| MTIO(4I) | Ioctl Requests | MTIO(4I) |
mtio — general
magnetic tape interface
#include
<sys/types.h>
#include <sys/ioctl.h>
#include <sys/mtio.h>
1/2", 1/4", 4mm, and 8mm magnetic tape drives all share the same general character device interface.
There are two types of tape records: data records and end-of-file (EOF) records. EOF records are also known as tape marks and file marks. A record is separated by interrecord (or tape) gaps on a tape.
End-of-recorded-media (EOM) is indicated by two EOF marks on 1/2" tape; by one EOF mark on 1/4", 4mm, and 8mm cartridge tapes.
Data bytes are recorded in parallel onto the 9-track tape. Since it is a variable-length tape device, the number of bytes in a physical record may vary.
The recording formats available (check specific tape drive) are 800 BPI, 1600 BPI, 6250 BPI, and data compression. Actual storage capacity is a function of the recording format and the length of the tape reel. For example, using a 2400 foot tape, 20 Mbyte can be stored using 800 BPI, 40 Mbyte using 1600 BPI, 140 Mbyte using 6250 BPI, or up to 700 Mbyte using data compression.
Data is recorded serially onto 1/4" cartridge tape. The number of bytes per record is determined by the physical record size of the device. The I/O request size must be a multiple of the physical record size of the device. For QIC-11, QIC-24, and QIC-150 tape drives, the block size is 512 bytes.
The records are recorded on tracks in a serpentine motion. As one track is completed, the drive switches to the next and begins writing in the opposite direction, eliminating the wasted motion of rewinding. Each file, including the last, ends with one file mark.
Storage capacity is based on the number of tracks the drive is capable of recording. For example, 4-track drives can only record 20 Mbyte of data on a 450 foot tape; 9-track drives can record up to 45 Mbyte of data on a tape of the same length. QIC-11 is the only tape format available for 4-track tape drives. In contrast, 9-track tape drives can use either QIC-24 or QIC-11. Storage capacity is not appreciably affected by using either format. QIC-24 is preferable to QIC-11 because it records a reference signal to mark the position of the first track on the tape, and each block has a unique block number.
The QIC-150 tape drives require DC-6150 (or equivalent) tape cartridges for writing. However, they can read other tape cartridges in QIC-11, QIC-24, or QIC-120 tape formats.
Data is recorded serially onto 8mm helical scan cartridge tape. Since it is a variable-length tape device, the number of bytes in a physical record may vary. The recording formats available (check specific tape drive) are standard 2Gbyte, 5Gbyte, and compressed format.
Data is recorded either in Digital Data Storage (DDS) tape format or in Digital Data Storage, Data Compressed (DDS-DC) tape format. Since it is a variable-length tape device, the number of bytes in a physical record may vary. The recording formats available are standard 2Gbyte and compressed format.
Persistent error handling is a modification of the current error handling behaviors, BSD and SVR4. With persistent error handling enabled, all tape operations after an error or exception will return immediately with an error. Persistent error handling can be most useful with asynchronous tape operations that use the aioread(3C) and aiowrite(3C) functions.
To enable persistent error handling, the ioctl
MTIOCPERSISTENT must be issued. If this ioctl
succeeds, then persistent error handling is enabled and changes the current
error behavior. This ioctl will fail if the device driver does not support
persistent error handling.
With persistent error handling enabled, all tape operations after
an exception or error will return with the same error as the first command
that failed; the operations will not be executed. An exception is some event
that might stop normal tape operations, such as an End Of File (EOF) mark or
an End Of Tape (EOT) mark. An example of an error is a media error. The
MTIOCLRERR ioctl must be issued to allow normal tape
operations to continue and to clear the error.
Disabling persistent error handling returns the error behavior to normal SVR4 error handling, and will not occur until all outstanding operations are completed. Applications should wait for all outstanding operations to complete before disabling persistent error handling. Closing the device will also disable persistent error handling and clear any errors or exceptions.
The Read Operation and Write Operation subsections contain more pertinent information regarding persistent error handling.
