and @code{len} arguments.

Most of the fields of the event record pointed to by @code{entry}

are left intact.  The following fields are filled in as follows:

@table @b

@item log_recid

This is set to a monotonically increasing log record id

maintained by the system for this individual log file.

@item log_size

This is set to the value of the @code{len} argument.

@end table

This allows existing log entries from one log file to be written to

another log file without destroying the logged information.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

This implementation can not return the @code{EPERM} error.

This function is not defined in the POSIX specification.  It is

an extension provided by this implementation.

@page

@subsection log_open - Open a log file

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_open(

  logd_t               *logdes,

  const char           *path,

  const log_query_t    *query

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_open()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item EACCES

Search permission is denied on a component of the @code{path} prefix,

or the log file exists and read permission is denied.

@item  EINTR

A signal interrupted the call to @code{log_open()}.

@item EINVAL

The log_severity field of the query argument exceeds

@code{LOG_SEVERITY_MAX}.

@item EINVAL

The @code{path} argument referred to a file that was not a log file.

@item EMFILE

Too many log file descriptors are currently in use by this

process.

@item ENAMETOOLONG

The length of the path string exceeds @code{PATH_MAX}, or a pathname

component is longer than @code{NAME_MAX} while @code{_POSIX_NO_TRUNC} is

in effect.

@item ENFILE

Too many files are currently open in the system.

@item ENOENT

The file specified by the @code{path} argument does not exist.

@item ENOTDIR

A component of the @code{path} prefix is not a directory.

@end table

@subheading DESCRIPTION:

The @code{log_open()} function establishes the connection between a

log file and a log file descriptor.  It creates an open log file

descriptor that refers to this query stream on the specified log file

The log file descriptor is used by the other log functions to refer

to that log query stream.  The @code{path} argument points to a

pathname for a log file.  A @code{path} argument of @code{NULL} specifies

the current system log file.

The @code{query} argument is not @code{NULL}, then it points to a log query

specification that is used to filter the records in the log file on

subsequent @code{log_read()} operations.  This restricts the set of

event records read using the returned log file descriptor to those

which match the query.  A query match occurs for a given record when

that record's facility is a member of the query's facility set and

the record's severity is greater than or equal to the severity specified

in the query.

If the value of the @code{query} argument is @code{NULL}, no query filter

shall be applied.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

POSIX specifies that @code{EINVAL} will be returned if the

@code{log_facilities} field of the @code{query} argument is not

a valid facility set.  In this implementation, this condition

can never occur.

Many error codes that POSIX specifies to be returned by @code{log_open()}

should actually be detected by @code{open()} and passed back by the

@code{log_open()} implementation.  In this implementation, @code{EACCESS},

@code{EMFILE}, @code{ENAMETOOLONG}, @code{ENFILE}, @code{ENOENT},

and @code{ENOTDIR} are detected in this manner.

@page

@subsection log_read - Read from a log file

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_read(

  const logd_t      logdes,

  struct log_entry *entry,

  void             *log_buf,

  const size_t      log_len,

  const size_t     *log_sizeread

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_read()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item E2BIG

This error indicates an inconsistency in the implementation.

Report this as a bug.

@item EBADF

The @code{logdes} argument is not a valid log file descriptor.

@item EFAULT

The @code{entry} argument is not a valid pointer to a log entry structure.

@item EFAULT

The @code{log_sizeread} argument is not a valid pointer to a size_t.

@item EBUSY

No data available.  There are no unread event records remaining

in this log file.

@item EINTR

A signal interrupted the call to @code{log_read()}.

@item EIO

An I/O error occurred in reading from the event log.

@item EINVAL

The matching event record has data associated with it and

@code{log_buf} was not a valid pointer.

@item EINVAL

The matching event record has data associated with it which is

longer than @code{log_len}.

@end table

@subheading DESCRIPTION:

The @code{log_read()} function reads the @code{log_entry}

structure and up to @code{log_len} bytes of data from the next

event record of the log file associated with the open log file

descriptor @code{logdes}.  The event record read is placed

into the @code{log_entry} structure pointed to by

@code{entry} and any data into the buffer pointed to by @code{log_buf}.

The log record ID of the returned event record is be stored in the

@code{log_recid} member of the @code{log_entry} structure for the event

record.

If the query attribute of the open log file description associated with

the @code{logdes} is set, the event record read will match that query.

If the @code{log_read()} is successful the call stores the actual length

of the data associated with the event record into the location specified by

@code{log_sizeread}.  This number will be less than or equal to

@code{log_len}.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

When @code{EINVAL} is returned, then no data is returned although the

event record is returned.  This is an extension to the POSIX specification.

The POSIX specification specifically allows @code{log_read()} to write

greater than @code{log_len} bytes into @code{log_buf}.  This is highly

undesirable and this implementation will NOT do this.

@page

@subsection log_notify - Notify Process of writes to the system log.

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_notify(

  const logd_t           logdes,

  const struct sigevent *notification

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_notify()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item EBADF

The logdes argument is not a valid log file descriptor.

@item EINVAL

The notification argument specifies an invalid signal.

@item EINVAL

The process has requested a notify on a log that will not be

written to.

@item ENOSYS

The function @code{log_notify()} is not supported by this implementation.

