2 .\" Copyright (c) 1998, 1999 Kenneth D. Merry.
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28 .\" $FreeBSD: src/lib/libdevstat/devstat.3,v 1.7.2.8 2001/12/17 10:08:29 ru Exp $
44 .Nd device statistics utility library
53 .Fn getgeneration "void"
57 .Fn checkversion "void"
59 .Fn getdevs "struct statinfo *stats"
62 .Fa "struct device_selection **dev_select"
63 .Fa "int *num_selected"
64 .Fa "int *num_selections"
65 .Fa "long *select_generation"
66 .Fa "long current_generation"
67 .Fa "struct devstat *devices"
69 .Fa "struct devstat_match *matches"
71 .Fa "char **dev_selections"
72 .Fa "int num_dev_selections"
73 .Fa "devstat_select_mode select_mode"
80 .Fa "struct devstat_match **matches"
81 .Fa "int *num_matches"
85 .Fa "struct devstat *current"
86 .Fa "struct devstat *previous"
87 .Fa "long double etime"
88 .Fa "u_int64_t *total_bytes"
89 .Fa "u_int64_t *total_transfers"
90 .Fa "u_int64_t *total_blocks"
91 .Fa "long double *kb_per_transfer"
92 .Fa "long double *transfers_per_second"
93 .Fa "long double *mb_per_second"
94 .Fa "long double *blocks_per_second"
95 .Fa "long double *ms_per_transaction"
99 .Fa "struct timeval cur_time"
100 .Fa "struct timeval prev_time"
105 library is a library of helper functions for dealing with the kernel
107 interface, which is accessible to users via
111 returns the number of devices registered with the
113 subsystem in the kernel.
116 returns the current generation of the
118 list of devices in the kernel.
121 returns the current kernel
126 checks the userland devstat version against the kernel devstat version.
127 If the two are identical, it returns zero.
128 Otherwise, it prints an appropriate error in
133 fetches the current list of devices and statistics into the supplied
138 structure can be found in
140 .Bd -literal -offset indent
142 long cp_time[CPUSTATES];
145 struct devinfo *dinfo;
146 struct timeval busy_time;
153 structure to be allocated, and it also expects the
155 subelement to be allocated and zeroed prior to the first invocation of
159 subelement is used to store state between calls, and should not be modified
160 after the first call to
164 subelement contains the following elements:
165 .Bd -literal -offset indent
167 struct devstat *devices;
177 variable contains an array of
179 structures, but at the head of the array is the current
182 The reason the generation is at the head of the buffer is so that userland
183 software accessing the devstat statistics information can atomically get
184 both the statistics information and the corresponding generation number.
185 If client software were forced to get the generation number via a separate
187 variable (which is available for convenience), the list of devices could
188 change between the time the client gets the generation and the time the
189 client gets the device list.
195 structure is a pointer to memory that is allocated, and resized if
198 The devices subelement of the
200 structure is basically a pointer to the beginning of the array of devstat
205 The generation subelement of the
207 structure contains the generation number from the
215 structure contains the current
216 number of devices registered with the kernel
221 selects devices to display based upon a number of criteria:
223 .It specified devices
224 Specified devices are the first selection priority.
225 These are generally devices specified by name by the user e.g. da0, da1, cd0.
227 These are pattern matching expressions generated by
231 If performance mode is enabled, devices will be sorted based on the
235 structure passed in to
239 value currently must be maintained by the user.
240 In the future, this may be done for him in a
243 If no devices have been selected by name or by pattern, the performance
244 tracking code will select every device in the system, and sort them by
246 If devices have been selected by name or pattern, the performance tracking
247 code will honor those selections and will only sort among the selected
249 .It order in the devstat list
250 If the selection mode is set to DS_SELECT_ADD, and if there are still less
255 will automatically select up to
261 performs selections in four different modes:
262 .Bl -tag -width DS_SELECT_ADDONLY
266 will select any unselected devices specified by name or matching pattern.
267 It will also select more devices, in devstat list order, until the number
268 of selected devices is equal to
270 or until all devices are
275 will clear all current selections, and will only select devices specified
276 by name or by matching pattern.