The read(2) function reads the
next record on the tape. The record size is passed back as the number of
bytes read, provided it is not greater than the number requested. When a
tape mark or end of data is read, a zero byte count is returned; all
successive reads after the zero read will return an error and
errno will be set to EIO. To
move to the next file, an MTFSF ioctl can be issued
before or after the read causing the error. This error handling behavior is
different from the older BSD behavior, where another read
will fetch the first record of the next tape file. If the
BSD behavior is required, device names containing the
letter ‘b’ (for BSD
behavior) in the final component should be used. If persistent error
handling was enabled with either the BSD or SVR4 tape device behavior, all
operations after this read error will return EIO
errors until the MTIOCLRERR ioctl is issued. An
MTFSF ioctl can then be issued.
Two successful successive reads that both return zero byte counts indicate EOM on the tape. No further reading should be performed past the EOM.
Fixed-length I/O tape devices require the number of bytes read to be a multiple of the physical record size. For example, 1/4" cartridge tape devices only read multiples of 512 bytes. If the blocking factor is greater than 64,512 bytes (minphys limit), fixed-length I/O tape devices read multiple records.
Most tape devices which support variable-length I/O operations may read a range of 1 to 65,535 bytes. If the record size exceeds 65,535 bytes, the driver reads multiple records to satisfy the request. These multiple records are limited to 65,534 bytes. Newer variable-length tape drivers may relax the above limitation and allow applications to read record sizes larger than 65,534. Refer to the specific tape driver man page for details.
Reading past logical EOT is transparent to the user. A read operation should never hit physical EOT.
Read requests that are lesser than a physical tape record are not allowed. Appropriate error is returned.
The write(2) function writes the next record on the tape. The record has the same length as the given buffer.
Writing is allowed on 1/4" tape at either the beginning of tape or after the last written file on the tape. With the Exabyte 8200, data may be appended only at the beginning of tape, before a filemark, or after the last written file on the tape.
Writing is not so restricted on 1/2", 4mm, and the other 8mm cartridge tape drives. Care should be used when appending files onto 1/2" reel tape devices, since an extra file mark is appended after the last file to mark the EOM. This extra file mark must be overwritten to prevent the creation of a null file. To facilitate write append operations, a space to the EOM ioctl is provided. Care should be taken when overwriting records; the erase head is just forward of the write head and any following records will also be erased.
Fixed-length I/O tape devices require the number of bytes written to be a multiple of the physical record size. For example, 1/4" cartridge tape devices only write multiples of 512 bytes.
Fixed-length I/O tape devices write multiple records if the blocking factor is greater than 64,512 bytes (minphys limit). These multiple writes are limited to 64,512 bytes. For example, if a write request is issued for 65,536 bytes using a 1/4" cartridge tape, two writes are issued; the first for 64,512 bytes and the second for 1024 bytes.
Most tape devices which support variable-length I/O operations may write a range of 1 to 65,535 bytes. If the record size exceeds 65,535 bytes, the driver writes multiple records to satisfy the request. These multiple records are limited to 65,534 bytes. As an example, if a write request for 65,540 bytes is issued, two records are written; one for 65,534 bytes followed by another record for 6 bytes. Newer variable-length tape drivers may relax the above limitation and allow applications to write record sizes larger than 65,534. Refer to the specific tape driver man page for details.
When logical EOT is encountered during a write,
that write operation completes and the number of bytes successfully
transferred is returned (note that a 'short write' may have occurred and not
all the requested bytes would have been transferred. The actual amount of
data written will depend on the type of device being used). The next write
will return a zero byte count. A third write will successfully transfer some
bytes (as indicated by the returned byte count, which again could be a short
write); the fourth will transfer zero bytes, and so on, until the physical
EOT is reached and all writes will fail with
EIO.
When logical EOT is encountered with persistent
error handling enabled, the current write may complete or be a short write.
The next write will return a zero byte count. At this point an application
should act appropriately for end of tape cleanup or issue yet another write,
which will return the error ENOSPC. After clearing
the exception with MTIOCLRERR, the next write will
succeed (possibly short), followed by another zero byte write count, and
then another ENOSPC error.
