2 .\" Copyright (c) 1998, 1999 Kenneth D. Merry.
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
13 .\" 3. The name of the author may not be used to endorse or promote products
14 .\" derived from this software without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 .Nm devstat_add_entry ,
36 .Nm devstat_end_transaction ,
37 .Nm devstat_end_transaction_bio ,
38 .Nm devstat_remove_entry ,
39 .Nm devstat_start_transaction
40 .Nd kernel interface for keeping device statistics
45 .Fa "struct devstat *ds"
46 .Fa "const char *dev_name"
48 .Fa "u_int32_t block_size"
49 .Fa "devstat_support_flags flags"
50 .Fa "devstat_type_flags device_type"
51 .Fa "devstat_priority priority"
54 .Fn devstat_remove_entry "struct devstat *ds"
56 .Fn devstat_start_transaction "struct devstat *ds"
58 .Fo devstat_end_transaction
59 .Fa "struct devstat *ds"
61 .Fa "devstat_tag_type tag_type"
62 .Fa "devstat_trans_flags flags"
65 .Fo devstat_end_transaction_bio
66 .Fa "struct devstat *ds"
70 The devstat subsystem is an interface for recording device
71 statistics, as its name implies.
72 The idea is to keep reasonably detailed
73 statistics while utilizing a minimum amount of CPU time to record them.
74 Thus, no statistical calculations are actually performed in the kernel
77 code. Instead, that is left for user programs to handle.
80 registers a device with the
83 The caller is expected to have already allocated \fBand zeroed\fR
84 the devstat structure before calling this function.
86 takes several arguments:
87 .Bl -tag -width device_type
91 structure, allocated and zeroed by the client.
93 The device name. e.g. da, cd, sa.
97 Block size of the device, if supported.
98 If the device does not support a
99 block size, or if the blocksize is unknown at the time the device is added
102 list, it should be set to 0.
104 Flags indicating operations supported or not supported by the device.
105 See below for details.
108 This is broken into three sections: base device type
109 (e.g. direct access, CDROM, sequential access), interface type (IDE, SCSI
110 or other) and a pass-through flag to indicate pas-through devices.
111 See below for a complete list of types.
114 The priority is used to determine how devices are
118 Devices are sorted first by priority (highest to lowest),
119 and then by attach order.
120 See below for a complete list of available
124 .Fn devstat_remove_entry
125 removes a device from the
128 It takes the devstat structure for the device in question as
132 generation number is incremented and the number of devices is decremented.
134 .Fn devstat_start_transaction
135 registers the start of a transaction with the
138 The busy count is incremented with each transaction start.
139 When a device goes from idle to busy, the system uptime is recorded in the
145 .Fn devstat_end_transaction
146 registers the end of a transaction with the
149 It takes four arguments:
150 .Bl -tag -width tag_type
154 structure for the device in question.
156 The number of bytes transferred in this transaction.
158 Transaction tag type.
159 See below for tag types.
161 Transaction flags indicating whether the transaction was a read, write, or
162 whether no data was transferred.
165 .Fn devstat_end_transaction_bio
167 .Fn devstat_end_transaction
168 which pulls all the information from a
170 which is ready for biodone().
174 structure is composed of the following fields:
175 .Bl -tag -width dev_creation_time
179 structure is placed in a linked list when it is registered.
182 field contains a pointer to the next entry in the list of
186 The device number is a unique identifier for each device.
188 number is incremented for each new device that is registered.
190 number is currently only a 32-bit integer, but it could be enlarged if
191 someone has a system with more than four billion device arrival events.
193 The device name is a text string given by the registering driver to
201 The unit number identifies the particular instance of the peripheral driver
204 This is the number of bytes that have been written to the device.
205 This number is currently an unsigned 64 bit integer.
207 eliminate the counter wrap that would come very quickly on some systems if
208 32 bit integers were used.
210 This is the number of bytes that have been read from the device.
212 This is the number of bytes that have been freed/erased on the device.
214 This is the number of reads from the device.
216 This is the number of writes to the device.
218 This is the number of free/erase operations on the device.
220 This is the number of transactions to the device which are neither reads or
224 drivers often send a test unit ready command to
227 The test unit ready command does not read or write any data.
228 It merely causes the device to return its status.
230 This is the current number of outstanding transactions for the device.
231 This should never go below zero, and on an idle device it should be zero.
232 If either one of these conditions is not true, it indicates a problem in
234 .Fn devstat_start_transaction
236 .Fn devstat_end_transaction
237 are being called in client code.
238 There should be one and only one
239 transaction start event and one transaction end event for each transaction.
241 This is the block size of the device, if the device has a block size.
243 This is an array of counters to record the number of various tag types that
244 are sent to a device.
245 See below for a list of tag types.
246 .It dev_creation_time
247 This is the time, as reported by
249 that the device was registered.
251 This is the amount of time that the device busy count has been greater than
253 This is only updated when the busy count returns to zero.
255 This is the time, as reported by
257 that the device busy count went from zero to one.
259 This is the time as reported by
261 that a transaction last completed.
262 It is used along with
264 to calculate the device busy time.
266 These flags indicate which statistics measurements are supported by a
268 These flags are primarily intended to serve as an aid
269 to userland programs that decipher the statistics.
