NAME

mtio − magtape interface

DESCRIPTION

The following description applies to any of the transport/controller pairs.  The files mt0, ..., mt7 are 800bpi, mt8, ..., mt15 are 1600bpi, and mt16, ..., mt23 are 6250bpi.  The files mt0, ..., mt3, mt8, ..., mt11, and mt16, ..., mt19 are rewound when closed; the others are not.  When a file open for writing is closed, two end-of-files are written.  If the tape is not to be rewound it is positioned with the head between the two tapemarks. 

A standard tape consists of a series of 1024 byte records terminated by an end-of-file.  To the extent possible, the system makes it possible, if inefficient, to treat the tape like any other file.  Seeks have their usual meaning and it is possible to read or write a byte at a time.  Writing in very small units is inadvisable, however, because it tends to create monstrous record gaps. 

The mt files discussed above are useful when it is desired to access the tape in a way compatible with ordinary files.  When foreign tapes are to be dealt with, and especially when long records are to be read or written, the ‘raw’ interface is appropriate.  The associated files are named rmt0, ..., rmt23, but the same minor-device considerations as for the regular files still apply.  A number of other ioctl operations are available on raw magnetic tape.  The following definitions are from <sys/mtio.h>:

/∗
 ∗ Structures and definitions for mag tape io control commands
 ∗/
 /∗ structure for MTIOCTOP − mag tape op command ∗/
structmtop    {
short   mt_op;          /∗ operations defined below ∗/
daddr_t mt_count;       /∗ how many of them ∗/
};
 /∗ operations ∗/
#define MTWEOF  0               /∗ write an end-of-file record ∗/
#define MTFSF   1               /∗ forward space file ∗/
#define MTBSF   2               /∗ backward space file ∗/
#define MTFSR   3               /∗ forward space record ∗/
#define MTBSR   4               /∗ backward space record ∗/
#define MTREW   5               /∗ rewind ∗/
#define MTOFFL  6               /∗ rewind and put the drive offline ∗/
#define MTNOP   7               /∗ no operation, sets status only ∗/
#define MTCACHE 8               /∗ enable controller cache ∗/
#define MTNOCACHE 9             /∗ disable controller cache ∗/
#ifdef sony_news
#define MTRETEN 10              /∗ retension the tape ∗/
#define MTERASE 11              /∗ erase the entire tape ∗/
#endif /∗ sony_news ∗/
 /∗ structure for MTIOCGET − mag tape get status command ∗/
 structmtget   {
short   mt_type;        /∗ type of magtape device ∗/
/∗ the following two registers are grossly device dependent ∗/
short   mt_dsreg;       /∗ “drive status” register ∗/
short   mt_erreg;       /∗ “error” register ∗/
/∗ end device-dependent registers ∗/
short   mt_resid;       /∗ residual count ∗/
/∗ the following two are not yet implemented ∗/
daddr_t mt_fileno;      /∗ file number of current position ∗/
daddr_t mt_blkno;       /∗ block number of current position ∗/
/∗ end not yet implemented ∗/
};
 /∗
 ∗ Constants for mt_type byte
 ∗/
#defineMT_ISTS0x01
#defineMT_ISHT0x02
#defineMT_ISTM0x03
#defineMT_ISMT0x04
#defineMT_ISUT0x05
#defineMT_ISCPC0x06
#defineMT_ISAR0x07
 /∗ mag tape io control commands ∗/
#defineMTIOCTOP_IOW(m, 1, struct mtop)/∗ do a mag tape op ∗/
#defineMTIOCGET_IOR(m, 2, struct mtget)/∗ get tape status ∗/
 #ifndef KERNEL
#ifdef sony_news
#define DEFTAPE "/dev/nrst00"
#else   /∗ sony_news ∗/
#define DEFTAPE "/dev/rmt12"
#endif  /∗ sony_news ∗/
#endif

Each read or write call reads or writes the next record on the tape.  In the write case the record has the same length as the buffer given.  During a read, the record size is passed back as the number of bytes read, provided it is no greater than the buffer size; if the record is long, an error is indicated.  In raw tape I/O seeks are ignored.  A zero byte count is returned when a tape mark is read, but another read will fetch the first record of the new tape file. 

FILES

/dev/rst?? 
/dev/nrst??
/dev/anrst??
/dev/rmt?

SEE ALSO

mt(1), tar(1), fd(4), sd(4), st(4)

BUGS

The status should be returned in a device independent format. 

NEWS-OSRelease 4.1C