Allowing writes after EOT has been encountered enables the flushing of buffers. However, it is strongly recommended to terminate the writing and close the file as soon as possible.
Seeks are ignored in tape I/O.
Magnetic tapes are rewound when closed, except when the
"no-rewind" devices have been specified. The names of no-rewind
device files use the letter ‘n’ as the
end of the final component. The no-rewind version of
/dev/rmt/0l is /dev/rmt/0ln.
In case of error for a no-rewind device, the next open rewinds the
device.
If the driver was opened for reading and a no-rewind device has
been specified, the close advances the tape past the next filemark (unless
the current file position is at EOM), leaving the tape
correctly positioned to read the first record of the next file. However, if
the tape is at the first record of a file it doesn't advance again to the
first record of the next file. These semantics are different from the older
BSD behavior. If BSD behavior is
required where no implicit space operation is executed on close, the
non-rewind device name containing the letter
‘b’ (for BSD
behavior) in the final component should be specified.
If data was written, a file mark is automatically written by the driver upon close. If the rewinding device was specified, the tape will be rewound after the file mark is written. If the user wrote a file mark prior to closing, then no file mark is written upon close. If a file positioning ioctl, like rewind, is issued after writing, a file mark is written before repositioning the tape.
All buffers are flushed on closing a tape device. Hence, it is
strongly recommended that the application wait for all buffers to be flushed
before closing the device. This can be done by writing a filemark via
MTWEOF, even with a zero count.
Note that for 1/2" reel tape devices, two file marks are written to mark the EOM before rewinding or performing a file positioning ioctl. If the user wrote a file mark before closing a 1/2" reel tape device, the driver will always write a file mark before closing to insure that the end of recorded media is marked properly. If the non-rewinding device was specified, two file marks are written and the tape is left positioned between the two so that the second one is overwritten on a subsequent open(2) and write(2).
If no data was written and the driver was opened for WRITE-ONLY access, one or two file marks are written, thus creating a null file.
After closing the device, persistent error handling will be disabled and any error or exception will be cleared.
Not all devices support all
ioctls.
The driver returns an ENOTTY error on unsupported
ioctls.
The following structure definitions for magnetic tape
ioctl(2) commands are from
<sys/mtio.h>.
The minor device byte structure is:
15 7 6 5 4 3 2 1 0 ________________________________________________________________________ Unit # BSD Reserved Density Density No rewind Unit # Bits 7-15 behavior Select Select on Close Bits 0-1
/*
* Layout of minor device byte:
*/
#define MTUNIT(dev) (((minor(dev) & 0xff80) >> 5) + (minor(dev) & 0x3))
#define MT_NOREWIND (1 <<2)
#define MT_DENSITY_MASK (3 <<3)
#define MT_DENSITY1 (0 <<3) /* Lowest density/format */
#define MT_DENSITY2 (1 <<3)
#define MT_DENSITY3 (2 <<3)
#define MT_DENSITY4 (3 <<3) /* Highest density/format */
#define MTMINOR(unit) (((unit & 0x7fc) << 5) + (unit & 0x3))
#define MT_BSD (1 <<6) /* BSD behavior on close */
/* Structure for MTIOCTOP - magnetic tape operation command */
struct mtop {
short mt_op; /* operation */
daddr_t mt_count; /* number of operations */
};
/* Structure for MTIOCLTOP - magnetic tape operation command */
Works exactly like MTIOCTOP except passes 64 bit mt_count values.
