sa.4 revision 13479
1.Dd January 17, 1996 2.Dt ST 4 3.Os FreeBSD 4.Sh NAME 5.Nm st 6.Nd SCSI tape driver 7.Sh SYNOPSIS 8.Cd tape st 9.Cd device st1 at scbus0 target 4 lun 0 10.Sh DESCRIPTION 11The 12.Nm 13driver provides support for a 14.Tn SCSI 15tape. It allows the tape 16to be run in upto four different modes depending on minor numbers 17and supports several different `submodes'. 18The device can have both a 19.Em raw 20interface 21and a 22.Em block 23interface; however, only the raw interface is usually used (or recommended). 24In general the interfaces are similar to those described by 25.Xr wt 4 26or 27.Xr mt 4 . 28.Pp 29Where the 30.Xr wt 4 31device has a fairly low level interface to the system, 32.Tn SCSI 33devices have a much higher level interface and talk to the system via 34a 35.Tn SCSI 36adapter and a 37.Tn SCSI 38adapter driver 39(e.g., 40.Xr ahc 4 ) . 41A 42.Tn SCSI 43adapter must also be separatly configured into the system 44before a 45.Tn SCSI 46tape can be configured. 47.Pp 48As the 49.Tn SCSI 50adapter is probed during boot, the 51.Tn SCSI 52bus is scanned for devices. Any devices found which answer as 53.Sq Em Sequential 54type devices will be attached to the 55.Nm 56driver. 57In 58.Tn FreeBSD 59releases prior to 2.1, the first found is attached as 60.Em st0 61and the next, 62.Em st1 , 63etc. 64Beginning in release 2.1 it is possible to specify what 65.Nm 66unit a device should 67come on line as; refer to 68.Xr scsi 4 69for details on kernel configuration. 70.Sh MOUNT SESSIONS 71The 72.Nm 73driver is based around the concept of a 74.Dq Em mount session , 75which is defined as the period between the time that a tape is 76mounted, and the time when it is unmounted. Any parameters set during 77a mount session remain in effect for the remainder of the session or 78until replaced. The tape can be unmounted, bringing the session to a 79close in several ways. These include: 80.Bl -enum 81.It 82Closing an `unmount device', 83referred to as sub-mode 00 below. An example is 84.Pa /dev/rst0 . 85.It 86Using the MTOFFL 87.Xr ioctl 2 88command, reachable through the 89.Sq Cm offline 90command of 91.Xr st 1 . 92.It 93Opening a different mode will implicitly unmount the tape, thereby closing 94off the mode that was previously mounted. All parameters will be loaded 95freshly from the new mode. (See below for more on modes.) 96.El 97.Pp 98Parameters that are required to last across the unmounting of a tape 99should be set on the control device. This is submode 3 (see below) and is 100reached through a file with a name of the form 101.Pa /dev/st Ns Ar y Ns Pa ctl. Ns Ar x , 102where 103.Ar y 104is the drive number and 105.Ar x 106is the mode number. 107.Sh MODES AND SUBMODES 108There are four 109.Sq operation 110modes. These are controlled by bits 2 and 3 of the minor number and 111are designed to allow users to easily read and write different formats 112of tape on devices that allow multiple formats. The parameters for 113each mode can be set individually by hand with the 114.Xr mt 1 115command. When a device corresponding to a particular mode is first 116mounted, The operating parameters for that 117mount session 118are copied from that mode. Further changes to the parameters during the 119session will change those in effect for the session but not those set 120in the operation mode. To change the parameters for an operation mode, 121one must either assign the parameters to the control device, or compile 122them into the 123.Dq Em Rogues Gallery 124table in the driver's source code. 125.Pp 126In addition to the four operating modes mentioned above, 127bits 0 and 1 of the minor number are interpreted as 128.Sq submodes . 129The submodes differ in the action taken when the device is closed: 130.Bl -tag -width XXXX 131.It 00 132A close will rewind the device; if the tape has been 133written, then a file mark will be written before the rewind is requested. 134The device is unmounted. 135.It 01 136A close will leave the tape mounted. 