sgm_dd.8

.TH SGM_DD "8" "February 2005" "sg3_utils-1.13" SG3_UTILS
.SH NAME
sgm_dd \- copies data to and from files and devices. Specialised for
devices that understand the SCSI command set.
.SH SYNOPSIS
.B sgm_dd
[\fIbpt=<n>\fR] [\fIbs=<n>\fR] [\fIcdbsz=6|10|12|16\fR] [\fIcount=<n>\fR]
[\fIdio=0|1\fR] [\fIfua=0|1|2|3\fR] [\fIibs=<n>\fR] [\fIif=<ifile>\fR]
[\fIobs=<n>\fR] [\fIof=<ofile>\fR] [\fIseek=<n>\fR] [\fIskip=<n>\fR]
[\fIsync=0|1\fR] [\fItime=0|1\fR] [\fI--version\fR]
.SH DESCRIPTION
.\" Add any additional description here
.PP
Copy data to and from any files. Specialised for "files" that are
Linux SCSI generic (sg) devices and raw devices. Uses memory mapped IO on
sg devices. Similar syntax and semantics to
.B dd(1) 
but does not perform any conversions.
.TP
bpt=BLOCKS
each IO transaction will be made using this number of blocks (or less if 
near the end of count). Default is 128.
.TP
bs=BYTES
this
.B must
be the block size of the physical device. Note that this differs from
.B dd(1)
which permits "bs" to be an integral multiple. Default is 512 which
is usually correct for disks but incorrect for cdroms (which normally
have 2048 byte blocks).
.TP
cdbsz=6 | 10 | 12 | 16
size of SCSI READ and/or WRITE commands issued on sg device
names (or block devices when "blk_sgio=1" is given).
Default is 10 byte SCSI command blocks (unless calculations indicate
that a 4 byte block number may be exceeded, in which case it defaults
to 16 byte SCSI commands).
.TP
count=BLOCKS
copy this number of blocks from 'if' to 'of'. Default is the
minimum (of 'if' and 'of') number of blocks that sg devices return from
READ CAPACITY SCSI commands or that block devices (or their partitions)
report. Normal files are not probed for their size. If 'skip'
or 'seek' are given and the count is derived (i.e. not explicitly given)
then the derived count is scaled back so that the copy will not overrun the
device. If the file name is a block device partition and count is not given
then the size of the partition rather than the size of the whole device is
used. If count is not given and cannot be derived then an error message
is issued and no copy takes place.
.TP
dio=0 | 1
permits direct IO to be selected on the write-side (i.e. "of"). Only
allowed when the read-side (i.e. "if") is a sg device. When 1 there
may be a "zero copy" copy (i.e. mmap-ed IO on the read into the user
space and direct IO from there on the write, potentially two DMAs and
no data copying from the CPU). Default is 0
.TP
fua=0 | 1 | 2 | 3
force unit access bit. When 3, fua is set on both "if" and "of", when 2, fua
is set on "if", when 1, fua is set on "of", when 0 (the default), fua is
cleared on both. 6 byte SCSI READ and WRITE commands (cdbsz=6) do not 
support the fua bit. Only active for sg device file names.
.TP
ibs=BYTES
if given must be the same as bs
.TP
if=FILE
read from FILE instead of stdin which is the default. A file name of "-" 
is taken to be stdin. Starts reading at the beginning of FILE 
unless "skip" is given.
.TP
obs=BYTES
if given must be the same as bs
.TP
of=FILE
write to FILE instead of stdout. A file name of - is taken to be stdout.
If FILE is /dev/null then no actual writes are performed. If FILE is .
(period) then it is treated the same way as /dev/null (this is a
shorthand notation)
.TP
seek=BLOCKS
start writing BLOCKS bs-sized blocks from the start of the output file.
Default is block 0 (i.e. start of file).
.TP
skip=BLOCKS
start reading BLOCKS bs-sized blocks from the start of input file.
Default is block 0 (i.e. start of file).
.TP
sync=0 | 1
when 1, does SYNCHRONIZE CACHE command on "of" at the end of the transfer.
Only active when "of" is a sg device file name
.TP
time=0 | 1
when 1, times transfer and does throughput calculation, outputting the
results (to stderr) at completion. When 0 (default) doesn't perform timing
.TP
--version
outputs version number information and exits
.PP
A raw device must be bound to a block device prior to using sgm_dd.
See
.B raw(8)
for more information about binding raw devices. To be safe, the sg device
mapping to SCSI block devices should be checked with "cat /proc/scsi/scsi"
before use.
.PP
Raw device partition information can often be found with
.B fdisk(8)
[the "-ul" argument is useful in this respect].
.PP
BYTES and BLOCKS may be followed by one of these multiplicative suffixes:
c C *1; w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB *1,048,576;
MB *1,000,000 . This pattern continues for "G", "T" and "P". The latter two
suffixes can only be used for count, skip and seek values). Also a suffix of
the form "x<n>" multiplies the leading number by <n>. These multiplicative
suffixes are compatible with GNU's dd command (since 2002) which claims
compliance with SI and with IEC 60027-2.
.PP
Alternatively numerical values can be given in hexadecimal preceded by
either "0x" or "0X". When hex numbers are given multipliers cannot be
used.
.PP
The count, skip and seek parameters can take 64 bit values (i.e. very
big numbers). Other values are limited to what can fit in a signed
32 bit number.
.PP
Data usually gets to the user space in a 2 stage process: first the
SCSI adapter DMAs into kernel buffers and then the sg driver copies
this data into user memory (write operations reverse this sequence).
With memory mapped IO a kernel buffer reserved by sg is memory mapped
(see the 
.B mmap(2) 
system call) into the user space. When this is done
the second (redundant) copy from kernel buffers to user space is
not needed. Hence the transfer is faster and requires less "grunt"
from the CPU.
.PP
All informative, warning and error output is sent to stderr so that
dd's output file can be stdout and remain unpolluted. If no options
are given, then the usage message is output and nothing else happens.
.SH EXAMPLES
.PP
See the examples given in the man page for 
.B sg_dd(8).
.SH NOTE
For sg devices this utility issues READ and WRITE (SBC) SCSI commands
which are appropriate for disks and reading from CD/DVD drives. Those
commands are not formatted correctly for tape devices so sgm_dd should
not be used on tape devices.
.SH SIGNALS
The signal handling has been borrowed from dd: SIGINT, SIGQUIT and
SIGPIPE output the number of remaining blocks to be transferred and
the records in + out counts; then they have their default action.
SIGUSR1 causes the same information to be output yet the copy continues.
All output caused by signals is sent to stderr.
.SH AUTHORS
Written by Doug Gilbert and Peter Allworth.
.SH "REPORTING BUGS"
Report bugs to <dgilbert at interlog dot com>.
.SH COPYRIGHT
Copyright \(co 2000-2005 Douglas Gilbert
.br
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
The simplest variant of this utility is called
.B sg_dd.
A POSIX threads version of this utility called
.B sgp_dd
is in the sg3_utils package. The lmbench package contains
.B lmdd
which is also interesting.
.B raw(8), dd(1)