struct mtlop {
short mt_op;
short pad[3];
int64_t mt_count;
};
The following operations of MTIOCTOP and
MTIOCLTOP ioctls are supported:
MTWEOFMTFSFMTBSFMTFSRMTBSRMTREWMTOFFLMTNOPMTRETENMTERASEMTEOMMTNBSFMTSRSZMTGRSZMTTELLMTSEEKMTFSSFMTBSSFMTLOCKMTUNLOCKMTLOADMTIOCGETERROR/* structure for MTIOCGET - magnetic tape get status command */
struct mtget {
short mt_type; /* type of magtape device */
/* the following two registers are device dependent */
short mt_dsreg; /* "drive status" register */
short mt_erreg; /* "error" register */
/* optional error info. */
daddr_t mt_resid; /* residual count */
daddr_t mt_fileno; /* file number of current position */
daddr_t mt_blkno; /* block number of current position */
ushort_t mt_flags;
short mt_bf; /* optimum blocking factor */
};
/* structure for MTIOCGETDRIVETYPE - get tape config data command */
struct mtdrivetype_request {
int size;
struct mtdrivetype *mtdtp;
};
struct mtdrivetype {
char name[64]; /* Name, for debug */
char vid[25]; /* Vendor id and product id */
char type; /* Drive type for driver */
int bsize; /* Block size */
int options; /* Drive options */
int max_rretries; /* Max read retries */
int max_wretries; /* Max write retries */
uchar_t densities[MT_NDENSITIES]; /* density codes,low->hi */
uchar_t default_density; /* Default density chosen */
uchar_t speeds[MT_NSPEEDS]; /* speed codes, low->hi */
ushort_t non_motion_timeout; /* Seconds for non-motion */
ushort_t io_timeout; /* Seconds for data to from tape */
ushort_t rewind_timeout; /* Seconds to rewind */
ushort_t space_timeout; /* Seconds to space anywhere */
ushort_t load_timeout; /* Seconds to load tape and ready */
ushort_t unload_timeout; /* Seconds to unload */
ushort_t erase_timeout; /* Seconds to do long erase */
};
/* structure for MTIOCGETPOS and MTIOCRESTPOS - get/set tape position */
/*
* eof/eot/eom codes.
*/
typedef enum {
ST_NO_EOF,
ST_EOF_PENDING, /* filemark pending */
ST_EOF, /* at filemark */
ST_EOT_PENDING, /* logical eot pend. */
ST_EOT, /* at logical eot */
ST_EOM, /* at physical eot */
ST_WRITE_AFTER_EOM /* flag allowing writes after EOM */
} pstatus;
typedef enum { invalid, legacy, logical } posmode;
typedef struct tapepos {
uint64_t lgclblkno; /* Blks from start of partition */
int32_t fileno; /* Num. of current file */
int32_t blkno; /* Blk number in current file */
int32_t partition; /* Current partition */
pstatus eof; /* eof states */
posmode pmode; /* which pos. data is valid */
char pad[4];
} tapepos_t;
If the pmode is logical, lgclblkno field is valid.
The MTWEOF ioctl is used for writing file
marks to tape. Not only does this signify the end of a file, but also
usually has the side effect of flushing all buffers in the tape drive to the
tape medium. A zero count MTWEOF will just flush all
the buffers and will not write any file marks. Because a successful
completion of this tape operation will guarantee that all tape data has been
written to the tape medium, it is recommended that this tape operation be
issued before closing a tape device.
When spacing forward over a record (either data or EOF), the tape head is positioned in the tape gap between the record just skipped and the next record. When spacing forward over file marks (EOF records), the tape head is positioned in the tape gap between the next EOF record and the record that follows it.
When spacing backward over a record (either data or EOF), the tape head is positioned in the tape gap immediately preceding the tape record where the tape head is currently positioned. When spacing backward over file marks (EOF records), the tape head is positioned in the tape gap preceding the EOF. Thus the next read would fetch the EOF.
Record skipping does not go past a file mark; file skipping does
not go past the EOM. After an
MTFSR <huge number> command, the driver leaves
the tape logically positioned before the
EOF. A related feature is that EOFs
remain pending until the tape is closed. For example, a program which first
reads all the records of a file up to and including the EOF and then
performs an MTFSF command will leave the tape
positioned just after that same EOF, rather than skipping
the next file.
The MTNBSF and
MTFSF operations are inverses. Thus, an
“MTFSF −1” is equivalent to an
“MTNBSF 1”. An
“MTNBSF 0” is the same as
“MTFSF 0”; both position the tape
device at the beginning of the current file.
MTBSF moves the tape backwards by file
marks. The tape position will end on the beginning of the tape side of the
desired file mark. An “MTBSF 0” will
position the tape at the end of the current file, before the filemark.
