Copyright (c) 1998, 1999, 2001 Kenneth D. Merry.
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$FreeBSD: head/lib/libdevstat/devstat.3 148910 2005-08-10 00:51:36Z ken $
.Dd March 18, 2003 .Dt DEVSTAT 3 .Os .Sh NAME .Nm devstat , .Nm devstat_getnumdevs , .Nm devstat_getgeneration , .Nm devstat_getversion , .Nm devstat_checkversion , .Nm devstat_getdevs , .Nm devstat_selectdevs , .Nm devstat_buildmatch , .Nm devstat_compute_statistics , .Nm devstat_compute_etime .Nd device statistics utility library .Sh LIBRARY .Lb libdevstat .Sh SYNOPSIS n devstat.h .Ft int .Fn devstat_getnumdevs "kvm_t *kd" .Ft long .Fn devstat_getgeneration "kvm_t *kd" .Ft int .Fn devstat_getversion "kvm_t *kd" .Ft int .Fn devstat_checkversion "kvm_t *kd" .Ft int .Fn devstat_getdevs "kvm_t *kd" "struct statinfo *stats" .Ft int .Fo devstat_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 devstat_buildmatch .Fa "char *match_str" .Fa "struct devstat_match **matches" .Fa "int *num_matches" .Fc .Ft int .Fo devstat_compute_statistics .Fa "struct devstat *current" .Fa "struct devstat *previous" .Fa "long double etime" .Fa "..." .Fc .Ft "long double" .Fo devstat_compute_etime .Fa "struct bintime *cur_time" .Fa "struct bintime *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 and .Xr kvm 3 . All functions that take a .Vt "kvm_t *" as first argument can be passed .Dv NULL instead of a kvm handle as this argument, which causes the data to be read via .Xr sysctl 3 . Otherwise, it is read via .Xr kvm 3 using the supplied handle. The .Fn devstat_checkversion function should be called with each kvm handle that is going to be used (or with .Dv NULL if .Xr sysctl 3 is going to be used).
p The .Fn devstat_getnumdevs function returns the number of devices registered with the .Nm subsystem in the kernel.
p The .Fn devstat_getgeneration function returns the current generation of the .Nm list of devices in the kernel.
p The .Fn devstat_getversion function returns the current kernel .Nm version.
p The .Fn devstat_checkversion function checks the userland .Nm version against the kernel .Nm version. If the two are identical, it returns zero. Otherwise, it prints an appropriate error in .Va devstat_errbuf and returns -1.
p The .Fn 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 n devstat.h : d -literal -offset indent struct statinfo { long cp_time[CPUSTATES]; long tk_nin; long tk_nout; struct devinfo *dinfo; long double snap_time; }; .Ed
p The .Fn devstat_getdevs function expects the .Vt 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 devstat_getdevs . The .Va dinfo subelement is used to store state between calls, and should not be modified after the first call to .Fn devstat_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 .Xr sysctl 8 variable contains an array of .Nm structures, but at the head of the array is the current .Nm generation. The reason the generation is at the head of the buffer is so that userland software accessing the .Nm 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 .Xr 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.
p The .Va mem_ptr subelement of the .Vt devinfo structure is a pointer to memory that is allocated, and resized if necessary, by .Fn 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 .Va kern.devstat.all .Xr sysctl 8 variable (or the corresponding values read via .Xr kvm 3 ) . The generation subelement of the .Vt devinfo structure contains the corresponding generation number. The .Va numdevs subelement of the .Vt devinfo structure contains the current number of devices registered with the kernel .Nm subsystem.
