path: root/doc/reference.texi

@node Reference Manual, , White Paper, Top
@chapter LibGTop Reference Manual

@menu
* System Dependent::            System Dependent Functions.
* Common Functions::            Common Functions.
* Library Functions::           Library Functions.
@end menu

@node System Dependent, Common Functions, Reference Manual, Reference Manual
@section System Dependent Functions

@menu
* glibtop_cpu::                 CPU Usage.
* glibtop_mem::                 Memory Usage.
* glibtop_swap::                Swap Usage.
* glibtop_uptime::              System Uptime.
* glibtop_loadavg::             Load Average.
* glibtop_proclist::            Process List.
* glibtop_proc_state::          Process State.
* glibtop_proc_uid::            Process UID and TTY Information.
* glibtop_proc_mem::            Process Memory Information.
* glibtop_proc_time::           Process Time Information.
* glibtop_proc_signal::         Process Signal Information.
* glibtop_proc_kernel::         Process Kernel Data Information.
* glibtop_proc_segment::        Process Segment Information.
* glibtop_proc_args::           Process Arguments.
* glibtop_proc_map::            Process Memory Maps.
* glibtop_netload::             Network Load.
* glibtop_ppp::                 PPP Usage.
* glibtop_disk::                DISK Usage.
@end menu

@node glibtop_cpu, glibtop_mem, System Dependent, System Dependent
@subsection CPU Usage

Library function @code{glibtop_get_cpu}:

@example
@cartouche
void glibtop_get_cpu (glibtop_cpu *buf);
void glibtop_get_cpu_l (glibtop *server, glibtop_cpu *buf);
@end cartouche
@end example

Declaration of @code{glibtop_cpu} in @file{<glibtop/cpu.h>}:

@example
@cartouche
typedef struct _glibtop_cpu     glibtop_cpu;

struct _glibtop_cpu
@{
    guint64   flags,
        total,
        user,
        nice,
        sys,
        idle,
        iowait,
        irq,
        softirq,
        frequency,
        xcpu_total [GLIBTOP_NCPU],
        xcpu_user [GLIBTOP_NCPU],
        xcpu_nice [GLIBTOP_NCPU],
        xcpu_sys  [GLIBTOP_NCPU],
        xcpu_idle [GLIBTOP_NCPU],
        xcpu_iowait [GLIBTOP_NCPU],
        xcpu_irq [GLIBTOP_NCPU],
        xcpu_softirq [GLIBTOP_NCPU],
        xcpu_flags;
@};
@end cartouche
@end example

All CPU units are measured in @dfn{jiffies} which are normally 1/100th of a
second (in which case @code{frequency} equals 100), but can also be in any
other unit. To get seconds, divide them by @code{frequency}.

@table @code
@item total
Number of clock ticks since system boot.

@item user
Number of clock ticks the system spent in user mode.

@item nice
Number of clock ticks the system spent in user mode (nice).

@item sys
Number of clock ticks the system spent in system mode.

@item idle
Number of clock ticks the system spent in the idle task.

@item iowait
Number of clock ticks the system spent waiting for I/O to complete.

@item irq
Number of clock ticks the system spent servicing interrupts.

@item softirq
Number of clock ticks the system spent servicing softirqs.

@item frequency
Tick frequency (default is 100).

@end table

The @samp{xcpu_} values are for SMP systems - they are the same than
@code{total}, @code{user}, @code{nice}, @code{sys}, @code{idle},
@code{iowait}, @code{irq} and @code{softirq}
except that they are arrays of @code{GLIBTOP_NCPU} (defined in
@file{<glibtop/cpu.h>}) elements and contain one value for each CPU
in the system.

@table @code
@item xcpu_flags
This is interpreted as a bit-field: on systems like Solaris, not all CPUs
need to be running all the time, so we set the corresponding bit for each
CPU that is currently running.
@end table

Please note that all of the cpu values are absolute values measured in
certain units (to get seconds, divide them by @code{frequency}) since system
boot. To get percentual values, you need to call @code{glibtop_cpu}, save the
result, wait some time and then call it again and divide the differences of
the two values by the time you have waited.

@page
@node glibtop_mem, glibtop_swap, glibtop_cpu, System Dependent
@subsection Memory Usage

Library function @code{glibtop_get_mem}:

@example
@cartouche
void glibtop_get_mem (glibtop_mem *buf);
void glibtop_get_mem_l (glibtop *server, glibtop_mem *buf);
@end cartouche
@end example

Declaration of @code{glibtop_mem} in @file{<glibtop/mem.h>}:

@example
@cartouche
typedef struct _glibtop_mem     glibtop_mem;

struct _glibtop_mem
@{
    guint64   flags,
        total,
        used,
        free,
        shared,
        buffer,
        cached,
        user,
        locked;
@};
@end cartouche
@end example

Unless explicitly stated otherwise, all memory units are in bytes.

@table @code
@item total
Total physical memory.

@item used
Used memory size.

@item free
Free memory size.

@item shared
Shared memory size.

This are both segments that are @code{mmap()}ed with @code{MAP_SHARED} and
IPC Shared Memory segments.

@item buffer
Size of buffers.

@item cached
Size of cached memory.

@item user
Memory used from user processes.

This is normally @code{total - free - shared - buffer - cached}.

@item locked
Memory in locked segments.

@end table

@page
@node glibtop_swap, glibtop_uptime, glibtop_mem, System Dependent
@subsection Swap Usage

Library function @code{glibtop_get_swap}:

@example
@cartouche
void glibtop_get_swap (glibtop_swap *buf);
void glibtop_get_swap_l (glibtop *server, glibtop_swap *buf);
@end cartouche
@end example

Declaration of @code{glibtop_swap} in @file{<glibtop/swap.h>}:

@example
@cartouche
typedef struct _glibtop_swap    glibtop_swap;

struct _glibtop_swap
@{
    guint64   flags,
        total,
        used,
        free,
        pagein,
        pageout;
@};
@end cartouche
@end example

The following units are in bytes.

@table @code
@item total
Total swap space in the system.

@item used
Used swap space.

@item free
Free swap space.
@end table

You can use @code{pagein} and @code{pageout} to get some measure about how
much the system is swapping at the moment. They're increased each time a page
is swapped in or out, so you need to save this values, wait a little bit, get
them again and then compare the two results to find out how much the system
swapped in the meantime.