MTBSR and MTFSR
operations perform much like space file operations, except that they move by
records instead of files. Variable-length I/O devices (1/2" reel, for
example) space actual records; fixed-length I/O devices space physical
records (blocks). 1/4" cartridge tape, for example, spaces 512 byte
physical records. The status ioctl residual count contains the number of
files or records not skipped.
MTFSSF and MTBSSF
space forward or backward, respectively, to the next occurrence of the
requested number of file marks, one following another. If there are more
sequential file marks on tape than were requested, it spaces over the
requested number and positions after the requested file mark. Note that not
all drives support this command and if a request is sent to a drive that
does not, ENOTTY is returned.
MTOFFL rewinds and, if appropriate, takes
the device off-line by unloading the tape. It is recommended that the device
be closed after offlining and then re-opened after a tape has been inserted
to facilitate portability to other platforms and other operating systems.
Attempting to re-open the device with no tape will result in an error unless
the O_NDELAY flag is used. (See
open(2).)
The MTRETEN retension ioctl applies only
to 1/4" cartridge tape devices. It is used to restore tape tension,
improving the tape's soft error rate after extensive start-stop operations
or long-term storage.
MTERASE rewinds the tape, erases it
completely, and returns to the beginning of tape. Erasing may take a long
time depending on the device and/or tapes. For time details, refer to the
drive specific manual.
MTEOM positions the tape at a location
just after the last file written on the tape. For 1/4" cartridge and
8mm tape, this is after the last file mark on the tape. For 1/2" reel
tape, this is just after the first file mark but before the second (and
last) file mark on the tape. Additional files can then be appended onto the
tape from that point.
Note the difference between
MTBSF (backspace over file mark) and
MTNBSF (backspace file to beginning of file). The
former moves the tape backward until it crosses an EOF
mark, leaving the tape positioned before the file mark.
The latter leaves the tape positioned
after the file
mark. Hence, “MTNBSF n” is equivalent
to “MTBSF (n+1)” followed by
“MTFSF 1”. The 1/4" cartridge
tape devices do not support MTBSF.
MTSRSZ and MTGRSZ
are used to set and get fixed record lengths. The
MTSRSZ ioctl allows variable length and fixed length
tape drives that support multiple record sizes to set the record length. The
mt_count field of the mtop
struct is used to pass the record size to/from the
st(4D) driver. A value of
‘0’ indicates variable record size.
The MTSRSZ ioctl makes a variable-length tape device
behave like a fixed-length tape device. Refer to the specific tape driver
man page for details.
MTLOAD loads the next tape cartridge into
the tape drive. This is generally only used with stacker and tower type tape
drives which handle multiple tapes per tape drive. A tape device without a
tape inserted can be opened with the O_NDELAY flag,
in order to execute this operation.
MTIOCGETERROR allows user-level
applications to retrieve error records from the
st(4D) driver. An error record consists
of the SCSI command cdb which causes the error and a
scsi_arq_status(9S)
structure if available. The user-level application is responsible for
allocating and releasing the memory for mtee_cdb_buf
and scsi_arq_status of each
mterror_entry. Before issuing the ioctl, the
mtee_arq_status_len value should be at least equal to
‘sizeof (struct scsi_arq_status)’. If
more sense data than the size of
scsi_arq_status(9S) is
desired, the mtee_arq_status_len may be larger than
‘sizeof (struct scsi_arq_status)’ by
the amount of additional extended sense data desired. The
es_add_len field of
scsi_extended_sense(9S)
can be used to determine the amount of valid sense data returned by the
device.
The MTIOCGET get status
ioctl(2) call returns the drive ID
(mt_type), sense key error
(mt_erreg), file number
(mt_fileno), optimum blocking factor
(mt_bf) and record number
(mt_blkno) of the last error. The residual count
(mt_resid) is set to the number of bytes not
transferred or files/records not spaced. The flags word
(mt_flags) contains information indicating if the
device is SCSI, if the device is a reel device and whether the device
supports absolute file positioning. The mt_flags also
indicates if the device is requesting cleaning media be used, whether the
device is capable of reporting the requirement of cleaning media and if the
currently loaded media is WORM (Write Once Read Many) media.
