2 .\" Copyright (c) 1998, 1999 Kenneth D. Merry.
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28 .\" $FreeBSD: src/share/man/man9/devstat.9,v 1.10.2.5 2001/12/17 11:30:18 ru Exp $
35 .Nm devstat_add_entry ,
36 .Nm devstat_end_transaction ,
37 .Nm devstat_end_transaction_buf ,
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_buf
66 .Fa "struct devstat *ds"
70 The devstat subsystem is an interface for recording device
71 statistics, as its name implies. The idea is to keep reasonably detailed
72 statistics while utilizing a minimum amount of CPU time to record them.
73 Thus, no statistical calculations are actually performed in the kernel
76 code. Instead, that is left for user programs to handle.
79 registers a device with the
81 subsystem. The caller is expected to have already allocated \fBand zeroed\fR
82 the devstat structure before calling this function.
84 takes several arguments:
85 .Bl -tag -width device_type
89 structure, allocated and zeroed by the client.
91 The device name. e.g. da, cd, sa.
95 Block size of the device, if supported. If the device does not support a
96 block size, or if the blocksize is unknown at the time the device is added
99 list, it should be set to 0.
101 Flags indicating operations supported or not supported by the device. See
104 The device type. This is broken into three sections: base device type
105 (e.g. direct access, CDROM, sequential access), interface type (IDE, SCSI
106 or other) and a passthrough flag to indicate pasthrough devices. See below
107 for a complete list of types.
109 The device priority. The priority is used to determine how devices are
112 list of devices. Devices are sorted first by priority (highest to lowest),
113 and then by attach order. See below for a complete list of available
117 .Fn devstat_remove_entry
118 removes a device from the
120 subsystem. It takes the devstat structure for the device in question as
123 generation number is incremented and the number of devices is decremented.
125 .Fn devstat_start_transaction
126 registers the start of a transaction with the
128 subsystem. The busy count is incremented with each transaction start.
129 When a device goes from idle to busy, the system uptime is recorded in the
135 .Fn devstat_end_transaction
136 registers the end of a transaction with the
138 subsystem. It takes four arguments:
139 .Bl -tag -width tag_type
143 structure for the device in question.
145 The number of bytes transferred in this transaction.
147 Transaction tag type. See below for tag types.
149 Transaction flags indicating whether the transaction was a read, write, or
150 whether no data was transferred.
153 .Fn devstat_end_transaction_buf
155 .Fn devstat_end_transaction
156 which pulls all the information from a
158 which is ready for biodone().
162 structure is composed of the following fields:
163 .Bl -tag -width dev_creation_time
167 structure is placed in a linked list when it is registered. The
169 field contains a pointer to the next entry in the list of
173 The device number is a unique identifier for each device. The device
174 number is incremented for each new device that is registered. The device
175 number is currently only a 32-bit integer, but it could be enlarged if
176 someone has a system with more than four billion device arrival events.
178 The device name is a text string given by the registering driver to
179 identify itself. (e.g.\&
185 The unit number identifies the particular instance of the peripheral driver
188 This is the number of bytes that have been written to the device. This
189 number is currently an unsigned 64 bit integer. This will hopefully
190 eliminate the counter wrap that would come very quickly on some systems if
191 32 bit integers were used.
193 This is the number of bytes that have been read from the device.
195 This is the number of bytes that have been freed/erased on the device.
197 This is the number of reads from the device.
199 This is the number of writes to the device.
201 This is the number of free/erase operations on the device.
203 This is the number of transactions to the device which are neither reads or
204 writes. For instance,
206 drivers often send a test unit ready command to
208 devices. The test unit ready command does not read or write any data. It
209 merely causes the device to return its status.
211 This is the current number of outstanding transactions for the device.
212 This should never go below zero, and on an idle device it should be zero.
213 If either one of these conditions is not true, it indicates a problem in
215 .Fn devstat_start_transaction
217 .Fn devstat_end_transaction
218 are being called in client code. There should be one and only one
219 transaction start event and one transaction end event for each transaction.
221 This is the block size of the device, if the device has a block size.
223 This is an array of counters to record the number of various tag types that
224 are sent to a device. See below for a list of tag types.
225 .It dev_creation_time
226 This is the time, as reported by
228 that the device was registered.
230 This is the amount of time that the device busy count has been greater than
231 zero. This is only updated when the busy count returns to zero.
233 This is the time, as reported by
235 that the device busy count went from zero to one.
237 This is the time as reported by
239 that a transaction last completed. It is used along with
241 to calculate the device busy time.
243 These flags indicate which statistics measurements are supported by a
244 particular device. These flags are primarily intended to serve as an aid
245 to userland programs that decipher the statistics.
247 This is the device type. It consists of three parts: the device type
248 (e.g. direct access, CDROM, sequential access, etc.), the interface (IDE,
249 SCSI or other) and whether or not the device in question is a passthrough
250 driver. See below for a complete list of device types.
252 This is the priority. This is the first parameter used to determine where
253 to insert a device in the
255 list. The second parameter is attach order. See below for a list of
256 available priorities.