p The .Fn devstat_selectdevs function selects devices to display based upon a number of criteria: l -tag -width indent t specified devices Specified devices are the first selection priority. These are generally devices specified by name by the user e.g.\& .Li da0 , da1 , cd0 . t match patterns These are pattern matching expressions generated by .Fn devstat_buildmatch from user input. t performance If performance mode is enabled, devices will be sorted based on the .Va bytes field in the .Vt device_selection structure passed in to .Fn devstat_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 .Dv DS_SELECT_ADD , and if there are still less than .Fa maxshowdevs devices selected, .Fn devstat_selectdevs will automatically select up to .Fa maxshowdevs devices. .El
p The .Fn devstat_selectdevs function performs selections in four different modes: l -tag -width ".Dv DS_SELECT_ADDONLY" t Dv DS_SELECT_ADD In .Dq add mode, .Fn 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 .Fa maxshowdevs or until all devices are selected. t Dv DS_SELECT_ONLY In .Dq only mode, .Fn devstat_selectdevs will clear all current selections, and will only select devices specified by name or by matching pattern. t Dv DS_SELECT_REMOVE In .Dq remove mode, .Fn devstat_selectdevs will remove devices specified by name or by matching pattern. It will not select any additional devices. t Dv DS_SELECT_ADDONLY In .Dq "add only" mode, .Fn devstat_selectdevs will select any unselected devices specified by name or matching pattern. In this respect it is identical to .Dq add mode. It will not, however, select any devices other than those specified. .El
p In all selection modes, .Fn devstat_selectdevs will not select any more than .Fa maxshowdevs devices. One exception to this is when you are in .Dq top mode and no devices have been selected. In this case, .Fn 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.
p The .Fn devstat_selectdevs function handles allocation and resizing of the .Fa dev_select structure passed in by the client. The .Fn devstat_selectdevs function uses the .Fa numdevs and .Fa current_generation fields to track the current .Nm 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 , .Fn devstat_selectdevs will resize the selection list as necessary, and re-initialize the selection array.
p The .Fn devstat_buildmatch function takes a comma separated match string and compiles it into a .Vt devstat_match structure that is understood by .Fn devstat_selectdevs . Match strings have the following format:
p .D1 Ar device , Ns Ar type , Ns Ar if
p The .Fn devstat_buildmatch function takes care of allocating and reallocating the match list as necessary. Currently known match types include: l -tag -width indent t device type: l -tag -width ".Li enclosure" -compact t Li da Direct Access devices t Li sa Sequential Access devices t Li printer Printers t Li proc Processor devices t Li worm Write Once Read Multiple devices t Li cd CD devices t Li scanner Scanner devices t Li optical Optical Memory devices t Li changer Medium Changer devices t Li comm Communication devices t Li array Storage Array devices t Li enclosure Enclosure Services devices t Li floppy Floppy devices .El t interface: l -tag -width ".Li enclosure" -compact t Li IDE Integrated Drive Electronics devices t Li SCSI Small Computer System Interface devices t Li other Any other device interface .El t passthrough: l -tag -width ".Li enclosure" -compact t Li pass Passthrough devices .El .El
p The .Fn devstat_compute_statistics function provides complete statistics calculation. There are four arguments for which values .Em must be supplied: .Fa current , .Fa previous , .Fa etime , and the terminating argument for the varargs list, .Dv 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 .Dv NULL pointer for the .Fa previous argument. In that case, .Fn 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: l -tag -width ".Dv DSM_TRANSFERS_PER_SECOND_OTHER" t Dv DSM_NONE type: N/A
p This .Em must be the last argument passed to .Fn devstat_compute_statistics . It is an argument list terminator. t Dv DSM_TOTAL_BYTES type: .Vt "u_int64_t *"
p The total number of bytes transferred between the acquisition of .Fa previous and .Fa current . t Dv DSM_TOTAL_BYTES_READ t Dv DSM_TOTAL_BYTES_WRITE t Dv DSM_TOTAL_BYTES_FREE type: .Vt "u_int64_t *"
p The total number of bytes in transactions of the specified type between the acquisition of .Fa previous and .Fa current . t Dv DSM_TOTAL_TRANSFERS type: .Vt "u_int64_t *"
p The total number of transfers between the acquisition of .Fa previous and .Fa current . t Dv DSM_TOTAL_TRANSFERS_OTHER t Dv DSM_TOTAL_TRANSFERS_READ t Dv DSM_TOTAL_TRANSFERS_WRITE t Dv DSM_TOTAL_TRANSFERS_FREE type: .Vt "u_int64_t *"