Note — When tape alert cleaning is managed by the st
driver, the tape target driver may continue to return a “drive needs
cleaning” status unless an MTIOCGET
ioctl(2) call is made while the
cleaning media is in the drive.
The MTIOCGETDRIVETYPE get drivetype ioctl
call returns the name of the tape drive as defined in
st.conf (name), Vendor
ID and model (product),
ID (vid), type of tape device
(type), block size (size), drive
options (options), maximum read retry count
(max_rretries), maximum write retry count
(max_wretries), densities supported by the drive
(densities), and default density of the tape drive
(default_density).
The MTIOCGETPOS ioctl returns the current
tape position of the drive. It is returned in struct tapepos as defined in
/usr/include/sys/scsi/targets/stdef.h.
The MTIOCRESTPOS ioctl restores a saved
position from the MTIOCGETPOS.
MTIOCPERSISTENTMTIOCPERSISTENTSTATUSMTIOCLRERRMTIOCGUARANTEEDORDERThe MTIOCPERSISTENT ioctl enables or
disables persistent error handling. It takes as an argument a pointer to an
integer that turns it either on or off. If the ioctl succeeds, the desired
operation was successful. It will wait for all outstanding I/O's to complete
before changing the persistent error handling status. For example,
int on = 1; ioctl(fd, MTIOCPERSISTENT, &on); int off = 0; ioctl(fd, MTIOCPERSISTENT, &off);
The MTIOCPERSISTENTSTATUS ioctl enables or
disables persistent error handling. It takes as an argument a pointer to an
integer inserted by the driver. The integer can be either 1 if persistent
error handling is ‘on’, or 0 if persistent error handling is
‘off’. It will not wait for outstanding I/O's. For
example,
int query; ioctl(fd, MTIOCPERSISTENTSTATUS, &query);
The MTIOCLRERR ioctl clears persistent
error handling and allows tape operations to continual normally. This ioctl
requires no argument and will always succeed, even if persistent error
handling has not been enabled. It will wait for any outstanding I/O's before
it clears the error.
The MTIOCGUARANTEEDORDER ioctl is used to
determine whether the driver guarantees the order of I/O's. It takes no
argument. If the ioctl succeeds, the driver will support guaranteed order.
If the driver does not support guaranteed order, then it should not be used
for asynchronous I/O with
libaio(3lib). It will wait for any
outstanding I/O's before it returns. For example,
ioctl(fd, MTIOCGUARANTEEDORDER)
See the Persistent Error Handling subsection above for more information on persistent error handling.
MTIOCSTATEMTIO_NONE. Upon return, the enum pointed to by the
argument is updated with the current state of the drive.
enum mtio_state {
MTIO_NONE /* Return tape's current state */
MTIO_EJECTED /* Tape state is "ejected" */
MTIO_INSERTED /* Tape state is "inserted" */
};
When using asynchronous operations, most ioctls will wait for all outstanding commands to complete before they are executed.
MTIOCRESERVEMTIOCRELEASEMTIOCFORCERESERVEThe MTIOCRESERVE ioctl reserves the tape
drive such that it does not release the tape drive at close. This changes
the default behavior of releasing the device upon close. Reserving the tape
drive that is already reserved has no effect. For example,
ioctl(fd, MTIOCRESERVE);
The MTIOCRELEASE ioctl reverts back to the
default behavior of reserve on open/release on close operation, and a
release will occur during the next close. Releasing the tape drive that is
already released has no effect. For example,
ioctl(fd, MTIOCRELEASE);
The MTIOCFORCERESERVE ioctl breaks a
reservation held by another host, interrupting any I/O in progress by that
other host, and then reserves the tape unit. This ioctl can be executed only
with super-user privileges. It is recommended to open the tape device in
O_NDELAY mode when this ioctl needs to be executed,
otherwise the open will fail if another host indeed has it reserved. For
example,
ioctl(fd, MTIOCFORCERESERVE);
MTIOCSHORTFMKMTIOCREADIGNOREILIMTIOCREADIGNOREEOFSThe MTIOCSHORTFMK ioctl enables or
disables support for short filemarks. This ioctl is only applicable to
Exabyte drives which support short filemarks. As an argument, it takes a
pointer to an integer. If 0 (zero) is the specified integer, then long
filemarks will be written. If 1 is the specified integer, then short
filemarks will be written. The specified tape behavior will be in effect
until the device is closed.
