Copyright (c) 1998, 1999 Kenneth D. Merry.
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$FreeBSD: head/lib/libdevstat/devstat.3 51598 1999-09-23 06:36:02Z ken $
.Dd May 21, 1998 .Dt DEVSTAT 3 .Os FreeBSD 3.0 .Sh NAME .Nm devstat , .Nm getnumdevs , .Nm getgeneration , .Nm getversion , .Nm checkversion , .Nm getdevs , .Nm selectdevs , .Nm buildmatch , .Nm compute_stats , .Nm compute_etime .Nd device statistics utility library .Sh SYNOPSIS .Fd #include <sys/dkstat.h> .Fd #include <devstat.h> .Ft int .Fn getnumdevs "void" .Ft long .Fn getgeneration "void" .Ft int .Fn getversion "void" .Ft int .Fn checkversion "void" .Ft int .Fn getdevs "struct statinfo *stats" .Ft int .Fo selectdevs .Fa "struct device_selection **dev_select" .Fa "int *num_selected" .Fa "int *num_selections" .Fa "long *select_generation" .Fa "long current_generation" .Fa "struct devstat *devices" .Fa "int numdevs" .Fa "struct devstat_match *matches" .Fa "int num_matches" .Fa "char **dev_selections" .Fa "int num_dev_selections" .Fa "devstat_select_mode select_mode" .Fa "int maxshowdevs" .Fa "int perf_select" .Fc .Ft int .Fo buildmatch .Fa "char *match_str" .Fa "struct devstat_match **matches" .Fa "int *num_matches" .Fc .Ft int .Fo compute_stats .Fa "struct devstat *current" .Fa "struct devstat *previous" .Fa "long double etime" .Fa "u_int64_t *total_bytes" .Fa "u_int64_t *total_transfers" .Fa "u_int64_t *total_blocks" .Fa "long double *kb_per_transfer" .Fa "long double *transfers_per_second" .Fa "long double *mb_per_second" .Fa "long double *blocks_per_second" .Fa "long double *ms_per_transaction" .Fc .Ft long double .Fo compute_etime .Fa "struct timeval cur_time" .Fa "struct timeval prev_time" .Fc .Sh DESCRIPTION The .Nm library is a library of helper functions for dealing with the kernel .Xr devstat 9 interface, which is accessible to users via .Xr sysctl 3 .
p .Fn getnumdevs returns the number of devices registered with the .Nm devstat subsystem in the kernel.
p .Fn getgeneration returns the current generation of the .Nm devstat list of devices in the kernel.
p .Fn getversion returns the current kernel .Nm devstat version.
p .Fn checkversion 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 .Va devstat_errbuf and returns -1.
p .Fn getdevs fetches the current list of devices and statistics into the supplied .Va statinfo structure. The .Va statinfo structure can be found in .Aq Pa devstat.h : d -literal -offset indent struct statinfo { long cp_time[CPUSTATES]; long tk_nin; long tk_nout; struct devinfo *dinfo; struct timeval busy_time; }; .Ed
p .Fn getdevs expects the .Va statinfo structure to be allocated, and it also expects the .Va dinfo subelement to be allocated and zeroed prior to the first invocation of .Fn getdevs . The .Va dinfo subelement is used to store state between calls, and should not be modified after the first call to .Fn getdevs . The .Va dinfo subelement contains the following elements: d -literal -offset indent struct devinfo { struct devstat *devices; u_int8_t *mem_ptr; long generation; int numdevs; }; .Ed
p The .Va kern.devstat.all .Nm sysctl variable contains an array of .Nm devstat structures, but at the head of the array is the current .Nm 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 .Nm sysctl 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.
p The .Va mem_ptr subelement of the .Va devinfo structure is a pointer to memory that is allocated, and resized if necessary, by .Fn getdevs . The devices subelement of the .Va devinfo structure is basically a pointer to the beginning of the array of devstat structures from the .Va kern.devstat.all .Nm sysctl variable. The generation subelement of the .Nm devinfo structure contains the generation number from the .Va kern.devstat.all .Nm sysctl variable. The .Va numdevs subelement of the .Va devinfo structure contains the current number of devices registered with the kernel .Nm devstat subsystem.
p .Fn selectdevs selects devices to display based upon a number of criteria: l -tag -width flag t specified devices Specified devices are the first selection priority. These are generally devices specified by name by the user. e.g. da0, da1, cd0. t match patterns These are pattern matching expressions generated by .Fn buildmatch from user input. t performance If performance mode is enabled, devices will be sorted based on the .Va bytes field in the .Va device_selection structure passed in to .Fn selectdevs . The .Va bytes value currently must be maintained by the user. In the future, this may be done for him in a .Nm 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. t order in the devstat list If the selection mode is set to DS_SELECT_ADD, and if there are still less than .Va maxshowdevs devices selected, .Fn selectdevs will automatically select up to .Va maxshowdevs devices. .El
p .Fn selectdevs performs selections in four different modes: l -tag -width DS_SELECT_ADDONLY t DS_SELECT_ADD In add mode, .Fn 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 .Va maxshowdevs or until all devices are selected. t DS_SELECT_ONLY In only mode, .Fn selectdevs will clear all current selections, and will only select devices specified by name or by matching pattern. t DS_SELECT_REMOVE In remove mode, .Fn selectdevs will remove devices specified by name or by matching pattern. It will not select any additional devices. t DS_SELECT_ADDONLY In add only mode, .Fn 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. .El
p In all selection modes, .Fn selectdevs will not select any more than .Va maxshowdevs devices. One exception to this is when you are in .Dq top mode and no devices have been selected. In this case, .Fn 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.
