freebsd/lib/libdevstat/devstat.3

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.Dd December 15, 2012
.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
.In 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).
.Pp
The
.Fn devstat_getnumdevs
function
returns the number of devices registered with the
.Nm
subsystem in the kernel.
.Pp
The
.Fn devstat_getgeneration
function
returns the current generation of the
.Nm
list of devices in the kernel.
.Pp
The
.Fn devstat_getversion
function
returns the current kernel
.Nm
version.
.Pp
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.
.Pp
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
.In devstat.h :
.Bd -literal -offset indent
struct statinfo {
	long            cp_time[CPUSTATES];
	long            tk_nin;
	long            tk_nout;
	struct devinfo  *dinfo;
	long double     snap_time;
};
.Ed
.Pp
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:
.Bd -literal -offset indent
struct devinfo {
	struct devstat	*devices;
	uint8_t		*mem_ptr;
	long		generation;
	int		numdevs;
};
.Ed
.Pp
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.
.Pp
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.
.Pp
The
.Fn devstat_selectdevs
function
selects devices to display based upon a number of criteria:
.Bl -tag -width indent
.It 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 .
.It match patterns
These are pattern matching expressions generated by
.Fn devstat_buildmatch
from user input.
.It 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.
.It 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
.Pp
The
.Fn devstat_selectdevs
function
performs selections in four different modes:
.Bl -tag -width ".Dv DS_SELECT_ADDONLY"
.It 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.
.It 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.
.It 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.
.It 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
.Pp
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.
.Pp
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.
.Pp
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:
.Pp
.D1 Ar device , Ns Ar type , Ns Ar if
.Pp
The
.Fn devstat_buildmatch
function
takes care of allocating and reallocating the match list as necessary.
Currently known match types include:
.Bl -tag -width indent
.It device type:
.Bl -tag -width ".Li enclosure" -compact
.It Li da
Direct Access devices
.It Li sa
Sequential Access devices
.It Li printer
Printers
.It Li proc
Processor devices
.It Li worm
Write Once Read Multiple devices
.It Li cd
CD devices
.It Li scanner
Scanner devices
.It Li optical
Optical Memory devices
.It Li changer
Medium Changer devices
.It Li comm
Communication devices
.It Li array
Storage Array devices
.It Li enclosure
Enclosure Services devices
.It Li floppy
Floppy devices
.El
.It interface:
.Bl -tag -width ".Li enclosure" -compact
.It Li IDE
Integrated Drive Electronics devices
.It Li SCSI
Small Computer System Interface devices
.It Li other
Any other device interface
.El
.It passthrough:
.Bl -tag -width ".Li enclosure" -compact
.It Li pass
Passthrough devices
.El
.El
.Pp
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 uint64_t
is used,
or floating point, for which a
.Vt "long double"
is used.
The statistics that may be calculated are:
.Bl -tag -width ".Dv DSM_TRANSFERS_PER_SECOND_OTHER"
.It Dv DSM_NONE
type: N/A
.Pp
This
.Em must
be the last argument passed to
.Fn devstat_compute_statistics .
It is an argument list terminator.
.It Dv DSM_TOTAL_BYTES
type:
.Vt "uint64_t *"
.Pp
The total number of bytes transferred between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_BYTES_READ
.It Dv DSM_TOTAL_BYTES_WRITE
.It Dv DSM_TOTAL_BYTES_FREE
type:
.Vt "uint64_t *"
.Pp
The total number of bytes in transactions of the specified type
between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_TRANSFERS
type:
.Vt "uint64_t *"
.Pp
The total number of transfers between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_TRANSFERS_OTHER
.It Dv DSM_TOTAL_TRANSFERS_READ
.It Dv DSM_TOTAL_TRANSFERS_WRITE
.It Dv DSM_TOTAL_TRANSFERS_FREE
type:
.Vt "uint64_t *"
.Pp
The total number of transactions of the specified type between
the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_DURATION
type:
.Vt "long double *"
.Pp
The total duration of transactions, in seconds, between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_DURATION_OTHER
.It Dv DSM_TOTAL_DURATION_READ
.It Dv DSM_TOTAL_DURATION_WRITE
.It Dv DSM_TOTAL_DURATION_FREE
type:
.Vt "long double *"
.Pp
The total duration of transactions of the specified type between
the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_BUSY_TIME
type:
.Vt "long double *"
.Pp
Total time the device had one or more transactions outstanding
between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TOTAL_BLOCKS
type:
.Vt "uint64_t *"
.Pp
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.