259 Each device is given a device type. Passthrough devices have the same
260 underlying device type and interface as the device they provide an
261 interface for, but they also have the passthrough flag set. The base
262 device types are identical to the
264 device type numbers, so with
266 peripherals, the device type returned from an inquiry is usually ORed with
269 interface type and the passthrough flag if appropriate. The device type
270 flags are as follows:
271 .Bd -literal -offset indent
273 DEVSTAT_TYPE_DIRECT = 0x000,
274 DEVSTAT_TYPE_SEQUENTIAL = 0x001,
275 DEVSTAT_TYPE_PRINTER = 0x002,
276 DEVSTAT_TYPE_PROCESSOR = 0x003,
277 DEVSTAT_TYPE_WORM = 0x004,
278 DEVSTAT_TYPE_CDROM = 0x005,
279 DEVSTAT_TYPE_SCANNER = 0x006,
280 DEVSTAT_TYPE_OPTICAL = 0x007,
281 DEVSTAT_TYPE_CHANGER = 0x008,
282 DEVSTAT_TYPE_COMM = 0x009,
283 DEVSTAT_TYPE_ASC0 = 0x00a,
284 DEVSTAT_TYPE_ASC1 = 0x00b,
285 DEVSTAT_TYPE_STORARRAY = 0x00c,
286 DEVSTAT_TYPE_ENCLOSURE = 0x00d,
287 DEVSTAT_TYPE_FLOPPY = 0x00e,
288 DEVSTAT_TYPE_MASK = 0x00f,
289 DEVSTAT_TYPE_IF_SCSI = 0x010,
290 DEVSTAT_TYPE_IF_IDE = 0x020,
291 DEVSTAT_TYPE_IF_OTHER = 0x030,
292 DEVSTAT_TYPE_IF_MASK = 0x0f0,
293 DEVSTAT_TYPE_PASS = 0x100
294 } devstat_type_flags;
297 Devices have a priority associated with them, which controls roughly where
298 they are placed in the
300 list. The priorities are as follows:
301 .Bd -literal -offset indent
303 DEVSTAT_PRIORITY_MIN = 0x000,
304 DEVSTAT_PRIORITY_OTHER = 0x020,
305 DEVSTAT_PRIORITY_PASS = 0x030,
306 DEVSTAT_PRIORITY_FD = 0x040,
307 DEVSTAT_PRIORITY_WFD = 0x050,
308 DEVSTAT_PRIORITY_TAPE = 0x060,
309 DEVSTAT_PRIORITY_CD = 0x090,
310 DEVSTAT_PRIORITY_DISK = 0x110,
311 DEVSTAT_PRIORITY_ARRAY = 0x120,
312 DEVSTAT_PRIORITY_MAX = 0xfff
316 Each device has associated with it flags to indicate what operations are
317 supported or not supported. The
318 .Va devstat_support_flags
319 values are as follows:
320 .Bl -tag -width DEVSTAT_NO_ORDERED_TAGS
321 .It DEVSTAT_ALL_SUPPORTED
322 Every statistic type is supported by the device.
323 .It DEVSTAT_NO_BLOCKSIZE
324 This device does not have a blocksize.
325 .It DEVSTAT_NO_ORDERED_TAGS
326 This device does not support ordered tags.
327 .It DEVSTAT_BS_UNAVAILABLE
328 This device supports a blocksize, but it is currently unavailable. This
329 flag is most often used with removable media drives.
332 Transactions to a device fall into one of three categories, which are
336 .Fn devstat_end_transaction .
337 The transaction types are as follows:
338 .Bd -literal -offset indent
340 DEVSTAT_NO_DATA = 0x00,
342 DEVSTAT_WRITE = 0x02,
344 } devstat_trans_flags;
347 There are four possible values for the
350 .Fn devstat_end_transaction :
351 .Bl -tag -width DEVSTAT_TAG_ORDERED
352 .It DEVSTAT_TAG_SIMPLE
353 The transaction had a simple tag.
355 The transaction had a head of queue tag.
356 .It DEVSTAT_TAG_ORDERED
357 The transaction had an ordered tag.
359 The device doesn't support tags.
362 The tag type values correspond to the lower four bits of the
364 tag definitions. In CAM, for instance, the
366 from the CCB is ORed with 0xf to determine the tag type to pass in to
367 .Fn devstat_end_transaction .
372 .Aq sys/devicestat.h .
373 This is the current version of the
375 subsystem, and it should be incremented each time a change is made that
376 would require recompilation of userland programs that access
378 statistics. Userland programs use this version, via the
379 .Va kern.devstat.version
381 variable to determine whether they are in sync with the kernel
393 statistics system appeared in
396 .An Kenneth Merry Aq ken@FreeBSD.org
398 There may be a need for
400 protection around some of the
402 list manipulation code to insure, for example, that the list of devices
403 is not changed while someone is fetching the
408 It is impossible with the current
410 architecture to accurately measure time per transaction. The only feasible
411 way to accurately measure time per transaction would be to record a
412 timestamp for every transaction. This measurement is probably not
413 worthwhile for most people as it would adversely affect the performance of
414 the system and cost space to store the timestamps for individual