SG_PERSIST(8)

NAME
sg_persist - use the Persistent Reservation In and Out SCSI commands to manipulate registrations and reservations

SYNOPSIS
sg_persist [<options>] [<scsi_device>]

DESCRIPTION

This utility allows Persistent reservations and registrations to be queried and changed. Persistent reservations and registrations are queried by sub-commands (called "service actions" in SPC-3) of the Persistent Reservation In (PRIN) SCSI command. Persistent reservations and registrations are changed by sub-commands of the Persistent Reservation Out (PROUT) SCSI command.

It is relatively safe to query the state of Persistent reservations and registrations. With no options this utility defaults to the READ KEYS sub-command of the PRIN command. Other PRIN sub-commands are READ RESERVATION, REPORT CAPABILITIES and READ FULL STATUS.

Before trying to change Persistent reservations and registrations users should be aware of what they are doing! The relevant sections of the SCSI Primary Commands document (SPC-3 most recent draft revision 21 dated 22nd September 2004) are sections 5.6 (general information), 6.11 (for PRIN) and 6.12 (for PROUT). To safeguard against accidental use, the '--out' option must be given when a PROUT sub-command (e.g. '--register') is used.

The older SCSI Reserve and Release commands (both 6 and 10 byte variants) are not supported by this utility. In SPC-3, Reserve and Release are deprecated, replaced by Persistent Reservations. See a utility called 'scsires' for support of the SCSI Reserve and Release commands.

The <scsi_device> is required by all variants of this utility apart from '--help' ('-h'). The <scsi_device> can be given either as an argument (typically but not necessarily the last one) or via the '--device=<scsi_device>' (or '-d <scsi_device') option.

SPC-3 does not use the term "sub-command". It uses the term "service action" for this and for part of a field's name in the parameter block associated with the PROUT command (i.e. "service action reservation key"). To lessen the potential confusion the term "sub-command" has been introduced.

OPTIONS

--clear | -C
    Clear is a sub-command of the PROUT command. It releases the persistent reservation (if any) and clears all registrations from the device. It is required to supply a reservation key that is registered for this I_T_L nexus (identified by --param-rk).

--device=<scsi_device> | -d <scsi_device>
    This utility needs to have a scsi_device to be specified. This can either be as an argument to '--device' or '-d' or just the first non-option argument.

--help | -h
    output a usage message.

--hex | -H
    the response to a valid PRIN sub-command will be output in hexadecimal. Normally if the PRIN sub-command is recognised then the response will be decoded as per SPC-3.

--in | -i
    specify that a Persistent Reservation In SCSI command is required. This is the default.

--out | -o
    specify that a Persistent Reservation Out SCSI command is required.

--no-inquiry | -n
    the default action is to do a standard INQUIRY SCSI command and output make, product and revision strings plus the peripheral device type prior to executing a PR In or Out command. With this option the INQUIRY command is skipped.

--param-alltgpt | -Y
    set the 'all target ports' (ALL_TG_PT) flag in the parameter block of the PROUT command. Only relevant for 'register' and 'register and ignore existing key' sub-commands.

--param-aptpl | -Z
    set the 'activate persist through power loss' (APTPL) flag in the parameter block of the PROUT command. Relevant for 'register', 'register and ignore existing key' and 'register and move' sub-commands.

--param-rk=<h> | -K <h>
    specify the reservation key found in the parameter block of the PROUT command. Argument is assumed to be hex (up to 8 bytes long). Default value is 0. This option is needed by most PROUT sub-commands.

--param-sark=<h> | -S <h>
    specify the service action reservation key found in the parameter block of the PROUT command. Argument is assumed to be hex (up to 8 bytes long). Default value is 0. This option is needed by some PROUT sub-commands.

--preempt | -P
    Preempt is a sub-command of the PROUT command. Preempts the existing persistent reservation (identified by '--param-sark') with the registration key that is registered for this I_T_L nexus (identified by '--param-rk'). The associated '--prout-type<h>' option needs to match the type of the reservation.

--preempt-abort | -A
    Preempt and Abort is a sub-command of the PROUT command. Preempts the existing persistent reservation (identified by '--param-sark') with the registration key that is registered for this I_T_L nexus (identified by '--param-rk'). The associated '--prout-type<h>' option needs to match the type of the reservation. ACA and other pending tasks are aborted.

--prout-type=<h> | -T <h>
    specify the PROUT command's 'type' argument. Required by the 'register-move', 'reserve', 'release' and 'preempt (and abort)' sub-commands. Valid arguments: 1-> write exclusive, 3-> exclusive access, 5-> write exclusive - registrants only, 6-> exclusive access - registrants only, 7-> write exclusive - all registrants, 8-> exclusive access - all registrants. Default value is 0 (which is an invalid type).

--read-full-status | -s
    Read Full Status is a sub-command of the PRIN command. For each registration with the given SCSI device, it lists the reservation key and associated information. TransportIDs, if supplied in the reponse, are decoded.

--read-keys | -k
    Read Keys is a sub-command of the PRIN command. Lists all the reservation keys registered (i.e. registrations) with the given SCSI device. This is the default sub-command for the PRIN SCSI command.

--read-reservation | -r
    Read Reservation is a sub-command of the PRIN command. List information about the current holder of the reservation on the given device. If there is no current reservation this will be noted. Information about the current holder of the reservation includes its reservation key, scope and type.

--read-status | -s
    same as 'read-full-status'.

