~ubuntu-branches/ubuntu/dapper/sg3-utils/dapper-backports

.TH SGM_DD "8" "June 2006" "sg3_utils-1.21" SG3_UTILS
.SH NAME
sgm_dd \- copies data to and from files and devices. Specialized for
devices that understand the SCSI command set and does memory mapped
transfers from sg devices.
.SH SYNOPSIS
.B sgm_dd
[\fIbs=<n>\fR] [\fIcount=<n>\fR] [\fIibs=<n>\fR] [\fIif=<ifile>\fR]
[\fIiflag=<flags>\fR] [\fIobs=<n>\fR] [\fIof=<ofile>\fR]
[\fIoflag=<flags>\fR] [\fIseek=<n>\fR] [\fIskip=<n>\fR]
[\fI--help\fR] [\fI--version\fR]
.PP
[\fIbpt=<n>\fR] [\fIcdbsz=6|10|12|16\fR] [\fIdio=0|1\fR]
[\fIsync=0|1\fR] [\fItime=0|1\fR] [\fIverbose=<n>\fR]
.SH DESCRIPTION
.\" Add any additional description here
.PP
Copy data to and from any files. Specialized for "files" that are
Linux SCSI generic (sg) devices and raw devices. Uses memory mapped 
transfers on sg devices. Similar syntax and semantics to
.B dd(1) 
but does not perform any conversions.
.PP
Will only perform memory mapped transfers when <ifile> or <ofile> are
SCSI generic (sg) devices. If both <ifile> and <ofile> are sg devices
then memory mapped transfers are only performed on <ifile>.
.PP
The first group in the synopsis above are "standard" Unix
.B dd(1)
arguments. The second group are extra arguments added by this utility.
Both groups are defined below.
.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 for block sizes less that 2048
bytes, otherwise the default is 32. So for bs=512 the reads and writes
will each convey 64 KiB of data by default (less if near the end of the
transfer or memory restrictions). When cd/dvd drives are accessed, the
block size is typically 2048 bytes and bpt defaults to 32 which again
implies 64 KiB transfers.
.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.
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 transfer 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
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
iflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below.
These flags are associated with <ifile> and are ignored when <ifile> is
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
oflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below.
These flags are associated with <ofile> and are ignored when <ofile>
is /dev/null, . (period), or stdout.
.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
verbose=<n>
as <n> increases so does the amount of debug output sent to stderr.
Default value is zero which yields the minimum amount of debug output.
A value of 1 reports extra information that is not repetitive. A value
2 reports cdbs and responses for SCSI commands that are not repetitive
(i.e. other that READ and WRITE). Error processing is not considered
repetitive. Values of 3 and 4 yield output for all SCSI commands (and
Unix read() and write() calls) so there can be a lot of output.
.TP
--version
outputs version number information and exits
.SH FLAGS
Here is a list of flags and their meanings:
.TP
append
causes the O_APPEND flag to be added to the open of <ofile>. For normal
files this will lead to data appended to the end of any existing data.
Cannot be used together with the 'seek=<n>' option as they conflict.
The default action of this utility is to overwrite any existing data
from the beginning of the file or, if 'seek=<n>' is given, starting at
block <n>. Note that attempting to 'append' to a device file will
usually be ignored or may cause an error to be reported.
.TP
direct
causes the O_DIRECT flag to be added to the open of <ifile> and/or <ofile>.
This flag requires some memory alignment on IO. Hence user memory buffers
are aligned to the page size. Has no effect on sg, normal or raw files.
.TP
dpo
set the DPO bit (disable page out) in READ and WRITE SCSI commands. Not
supported for 6 byte cdb variants of READ and WRITE. Indicates that
data is unlikely to be required to stay in device (e.g. disk) cache.
May speed media copy and/or cause a media copy to have less impact
on other device users.
.TP
dsync
causes the O_SYNC flag to be added to the open of <ifile> and/or <ofile>.
The "d" is prepended to lower confusion with the 'sync=0|1' option which
has another action (i.e. a synchronisation to media at the end of the
transfer).
.TP
excl
causes the O_EXCL flag to be added to the open of <ifile> and/or <ofile>.
.TP
fua
causes the FUA (force unit access) bit to be set in READ and/or WRITE
SCSI commands. This only has effect with sg devices. The 6 byte variants
of the READ and WRITE SCSI commands do not support the FUA bit.
Only active for sg device file names.
.SH RETIRED OPTIONS
Here are some retired options that are still present:
.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 (default), fua is cleared
on both. See the 'fua' flag.
.SH NOTES
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" (or with a trailing "h" or "H"). 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 transfers 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.
.PP
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.
.PP
This utility stops the copy if any error is encountered. For more
advanced "copy on error" logic see the
.B sg_dd
utility (and its 'coe' flag).
.SH EXAMPLES
.PP
See the examples given in the man page for 
.B sg_dd(8).
.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 EXIT STATUS
The exit status of sgm_dd is 0 when it is successful. Otherwise see
the sg3_utils(8) man page. Since this utility works at a higher level
than individual commands, and there are 'coe' and 'retries' flags,
individual SCSI command failures do not necessary cause the process
to exit.
.SH AUTHORS
Written by Doug Gilbert and Peter Allworth.
.SH "REPORTING BUGS"
Report bugs to <dgilbert at interlog dot com>.
.SH COPYRIGHT
Copyright \(co 2000-2006 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)