@table @code
@item pagein
Total number of swap pages that have been brought in since system boot

@item pageout
Total number of swap pages that have been brought out since system boot

@end table

@page
@node glibtop_uptime, glibtop_loadavg, glibtop_swap, System Dependent
@subsection Uptime

Library function @code{glibtop_get_uptime}:

@example
@cartouche
void glibtop_get_uptime (glibtop_uptime *buf);
void glibtop_get_uptime_l (glibtop *server, glibtop_uptime *buf);
@end cartouche
@end example

Declaration of @code{glibtop_uptime} in @file{<glibtop/uptime.h>}:

@example
@cartouche
typedef struct _glibtop_uptime  glibtop_uptime;

struct _glibtop_uptime
@{
    guint64 flags;
    double uptime,
        idletime;
    guint64 boot_time;
@};
@end cartouche
@end example

When porting LibGTop to a new system, you only need to implement @code{uptime}
and @code{idletime} if there's a faster or better way to obtain them as using
@code{glibtop_cpu} for it. Look at @file{sysdeps/freebsd/uptime.c} for an
example on how to obtain them using @code{glibtop_cpu}.

@table @code
@item uptime
Time in seconds since system boot.

@item idletime
Time in seconds the system spent in the idle task since system boot.
@end table

The following one was from a request on the @samp{linux-kernel} mailing list;
on a laptop with advanced power management @code{glibtop_cpu.total} may not
reflect the correct boot time of the system if the power was turned off by
means of APM in the meantime.

@table @code
@item boot_time
Time of last system boot in seconds since the epoch.
@end table

@page
@node glibtop_loadavg, glibtop_proclist, glibtop_uptime, System Dependent
@subsection Load Average

Library function @code{glibtop_get_loadavg}:

@example
@cartouche
void glibtop_get_loadavg (glibtop_loadavg *buf);
void glibtop_get_loadavg_l (glibtop *server, glibtop_loadavg *buf);
@end cartouche
@end example

Declaration of @code{glibtop_loadavg} in @file{<glibtop/loadavg.h>}:

@example
@cartouche
typedef struct _glibtop_loadavg glibtop_loadavg;

struct _glibtop_loadavg
@{
    guint64 flags;
    double loadavg [3];
    guint64 nr_running,
        nr_tasks,
        last_pid;
@};
@end cartouche
@end example

@table @code
@item loadavg

Number of jobs running simultaneously averaged over 1, 5 and 15 minutes.

@end table

The following fields are Linux specific and deprecated. You don't need to
implement them when porting LibGTop to a new system as they may be removed
in a future version.

@table @code
@item nr_running
Number of tasks currently running.

@item nr_tasks
Total number of tasks.

@item last_pid
Last PID.
@end table

@page
@node glibtop_proclist, glibtop_proc_state, glibtop_loadavg, System Dependent
@subsection Process List

Library function @code{glibtop_get_proclist}:

@example
@cartouche
unsigned *
glibtop_get_proclist (glibtop_proclist *buf,
                      gint64 which, gint64 arg);

unsigned *
glibtop_get_proclist_l (glibtop *server, glibtop_proclist *buf,
                        gint64 which, gint64 arg);
@end cartouche
@end example

Constants for the @code{which} argument:

@example
@cartouche
#define GLIBTOP_KERN_PROC_ALL           0
#define GLIBTOP_KERN_PROC_PID           1
#define GLIBTOP_KERN_PROC_PGRP          2
#define GLIBTOP_KERN_PROC_SESSION       3
#define GLIBTOP_KERN_PROC_TTY           4
#define GLIBTOP_KERN_PROC_UID           5
#define GLIBTOP_KERN_PROC_RUID          6

#define GLIBTOP_KERN_PROC_MASK          15

#define GLIBTOP_EXCLUDE_IDLE            0x1000
#define GLIBTOP_EXCLUDE_SYSTEM          0x2000
#define GLIBTOP_EXCLUDE_NOTTY           0x4000
@end cartouche
@end example

Declaration of @code{glibtop_proclist} in @file{<glibtop/proclist.h>}:

@example
@cartouche
typedef struct _glibtop_proclist        glibtop_proclist;

struct _glibtop_proclist
@{
    guint64   flags,
        number,
        total,
        size;
@};
@end cartouche
@end example

This function returns a list of all or a selected subset of all running
processes. You can use the @code{which} and @code{arg} arguments to
specify which processes should be returned.

You can use the following values for the @code{which} argument:

@table @code
@item GLIBTOP_KERN_PROC_ALL
Return information about all processes (the @code{arg} argument is ignored).

@item GLIBTOP_KERN_PROC_PID
Return information about all process with the pid @var{PID} which is passed
in @code{arg}. You can use this to find out whether some process still exists.

@item GLIBTOP_KERN_PROC_PGRP
Return all processes in process group @var{PGRP} which is passed in
@code{arg}.

@item GLIBTOP_KERN_PROC_SESSION
Return all processes in session @var{SESSION} which is passed in @code{arg}.

@item GLIBTOP_KERN_PROC_TTY
Return all processes which have the controlling tty @var{TTY} which is passed
in @code{arg} (@var{TTY} is interpreted as device number).

@item GLIBTOP_KERN_PROC_UID
Return all processes with effective uid @var{UID} which is passed in @code{arg}.

@item GLIBTOP_KERN_PROC_RUID
Return all processes with real uid @var{RUID} which is passed in @code{arg}.

@end table

You can alter the list of returned processes by using a binary OR of
@code{which} and the following constants:

@table @code
@item GLIBTOP_EXCLUDE_IDLE
Exclude idle processes.
@item GLIBTOP_EXCLUDE_SYSTEM
Exclude system processes.
@item GLIBTOP_EXCLUDE_NOTTY
Exclude processes without a controlling terminal.
@end table

The return value of @code{glibtop_get_proclist} is either @code{NULL} on
error or a @code{unsigned *} list of pids. Additionally, the following fields
of @code{glibtop_proclist} are set:

@table @code
@item number
Number of entries in the returned list.

@item total
Total size of the returned list (this equals @code{number * size}).

@item size
Size of a single entry in the returned list
(this equals @code{sizeof (unsigned)}).
@end table

The returned list is allocated using @code{g_malloc} and must be freed
using @code{g_free} to avoid a memory leak.