For example:
int on = 1; int off = 0; /* enable short filemarks */ ioctl(fd, MTIOSHORTFMK, &on); /* disable short filemarks */ ioctl(fd, MTIOCSHORTFMK, &off);
Tape drives which do not support short filemarks will return an
errno of ENOTTY.
The MTIOCREADIGNOREILI ioctl enables or
disables the suppress incorrect length indicator (SILI) support during
reads. As an argument, it takes a pointer to an integer. If 0 (zero) is the
specified integer, SILI will not be used during reads and incorrect length
indicator will not be suppressed. If 1 is the specified integer, SILI will
be used during reads and incorrect length indicator will be suppressed. The
specified tape behavior will be in effect until the device is closed.
For example:
int on = 1; int off = 0; ioctl(fd, MTIOREADIGNOREILI, &on); ioctl(fd, MTIOREADIGNOREILI, &off);
The MTIOCREADIGNOREEOFS ioctl enables or
disables support for reading past double EOF marks which otherwise indicate
End-Of-recorded-media (EOM) in the case of 1/2" reel tape drives. As an
argument, it takes a pointer to an integer. If 0 (zero) is the specified
integer, then double EOF marks indicate End-Of-recorded-media (EOM). If 1 is
the specified integer, the double EOF marks no longer indicate EOM, thus
allowing applications to read past two EOF marks. In this case it is the
responsibility of the application to detect End-Of-recorded-media (EOM). The
specified tape behavior will be in effect until the device is closed.
For example:
int on = 1; int off = 0; ioctl(fd, MTIOREADIGNOREEOFS, &on); ioctl(fd, MTIOREADIGNOREEOFS, &off);
Tape drives other than 1/2" reel tapes will return an
errno of ENOTTY.
/dev/rmt/⟨unit number⟩⟨density⟩[⟨BSD behavior⟩][⟨no rewind⟩]
Where ⟨density⟩ can be
‘l’,
‘m’,
‘h’,
‘u/c’ (low, medium, high,
ultra/compressed, respectively), the ⟨BSD behavior⟩ option is
‘b, and the’ ⟨no rewind⟩
option is ‘n’.
For example, /dev/rmt/0hbn specifies unit 0, high density, BSD behavior and no rewind.
Suppose you have written three files to the non-rewinding 1/2" tape device, /dev/rmt/0ln, and that you want to go back and dd(8) the second file off the tape. The commands to do this are:
mt -F /dev/rmt/0lbn bsf 3 mt -F /dev/rmt/0lbn fsf 1 dd if=/dev/rmt/0ln
To accomplish the same tape positioning in a C program, followed by a get status ioctl:
struct mtop mt_command; struct mtget mt_status; mt_command.mt_op = MTBSF; mt_command.mt_count = 3; ioctl(fd, MTIOCTOP, &mt_command); mt_command.mt_op = MTFSF; mt_command.mt_count = 1; ioctl(fd, MTIOCTOP, &mt_command); ioctl(fd, MTIOCGET, (char *)&mt_status);
or
mt_command.mt_op = MTNBSF; mt_command.mt_count = 2; ioctl(fd, MTIOCTOP, &mt_command); ioctl(fd, MTIOCGET, (char *)&mt_status);
To get information about the tape drive:
struct mtdrivetype mtdt; struct mtdrivetype_request mtreq; mtreq.size = sizeof(struct mtdrivetype); mtreq.mtdtp = &mtdt; ioctl(fd, MTIOCGETDRIVETYPE, &mtreq);
mt(1), tar(1), open(2), read(2), write(2), aioread(3C), aiowrite(3C), ar.h(3HEAD), st(4D), dd(8)
1/4 Inch Tape Drive Tutorial
| March 13, 2022 | OmniOS |