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SG_WRITE_BUFFER(8) SG3_UTILS SG_WRITE_BUFFER(8)
NAME
sg_write_buffer - send SCSI WRITE BUFFER commands
SYNOPSIS
sg_write_buffer [--bpw=CS] [--dry-run] [--help] [--id=ID] [--in=FILE] [--length=LEN]
[--mode=MO] [--offset=OFF] [--read-stdin] [--skip=SKIP] [--specific=MS] [--timeout=TO]
[--verbose] [--version] DEVICE
DESCRIPTION
Sends one or more SCSI WRITE BUFFER commands to DEVICE, along with data provided by the
user. In some cases no data is required, or data can be read from the file given in the
--in=FILE option, or data is read from stdin when either --read-stdin or --in=- is given.
Some WRITE BUFFER command variants do not have associated data to send to the device. For
example "activate_mc" activates deferred microcode that was sent via prior WRITE BUFFER
commands. There is a different method used to download microcode to SES devices, see the
sg_ses_microcode utility.
OPTIONS
Arguments to long options are mandatory for short options as well. The options are ar-
ranged in alphabetical order based on the long option name.
-b, --bpw=CS
where CS is the chunk size in bytes. This will be the maximum number of bytes sent
per WRITE BUFFER command. So if CS is less than the effective length then multiple
WRITE BUFFER commands are sent, each taking the next chunk from the read data and
increasing the buffer offset field in the WRITE BUFFER command by the appropriate
amount. The default is a chunk size of 0 which is interpreted as a very large num-
ber hence only one WRITE BUFFER command will be sent. This option should only be
used with modes that "download microcode, with offsets ..."; namely either mode
0x6, 0x7, 0xd or 0xe.
The number in CS can optionally be followed by ",act" or ",activate". In this case
after WRITE BUFFER commands have been sent until the effective length is exhausted
another WRITE BUFFER command with its mode set to "Activate deferred microcode
mode" [mode 0xf] is sent.
-d, --dry-run
Do all the command line processing and sanity checks including reading the input
file. However at the point where a WRITE BUFFER SCSI command(s) would be sent, step
over that call and assume it completed without errors and continue. DEVICE is still
opened but can be /dev/null (in Unix). It is recommended to use --verbose with
this option to get an overview of what would have happened.
-h, --help
output the usage message then exit. If used multiple times also prints the mode
names and their acronyms.
-i, --id=ID
this option sets the buffer id field in the cdb. ID is a value between 0 (default)
and 255 inclusive.
-I, --in=FILE
read data from file FILE that will be sent with the WRITE BUFFER command. If FILE
is '-' then stdin is read until an EOF is detected (this is the same action as
--read-stdin). Data is read from the beginning of FILE except in the case when it
is a regular file and the --skip=SKIP option is given.
-l, --length=LEN
where LEN is the length, in bytes, of data to be written to the device. If not
given (and the length cannot be deduced from --in=FILE or --read-stdin) then de-
faults to zero. If the option is given and the length deduced from --in=FILE or
--read-stdin is less (or no data is provided), then bytes of 0xff are used as fill
bytes.
-m, --mode=MO
this option sets the MODE field in the cdb. MO is a value between 0 (default) and
31 inclusive. Alternatively an abbreviation can be given. See the MODES section
below. To list the available mode abbreviations at run time give an invalid one
(e.g. '--mode=xxx') or use the '-hh' option.
-o, --offset=OFF
this option sets the BUFFER OFFSET field in the cdb. OFF is a value between 0 (de-
fault) and 2**24-1 . It is a byte offset.
-r, --read-stdin
read data from stdin until an EOF is detected. This data is sent with the WRITE
BUFFER command to DEVICE. The action of this option is the same as using '--in=-'.
Previously this option's long name was --raw and it may still be used for backward
compatibility.
-s, --skip=SKIP
this option is only active when --in=FILE is given and FILE is a regular file,
rather than stdin. Data is read starting at byte offset SKIP to the end of file (or
the amount given by --length=LEN). If not given the byte offset defaults to 0
(i.e. the start of the file).
-S, --specific=MS
MS is the MODE SPECIFIC field in the cdb. This is a 3-bit field so the values 0 to
7 are accepted. This field was introduced in SPC-4 revision 32 and can be used to
specify additional events that activate deferred microcode (when MO is 0xD).
-t, --timeout=TO
TO is the command timeout (in seconds) for each WRITE BUFFER command issued by this
utility. Its default value is 300 seconds (5 minutes) and should only be altered if
this is not sufficient.