@page
@node glibtop_proc_state, glibtop_proc_uid, glibtop_proclist, System Dependent
@subsection Process State

Library function @code{glibtop_get_proc_state}:

@example
@cartouche
void
glibtop_get_proc_state (glibtop_proc_state *buf, pid_t pid);

void
glibtop_get_proc_state_l (glibtop *server, glibtop_proc_state *buf,
                          pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_state} in @file{<glibtop/procstate.h>}:

@example
@cartouche
typedef struct _glibtop_proc_state      glibtop_proc_state;

struct _glibtop_proc_state
@{
    guint64 flags;
    char cmd[40];
@ifset LIBGTOP-1-1
    unsigned state;
@end ifset
@ifclear LIBGTOP-1-1
    char state;
@end ifclear
    int uid,
        gid,
        ruid,
        rgid;
    int has_cpu,
        processor,
        last_processor;

@};
@end cartouche
@end example

@table @code
@item cmd
Basename of the executable file in the call to @code{exec}.
@item state
@ifset LIBGTOP-1-1
Process state (see the constants defined below).
@end ifset
@ifclear LIBGTOP-1-1
Process state ('R' = running, 'S' = sleeping, 'D' = uninterruptible,
'Z' = zombie, 'T' = stopped, 'I' = idle).

This was changed to an @code{unsigned} bitfield in LibGTop 1.1.x where there
are also some constants for it.
@end ifclear
@end table

When porting LibGTop, please @emph{try hard} to implement the following
fields. For security reasons, it is @strong{very important} that you
@strong{only} set the @code{flags} bits for those fields if their
@strong{values are correct}.

@table @code
@item uid
Effective UID of the process.
@item gid
Effective GID of the process.
@item ruid
Real UID of the process.
@item rgid
Read GID of the process.
@end table

The following fields are for SMP systems:

@table @code
@item has_cpu
This is either 0 or 1 depending on whether the process currently has a CPU
or not.

@item processor
This is the processor id of the CPU this process is currently running on
(which can be used as index in the @samp{xcpu_} fields of @code{glibtop_cpu}
for instance; since zero is a valid processor id, you must check @code{has_cpu}
in this case to find out whether the process really has a CPU).

@item last_processor
The is the processor id of the CPU the process was last running on.
@end table

@ifset LIBGTOP-1-1
There are some constants for the @code{state} field:

@example
@cartouche
#define GLIBTOP_PROCESS_RUNNING                 1
#define GLIBTOP_PROCESS_INTERRUPTIBLE           2
#define GLIBTOP_PROCESS_UNINTERRUPTIBLE         4
#define GLIBTOP_PROCESS_ZOMBIE                  8
#define GLIBTOP_PROCESS_STOPPED                 16
#define GLIBTOP_PROCESS_SWAPPING                32
#define GLIBTOP_PROCESS_DEAD                    64
@end cartouche
@end example
@end ifset

@table @code
@item GLIBTOP_PROCESS_RUNNING
The process is currently running.
@item GLIBTOP_PROCESS_INTERRUPTIBLE
The process is currently in an interruptible sleep.
@item GLIBTOP_PROCESS_UNINTERRUPTIBLE
The process is currently in uninterruptible sleep
(the so-called @dfn{disk sleep}).
@item GLIBTOP_PROCESS_ZOMBIE
The process is a zombie.
@item GLIBTOP_PROCESS_STOPPED
The process is currently stopped (received @code{SIGSTOP}
or attached to a debugger).
@item GLIBTOP_PROCESS_SWAPPING
The process is currently swapping.
@end table

@page
@node glibtop_proc_uid, glibtop_proc_mem, glibtop_proc_state, System Dependent
@subsection Process UID and TTY information

Library function @code{glibtop_get_proc_uid}:

@example
@cartouche
void
glibtop_get_proc_uid (glibtop_proc_uid *buf, pid_t pid);

void
glibtop_get_proc_uid_l (glibtop *server, glibtop_proc_uid *buf,
                        pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_uid} in @file{<glibtop/procuid.h>}:

@example
@cartouche
typedef struct _glibtop_proc_uid        glibtop_proc_uid;

struct _glibtop_proc_uid
@{
    guint64 flags;
    int uid,
        euid,
        gid,
        egid,
        suid,
        sgid,
        fsuid,
        fsgid,
        pid,
        ppid,
        pgrp,
        session,
        tty,
        tpgid,
        priority,
        nice,
        ngroups,
        groups [GLIBTOP_MAX_GROUPS];
@};
@end cartouche
@end example

@table @code
@item uid
User ID
@item euid
Effective User ID
@item gid
Group ID
@item egid
Effective Group ID
@item pid
Process ID
@item ppid
PID of parent process
@item pgrp
Process group ID
@item session
Session ID
@item tty
Full device number of controlling terminal
@item tpgid
Terminal process group ID
@item priority
Kernel scheduling priority.
@item nice
Standard unix nice level of process.
@item ngroups
Number of additional process groups.
@item groups
Array of additional process groups@*
(@code{GLIBTOP_MAX_GROUPS} is defined in @file{<glibtop/procuid.h>}).
@end table

@page
@node glibtop_proc_mem, glibtop_proc_time, glibtop_proc_uid, System Dependent
@subsection Process Memory information

Library function @code{glibtop_get_proc_mem}:

@example
@cartouche
void
glibtop_get_proc_mem (glibtop_proc_mem *buf, pid_t pid);

void
glibtop_get_proc_mem_l (glibtop *server, glibtop_proc_mem *buf,
                        pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_mem} in @file{<glibtop/procmem.h>}:

@example
@cartouche
typedef struct _glibtop_proc_mem        glibtop_proc_mem;

struct _glibtop_proc_mem
@{
    guint64   flags,
        size,
        vsize,
        resident,
        share,
        rss,
        rss_rlim;
@};
@end cartouche
@end example

@table @code
@item size
Total number of pages of memory.
@item vsize
Number of pages of virtual memory.
@item resident
Number of residnet set (non-swapped) pages.
@item share
Number of pages of shared (mmap\'d) memory.
@item rss
Number of pages the process has in real memory, minus 3 for administrative
purposes.

This is just the pages which count towards text, data, or stack space.
This does not include pages which have not been demand-loaded in, or which
are swapped out.
@item rss_rlim
Current limit in bytes on the rss of the process (usually 2,147,483,647).
@end table

The description above is taken from the manual page of the @file{/proc}
filesystem under Linux and is a little bit confusing, so I make this clear
here. 

@strong{A word for people porting LibGTop to other systems:}
Every operating system has its own idea about the memory usage of a process
and also system utilities like @code{ps} show different things on different
systems.

Nevertheless, we should try to make LibGTop as system independent as possible,
so I give you some hints here how @code{glibtop_get_proc_mem} should work. 

