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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 regis-
     tered 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 ver-
     sion.

     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 allo-
     cated, 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	modi-
     fied 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 genera-
     tion.  The	reason the generation is at the	head of	the buffer is so that
     userland software accessing the devstat statistics	information can	atomi-
     cally get both the	statistics information and the corresponding genera-
     tion 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 con-
     tains 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 main-
	     tained 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 pat-
			tern.  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 spec-
			ified 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 pro-
     grams 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 cur-
     rent 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 reallocat-
     ing 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 statis-
     tics 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 acqui-
				     sition 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 calcula-
				     tion.

     DSM_TOTAL_BLOCKS_READ

     DSM_TOTAL_BLOCKS_WRITE

     DSM_TOTAL_BLOCKS_FREE	     type: uint64_t *

				     The total number of blocks	of the speci-
				     fied 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 sec-
				     ond 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 trans-
				     ferred 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 sec-
				     ond 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 calcula-
				     tion.

     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 acquisi-
				     tion 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 transac-
				     tions 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 com-
     monly 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 swap-
     ping 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	9.2		       December	15, 2012		   FreeBSD 9.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS | BUGS

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