137If the tape was written to, a file mark will be written. 138No other head positioning takes place. 139Any further reads or writes will occur directly after the 140last read, or the written file mark. 141.It 10 142A close will rewind the device. If the tape has been 143written, then a file mark will be written before the rewind is requested. 144On completion of the rewind an unload command will be issued. 145The device is unmounted. 146.It 11 147This is a special mode, known as the 148.Dq control device 149for the mode. Parameters set for the mode while in this sub mode will 150be remembered from one mount to the next. This allows the system 151administrator to set different characteristics (e.g., density, 152blocksize) 153.\" (and eventually compression) 154on each mode, and have the different modes keep those parameters 155independent of any parameter changes a user may invoke during a single 156mount session. At the completion of the user's mount session, drive 157parameters will revert to those set by the administrator. I/O 158operations cannot be performed on this device/submode. General 159.Xr scsi 4 160ioctls can 161.Em only 162be performed against the control device. 163.El 164.Sh BLOCKING MODES 165.Tn SCSI 166tapes may run in either 167.Sq Em variable 168or 169.Sq Em fixed 170 block-size modes. 171Most 172.Tn QIC Ns -type 173devices run in fixed block-size mode, where most nine-track tapes and 174many new cartridge formats allow variable block-size. The difference 175between the two is as follows: 176.Bl -inset 177.It Variable block-size: 178Each write made to the device results in a single logical record 179written to the tape. One can never read or write 180.Em part 181of a record from tape (though you may request a larger block and read 182a smaller record); nor can one read multiple blocks. Data from a 183single write is therefore read by a single read. The block size used 184may be any value supported by the device, the 185.Tn SCSI 186adapter and the system (usually between 1 byte and 64 Kbytes, 187sometimes more). 188.Pp 189When reading a variable record/block from the tape, the head is 190logically considered to be immediately after the last item read, 191and before the next item after that. If the next item is a file mark, 192but it was never read, then the next 193process to read will immediately hit the file mark and receive an end-of-file nification. 194.It Fixed block-size 195Data written by the user is passed to the tape as a succession of 196fixed size blocks. It may be contiguouse in memory, but it is 197considered to be a series of independent blocks. One may never write 198an amount of data that is not an exact multiple of the blocksize. One 199may read and write the same data as a different set of records, In 200other words, blocks that were written together may be read separately, 201and vice-versa. 202.Pp 203If one requests more blocks than remain in the file, the drive will 204encounter the file mark. Because there is some data to return (unless 205there were no records before the file mark), the read will succeed, 206returning that data, The next read will return immediately with an 207EOF. (As above, if the file mark is never read, it remains for the next process to read if in no-rewind mode.) 208.El 209.Sh FILE MARK HANDLING 210The handling of file marks on write is automatic. If the user has 211written to the tape, and has not done a read since the last write, 212then a file mark will be written to the tape when the device is 213closed. If a rewind is requested after a write, then the driver 214assumes that the last file on the tape has been written, and ensures 215that there are two filemarks written to the tape. The exception to 216this is that there seems to be a standard (which we follow, but don't 217understand why) that certain types of tape do not actually write two 218filemarks to tape, but when read, report a `phantom' filemark when the 219last file is read. These devices include the QIC family of devices. 