271 This is the device type.
272 It consists of three parts: the device type
273 (e.g. direct access, CDROM, sequential access, etc.), the interface (IDE,
274 SCSI or other) and whether or not the device in question is a pass-through
276 See below for a complete list of device types.
278 This is the priority.
279 This is the first parameter used to determine where
280 to insert a device in the
283 The second parameter is attach order.
284 See below for a list of
285 available priorities.
288 Each device is given a device type.
289 Pass-through devices have the same
290 underlying device type and interface as the device they provide an
291 interface for, but they also have the pass-through flag set.
293 device types are identical to the
295 device type numbers, so with
297 peripherals, the device type returned from an inquiry is usually ORed with
300 interface type and the pass-through flag if appropriate.
302 flags are as follows:
303 .Bd -literal -offset indent
305 DEVSTAT_TYPE_DIRECT = 0x000,
306 DEVSTAT_TYPE_SEQUENTIAL = 0x001,
307 DEVSTAT_TYPE_PRINTER = 0x002,
308 DEVSTAT_TYPE_PROCESSOR = 0x003,
309 DEVSTAT_TYPE_WORM = 0x004,
310 DEVSTAT_TYPE_CDROM = 0x005,
311 DEVSTAT_TYPE_SCANNER = 0x006,
312 DEVSTAT_TYPE_OPTICAL = 0x007,
313 DEVSTAT_TYPE_CHANGER = 0x008,
314 DEVSTAT_TYPE_COMM = 0x009,
315 DEVSTAT_TYPE_ASC0 = 0x00a,
316 DEVSTAT_TYPE_ASC1 = 0x00b,
317 DEVSTAT_TYPE_STORARRAY = 0x00c,
318 DEVSTAT_TYPE_ENCLOSURE = 0x00d,
319 DEVSTAT_TYPE_FLOPPY = 0x00e,
320 DEVSTAT_TYPE_MASK = 0x00f,
321 DEVSTAT_TYPE_IF_SCSI = 0x010,
322 DEVSTAT_TYPE_IF_IDE = 0x020,
323 DEVSTAT_TYPE_IF_OTHER = 0x030,
324 DEVSTAT_TYPE_IF_MASK = 0x0f0,
325 DEVSTAT_TYPE_PASS = 0x100
326 } devstat_type_flags;
329 Devices have a priority associated with them, which controls roughly where
330 they are placed in the
333 The priorities are as follows:
334 .Bd -literal -offset indent
336 DEVSTAT_PRIORITY_MIN = 0x000,
337 DEVSTAT_PRIORITY_OTHER = 0x020,
338 DEVSTAT_PRIORITY_PASS = 0x030,
339 DEVSTAT_PRIORITY_FD = 0x040,
340 DEVSTAT_PRIORITY_WFD = 0x050,
341 DEVSTAT_PRIORITY_TAPE = 0x060,
342 DEVSTAT_PRIORITY_CD = 0x090,
343 DEVSTAT_PRIORITY_DISK = 0x110,
344 DEVSTAT_PRIORITY_ARRAY = 0x120,
345 DEVSTAT_PRIORITY_MAX = 0xfff
349 Each device has associated with it flags to indicate what operations are
350 supported or not supported.
352 .Va devstat_support_flags
353 values are as follows:
354 .Bl -tag -width DEVSTAT_NO_ORDERED_TAGS
355 .It DEVSTAT_ALL_SUPPORTED
356 Every statistic type is supported by the device.
357 .It DEVSTAT_NO_BLOCKSIZE
358 This device does not have a blocksize.
359 .It DEVSTAT_NO_ORDERED_TAGS
360 This device does not support ordered tags.
361 .It DEVSTAT_BS_UNAVAILABLE
362 This device supports a blocksize, but it is currently unavailable.
364 flag is most often used with removable media drives.
367 Transactions to a device fall into one of three categories, which are
371 .Fn devstat_end_transaction .
372 The transaction types are as follows:
373 .Bd -literal -offset indent
375 DEVSTAT_NO_DATA = 0x00,
377 DEVSTAT_WRITE = 0x02,
379 } devstat_trans_flags;
382 There are four possible values for the
385 .Fn devstat_end_transaction :
386 .Bl -tag -width DEVSTAT_TAG_ORDERED
387 .It DEVSTAT_TAG_SIMPLE
388 The transaction had a simple tag.
390 The transaction had a head of queue tag.
391 .It DEVSTAT_TAG_ORDERED
392 The transaction had an ordered tag.
394 The device doesn't support tags.
397 The tag type values correspond to the lower four bits of the
400 In CAM, for instance, the
402 from the CCB is ORed with 0xf to determine the tag type to pass in to
403 .Fn devstat_end_transaction .
408 .In sys/devicestat.h .
409 This is the current version of the
411 subsystem, and it should be incremented each time a change is made that
412 would require recompilation of userland programs that access
415 Userland programs use this version, via the
416 .Va kern.devstat.version
418 variable to determine whether they are in sync with the kernel
430 statistics system appeared in
433 .An Kenneth Merry Aq ken@FreeBSD.org
435 There may be a need for
437 protection around some of the
439 list manipulation code to insure, for example, that the list of devices
440 is not changed while someone is fetching the
445 It is impossible with the current
447 architecture to accurately measure time per transaction.
449 way to accurately measure time per transaction would be to record a
450 timestamp for every transaction.
451 This measurement is probably not
452 worthwhile for most people as it would adversely affect the performance of
453 the system and cost space to store the timestamps for individual