DEVSTAT(3) FreeBSD Library Functions Manual DEVSTAT(3)
NAME
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
LIBRARY
Device Statistics Library (libdevstat, -ldevstat)
SYNOPSIS
#include <devstat.h>
int
devstat_getnumdevs(kvm_t *kd);
long
devstat_getgeneration(kvm_t *kd);
int
devstat_getversion(kvm_t *kd);
int
devstat_checkversion(kvm_t *kd);
int
devstat_getdevs(kvm_t *kd, struct statinfo *stats);
int
devstat_selectdevs(struct device_selection **dev_select,
int *num_selected, int *num_selections, long *select_generation,
long current_generation, struct devstat *devices, int numdevs,
struct devstat_match *matches, int num_matches,
char **dev_selections, int num_dev_selections,
devstat_select_mode select_mode, int maxshowdevs, int perf_select);
int
devstat_buildmatch(char *match_str, struct devstat_match **matches,
int *num_matches);
int
devstat_compute_statistics(struct devstat *current,
struct devstat *previous, long double etime, ...);
long double
devstat_compute_etime(struct bintime *cur_time,
struct bintime *prev_time);
DESCRIPTION
The devstat library is a library of helper functions for dealing with the
kernel devstat(9) interface, which is accessible to users via sysctl(3)
and kvm(3). All functions that take a kvm_t * as first argument can be
passed NULL instead of a kvm handle as this argument, which causes the
data to be read via sysctl(3). Otherwise, it is read via kvm(3) using
the supplied handle. The devstat_checkversion() function should be
called with each kvm handle that is going to be used (or with NULL if
sysctl(3) is going to be used).
The devstat_getnumdevs() function returns the number of devices
registered with the devstat subsystem in the kernel.
The devstat_getgeneration() function returns the current generation of
the devstat list of devices in the kernel.
The devstat_getversion() function returns the current kernel devstat
version.
The devstat_checkversion() function checks the userland devstat version
against the kernel devstat 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 statinfo structure. The statinfo structure
can be found 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 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;
uint8_t *mem_ptr;
long generation;
int numdevs;
};
The kern.devstat.all sysctl(8) variable contains an array of devstat
structures, but at the head of the array is the current devstat
generation. The reason the generation is at the head of the buffer is so
that userland software accessing the devstat 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 devinfo structure is a pointer to memory
that is allocated, and resized if necessary, by devstat_getdevs(). The
devices subelement of the 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 devinfo structure contains the corresponding
generation number. The numdevs subelement of the devinfo structure
contains the current number of devices registered with the kernel devstat
subsystem.
The devstat_selectdevs() function selects devices to display based upon a
number of criteria:
specified devices
Specified devices are the first selection priority. These are
generally devices specified by name by the user e.g. da0, da1,
cd0.
match patterns
These are pattern matching expressions generated by
devstat_buildmatch() from user input.
performance
If performance mode is enabled, devices will be sorted based on
the bytes field in the device_selection structure passed in to
devstat_selectdevs(). The bytes value currently must be
maintained by the user. In the future, this may be done for him
in a devstat library routine. If no devices have been selected
by name or by pattern, the performance tracking code will select
every device in the system, and sort them by performance. If
devices have been selected by name or pattern, the performance
tracking code will honor those selections and will only sort
among the selected devices.
order in the devstat list
If the selection mode is set to DS_SELECT_ADD, and if there are
still less than maxshowdevs devices selected,
devstat_selectdevs() will automatically select up to maxshowdevs
devices.
The devstat_selectdevs() function performs selections in four different
modes:
DS_SELECT_ADD In "add" mode, devstat_selectdevs() will select
any unselected devices specified by name or
matching pattern. It will also select more
devices, in devstat list order, until the number
of selected devices is equal to maxshowdevs or
until all devices are selected.
DS_SELECT_ONLY In "only" mode, devstat_selectdevs() will clear
all current selections, and will only select
devices specified by name or by matching pattern.
DS_SELECT_REMOVE In "remove" mode, devstat_selectdevs() will remove
devices specified by name or by matching pattern.
It will not select any additional devices.
DS_SELECT_ADDONLY In "add only" mode, devstat_selectdevs() will
select any unselected devices specified by name or
matching pattern. In this respect it is identical
to "add" mode. It will not, however, select any
devices other than those specified.
In all selection modes, devstat_selectdevs() will not select any more
than 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
dev_select structure passed in by the client. The devstat_selectdevs()
function uses the numdevs and current_generation fields to track the
current devstat generation and number of devices. If num_selections is
not the same as numdevs or if select_generation is not the same as
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 devstat_match structure that is understood by
devstat_selectdevs(). Match strings have the following format:
device,type,if
The devstat_buildmatch() function takes care of allocating and
reallocating the match list as necessary. Currently known match types
include:
device type:
da Direct Access devices
sa Sequential Access devices
printer Printers
proc Processor devices
worm Write Once Read Multiple devices
cd CD devices
scanner Scanner devices
optical Optical Memory devices
changer Medium Changer devices
comm Communication devices
array Storage Array devices
enclosure Enclosure Services devices
floppy Floppy devices
interface:
IDE Integrated Drive Electronics devices
SCSI Small Computer System Interface devices
other Any other device interface
passthrough:
pass Passthrough devices
The devstat_compute_statistics() function provides complete statistics
calculation. There are four arguments for which values must be supplied:
current, previous, etime, and the terminating argument for the varargs
list, DSM_NONE. For most applications, the user will want to supply
valid devstat structures for both current and previous. In some
instances, for instance when calculating statistics since system boot,
the user may pass in a NULL pointer for the previous argument. In that
case, devstat_compute_statistics() will use the total stats in the
current structure to calculate statistics over 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 uint64_t is used, or
floating point, for which a long double is used. The statistics that may
be calculated are:
DSM_NONE type: N/A
This must be the last argument passed
to devstat_compute_statistics(). It
is an argument list terminator.