@itemize @bullet
@item
When you use @code{mmap} with either @code{MAP_SHARED} or @code{MAP_PRIVATE},
this should only affect the @code{vsize} of the process and none of its
@code{size}, @code{resident}, @code{shared} and @code{rss} sizes.

@item
As soon as you read some of the @code{mmap()}ed pages, they will be demand-
oaded and thus count towards the @code{size} of the process.

Also - we assume there is enough free memory - they are resident in memory
until they get stolen or swapped out and thus increase the @code{resident} and
@code{rss} sizes of the process.

@item
If the process has used @code{MAP_SHARED} and another process attaches the
same file also @code{MAP_SHARED}, some of the pages are shared with this
process and thus increase the @code{shared} sizes of both processes.

@item
If the process has used @code{MAP_PRIVATE} and writes to the @code{mmap()}ed
pages, the only difference to reading from them is that they get dirty and
cannot be stolen any longer but will get swapped out.

@item
When memory gets rare, clean pages are normally stolen, which decreases the
@code{size}, @code{resident}, @code{shared} and @code{rss} sizes of the process.

@item
When dirty pages are swapped out, this will not decrease the @code{size} of the
process but only its @code{resident} and @code{rss} sizes (dirty pages cannot
be shared).

@item
The @code{vsize} of a process can @emph{only} be changed by the process
itself when it requests or frees memory but @emph{never} due to swapping
activity of the system.

@item
If the @code{shared} size changes, this @emph{only} means that the number of
pages that are currently shared with other processes has changed; if this
happens, this will @emph{never} affect any of the other sizes of the process.
@end itemize

The hints above describe how it works under Linux - but we should try to make
@code{glibtop_get_proc_mem} show the same behavior under every other system.

@page
@node glibtop_proc_time, glibtop_proc_signal, glibtop_proc_mem, System Dependent
@subsection Process Time information

Library function @code{glibtop_get_proc_time}:

@example
@cartouche
void
glibtop_get_proc_time (glibtop_proc_time *buf, pid_t pid);

void
glibtop_get_proc_time_l (glibtop *server, glibtop_proc_time *buf,
                         pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_time} in @file{<glibtop/proctime.h>}:

@example
@cartouche
typedef struct _glibtop_proc_time       glibtop_proc_time;

struct _glibtop_proc_time
@{
    guint64   flags,
        start_time,
        rtime,
        utime,
        stime,
        cutime,
        cstime,
        timeout,
        it_real_value,
        frequency,
        xcpu_utime [GLIBTOP_NCPU],
        xcpu_stime [GLIBTOP_NCPU],
        xcpu_flags;
@};
@end cartouche
@end example


@table @code
@item start_time
Start time of process in seconds since the epoch
@item rtime
Real time accumulated by process (should be @code{utime} + @code{stime})
@item utime
User-mode CPU time accumulated by process
@item stime
Kernel-mode CPU time accumulated by process
@item cutime
Cumulative utime of process and reaped children
@item cstime
Cumulative stime of process and reaped children
@item timeout
The time (in jiffies) of the process's next timeout
@item it_real_value
The time (in jiffies) before the next SIGALRM is sent to the process due
to an interval timer.
@item frequency
Tick frequency
@item xcpu_utime
SMP user-mode CPU time accumulated by process
@item xcpu_stime
SMP kernel-mode CPU time accumulated by process
@end table


Please note that under Linux, @code{start_time} value may be strange.
Linux kernel defines @code{INITIAL_JIFFIES} which implies a time
shift. Because @code{INITIAL_JIFFIES} is not user-space defined, we
cannot use it to compute accurate @code{start_time}. On Linux2.6,
@code{INITIAL_JIFFIES} is 300 so @code{start_time} is always 3s
different from real start time of the given process. You may also get
shift results if your system clock is not synchronised with your
hardware clock. See @samp{man hwclock}.



@page
@node glibtop_proc_signal, glibtop_proc_kernel, glibtop_proc_time, System Dependent
@subsection Process Signal information

Library function @code{glibtop_get_proc_signal}:

@example
@cartouche
void
glibtop_get_proc_signal (glibtop_proc_signal *buf, pid_t pid);

void
glibtop_get_proc_signal_l (glibtop *server, glibtop_proc_signal *buf,
                           pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_signal} in @file{<glibtop/procsignal.h>}:

@example
@cartouche
typedef struct _glibtop_proc_signal     glibtop_proc_signal;

struct _glibtop_proc_signal
@{
    guint64   flags,
        signal [2],
        blocked [2],
        sigignore [2],
        sigcatch [2];
@};
@end cartouche
@end example

@table @code
@item signal
Mask of pending signals
@item blocked
Mask of blocked signals
@item sigignore
Mask of ignored signals
@item sigcatch
Mask of caught signals
@end table

All signal masks are interpreted as bit mask; it is an array of two
@code{guint64}'s so we can save 128 signals there.

@page
@node glibtop_proc_kernel, glibtop_proc_segment, glibtop_proc_signal, System Dependent
@subsection Process Kernel Data information

Library function @code{glibtop_get_proc_kernel}:

@example
@cartouche
void
glibtop_get_proc_kernel (glibtop_proc_kernel *buf, pid_t pid);

void
glibtop_get_proc_kernel_l (glibtop *server, glibtop_proc_kernel *buf,
                           pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_kernel} in @file{<glibtop/prockernel.h>}:

@example
@cartouche
typedef struct _glibtop_proc_kernel     glibtop_proc_kernel;

struct _glibtop_proc_kernel
@{
    guint64 flags;
    guint64 k_flags,
        min_flt,
        maj_flt,
        cmin_flt,
        cmaj_flt,
        kstk_esp,
        kstk_eip,
        nwchan;
    char wchan [40];
@};
@end cartouche
@end example

@table @code
@item k_flags
Kernel flags of the process. See the constants defined below.
@item min_flt
The number of minor faults the process has made, those which have not required
loading a memory page from disk.
@item maj_flt
The number of major faults the process has made, those which have required loading
a memory page from disk.
@item cmin_flt
The number of minor faults that the process and its children have made.
@item cmaj_flt
The number of major faults that the process and its children have made.
@item kstk_esp
The current value of @code{esp} (32-bit stack pointer), as found in the kernel stack
page for the process.
@item kstk_eip
The current @code{eip} (32-bit instruction pointer).
@item nwchan
This is the "channel" in which the process is waiting. This is the address of a system
call, and can be looked up in a namelist if you need a textual name.
(If you have an up-to-date @file{/etc/psdatabase}, then try @code{ps -l} to see the
WCHAN field in action).
@item wchan
This is the textual name of the @code{nwchan} field.
@end table

