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devstat devstat_getnumdevs devstat_getgeneration devstat_getversion devstat_checkversion devstat_getdevs devstat_selectdevs devstat_buildmatch devstat_compute_statistics devstat_compute_etime - device statistics utility library
Lb libdevstat
The
devstat_getnumdevs ();
function
returns the number of devices registered with the
subsystem in the kernel.
The
devstat_getgeneration ();
function
returns the current generation of the
list of devices in the kernel.
The
devstat_getversion ();
function
returns the current kernel
version.
The
devstat_checkversion ();
function
checks the userland
version against the kernel
version.
If the two are identical, it returns zero.
Otherwise, it prints an appropriate error in
devstat_errbuf
and returns -1.
The
devstat_getdevs ();
function
fetches the current list of devices and statistics into the supplied
Vt statinfo
structure.
The
Vt statinfo
structure can be found in
In devstat.h :
struct statinfo {
long cp_time[CPUSTATES];
long tk_nin;
long tk_nout;
struct devinfo *dinfo;
long double snap_time;
};
The
devstat_getdevs ();
function
expects the
Vt statinfo
structure to be allocated, and it also expects the
dinfo
subelement to be allocated and zeroed prior to the first invocation of
devstat_getdevs (.);
The
dinfo
subelement is used to store state between calls, and should not be modified
after the first call to
devstat_getdevs (.);
The
dinfo
subelement contains the following elements:
struct devinfo {
struct devstat *devices;
u_int8_t *mem_ptr;
long generation;
int numdevs;
};
The kern.devstat.all sysctl(8) variable contains an array of structures, but at the head of the array is the current generation. The reason the generation is at the head of the buffer is so that userland software accessing the statistics information can atomically get both the statistics information and the corresponding generation number. If client software were forced to get the generation number via a separate sysctl(8) variable (which is available for convenience), the list of devices could change between the time the client gets the generation and the time the client gets the device list.
The
mem_ptr
subelement of the
Vt devinfo
structure is a pointer to memory that is allocated, and resized if
necessary, by
devstat_getdevs (.);
The devices subelement of the
Vt devinfo
structure is basically a pointer to the beginning of the array of devstat
structures from the
kern.devstat.all
sysctl(8)
variable (or the corresponding values read via
kvm(3)).
The generation subelement of the
Vt devinfo
structure contains the corresponding generation number.
The
numdevs
subelement of the
Vt devinfo
structure contains the current
number of devices registered with the kernel
subsystem.
The
devstat_selectdevs ();
function
selects devices to display based upon a number of criteria:
The
devstat_selectdevs ();
function
performs selections in four different modes:
In all selection modes,
devstat_selectdevs ();
will not select any more than
Fa maxshowdevs
devices.
One exception to this is when you are in
``top''
mode and no devices have been selected.
In this case,
devstat_selectdevs ();
will select every device in the system.
Client programs must pay attention to selection order when deciding whether
to pay attention to a particular device.
This may be the wrong behavior, and probably requires additional thought.
The
devstat_selectdevs ();
function
handles allocation and resizing of the
Fa dev_select
structure passed in
by the client.
The
devstat_selectdevs ();
function
uses the
Fa numdevs
and
Fa current_generation
fields to track the
current
generation and number of devices.
If
Fa num_selections
is not the same
as
Fa numdevs
or if
Fa select_generation
is not the same as
Fa current_generation ,
devstat_selectdevs ();
will resize the selection list as necessary, and re-initialize the
selection array.
The
devstat_buildmatch ();
function
takes a comma separated match string and compiles it into a
Vt devstat_match
structure that is understood by
devstat_selectdevs (.);
Match strings have the following format:
The
devstat_buildmatch ();
function
takes care of allocating and reallocating the match list as necessary.
Currently known match types include:
The
devstat_compute_statistics ();
function provides complete statistics calculation.
There are four arguments for which values
must
be supplied:
Fa current ,
Fa previous ,
Fa etime ,
and the terminating argument for the varargs list,
DSM_NONE
For most applications, the user will want to supply valid
Vt devstat
structures for both
Fa current
and
Fa previous .
In some instances, for instance when calculating statistics since system
boot, the user may pass in a
NULL
pointer for the
Fa previous
argument.
