NAME

rscsi - remote generic SCSI transport protocol server

SYNOPSIS

/opt/schily/sbin/rscsi

DESCRIPTION

The rscsi command is a remote generic SCSI transport server program. rscsi is a program that is run locally on the machine with SCSI devices, it is used by remote programs like cdrecord(1), cdda2wav(1), readcd(1), and sformat(1) that like to access SCSI devices through an interprocess communication connection via libscg. rscsi is normally started up with an rexec(3) or rcmd(3) call but it may also be connected via an internal pipe to an ssh(1) session that was set up by the remote user.

The rscsi program accepts scg_open, scg_close, scg_cmd and similar requests that are all related to the interface of libscg. rscsi performs the commands and then responds with a status indication.

The rscsi program is prepared to be installed as a user shell in the passwd file to create remote SCSI specific logins and security checking.

All requests are send to the rscsi program in ASCII and thus are byte order and machine independent.

All responses are send back in ASCII and in one of the following two forms.

All successful commands (except for the "S" command that sends SCSI commands) have responses of

: Anumber\n

where number is the ASCII representation of a decimal number that usually is the return code of the corresponding system call or function.

All unsuccessful commands are responded to with

: Eerror-number\nerror-message\nxerror-len\nxerror-txt

where error-number is one of the possible error numbers described in intro(2), and error-message is the corresponding error string as retrieved by strerror(3), xerror-len is the length of the additional error text xerror-txt and may be 0. In case xerror-len is 0, no xerror-txt is send. Note that a failed SCSI command that returned SCSI sense data counts as a successful command and does not use the default error format.

The rscsi protocol implements the following commands:

Vwhat\n: Return the version for several instances of the software in the rscsi server. The parameter what may have the following values:

0: Return SCG_VERSION from libscg on the rscsi server. This returns the version string for the low level SCSI transport adaptation layer.
1: Return SCG_AUTHOR from libscg on the rscsi server. This returns the author name for the low level SCSI transport adaptation layer.
2: Return SCG_SCCS_ID from libscg on the rscsi server. This returns the SCCS version string for the low level SCSI transport adaptation layer.
20: Return SCG_KVERSION from libscg on the rscsi server. This returns the version of kernel instance of the driver that is underneath the low level SCSI transport adaptation layer.
This call may not be supported for all operating systems.

This command corresponds to the scg_version(3) function from libscg.

Odevice\n

Open the specified SCSI device.

See the description of the dev= option in cdrecord(1) for more information on possible values of the device parameter.

If a device is already open, it is closed before a new open is performed.

This command corresponds to the scg_open(3) function from libscg.

The return value in case of success is 0.

Cdevice\n

Close the currently open device or file. The argument device is ignored.

This command corresponds to the scg_close(3) function from libscg.

The return value is the return value from the scg_close(3) function.

Dsize\n

Set up the maximum DMA size for the currently open SCSI device. The size parameter is the desired DMA size in bytes.

This command corresponds to the scg_bufsize(3) function from libscg.

The returned value is the actual DMA size that could be set up. This value may be lower than the size parameter.

Msize\n

Allocate a buffer suitable for SCSI DMA transfers.

This command corresponds to the scg_getbuf(3) function from libscg.

The returned value is the actual DMA size that could be set up. This value may be lower than the size parameter.

F\n

Free a previously allocated buffer.

This command corresponds to the scg_freebuf(3) function from libscg.

The return value in case of success is 0.

N\n

Retrieve the maximum permitted value for the SCSI bus number.

This command corresponds to the scg_numbus(3) function from libscg.

The return value is the return value from the scg_numbus(3) function.

Bbusno\nchan\n

Checks whether there is a SCSI bus with a busnumber that is equal to busno. The chan parameter is currently ignored.

This command corresponds to the scg_havebus(3) function from libscg.

The return value is the return value from the scg_havebus(3) function.

Tbusno\nchan\ntarget\nlun\n

Set the SCSI target address to busno, target, lun. The parameter chan is currently ignored.

This command corresponds to the scg_settarget(3) function from libscg.

The return value is the return value from the scg_havebus(3) function.

I\n

Retrieve the SCSI initiator ID for the current SCSI bus.

This command corresponds to the scg_initiator_id(3) function from libscg.

The return value is the return value from the scg_initiator_id(3) function.

A\n

Check whether the current target is or may be an ATAPI device.

This command corresponds to the scg_isatapi(3) function from libscg.

The return value is the return value from the scg_isatapi(3) function.

Rwhat\n

Perform a SCSI reset. The parameter what may have the following values:

0: Test whether a SCSI reset is supported as with the SCG_RESET_NOP parameter.
1: Perform a SCSI target reset as with the SCG_RESET_TGT parameter.
2: Perform a SCSI bus reset as with the SCG_RESET_BUS parameter.