There are some constants for the @code{k_flags} field:

@example
@cartouche
#define GLIBTOP_KFLAGS_STARTING         1
#define GLIBTOP_KFLAGS_EXITING          2
#define GLIBTOP_KFLAGS_PTRACED          4
#define GLIBTOP_KFLAGS_TRACESYS         8
#define GLIBTOP_KFLAGS_FORKNOEXEC       16
#define GLIBTOP_KFLAGS_SUPERPRIV        32
#define GLIBTOP_KFLAGS_DUMPEDCORE       64
#define GLIBTOP_KFLAGS_SIGNALED         128
@end cartouche
@end example

@table @code
@item GLIBTOP_KFLAGS_STARTING
Process is being created.
@item GLIBTOP_KFLAGS_EXITING
Process is exiting.
@item GLIBTOP_KFLAGS_PTRACED
Process is being traced (via @code{ptrace ()}).
@item GLIBTOP_KFLAGS_TRACESYS
Process is tracing system calls.
@item GLIBTOP_KFLAGS_FORKNOEXEC
Process @code{fork()}ed, but didn't @code{exec()} yet.
@item GLIBTOP_KFLAGS_SUPERPRIV
Process used super-user privileges.
@item GLIBTOP_KFLAGS_DUMPEDCORE
Process dumped core.
@item GLIBTOP_KFLAGS_SIGNALED
Process was killed by a signal.
@end table

@page
@node glibtop_proc_segment, glibtop_proc_args, glibtop_proc_kernel, System Dependent
@subsection Process Segment information

Library function @code{glibtop_get_proc_segment}:

@example
@cartouche
void
glibtop_get_proc_segment (glibtop_proc_segment *buf, pid_t pid);

void
glibtop_get_proc_segment_l (glibtop *server, glibtop_proc_segment *buf,
                            pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_segment} in @file{<glibtop/procsegment.h>}:

@example
@cartouche
typedef struct _glibtop_proc_segment    glibtop_proc_segment;

struct _glibtop_proc_segment
@{
    guint64   flags,
        text_rss,
        shlib_rss,
        data_rss,
        stack_rss,
        dirty_size,
        start_code,
        end_code,
        start_stack;
@};
@end cartouche
@end example

@table @code
@item text_rss
Text resident set size
@item shlib_rss
Shared-Lib resident set size
@item data_rss
Data resident set size
@item stack_rss
Stack resident set size
@item dirty_size
Total size of dirty pages
@item start_code
Address of beginning of code segment
@item end_code
Address of end of code segment
@item start_stack
Address of the bottom of stack segmen
@end table

@page
@node glibtop_proc_args, glibtop_proc_map, glibtop_proc_segment, System Dependent
@subsection Process Arguments

Library function @code{glibtop_get_proc_args}:

@example
@cartouche
char *
glibtop_get_proc_args(glibtop_proc_args *buf, pid_t pid,
                         unsigned max_len);

char *
glibtop_get_proc_args_l (glibtop *server, glibtop_proc_args *buf,
                         pid_t pid, unsigned max_len);
@end cartouche
@end example

Declaration of @code{glibtop_proc_args} in @file{<glibtop/procargs.h>}:

@example
@cartouche
typedef struct _glibtop_proc_args       glibtop_proc_args;

struct _glibtop_proc_args
@{
    guint64   flags,
        size;
@};
@end cartouche
@end example

Returns a string with all command line arguments of process @code{pid}
(up to @code{max_len} characters, use zero to get all arguments).

The command line arguments in the returned string are separated by zero bytes;
the lenght of this string is returned in the @code{size} field.

Remember to @code{g_free} the returned string to avoid a memory leak.

@strong{New functions}

@example
@cartouche
char **
glibtop_get_proc_argv(glibtop_proc_args *buf, pid_t pid,
                         unsigned max_len);

char **
glibtop_get_proc_argv_l (glibtop *server, glibtop_proc_args *buf,
                         pid_t pid, unsigned max_len);
@end cartouche
@end example

Returns a NULL-terminated array of strings with all arguments of
process @code{pid} (up to @code{max_len} characters, use zero to get
all arguments). @code{glibtop_get_proc_argv()} and
@code{glibtop_get_proc_argv_l()} are wrappers to
@code{glibtop_get_proc_args()} and @code{glibtop_get_proc_args_l()}
that return process' arguments like the C @code{argv}.

Remember to @code{g_strfreev} the returned array to avoid a memory
leak.

@page
@node glibtop_proc_map, glibtop_netload, glibtop_proc_args, System Dependent
@subsection Process Memory Maps

Library function @code{glibtop_get_proc_map}:

@example
@cartouche
glibtop_map_entry *
glibtop_get_proc_map (glibtop_proc_map *buf, pid_t pid);

glibtop_map_entry *
glibtop_get_proc_map_l (glibtop *server, glibtop_proc_map *buf,
                        pid_t pid);
@end cartouche
@end example

Declaration of @code{glibtop_proc_map} in @file{<glibtop/procmap.h>}:

@example
@cartouche
typedef struct _glibtop_proc_map        glibtop_proc_map;

struct _glibtop_proc_map
@{
    guint64   flags,
        number,
        total,
        size;
@};
@end cartouche
@end example

Returns a @code{glibtop_map_entry *} list (which needs to be freed with
@code{g_free}) of memory maps of process @code{pid}.

@table @code
@item number
Number of entries in the returned list.

@item total
Total size of the returned list (this equals @code{number * size}).