--register | -G
    Register is a sub-command of the PROUT command. It has 3 different actions depending on associated parameters. 1) add a new registration with '--param-rk=0' and '--param-sark=<new_rk>'. 2) Change an existing registration with '--param-rk=<old_rk>' and '--param-sark=<new_rk>'. 3) Delete an existing registration with '--param-rk=<old_rk>' and '--param-sark=0'.

--register-ignore | -I
    Register and Ignore Existing Key is a sub-command of the PROUT command. Similar to '--register' except that when changing a reservation key the old key is not specified. The '--prout-sark=<new_rk>' option should also be given.

--register-move | -M
    register (another initiator) and move (the reservation held by the current initiator to that other initiator) is a sub-command of the PROUT command. It requires the transportID of the other initiator. [The standard uses the term I_T nexus but the point to stress is that there are two initiators (the one sending this command and another one) but only one target.] The '--param-type=<h>' and '--param-rk=<h>' options need to match that of the existing reservation while '--param-sark=<h>' option specifies the reservation key of the new (i.e. destination) registration.

--relative-target-port=<h> | -Q <h>
    relative target port number that reservation is to be moved to by PROUT 'register and move' sub-command. <h> is assumed to be hex in the range 0 to ffff inclusive. Defaults to 0 .

--release | -L
    Release is a sub-command of the PROUT command. It releases the current persistent reservation. The '--prout-type=<h>' and '--prout-rk=<h>' options, matching the reservation, must also be specified.

--report-capabilities | -c
    Report Capabilities is a sub-command of the PRIN command. It lists information about the aspects of persistent reservations that the given device supports.

--reserve | -R
    Reserve is a sub-command of the PROUT command. It creates a new persistent reservation (if permitted). The '--prout-type=<h>' and '--prout-rk=<h>' options must also be specified.

--transport-id=<h>,<h>... | -X <h>,<h>...
    a transportID is required for the PROUT 'register and move' sub-command and is optional for the PROUT 'register' and 'register and ignore existing key' sub-commands. The latter two sub-commands can take multiple transportIDs in a list but only one is supported on the command line. The argument is a comma separated list of hex numbers representing the bytes of the transportID. The list of hex numbers will be padded out with zeroes to 24 bytes which is the minimum length of a transportID. A transportID longer than 24 bytes (e.g. for iSCSI) is padded with zeroes so its length is a multiple of 4.

--transport-id=- | -X -
    a transportID is required for the PROUT 'register and move' sub-command and is optional for the PROUT 'register' and 'register and ignore existing key' sub-commands. The latter two sub-commands can take multiple transportIDs in a list. The argument is '-' which indicates stdin should be read for the transportID(s). Empty lines are ignored. Everything from and including a "#" on a line is ignored. Leading spaces and tabs are ignored. All numbers are assumed to be hexadecimal and can be separated by space, comma or tab. There can be one transportID per line. TranportIDs will be padded out with zeroes to 24 bytes which is the minimum length of a transportID. A transportID longer than 24 bytes (e.g. for iSCSI) is padded with zeroes so its length is a multiple of 4.

--unreg | -U
    optional when the PROUT register and move sub-command is invoked. If given it will unregister the current initiator (I_T nexus) after the other initiator has been registered and the reservation moved to it. When not given the initiator (I_T nexus) that sent the PROUT command remains registered.

--verbose | -v
    print out cdb of issued commands prior to execution. If used twice prints out the parameter block associated with the PROUT command prior to its execution as well. If used thrice decodes given transportID(s) as well. To see the response to a PRIN command in low level form use the '--hex' option.

--version | -V
    print out version string. Ignore all other parameters.

-?  output usage message. Ignore all other parameters.

NOTES
In the 2.4 series of Linux kernels the given device must be a SCSI generic (sg) device. In the 2.6 series any SCSI device name (e.g. /dev/sdc, /dev/st1m or /dev/sg3) can be specified. For example "sg_persist --read-keys /dev/sda" will work in the 2.6 series kernels.

The only scope for PROUT commands supported in the current draft of SPC-3 is "LU_SCOPE". Hence there seems to be no point in offering an option to set scope to another value.

Most errors with the PROUT sub-commands (e.g. missing or mismatched '--prout-type=<h>' option) will result in a RESERVATION CONFLICT status. This can be a bit confusing when you know there is only one (active) initiator: the "conflict" is with the SPC standard, not another initiator.

EXAMPLES

Due to defaults the simplest example executes the 'read keys' sub-command of the PRIN command:

   sg_persist /dev/sda

This is the same as the following (long-winded) command:

   sg_persist --in --read-keys --device=/dev/sda

To read the current reservation either the '--read-reservation' form or the shorter '-r' can be used:

   sg_persist -r /dev/sda

To register the new reservation key 0x123abc the following could be used:

   sg_persist --out --register --param-sark=123abc /dev/sda

Given the above registration succeeds, to reserve the given device (with type 'write exclusive') the following could be used:

   sg_persist --out --reserve --param-rk=123abc
              --prout-type=1 /dev/sda

To release the reservation the following can be given (note that the --param-rk and --prout-type arguments must match those of the reservation):

   sg_persist --out --release --param-rk=123abc
              --prout-type=1 /dev/sda

Finally to unregister a reservation key (and not effect other registrations which is what '--clear' would do) the command is a little surprising:

   sg_persist --out --register --param-rk=123abc /dev/sda

Now have a close look at the difference between the register and unregister examples above.

An example file that is suitably formatted to pass transportIDs via the '-transport-id=-' option can be found in the examples sub-directory of the sg3_utils package. That file is called 'transport_ids.txt'.

AUTHOR
Written by Doug Gilbert

REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT
Copyright © 2004 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
scsires(internet), examples/sg_persist_tst.sh(sg3_utils tarball)