220(It might be that this set of devices is the same set as that of fixed 221block devices. This has not been detirmined yet, and they are treated 222as separate behaviors by the driver at this time.) 223.Sh KERNEL CONFIGURATION 224Because different tape drives behave differently, there is a mechanism 225within the source to 226.Nm 227to quickly and conveniently recognise and deal 228with brands and models of drive that have special requirements. 229.Pp 230There is a table (called the 231.Dq Em Rogues' Gallery ) 232in which the indentification 233strings of known errant drives can be stored. Alongside each is 234a set of flags that allows the setting of densities and blocksizes for each 235of the four modes, along with a set of `QUIRK' flags that can be 236used to enable or disable sections of code within the driver if a particular 237drive is recognised. 238.Sh IOCTLS 239The following 240.Xr ioctl 2 241calls apply to 242.Tn SCSI 243tapes. Some also apply to other tapes. They are defined 244in the header file 245.Aq Pa /sys/mtio.h . 246.Pp 247.Bl -tag -width MTIOCEEOT 248.It Dv MTIOCGET 249Get the mt control structure filled out by the driver, showing 250all the present settings. 251.It Dv MTIOCTOP 252Perform one of the following operations. These operations all have a 253single argument, which is either a boolean, or a signed integer, depending 254on the operation. 255.Bl -tag -width MTSELDNSTY 256.It Dv MTWEOF 257Write N end of file marks at the present head position. 258.It Dv MTFSF 259Skip over N Filemarks. Leave the head on the EOM side of the last skipped 260Filemark. 261.It Dv MTBSF 262Skip BACKWARDS over N Filemarks. Leave the head on the BOM (beginning of media) 263side of the last skipped Filemark. 264.It Dv MTFSR 265Skip forwards over N records. 266.It Dv MTBSR 267Skip backwards over N records. 268.It Dv MTREW 269Rewind the device to the beginning of the media. 270.It Dv MTOFFL 271Rewind the media (and, if possible, eject). Even if the device cannot 272eject the media it will often no longer respond to normal requests. 273.It Dv MTNOP 274No Op, set status only.. 275.It Dv MTCACHE 276Enable controller buffering. 277.It Dv MTNOCACHE 278Disable controller buffering. 279.It Dv MTSETBSIZ 280Set the blocksize to use for the device/mode. If the device is capable of 281variable blocksize operation, and the blocksize is set to 0, then the drive 282will be driven in variable mode. This parameter is in effect for the present 283mount session only, unless set on the control device. 284.It Dv MTSETDNSTY 285Set the Density value (see 286.Xr mt 1 ) 287to use when running in the mode opened (minor bits 2 and 3). 288This parameter is in effect for the present 289mount session only, unless set on the control device. 290.El 291.It Dv MTIOCIEOT 292?Set END of TAPE processing... not yet supported. 293.It Dv MTIOCEEOT 294?Set END of TAPE processing... not yet supported. 295.El 296.Pp 297In addition, the 298.Nm 299driver will allow the use of any of the general 300.Xr scsi 4 301.Fn ioctl 302commands, on the control device only. 303.Sh FILES 304.Bl -tag -width /dev/[n][e]rst[0-9].[0-3] -compact 305.It Pa /dev/[n][e]rst[0-9].[0-3] 306general form: 307.It Pa /dev/rst0.0 308Mode 0, rewind on close 309.It Pa /dev/nrst0.2 310Mode 2, No rewind on close 311.It Pa /dev/erst0.3 312Mode 3, Eject on close (if capable) 313.It Pa /dev/rst0 314Another name for rst0.0 315.It Pa /dev/nrst0 316Another name for nrst0.0 317.It Pa /dev/st0ctl.0 318Parameters set to this device become the default parameters for [en]rst0.0 319.It Pa /dev/st0ctl.1 320Parameters set to this device become the default parameters for [en]rst0.1 321.It Pa /dev/st0ctl.2 322Parameters set to this device become the default parameters for [en]rst0.2 323.It Pa /dev/st0ctl.3 324Parameters set to this device become the default parameters for [en]rst0.3 325.El 326.Sh DIAGNOSTICS 327None. 328.Sh SEE ALSO 329.Xr mt 1 330.Sh HISTORY 331This 332.Nm 333driver was originally written for 334.Tn Mach 3352.5, and was ported to 336.Tn FreeBSD 337by Julian Elischer. 338