@end table

@subheading DESCRIPTION:

If the argument @code{notification} is not @code{NULL} this function registers

the calling process to be notified of event records received by the system

log, which match the query parameters associated with the open log descriptor

specified by @code{logdes}.  The notification specified by the

@code{notification} argument shall be sent to the process when an event

record received by the system log is matched by the query attribute of the

open log file description associated with the @code{logdes} log file

descriptor.  If the calling process has already registered a notification

for the @code{logdes} log file descriptor, the new notification shall

replace the existing notification registration.

If the @code{notification} argument is @code{NULL} and the calling process is

currently registered to be notified for the @code{logdes} log file

descriptor, the existing registration shall be removed.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

@page

@subsection log_close - Close log descriptor

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_close(

  const logd_t   logdes

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_close()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item EBADF

The logdes argument is not a valid log file descriptor.

@end table

@subheading DESCRIPTION:

The @code{log_close()} function deallocates the open log file descriptor

indicated by @code{log_des}.

When all log file descriptors associated with an open log file description

have been closed, the open log file description is freed.

If the link count of the log file is zero, when all log file descriptors

have been closed, the space occupied by the log file is freed and the

log file shall no longer be accessible.

If the process has successfully registered a notification request for the

log file descriptor, the registration is removed.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

@page

@subsection log_seek - Reposition log file offset

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_seek(

  const logd_t    logdes,

  log_recid_t     log_recid

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_seek()} returns a value of zero

and an unsuccessful call returns the @code{errno}.

@table @b

@item EBADF

The @code{logdes} argument is not a valid log file descriptor.

@item EINVAL

The @code{log_recid} argument is not a valid record id.

@end table

@subheading DESCRIPTION:

The @code{log_seek()} function sets the log file offset of the open

log description associated with the @code{logdes} log file descriptor

to the event record in the log file identified by @code{log_recid}.

The @code{log_recid} argument is either the record id of a valid event

record or one of the following values, as defined in the header file

@code{:}

@table @b

@item LOG_SEEK_START

Set log file position to point at the first event

record in the log file.

@item LOG_SEEK_END

Set log file position to point after the last event

record in the log file.

@end table

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

This implementation can not return EINTR.

This implementation can not return EINVAL to indicate that

the @code{log_recid} argument is not a valid record id.

@page

@subsection log_severity_before - Compare event record severities

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_severity_before(

  log_severity_t  s1,

  log_severity_t  s2

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

@table @b

@item 0

The severity of @code{s1} is less than that of @code{s2}.

@item 1

The severity of @code{s1} is greater than or equal that of @code{s2}.

@item EINVAL

The value of either s1 or s2 exceeds @code{LOG_SEVERITY_MAX}.

@end table

@subheading DESCRIPTION:

The @code{log_severity_before()} function compares the severity order

of the @code{s1} and @code{s2} arguments.  If @code{s1} is of

severity greater than or equal to that of @code{s2}, then this

function returns 1.  Otherwise, it returns 0.

If either @code{s1} or @code{s2} specify invalid severity values, the

return value of @code{log_severity_before()} is unspecified.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

The POSIX specification of the return value for this function is ambiguous.

If EINVAL is equal to 1 in an implementation, then the application

can not distinguish between greater than and an error condition.

@page

@subsection log_facilityemptyset - Manipulate log facility sets

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_facilityemptyset(

  log_facility_set_t  *set

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_facilityemptyset()} returns a value of zero

and a unsuccessful call returns the @code{errno}.

@table @b

@item EFAULT

The @code{set} argument is an invalid pointer.

@end table

@subheading DESCRIPTION:

The @code{log_facilityemptyset()} function initializes the facility

set pointed to by the argument @code{set}, such that all facilities

are excluded.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

Applications shall call either @code{log_facilityemptyset()} or

@code{log_facilityfillset()} at least once for each object of type

@code{log_facilityset_t} prior to any other use of that object.  If

such an object is not initialized in this way, but is nonetheless

supplied as an argument to any of the @code{log_facilityaddset()},

@code{logfacilitydelset()}, @code{log_facilityismember()} or

@code{log_open()} functions, the results are undefined.

@page

@subsection log_facilityfillset - Manipulate log facility sets

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include 

int log_facilityfillset(

  log_facility_set_t  *set

);

@end example

@end ifset

@ifset is-Ada

@end ifset

@subheading STATUS CODES:

A successful call to @code{log_facilityfillset()} returns a value of zero

and a unsuccessful call returns the @code{errno}.

@table @b

@item EFAULT

The @code{set} argument is an invalid pointer.

@end table

@subheading DESCRIPTION:

The @code{log_facilityfillset()} function initializes the facility

set pointed to by the argument @code{set}, such that all facilities

are included.

@subheading NOTES:

The @code{_POSIX_LOGGING} feature flag is defined to indicate

this service is available.

Applications shall call either @code{log_facilityemptyset()} or

@code{log_facilityfillset()} at least once for each object of type

@code{log_facilityset_t} prior to any other use of that object.  If

such an object is not initialized in this way, but is nonetheless

supplied as an argument to any of the @code{log_facilityaddset()},

@code{logfacilitydelset()}, @code{log_facilityismember()} or

@code{log_open()} functions, the results are undefined.

@page

@subsection log_facilityaddset - Manipulate log facility sets

@subheading CALLING SEQUENCE:

@ifset is-C

@example

#include