DSM_TOTAL_BYTES type: uint64_t *
The total number of bytes transferred
between the acquisition of previous
and current.
DSM_TOTAL_BYTES_READ
DSM_TOTAL_BYTES_WRITE
DSM_TOTAL_BYTES_FREE type: uint64_t *
The total number of bytes in
transactions of the specified type
between the acquisition of previous
and current.
DSM_TOTAL_TRANSFERS type: uint64_t *
The total number of transfers between
the acquisition of previous and
current.
DSM_TOTAL_TRANSFERS_OTHER
DSM_TOTAL_TRANSFERS_READ
DSM_TOTAL_TRANSFERS_WRITE
DSM_TOTAL_TRANSFERS_FREE type: uint64_t *
The total number of transactions of
the specified type between the
acquisition of previous and current.
DSM_TOTAL_DURATION type: long double *
The total duration of transactions,
in seconds, between the acquisition
of previous and current.
DSM_TOTAL_DURATION_OTHER
DSM_TOTAL_DURATION_READ
DSM_TOTAL_DURATION_WRITE
DSM_TOTAL_DURATION_FREE type: long double *
The total duration of transactions of
the specified type between the
acquisition of previous and current.
DSM_TOTAL_BUSY_TIME type: long double *
Total time the device had one or more
transactions outstanding between the
acquisition of previous and current.
DSM_TOTAL_BLOCKS type: uint64_t *
The total number of blocks
transferred between the acquisition
of previous and 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.
DSM_TOTAL_BLOCKS_READ
DSM_TOTAL_BLOCKS_WRITE
DSM_TOTAL_BLOCKS_FREE type: uint64_t *
The total number of blocks of the
specified type between the
acquisition of previous and 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.
DSM_KB_PER_TRANSFER type: long double *
The average number of kilobytes per
transfer between the acquisition of
previous and current.
DSM_KB_PER_TRANSFER_READ
DSM_KB_PER_TRANSFER_WRITE
DSM_KB_PER_TRANSFER_FREE type: long double *
The average number of kilobytes in
the specified type transaction
between the acquisition of previous
and current.
DSM_TRANSFERS_PER_SECOND type: long double *
The average number of transfers per
second between the acquisition of
previous and current.
DSM_TRANSFERS_PER_SECOND_OTHER
DSM_TRANSFERS_PER_SECOND_READ
DSM_TRANSFERS_PER_SECOND_WRITE
DSM_TRANSFERS_PER_SECOND_FREE type: long double *
The average number of transactions of
the specified type per second between
the acquisition of previous and
current.
DSM_MB_PER_SECOND type: long double *
The average number of megabytes
transferred per second between the
acquisition of previous and current.
DSM_MB_PER_SECOND_READ
DSM_MB_PER_SECOND_WRITE
DSM_MB_PER_SECOND_FREE type: long double *
The average number of megabytes per
second in the specified type of
transaction between the acquisition
of previous and current.
DSM_BLOCKS_PER_SECOND type: long double *
The average number of blocks
transferred per second between the
acquisition of previous and 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.
DSM_BLOCKS_PER_SECOND_READ
DSM_BLOCKS_PER_SECOND_WRITE
DSM_BLOCKS_PER_SECOND_FREE type: long double *
The average number of blocks per
second in the specified type of
transaction between the acquisition
of previous and 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.
DSM_MS_PER_TRANSACTION type: long double *
The average duration of transactions
between the acquisition of previous
and current.
DSM_MS_PER_TRANSACTION_OTHER
DSM_MS_PER_TRANSACTION_READ
DSM_MS_PER_TRANSACTION_WRITE
DSM_MS_PER_TRANSACTION_FREE type: long double *
The average duration of transactions
of the specified type between the
acquisition of previous and current.
DSM_BUSY_PCT type: long double *
The percentage of time the device had
one or more transactions outstanding
between the acquisition of previous
and current.
DSM_QUEUE_LENGTH type: uint64_t *
The number of not yet completed
transactions at the time when current
was acquired.
DSM_SKIP type: N/A
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 bintime structures. This is most
commonly used in conjunction with the time recorded by the
devstat_getdevs() function (in struct statinfo) each time it fetches the
current devstat list.
RETURN VALUES
The devstat_getnumdevs(), devstat_getgeneration(), and
devstat_getversion() function return the indicated sysctl variable, or -1
if there is an error fetching the variable.
The devstat_checkversion() function returns 0 if the kernel and userland
devstat 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 devstat library functions, the
reason for the error is generally printed in the global string
devstat_errbuf which is DEVSTAT_ERRBUF_SIZE characters long.
SEE ALSO
systat(1), kvm(3), sysctl(3), iostat(8), rpc.rstatd(8), sysctl(8),
vmstat(8), devstat(9)
HISTORY
The devstat statistics system first appeared in FreeBSD 3.0. The new
interface (the functions prefixed with devstat_) first appeared in
FreeBSD 5.0.
AUTHORS
Kenneth Merry <ken@FreeBSD.org>
BUGS
There should probably be an interface to de-allocate memory allocated by
devstat_getdevs(), devstat_selectdevs(), and devstat_buildmatch().
The devstat_selectdevs() function should probably not select more than
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 statinfo and devinfo structures should probably be cleaned up and
thought out a little more.
FreeBSD 13.1-RELEASE-p6 December 15, 2012 FreeBSD 13.1-RELEASE-p6
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