@item size
Size of a single entry in the returned list
(this equals @code{sizeof (glibtop_map_entry)}).
@end table

@example
@cartouche
typedef struct _glibtop_map_entry       glibtop_map_entry;

struct _glibtop_map_entry
@{
    guint64 flags, start, end, offset, perm, inode, device;
    char filename [GLIBTOP_MAP_FILENAME_LEN+1];
@};
@end cartouche
@end example

The @code{flags} member is a bit field and specifies which of the other
fields are valid:

@example
@cartouche
#define GLIBTOP_MAP_ENTRY_START         0
#define GLIBTOP_MAP_ENTRY_END           1
#define GLIBTOP_MAP_ENTRY_OFFSET        2
#define GLIBTOP_MAP_ENTRY_PERM          3
#define GLIBTOP_MAP_ENTRY_INODE         4
#define GLIBTOP_MAP_ENTRY_DEVICE        5
#define GLIBTOP_MAP_ENTRY_FILENAME      6
@end cartouche
@end example

Constants for the @code{perm} member:

@example
@cartouche
#define GLIBTOP_MAP_PERM_READ           1
#define GLIBTOP_MAP_PERM_WRITE          2
#define GLIBTOP_MAP_PERM_EXECUTE        4
#define GLIBTOP_MAP_PERM_SHARED         8
#define GLIBTOP_MAP_PERM_PRIVATE        16
@end cartouche
@end example

@page
@node glibtop_netload, glibtop_ppp, glibtop_proc_map, System Dependent
@subsection Network Load

Library function @code{glibtop_get_netload}:

@example
@cartouche
void
glibtop_get_netload (glibtop_netload *buf, const char *interface);

void
glibtop_get_netload_l (glibtop *server, glibtop_netload *buf,
                       const char *interface);
@end cartouche
@end example

Declaration of @code{glibtop_netload} in @file{<glibtop/netload.h>}:

@example
@cartouche
typedef struct _glibtop_netload glibtop_netload;

struct _glibtop_netload
@{
    guint64   flags,
        if_flags,
        mtu,
        subnet,
        address,
        packets_in,
        packets_out,
        packets_total,
        bytes_in,
        bytes_out,
        bytes_total,
        errors_in,
        errors_out,
        errors_total,
        collisions;
@};
@end cartouche
@end example

Returns network statistics for interface @code{interface} (which is the same
than in @code{ifconfig}).

@table @code
@item if_flags
Interface flags. See the contants defined below.
@item mtu
Maximum Transfer Unit (MTU)
@item subnet
Subnet Address
@item address
Interface Address
@item packets_in
Total number of incoming packets
@item packets_out
Total number of outgoing packets
@item packets_total
Total number of packets
@item bytes_in
Total number of incoming bytes
@item bytes_out
Total number of outgoing bytes
@item bytes_total
Total number of bytes
@item errors_in
Total number of errors in incoming direction
@item errors_out
Total number of errors in outgoing direction
@item errors_total
Total number of errors
@item collisions
Total number of collisions
@end table

Please note that not all operating systems distinguish between incoming/outgoing
bytes/packets/errors - in this case only the @samp{_total} fields are valid.
Otherwise, they're just @samp{_in} plus @samp{_out}.

Constants for @code{if_flags}:

@example
@cartouche
enum @{
    GLIBTOP_IF_FLAGS_UP = 1,
    GLIBTOP_IF_FLAGS_BROADCAST,
    GLIBTOP_IF_FLAGS_DEBUG,
    GLIBTOP_IF_FLAGS_LOOPBACK,
    GLIBTOP_IF_FLAGS_POINTOPOINT,
    GLIBTOP_IF_FLAGS_RUNNING,
    GLIBTOP_IF_FLAGS_NOARP,
    GLIBTOP_IF_FLAGS_PROMISC,
    GLIBTOP_IF_FLAGS_ALLMULTI,
    GLIBTOP_IF_FLAGS_OACTIVE,
    GLIBTOP_IF_FLAGS_SIMPLEX,
    GLIBTOP_IF_FLAGS_LINK0,
    GLIBTOP_IF_FLAGS_LINK1,
    GLIBTOP_IF_FLAGS_LINK2,
    GLIBTOP_IF_FLAGS_ALTPHYS,
    GLIBTOP_IF_FLAGS_MULTICAST
@};
@end cartouche
@end example

@page
@node glibtop_ppp, glibtop_disk, glibtop_netload, System Dependent
@subsection PPP Statistics

Library function @code{glibtop_get_ppp}:

@example
@cartouche
void
glibtop_get_ppp_l (glibtop *server, glibtop_ppp *buf,
                   unsigned short device);

void
glibtop_get_ppp (glibtop_ppp *buf, unsigned short device);
@end cartouche
@end example

Declaration of @code{glibtop_ppp} in @file{<glibtop/ppp.h>}:

@example
@cartouche
typedef struct _glibtop_ppp     glibtop_ppp;

struct _glibtop_ppp
@{
    guint64   flags,
        state,
        bytes_in,
        bytes_out;
@};
@end cartouche
@end example

@table @code
@item bytes_in
Number of input bytes
@item bytes_out
Number of output bytes
@end table

There are some constants for @code{state}:

@example
@cartouche
enum @{
    GLIBTOP_PPP_STATE_UNKNOWN = 0,
    GLIBTOP_PPP_STATE_HANGUP,
    GLIBTOP_PPP_STATE_ONLINE
@};
@end cartouche
@end example

@table @code
@item GLIBTOP_PPP_STATE_UNKNOWN
LibGTop was unable to determine the current ppp state.
@item GLIBTOP_PPP_STATE_HANGUP
We're currently offline.
@item GLIBTOP_PPP_STATE_ONLINE
We're currently online.
@end table

@page
@node glibtop_disk, , glibtop_ppp, System Dependent
@subsection DISK Usage

Library function @code{glibtop_get_disk}:

@example
@cartouche
void glibtop_get_disk (glibtop_disk *buf);
void glibtop_get_disk_l (glibtop *server, glibtop_disk *buf);
@end cartouche
@end example

Declaration of @code{glibtop_disk} in @file{<glibtop/disk.h>}:

@example
@cartouche
typedef struct _glibtop_disk     glibtop_disk;

struct _glibtop_disk
@{
    xdisk_sectors_read [GLIBTOP_NDISK],
    xdisk_time_read [GLIBTOP_NDISK],
    xdisk_sectors_write [GLIBTOP_NDISK],
    xdisk_time_write [GLIBTOP_NDISK],
@};
@end cartouche
@end example

All DISK reads and writes are measured by @dfn{sectors} which are normally 512 bytes each. 
All disk time are measured in milliseconds which is 1/1000th of a second.

@table @code
@item xdisk_sectors_read
Number of sectors read since system boot.

@item xdisk_time_read
Number of milliseconds spent reading since system boot.

@item xdisk_sectors_write
Number of sectors written since system boot.

@item xdisk_time_write
Number of milliseconds spent writing since system boot.

@end table

The @samp{xdisk_} are values from arrays of @code{GLIBTOP_NDISK} (defined in
@file{<glibtop/disk.h>}) elements and contain one value for each DISK
in the system.

