Manual Pages  — DEVSTAT

#include <devstat.h>

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.amp; 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:

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.

systat(1), kvm(3), sysctl(3), iostat(8), rpc.rstatd(8), sysctl(8), vmstat(8), devstat(9)