.It Dv DSM_TOTAL_BLOCKS_READ
.It Dv DSM_TOTAL_BLOCKS_WRITE
.It Dv DSM_TOTAL_BLOCKS_FREE
type:
.Vt "uint64_t *"
.Pp
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.
.It Dv DSM_KB_PER_TRANSFER
type:
.Vt "long double *"
.Pp
The average number of kilobytes per transfer between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_KB_PER_TRANSFER_READ
.It Dv DSM_KB_PER_TRANSFER_WRITE
.It Dv DSM_KB_PER_TRANSFER_FREE
type:
.Vt "long double *"
.Pp
The average number of kilobytes in the specified type transaction between
the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TRANSFERS_PER_SECOND
type:
.Vt "long double *"
.Pp
The average number of transfers per second between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_TRANSFERS_PER_SECOND_OTHER
.It Dv DSM_TRANSFERS_PER_SECOND_READ
.It Dv DSM_TRANSFERS_PER_SECOND_WRITE
.It Dv DSM_TRANSFERS_PER_SECOND_FREE
type:
.Vt "long double *"
.Pp
The average number of transactions of the specified type per second
between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_MB_PER_SECOND
type:
.Vt "long double *"
.Pp
The average number of megabytes transferred per second between the
acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_MB_PER_SECOND_READ
.It Dv DSM_MB_PER_SECOND_WRITE
.It Dv DSM_MB_PER_SECOND_FREE
type:
.Vt "long double *"
.Pp
The average number of megabytes per second in the specified type of
transaction between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_BLOCKS_PER_SECOND
type:
.Vt "long double *"
.Pp
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.
.It Dv DSM_BLOCKS_PER_SECOND_READ
.It Dv DSM_BLOCKS_PER_SECOND_WRITE
.It Dv DSM_BLOCKS_PER_SECOND_FREE
type:
.Vt "long double *"
.Pp
The average number of blocks per second in the specified 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.
.It Dv DSM_MS_PER_TRANSACTION
type:
.Vt "long double *"
.Pp
The average duration of transactions between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_MS_PER_TRANSACTION_OTHER
.It Dv DSM_MS_PER_TRANSACTION_READ
.It Dv DSM_MS_PER_TRANSACTION_WRITE
.It Dv DSM_MS_PER_TRANSACTION_FREE
type:
.Vt "long double *"
.Pp
The average duration of transactions of the specified type between the
acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_BUSY_PCT
type:
.Vt "long double *"
.Pp
The percentage of time the device had one or more transactions outstanding
between the acquisition of
.Fa previous
and
.Fa current .
.It Dv DSM_QUEUE_LENGTH
type:
.Vt "uint64_t *"
.Pp
The number of not yet completed transactions at the time when
.Fa current
was acquired.
.It Dv DSM_SKIP
type: N/A
.Pp
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
.Pp
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.
.Pp
The
.Fn devstat_checkversion
function
returns 0 if the kernel and userland
.Nm
versions match.
If they do not match, it returns \-1.
.Pp
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.
.Pp
The
.Fn devstat_buildmatch
function returns \-1 for error, and 0 if there is no error.
.Pp
The
.Fn devstat_compute_etime
function
returns the computed elapsed time.
.Pp
The
.Fn devstat_compute_statistics
function returns \-1 for error, and 0 for success.
.Pp
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 Mt 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 .
.Pp
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.
.Pp
There should probably be functions to perform the statistics buffer
swapping that goes on in most of the clients of this library.
.Pp
The
.Vt statinfo
and
.Vt devinfo
structures should probably be cleaned up and thought out a little more.