Please note that all of the disk values are absolute values measured in
certain units since system boot. To get bandwidth values (bytes/s), you need to call @code{glibtop_disk}, save the
result, wait some time and then call it again and divide the differences of
the two values by the time spent reading or writing.

@page
@node Common Functions, Library Functions, System Dependent, Reference Manual
@section Common Functions

This are functions which a common implementation for all systems; we never
use the server for them.

The file system code is taken from GNU Fileutils.

@menu
* glibtop_mountlist::           Mount List.
* glibtop_fsusage::             File System Usage.
@end menu

@node glibtop_mountlist, glibtop_fsusage, Common Functions, Common Functions
@subsection Mount List

Library function @code{glibtop_get_mountlist}:

@example
@cartouche
glibtop_mountentry *
glibtop_get_mountlist_l (glibtop *server, glibtop_mountlist *buf,
                         int all_fs);

glibtop_mountentry *
glibtop_get_mountlist (glibtop_mountlist *buf, int all_fs);
@end cartouche
@end example

The @code{all_fs} parameter specifies whether information about all
filesystems should be returned; this will include filesystem types like
@code{autofs} and @code{procfs}. You should not use this in disk usage
programs, but it can be useful to get a list of all currently mounted
filesystems.

Declaration of @code{glibtop_proc_map} in @file{<glibtop/procmap.h>}:

@example
@cartouche
typedef struct _glibtop_mountlist       glibtop_mountlist;

struct _glibtop_mountlist
@{
    guint64   flags,
        number,
        total,
        size;
@};
@end cartouche
@end example

Returns a @code{glibtop_mountentry *} list (which needs to be freed with
@code{g_free}) of mounted filesystems.

@table @code
@item number
Number of entries in the returned list.

@item total
Total size of the returned list (this equals @code{number * size}).

@item size
Size of a single entry in the returned list
(this equals @code{sizeof (glibtop_mountentry)}).
@end table

@example
@cartouche
typedef struct _glibtop_mountentry      glibtop_mountentry;

struct _glibtop_mountentry
@{
    guint64 dev;
    char devname [GLIBTOP_MOUNTENTRY_LEN+1];
    char mountdir [GLIBTOP_MOUNTENTRY_LEN+1];
    char type [GLIBTOP_MOUNTENTRY_LEN+1];
@};
@end cartouche
@end example

@code{GLIBTOP_MOUNTENTRY_LEN} is defined in @file{<glibtop.h>}.

@table @code
@item devname
Full pathname (such as @samp{/dev/sdb1} for instance) to the mounted device.
@item mountdir
Full pathname of the mountpoint (such as @samp{/usr/local} for instance).
@item type
Filesystem type as a textual string (such as @samp{ext2fs}).
@end table

@page
@node glibtop_fsusage,  , glibtop_mountlist, Common Functions
@subsection File System Usage

Library function @code{glibtop_get_fsusage}:

@example
@cartouche
void
glibtop_get_fsusage_l (glibtop *server, glibtop_fsusage *buf,
                       const char *mount_dir);

void
glibtop_get_fsusage (glibtop_fsusage *buf, const char *mount_dir);
@end cartouche
@end example

Declaration of @code{glibtop_fsusage} in @file{<glibtop/fsusage.h>}:

@example
@cartouche
typedef struct _glibtop_fsusage         glibtop_fsusage;

struct _glibtop_fsusage
@{
    guint64   flags,
        blocks,
        bfree,
        bavail,
        files,
        ffree;
    guint32   block_size;
    guint64 read,
        write;
@};
@end cartouche
@end example

@table @code
@item blocks
Total blocks in the filesystem.
@item bfree
Free blocks available to the superuser.
@item bavail
Free blocks available to ordinary users.
@item files
Total file nodes.
@item ffree
Free file nodes.
@item block_size
Block size in bytes.
@item read
Total blocks read.
@item write
Total blocks written.
@end table

@page
@node Library Functions,  , Common Functions, Reference Manual
@section Library Functions

This are general library functions which can be used to get information
about the library and to control its behavior.

@menu
* glibtop_init::                Server Initialization.
* glibtop_sysdeps::             Server Sysdeps.
* Library Parameters::          Library Parameters.
@end menu

@node glibtop_init, glibtop_sysdeps, Library Functions, Library Functions
@subsection Server Initialization

You do not need to worry about the @code{glibtop *} server structure if
you don't need - the library exports a @code{glibtop_global_server}
which you can use everywhere a @code{glibtop *} is expected.

Most of the library and all of the sysdeps function also have an alias
(which is the function name without the @samp{_l}, @samp{_s} or @samp{_r}
suffix) which don't take a @code{glibtop *} as argument but uses the
@code{glibtop_global_server} instead.

@example
@cartouche
extern glibtop *glibtop_global_server;
@end cartouche
@end example

Library function @code{glibtop_init}:

@example
@cartouche
glibtop *
glibtop_init_r (glibtop **server_ptr, unsigned long features,
                unsigned flags);

void
glibtop_init (void);
@end cartouche
@end example

This function initializes a LibGTop server. It is automatically called
when you use any of the LibGTop functions and will use the global server
in this case.

However, it's appreciated to call @code{glibtop_init} during the
initialization of your application.

You can for instance use

@example
glibtop_init ();
@end example

@noindent
which is equivalent to

@example
glibtop_init_r (&glibtop_global_server, 0, 0);
@end example

Please note that the @code{server_ptr} argument is a pointer to a pointer
(and thus is of type @code{glibtop **}).

To control what @code{glibtop_init} should actually do, you can use the
@code{features} and @code{flags} arguments.

The @code{features} argument is a bit-mask (interpreted in the same way
than @samp{sysdeps.features}) and tells the library which features you're
interested in. The library will only start the server if this is required
for any of those features.