-v, --verbose
increase the level of verbosity, (i.e. debug output).
-V, --version
print the version string and then exit.
MODES
Following is a list of WRITE BUFFER command settings for the MODE field. First is an
acronym accepted by the MO argument of this utility. Following the acronym in square
brackets are the corresponding decimal and hex values that may also be given for MO. The
following are listed in numerical order.
hd [0, 0x0]
Combined header and data (obsolete in SPC-4).
vendor [1, 0x1]
Vendor specific.
data [2, 0x2]
Data (was called "Write Data" in SPC-3).
dmc [4, 0x4]
Download microcode and activate (was called "Download microcode" in SPC-3).
dmc_save [5, 0x5]
Download microcode, save, and activate (was called "Download microcode and save" in
SPC-3).
dmc_offs [6, 0x6]
Download microcode with offsets and activate (was called "Download microcode with
offsets" in SPC-3).
dmc_offs_save [7, 0x7]
Download microcode with offsets, save, and activate (was called "Download microcode
with offsets and save" in SPC-3).
echo [10, 0xa]
Write data to echo buffer (was called "Echo buffer" in SPC-3).
dmc_offs_ev_defer [13, 0xd]
Download microcode with offsets, select activation events, save, and defer activate
(introduced in SPC-4).
dmc_offs_defer [14, 0xe]
Download microcode with offsets, save, and defer activate (introduced in SPC-4).
activate_mc [15, 0xf]
Activate deferred microcode (introduced in SPC-4).
en_ex [26, 0x1A]
Enable expander communications protocol and Echo buffer (obsolete in SPC-4).
dis_ex [27, 0x1B]
Disable expander communications protocol (obsolete in SPC-4).
deh [28, 0x1C]
Download application client error history (was called "Download application log" in
SPC-3).
NOTES
If no --length=LEN is given this utility reads up to 8 MiB of data from the given file
FILE (or stdin). If a larger amount of data is required then the --length=LEN option
should be given.
The user should be aware that most operating systems have limits on the amount of data
that can be sent with one SCSI command. In Linux this depends on the pass through mecha-
nism used (e.g. block SG_IO or the sg driver) and various setting in sysfs in the Linux lk
2.6/3 series (e.g. /sys/block/sda/queue/max_sectors_kb). Devices (i.e. logical units) also
typically have limits on the maximum amount of data they can handle in one command. These
two limitations suggest that modes containing the word "offset" together with the --bpw=CS
option are required as firmware files get larger and larger. And CS can be quite small,
for example 4096 bytes, resulting in many WRITE BUFFER commands being sent.
Attempting to download a microcode/firmware file that is too large may cause an error to
occur in the pass-through layer (i.e. before the SCSI command is issued). In Linux such
error reports can be obscure as in "pass through os error invalid argument". FreeBSD re-
ports such errors well to the machine's console but returns a cryptic error message to
this utility.
Downloading incorrect microcode into a device has the ability to render that device inop-
erable. One would hope that the device vendor verifies the data before activating it. If
the SCSI WRITE BUFFER command is given values in its cdb (e.g. LEN) that are inappropriate
(e.g. too large) then the device should respond with a sense key of ILLEGAL REQUEST and an
additional sense code of INVALID FIELD in CDB. If a WRITE BUFFER command (or a sequence of
them) fails due to device vendor verification checks then it should respond with a sense
key of ILLEGAL REQUEST and an additional sense code of COMMAND SEQUENCE ERROR.
All numbers given with options are assumed to be decimal. Alternatively numerical values
can be given in hexadecimal preceded by either "0x" or "0X" (or has a trailing "h" or
"H").
EXAMPLES
The following sends new firmware to an enclosure. Sending a 1.5 MB file in one WRITE BUF-
FER command caused the enclosure to lock up temporarily and did not update the firmware.
Breaking the firmware file into 4 KB chunks (an educated guess) was more successful:
sg_write_buffer -b 4k -m dmc_offs_save -I firmware.bin /dev/sg4
The firmware update occurred in the following enclosure power cycle. With a modern enclo-
sure the Extended Inquiry VPD page gives indications in which situations a firmware up-
grade will take place.
EXIT STATUS
The exit status of sg_write_buffer is 0 when it is successful. Otherwise see the
sg3_utils(8) man page.
AUTHORS
Written by Luben Tuikov and Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright (C) 2006-2018 Luben Tuikov and Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
sg_read_buffer, sg_ses_microcode(sg3_utils)
sg3_utils-1.45 November 2018 SG_WRITE_BUFFER(8)
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