280 will remove devices specified by name or by matching pattern.
281 It will not select any additional devices.
282 .It DS_SELECT_ADDONLY
285 will select any unselected devices specified by name or matching pattern.
286 In this respect it is identical to add mode.
287 It will not, however, select any devices other than those specified.
290 In all selection modes,
292 will not select any more than
295 One exception to this is when you are in
297 mode and no devices have been selected.
300 will select every device in the system.
301 Client programs must pay attention to selection order when deciding whether
302 to pay attention to a particular device.
303 This may be the wrong behavior, and probably requires additional thought.
306 handles allocation and resizing of the
314 .Va current_generation
318 generation and number of devices.
325 .Va select_generation
327 .Va current_generation ,
329 will resize the selection list as necessary, and re-initialize the
333 takes a comma separated match string and compiles it into a
334 \fBdevstat_match\fR structure that is understood by
336 Match strings have the following format:
338 .Bd -literal -offset indent
343 takes care of allocating and reallocating the match list as necessary.
344 Currently known match types include:
346 .Bl -tag -width indent -compact
348 .Bl -tag -width 9n -compact
350 Direct Access devices
352 Sequential Access devices
358 Write Once Read Multiple devices
364 Optical Memory devices
366 Medium Changer devices
368 Communication devices
370 Storage Array devices
372 Enclosure Services devices
378 .Bl -tag -width 9n -compact
380 Integrated Drive Electronics devices
382 Small Computer System Interface devices
384 Any other device interface
388 .Bl -tag -width 9n -compact
395 provides an easy way to obtain various device statistics.
396 Only two arguments are mandatory:
400 Every other argument is optional.
401 For most applications, the user will want to supply both
405 devstat structures so that statistics may be calculated over a given period
407 In some instances, for instance when calculating statistics since system boot,
408 the user may pass in a NULL pointer for the
413 will use the total stats in the
415 structure to calculate statistics over
417 The various statistics that may be calculated by
419 should be mostly explained by the function declaration itself, but for
420 completeness here is a list of variable names and the statistics that will
422 .Bl -tag -width transfers_per_second
424 This is the total number of bytes transferred on the given device, both
425 reads and writes, between the acquisition of
427 and the acquisition of
431 is NULL, the result will be the total reads and writes given in
434 This is the total number of transfers completed between the
437 and the acquisition of
441 is NULL, the result will be the total number of transactions listed in
446 divided by the device blocksize.
447 If the device blocksize is listed as
449 the device blocksize will default to 512 bytes.
451 This is the average number of kilobytes per transfer during the measurement
453 .It transfers_per_second
454 This is the average number of transfers per second.
456 This is average megabytes per second.
457 .It blocks_per_second
458 This is average blocks per second.
459 If the device blocksize is
461 a default blocksize of 512 bytes will be used instead.
462 .It ms_per_transaction
463 The average number of milliseconds per transaction.
467 provides an easy way to find the difference in seconds between two
470 This is most commonly used in conjunction with the time recorded by the
474 each time it fetches the current
482 return the indicated \fBsysctl\fR variable, or -1 if there is an error
483 fetching the variable.
486 returns 0 if the kernel and userland
489 If they do not match, it returns -1.
494 return -1 in case of an error, 0 if there is no error and 1 if the device
495 list or selected devices have changed.
496 A return value of 1 from
498 is usually a hint to re-run
500 because the device list has changed.
503 returns -1 for error, and 0 if there is no error.
506 returns -1 for error, and 0 for success.
509 returns the computed elapsed time.
511 If an error is returned from one of the
513 library functions, the reason for the error is generally printed in
517 .Dv DEVSTAT_ERRBUF_SIZE
528 statistics system first appeared in
531 .An Kenneth Merry Aq ken@FreeBSD.org
533 There should probably be an interface to de-allocate memory allocated by
540 should probably not select more than
544 mode when no devices have been selected previously.
546 There should probably be functions to perform the statistics buffer
547 swapping that goes on in most of the clients of this library.
553 structures should probably be cleaned up and thought out a little more.