You can use the following constants for the @code{flags} parameter to
control the behavior of the library:

@table @code
@item GLIBTOP_INIT_NO_INIT
Tells the library to do nothing. If the value pointed to by the
@code{server_ptr} argument is @code{NULL}, it will set it to the
@code{glibtop_global_server} and then return.
@item GLIBTOP_INIT_NO_OPEN
Do the initialization, but do not start the server.
@end table

To modify the way the @code{features} are interpretet, you can use the
following constants for @code{flags} (as a bit mask):

@table @code
@item GLIBTOP_FEATURES_NO_SERVER
Never use the server, always call the sysdeps code directly.
If you require any privileges to get them and you don't have those
privileges, the this will obviously not work and the library will
fail to return some or all of the requested values.
@item GLIBTOP_FEATURES_EXCEPT
Inverts the matching of the @code{features} parameter, i.e. if you use
this flag this means that @code{features} are all the features you are
@emph{not} interested in.
Might be useful to say something like "I want everything but ppp".
@end table

@node glibtop_sysdeps, Library Parameters, glibtop_init, Library Functions
@subsection Server Sysdeps

Library function @code{glibtop_get_sysdeps}:

@example
@cartouche
void
glibtop_get_sysdeps_r (glibtop *server, glibtop_sysdeps *buf);

void
glibtop_get_sysdeps (glibtop_sysdeps *buf);
@end cartouche
@end example

Declaration of @code{glibtop_sysdeps} in @file{<glibtop/sysdeps.h>}:

@example
@cartouche
typedef struct _glibtop_sysdeps         glibtop_sysdeps;

struct _glibtop_sysdeps
@{
    guint64 flags,
        features,
        pointer_size,
        cpu,
        mem,
        swap,
        uptime,
        loadavg,
        shm_limits,
        msg_limits,
        sem_limits,
        proclist,
        proc_state,
        proc_uid,
        proc_mem,
        proc_time,
        proc_signal,
        proc_kernel,
        proc_segment,
        proc_args,
        proc_map,
        mountlist,
        fsusage,
        netload,
        ppp;
@};
@end cartouche
@end example

@table @code
@item features
This is a bit field (the so-called @dfn{server features}) stating
for which features we need to use the server.
@item pointer_size
This was added in LibGTop 1.1.0 and tells you the number of bits a
@code{void*} has in the server (this may be different from the
size on the client machine if we're talking over the daemon to a
remove machine).
@end table

The following constants from @file{<glibtop/sysdeps.h>} serve as bit-indices
for the @code{features} field:

@example
@cartouche
#define GLIBTOP_SYSDEPS_CPU             0
#define GLIBTOP_SYSDEPS_MEM             1
#define GLIBTOP_SYSDEPS_SWAP            2
#define GLIBTOP_SYSDEPS_UPTIME          3
#define GLIBTOP_SYSDEPS_LOADAVG         4
#define GLIBTOP_SYSDEPS_SHM_LIMITS      5
#define GLIBTOP_SYSDEPS_MSG_LIMITS      6
#define GLIBTOP_SYSDEPS_SEM_LIMITS      7
#define GLIBTOP_SYSDEPS_PROCLIST        8
#define GLIBTOP_SYSDEPS_PROC_STATE      9
#define GLIBTOP_SYSDEPS_PROC_UID        10
#define GLIBTOP_SYSDEPS_PROC_MEM        11
#define GLIBTOP_SYSDEPS_PROC_TIME       12
#define GLIBTOP_SYSDEPS_PROC_SIGNAL     13
#define GLIBTOP_SYSDEPS_PROC_KERNEL     14
#define GLIBTOP_SYSDEPS_PROC_SEGMENT    15
#define GLIBTOP_SYSDEPS_PROC_ARGS       16
#define GLIBTOP_SYSDEPS_PROC_MAP        17
#define GLIBTOP_SYSDEPS_MOUNTLIST       18
#define GLIBTOP_SYSDEPS_FSUSAGE         19
#define GLIBTOP_SYSDEPS_NETLOAD         20
#define GLIBTOP_SYSDEPS_PPP             21
@end cartouche
@end example

@node Library Parameters,  , glibtop_sysdeps, Library Functions
@subsection Library Parameters

Library function @code{glibtop_get_parameter}:

@example
@cartouche
size_t
glibtop_get_parameter_l (glibtop *server, const unsigned parameter,
                         void *data_ptr, size_t data_size);

size_t
glibtop_get_parameter (const unsigned parameter, void *data_ptr,
                       size_t data_size);
@end cartouche
@end example

This function is used to retrieve a library parameter (see below for a more
detailed description). It returns the size of the retrieved parameter on
success, zero on failure or minus the actual size of the parameter if
@code{data_size} was too small.

You may call this function with @code{data_ptr} set to @code{NULL} to get the
actual size of a parameter (as a negative value).

@table @code
@item parameter
The parameter you want to retrieve (see below for constants).
@item data_ptr
Pointer to a place where the parameter should be stored.
@item data_size
Maximum size of the parameter.
@end table

Library function @code{glibtop_set_parameter}:

@example
@cartouche
void
glibtop_set_parameter_l (glibtop *server, const unsigned parameter,
                         const void *data_ptr, size_t data_size);

void
glibtop_set_parameter (const unsigned parameter, const void *data_ptr,
                       size_t data_size);
@end cartouche
@end example

This function is used to modify a library parameter. Please not that you
may not set all parameters since some of them are read-only.

@table @code
@item parameter
The parameter you want to modify (see below for constants).
@item data_ptr
Pointer to the value which should be set.
@item data_size
Size of the new value. For fixed-size parameters, this must match
the exact size of the parameter or you'll get an error.
@end table

The following parameters are defined in @file{<glibtop/parameter.h>}:

@table @code
@item GLIBTOP_PARAM_FEATURES
This is a read-only @code{unsigned long} representing the @code{features}
field of @code{glibtop_sysdeps}.
@item GLIBTOP_PARAM_REQUIRED
This is a @code{glibtop_sysdeps} structure specifying which features the
client requires the library return. If it fails to get any of them, you'll
get an error.
@item GLIBTOP_PARAM_ERROR_METHOD
This is an @code{unsigned} telling the library what to do if it fails to
get any of the features that are marked as required via the
@code{GLIBTOP_PARAM_REQUIRED} parameter (see below for constants).
@end table

You can use the following constants for @code{GLIBTOP_PARAM_ERROR_METHOD}
(defined in @file{<glibtop/open.h>}):

@table @code
@item GLIBTOP_ERROR_METHOD_IGNORE
Ignore the error condition.
@item GLIBTOP_ERROR_METHOD_WARN_ONCE
Warn once about the absense of some of the required features, then modify
@code{GLIBTOP_PARAM_REQUIRED} so that the missing ones are no longer
required. This is the prefered value for applications since it'll only
print out the warning message once and not each time the library tries to
get one of those features.
@item GLIBTOP_ERROR_METHOD_WARN
Warn each time the library fails to get some of the required features.
@item GLIBTOP_ERROR_METHOD_ABORT
Abort if the library fails to get some of the required features. This
should not be used by applications.
@end table