p .Fn selectdevs handles allocation and resizing of the .Va dev_select structure passed in by the client. .Fn selectdevs uses the .Va numdevs and .Va current_generation fields to track the current .Nm generation and number of devices. If .Va num_selections is not the same as .Va numdevs or if .Va select_generation is not the same as .Va current_generation , .Fn selectdevs will resize the selection list as necessary, and re-initialize the selection array.
p .Fn buildmatch takes a comma separated match string and compiles it into a devstat_match structure that is understood by .Fn selectdevs . Match strings have the following format:
p d -literal -offset indent device,type,if .Ed
p .Fn buildmatch takes care of allocating and reallocating the match list as necessary. Currently known match types include:
p l -tag -width indent -compact t device type: l -tag -width 123456789 -compact t da Direct Access devices t sa Sequential Access devices t printer Printers t proc Processor devices t worm Write Once Read Multiple devices t cd CD devices t scanner Scanner devices t optical Optical Memory devices t changer Medium Changer devices t comm Communication devices t array Storage Array devices t enclosure Enclosure Services devices t floppy Floppy devices .El
p t interface: l -tag -width 123456789 -compact t IDE Integrated Drive Electronics devices t SCSI Small Computer System Interface devices t other Any other device interface .El
p t passthrough: l -tag -width 123456789 -compact t pass Passthrough devices .El .El
p .Fn compute_stats provides an easy way to obtain various device statistics. Only two arguments are mandatory: .Va current and .Va etime . Every other argument is optional. For most applications, the user will want to supply both .Va current and .Va previous devstat structures so that statistics may be calculated over a given period of time. In some instances, for instance when calculating statistics since system boot, the user may pass in a NULL pointer for the .Va previous argument. In that case, .Fn compute_stats will use the total stats in the .Va current structure to calculate statistics over .Va etime . The various statistics that may be calculated by .Fn compute_stats should be mostly explained by the function declaration itself, but for completeness here is a list of variable names and the statistics that will be put in them: l -tag -width transfers_per_second t total_bytes This is the total number of bytes transferred on the given device, both reads and writes, between the acquisition of .Va previous and the acquisition of .Va current . If .Va previous is NULL, the result will be the total reads and writes given in .Va current . t total_transfers This is the total number of transfers completed between the acquisition of .Va previous and the acquisition of .Va current . If .Va previous is NULL, the result will be the total number of transactions listed in .Va current . t total_blocks This is basically .Va total_bytes divided by the device blocksize. If the device blocksize is listed as .Sq 0 , the device blocksize will default to 512 bytes. t kb_per_transfer This is the average number of kilobytes per transfer during the measurement period. t transfers_per_second This is the average number of transfers per second. t mb_per_second This is average megabytes per second. t blocks_per_second This is average blocks per second. If the device blocksize is .Sq 0 , a default blocksize of 512 bytes will be used instead. t ms_per_transaction The average number of milliseconds per transaction. .El
p .Fn compute_etime provides an easy way to find the difference in seconds between two .Va timeval structures. This is most commonly used in conjunction with the time recorded by the .Fn getdevs function (in struct .Va statinfo ) each time it fetches the current .Nm list. .Sh RETURN VALUES .Fn getnumdevs , .Fn getgeneration , and .Fn getversion return the indicated sysctl variable, or -1 if there is an error fetching the variable.
p .Fn checkversion returns 0 if the kernel and userland .Nm devstat versions match. If they do not match, it returns -1.
p .Fn getdevs and .Fn selectdevs 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 .Fn getdevs is usually a hint to re-run .Fn selectdevs because the device list has changed.
p .Fn buildmatch returns -1 for error, and 0 if there is no error.
p .Fn compute_stats returns -1 for error, and 0 for success.
p .Fn compute_etime returns the computed elapsed time.
p If an error is returned from one of the .Nm library functions, the reason for the error is generally printed in the global string .Va devstat_errbuf which is .Dv DEVSTAT_ERRBUF_SIZE characters long. .Sh SEE ALSO .Xr systat 1 , .Xr iostat 8 , .Xr rpc.rstatd 8 , .Xr vmstat 8 , .Xr devstat 9 .Sh HISTORY The .Nm statistics system first appeared in .Fx 3.0 . .Sh AUTHORS .An Kenneth Merry Aq ken@FreeBSD.ORG .Sh BUGS There should probably be an interface to de-allocate memory allocated by .Fn getdevs , .Fn selectdevs , and .Fn buildmatch .
p .Fn selectdevs should probably not select more than .Va maxshowdevs devices in .Dq top mode when no devices have been selected previously.
p There should probably be functions to perform the statistics buffer swapping that goes on in most of the clients of this library.
p The .Va statinfo and .Va devinfo structures should probably be cleaned up and thought out a little more.