In that case,
devstat_compute_statistics ();
will use the total stats in the
Fa current
structure to calculate statistics over
Fa etime .
For each statistics to be calculated, the user should supply the proper
enumerated type (listed below), and a variable of the indicated type.
All statistics are either integer values, for which a
Vt u_int64_t
is used,
or floating point, for which a
Vt long double
is used.
The statistics that may be calculated are:
This
must
be the last argument passed to
devstat_compute_statistics (.);
It is an argument list terminator.
The total number of bytes transferred between the acquisition of Fa previous and Fa current .
The total number of bytes in transactions of the specified type between the acquisition of Fa previous and Fa current .
The total number of transfers between the acquisition of Fa previous and Fa current .
The total number of transactions of the specified type between the acquisition of Fa previous and Fa current .
The total number of blocks transferred between the acquisition of Fa previous and Fa current . This number is in terms of the blocksize reported by the device. If no blocksize has been reported (i.e., the block size is 0), a default blocksize of 512 bytes will be used in the calculation.
The total number of blocks of the specified type between the acquisition of Fa previous and Fa current . This number is in terms of the blocksize reported by the device. If no blocksize has been reported (i.e., the block size is 0), a default blocksize of 512 bytes will be used in the calculation.
The average number of kilobytes per transfer between the acquisition of Fa previous and Fa current .
The average number of kilobytes in the specified type transaction between the acquisition of Fa previous and Fa current .
The average number of transfers per second between the acquisition of Fa previous and Fa current .
The average number of transactions of the specified type per second between the acquisition of Fa previous and Fa current .
The average number of megabytes transferred per second between the acquisition of Fa previous and Fa current .
The average number of megabytes per second in the specified type of transaction between the acquisition of Fa previous and Fa current .
The average number of blocks transferred per second between the acquisition of Fa previous and Fa current . This number is in terms of the blocksize reported by the device. If no blocksize has been reported (i.e., the block size is 0), a default blocksize of 512 bytes will be used in the calculation.
The average number of blocks per second in the specificed type of transaction between the acquisition of Fa previous and Fa current . This number is in terms of the blocksize reported by the device. If no blocksize has been reported (i.e., the block size is 0), a default blocksize of 512 bytes will be used in the calculation.
The average duration of transactions between the acquisition of Fa previous and Fa current .
The average duration of transactions of the specified type between the acquisition of Fa previous and Fa current .
The percentage of time the device had one or more transactions outstanding between the acquisition of Fa previous and Fa current .
The number of not yet completed transactions at the time when Fa current was acquired.
If you do not need a result from
devstat_compute_statistics (,);
just put
DSM_SKIP
as first (type) parameter and
NULL
as second parameter.
This can be useful in scenarios where the statistics to be calculated
are determined at run time.
The
devstat_compute_etime ();
function
provides an easy way to find the difference in seconds between two
Vt bintime
structures.
This is most commonly used in conjunction with the time recorded by the
devstat_getdevs ();
function (in
Vt struct statinfo )
each time it fetches the current
list.
The
devstat_checkversion ();
function
returns 0 if the kernel and userland
versions match.
If they do not match, it returns -1.
The
devstat_getdevs ();
and
devstat_selectdevs ();
functions
return -1 in case of an error, 0 if there is no error, and 1 if the device
list or selected devices have changed.
A return value of 1 from
devstat_getdevs ();
is usually a hint to re-run
devstat_selectdevs ();
because the device list has changed.
The
devstat_buildmatch ();
function returns -1 for error, and 0 if there is no error.
The
devstat_compute_etime ();
function
returns the computed elapsed time.
The
devstat_compute_statistics ();
function returns -1 for error, and 0 for success.
If an error is returned from one of the library functions, the reason for the error is generally printed in the global string devstat_errbuf which is DEVSTAT_ERRBUF_SIZE characters long.
The
devstat_selectdevs ();
function
should probably not select more than
Fa maxshowdevs
devices in
``top''
mode when no devices have been selected previously.
There should probably be functions to perform the statistics buffer swapping that goes on in most of the clients of this library.
The Vt statinfo and Vt devinfo structures should probably be cleaned up and thought out a little more.
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