sgm_dd.8

.TH SGM_DD "8" "May 2002" "sg3_utils-1.00" SG3_UTILS
.SH NAME
sgm_dd \- copies data to and from sg and raw devices
.SH SYNOPSIS
.B sgm_dd
[\fIOPTION\fR]...
.SH DESCRIPTION
.\" Add any additional description here
.PP
Copy data to and from Linux SCSI generic (sg) and raw devices
using memory mapped IO. 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
count=BLOCKS
copy this number of blocks. Default is minimum number that sg devices
return from READ CAPACITY (if that works) or 0
.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, 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. A file name of - is taken to be stdin
.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
skip BLOCKS bs-sized blocks at start of output
.TP
skip=BLOCKS
skip BLOCKS bs-sized blocks at start of input
.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
The count is only deduced for sg devices (minimum > 0 if both input and
output are sg devices) otherwise it defaults to 0. This is for safety!
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 the following multiplicative suffixes:
c C *1; b B *512; k *1,024; K *1,000; m *1,048,576; M *1,000,000;
g *1,073,741,824; and G *1,000,000,000
.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 command issues READ_10 and WRITE_10 SCSI commands which
are appropriate for disks and CDROM players. 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@interlog.com>.
.SH COPYRIGHT
Copyright \(co 2000-2002 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 command is called
.B sg_dd.
A POSIX threads version of this command 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)