This command corresponds to the scg_reset(3) function from libscg.

The return value is the return value from the scg_reset(3) function.

Scount\nflags\ncdb_len\nsense_len\ntimeout\n: Send a SCSI command to the currently selected target. This command takes the following parameters:

count: The DMA count for this command. If the command is a command that transfers data to the target, the related data is send directly after the SCSI command descriptor block. that is described above.
flags: The flags that apply to this SCSI command:

1: Tell the kernel that the SCSI command will transfer data from the target to the host. This corresponds to the flag value SCG_RECV_DATA.
2: Tell the kernel to send the SCSI command with disconnect/reconnect enabled. This corresponds to the flag value SCG_DISRE_ENA. This flag is not supported on all platforms.
4: Make the kernel silent on SCSI errors. This corresponds to the flag value SCG_SILENT. This flag is not supported on all platforms.
8: Tell the kernel to retry the SCSI command in case of a retryable SCSI transport error. This corresponds to the flag value SCG_CMD_RETRY. This flag is not supported on all platforms.
16: Tell the kernel to send the SCSI command with parity disabled. This corresponds to the flag value SCG_NOPARITY. This flag is not supported on all platforms.

cdb_len: The SCSI command descriptor length for this command. The SCSI command descriptor has to be send with the correct length directly after the new line past the timeout value.
sense_len: The amount of sense data that is expected in return of a failed SCSI command that produces SCSI sense data.
timeout: The timeout for the SCSI command in seconds. Fractions of a second may be specified by sending a floating point number.

The reply for a SCSI command that could be send to the target is:

Acount\nerror\nerrno\nscb\nsense_count\n

count: The DMA count of any data returned from the target. If this count is nonzero, the data is send back directly after the reply block mentioned above.
error: A SCSI error classification from one of the following values:

0: No error occurred. This value corresponds to the value SCG_NO_ERROR .
1: A retryable error occurred while trying to transport the SCSI command to the target. This value corresponds to the value SCG_RETRYABLE .
2: A fatal error occurred while trying to transport the SCSI command to the target. This value corresponds to the value SCG_FATAL .
3: A SCSI timeout occurred. This value corresponds to the value SCG_TIMEOUT .

errno

Any possible UNIX errno value for the SCSI command.

scb

The SCSI status byte

sense_count

The sense count returned for the SCSI command. The SCSI sense data is send back directly after any possible SCSI DMA data received from the target.

This command corresponds to the scg_cmd(3) function from libscg.

The return value is the return value from the scg_cmd(3) function.

Any other command causes rscsi to exit.

FILES

/etc/default/rscsi

Default values can be set for the following options in /etc/default/rscsi. For example:

DEBUG=/tmp/rscsi.debug
USER=rscsi
ACCESS=rscsi myhost.mydomain.org 1 -1 3 0

All keywords must be on the beginning of a line.

DEBUG: If you like to get debug information, set this to a file name where rscsi should put debug information.
USER: The name of a user (local to the RSCSI server) that may use the services of the rscsi server. More than one USER=name line is possible. A line USER=* grants access to all users.
ACCESS: This keyword is followed by six parameters separated by a TAB. The name of a user (local to the RSCSI server host) that may use the services of the rscsi server followed by the name of a host from where operation is granted followed by a SCSI device specification that is made of bus-number channel (ignored for now) target-id and lun that specify a SCSI device that may be accessed if this ACCESS line matches. If one or more entries of the bus-number channel target-id lun specification is set to -1, this matches any possible value for the related part of the SCSI device specification. More than one ACCESS=name host SCSI-device line is possible.
If standard input of rscsi is not a socket from a remote host, rscsi will compare the host entry from /etc/default/rscsi with the following strings:

PIPE: If stdin is a UNIX pipe.
If you like to allow remote connections that use the ssh protocol, you need to use the word PIPE instead of the real hostname in the matching ACCESS= line.
ILLEGAL_SOCKET: If getpeername() does not work for stdin.
NOT_IP: If getpeername() works for stdin but is not connected to an internet socket.

DIAGNOSTICS

All responses are send to the network connection. They use the form described above.

NOTES

The possibility to create a debug file by calling rscsi file has been disabled for security reasons. If you like to debug rscsi edit /etc/default/rscsi and insert a DEBUG entry.

BUGS

None known.

HISTORY

The rscsi command has been developed by Joerg Schilling in June 2000.

AUTHOR

Joerg Schilling
D-13353 Berlin
Germany

Mail bugs and suggestions to:

joerg@schily.net

INTERFACE STABILITY

The interfaces provided by rscsi are designed for long term stability. As rscsi depends on interfaces provided by the underlying operating system, the stability of the interfaces offered by rscsi depends on the interface stability of the OS interfaces. Modified interfaces in the OS may enforce modified interfaces in rscsi.