p The total number of transactions of the specified type between the acquisition of .Fa previous and .Fa current . t Dv DSM_TOTAL_BLOCKS type: .Vt "u_int64_t *"
p 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. t Dv DSM_TOTAL_BLOCKS_READ t Dv DSM_TOTAL_BLOCKS_WRITE t Dv DSM_TOTAL_BLOCKS_FREE type: .Vt "u_int64_t *"
p 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. t Dv DSM_KB_PER_TRANSFER type: .Vt "long double *"
p The average number of kilobytes per transfer between the acquisition of .Fa previous and .Fa current . t Dv DSM_KB_PER_TRANSFER_READ t Dv DSM_KB_PER_TRANSFER_WRITE t Dv DSM_KB_PER_TRANSFER_FREE type: .Vt "long double *"
p The average number of kilobytes in the specified type transaction between the acquisition of .Fa previous and .Fa current . t Dv DSM_TRANSFERS_PER_SECOND type: .Vt "long double *"
p The average number of transfers per second between the acquisition of .Fa previous and .Fa current . t Dv DSM_TRANSFERS_PER_SECOND_OTHER t Dv DSM_TRANSFERS_PER_SECOND_READ t Dv DSM_TRANSFERS_PER_SECOND_WRITE t Dv DSM_TRANSFERS_PER_SECOND_FREE type: .Vt "long double *"
p The average number of transactions of the specified type per second between the acquisition of .Fa previous and .Fa current . t Dv DSM_MB_PER_SECOND type: .Vt "long double *"
p The average number of megabytes transferred per second between the acquisition of .Fa previous and .Fa current . t Dv DSM_MB_PER_SECOND_READ t Dv DSM_MB_PER_SECOND_WRITE t Dv DSM_MB_PER_SECOND_FREE type: .Vt "long double *"
p The average number of megabytes per second in the specified type of transaction between the acquisition of .Fa previous and .Fa current . t Dv DSM_BLOCKS_PER_SECOND type: .Vt "long double *"
p 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. t Dv DSM_BLOCKS_PER_SECOND_READ t Dv DSM_BLOCKS_PER_SECOND_WRITE t Dv DSM_BLOCKS_PER_SECOND_FREE type: .Vt "long double *"
p 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. t Dv DSM_MS_PER_TRANSACTION type: .Vt "long double *"
p The average duration of transactions between the acquisition of .Fa previous and .Fa current . t Dv DSM_MS_PER_TRANSACTION_OTHER t Dv DSM_MS_PER_TRANSACTION_READ t Dv DSM_MS_PER_TRANSACTION_WRITE t Dv DSM_MS_PER_TRANSACTION_FREE type: .Vt "long double *"
p The average duration of transactions of the specified type between the acquisition of .Fa previous and .Fa current . t Dv DSM_BUSY_PCT type: .Vt "long double *"
p The percentage of time the device had one or more transactions outstanding between the acquisition of .Fa previous and .Fa current . t Dv DSM_QUEUE_LENGTH type: .Vt "u_int64_t *"
p The number of not yet completed transactions at the time when .Fa current was acquired. t Dv DSM_SKIP type: N/A
p If you do not need a result from .Fn devstat_compute_statistics , just put .Dv DSM_SKIP as first (type) parameter and .Dv NULL as second parameter. This can be useful in scenarios where the statistics to be calculated are determined at run time. .El
p The .Fn 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 .Fn devstat_getdevs function (in .Vt "struct statinfo" ) each time it fetches the current .Nm list. .Sh RETURN VALUES The .Fn devstat_getnumdevs , .Fn devstat_getgeneration , and .Fn devstat_getversion function return the indicated sysctl variable, or -1 if there is an error fetching the variable.
p The .Fn devstat_checkversion function returns 0 if the kernel and userland .Nm versions match. If they do not match, it returns -1.
p The .Fn devstat_getdevs and .Fn 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 .Fn devstat_getdevs is usually a hint to re-run .Fn devstat_selectdevs because the device list has changed.
p The .Fn devstat_buildmatch function returns -1 for error, and 0 if there is no error.
p The .Fn devstat_compute_etime function returns the computed elapsed time.
p The .Fn devstat_compute_statistics function returns -1 for error, and 0 for success.
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 kvm 3 , .Xr sysctl 3 , .Xr iostat 8 , .Xr rpc.rstatd 8 , .Xr sysctl 8 , .Xr vmstat 8 , .Xr devstat 9 .Sh HISTORY The .Nm statistics system first appeared in .Fx 3.0 . The new interface (the functions prefixed with .Li devstat_ ) first appeared in .Fx 5.0 . .Sh AUTHORS .An Kenneth Merry Aq ken@FreeBSD.org .Sh BUGS There should probably be an interface to de-allocate memory allocated by .Fn devstat_getdevs , .Fn devstat_selectdevs , and .Fn devstat_buildmatch .
p The .Fn devstat_selectdevs function should probably not select more than .Fa 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 .Vt statinfo and .Vt devinfo structures should probably be cleaned up and thought out a little more.