Commands¶

class squishy.scsi.command.GroupCode(value)¶

SCSI Command Group Code

Each SCSI command belongs to a group that defines its characteristics. It also defines which commands are optional (o), mandatory (m), reserved (r), shared (s), or vendor specific (v).

If a command is optional (o) then the target does not need to implement it. If the command is mandatory (m) then it must be implemented by the target. If a command is reserved (r) then it should not be implemented by the target, if a command is shared (s) then the opcode depends on the target device class, and may have multiple meanings. Finally, if the command is vendor specific (v) then the command might be implemented depending on the target vendor and its meaning is not standardized.

Each group code is three-bits long, allowing for a maximum of eight groups, with the remaining five-bits in the command opcode for the command identifier itself.

Groupe Code	Group Description
`0b000`	Six-byte Commands
`0b001`	Ten-byte Commands
`0b010`	Reserved Groups
`0b011`
`0b100`
`0b101`	Twelve-byte Commands
`0b110`	Vendor Specific
`0b111`	Vendor Specific

GROUP0 = 0¶

Six-byte Commands

opcode	Type	Command
`0x00`	`o`	Test Unit Ready
`0x01`	`s`
`0x02`	`v`
`0x03`	`m`	Request Sense
`0x04` & `0x05`	`s`
`0x06`	`v`
`0x07` & `0x08`	`s`
`0x09`	`v`
`0x0A` & `0x0B`	`s`
`0x0C` to `0x0E`	`v`
`0x0F` to `0x11`	`s`
`0x12`	`m`	Inquiry
`0x13` to `0x17`	`s`
`0x18`	`o`	Copy
`0x19` to 0x`B	`s`
`0x1C`	`o`	Recv Diagnostic
`0x1D`	`o`	Send Diagnostic
`0x1E`	`s`
`0x1F`	`r`

GROUP1 = 1¶

Ten-byte Commands

opcode	Type	Command
`0x00` to `0x04`	`v`
`0x05`	`s`
`0x06` & `0x07`	`v`
`0x08`	`s`
`0x09`	`v`
`0x0A` & `0x0B`	`s`
`0x0C` & `0x0D`	`v`
`0x0E` to `0x13`	`s`
`0x14` to `0x18`	`r`
`0x19`	`o`	Compare
`0x1A`	`o`	Copy and Verify
`0x1B` to `0x1F`	`r`

GROUP2 = 2¶

Reserved Group

opcode	Type	Command
`0x00` to `0x0F`	`r`

GROUP3 = 3¶

Reserved Group

opcode	Type	Command
`0x00` to `0x0F`	`r`

GROUP4 = 4¶

Reserved Group

opcode	Type	Command
`0x00` to `0x0F`	`r`

GROUP5 = 5¶

Twelve-byte Commands

opcode	Type	Command
`0x00` to `0x0F`	`v`
`0x10` to `0x1F`	`r`

GROUP6 = 6¶

Vendor Specific Commands

opcode	Type	Command
`0x00` to `0x1F`	`v`

GROUP7 = 7¶

Vendor Specific Commands

opcode	Type	Command
`0x00` to `0x1F`	`v`

class squishy.scsi.command.SCSICommand(opcode: int, group_code: GroupCode, *subcons, size: int | None = None, **subconskw) → None¶

SCSI Command Structure

Creates a construct.Struct for arbitrary SCSI Commands. This wraps the structure and gives it some useful common operations needed to consume and generate SCSI commands.

This class automatically creates the opcode and control sections of the command and surrounds the provided *subcons with them.

The rough layout of a SCSI command looks like this:

Byte	7	6	5	4	3	2	1	0
`0`	`opcode`
`n`	`data`
`n+1`	`control`

Both the opcode and control fields of the command are fixed size at 8 bits, but the data section may span multiple bytes and is command dependent.

The size of the command represents the full size of the structure, where the size of the command data itself is sizeof(data) - 2 to account for the opcode and control bytes. Therefore a Six-byte command has four-bytes of actual command data for example.

The layout of the opcode itself is a ‘sub structure’ which describes the group the command is in as well as the command itself.

7	6	5	4	3	2	1	0
`group code`			`command code`

The group code (GroupCode) is the top three bits of the opcode, followed by the command code which is the remaining seven bits.

Due to the split between group code and command code as well as the different classes that implement commands, there is a large re-use of opcode’s, this complicates things, as we need to know ahead of time what the device is in order to succesfully dispatch and parse commands.

The control byte also has it’s own ‘sub structure’.

7	6	5	4	3	2	1	0
`vendor`		`reserved`				`flag`	`link`

The vendor field makes up the top two bits of the control byte, and is vendor unique.

The reserved field follows and is made up of the next four bits.

The flag bit can only be set if the link bit is set. If link is set and the command completes successfully then the target sends a LINKED COMMAND COMPLETE message if flag is zero and a LINKED COMMAND COMPLETE WITH FLAG message if flag is set. This behavior is commonly used to trigger an interrupt in the initiator.

The link bit represents an automatic link to the next command is requested by the initiator if the command is successful. Implementation of this is optional, and depending on if it is supported or not, one of the following two behaviors is expected if the link flag is set.

If supported, when a command completes successfully. The target will return a INTERMEDIATE status and then send a message depending on the state of flag.

If unsupported, the target will return a CHECK CONDITION status and depending if extended sense is implemented, it will set the sense key to ILLEGAL REQUEST if either flag or link are set.

Examples

You can define a new SCSICommand like any other construct structure.

Command = SCSICommand(
        # Final command opcode is calculated by ``opcode | group_code``
        # And then prefixed prior to the given fields
        0x01,             # Command Opcode
        GroupCode.GROUP0, # Command Group
        'Foo' / construct.Int8ul,
        'Bar' / construct.BitStruct(
                'Nya', construct.BitsInteger(3),
                'UwU', construct.BitsInteger(5)
        )
        # The SCSI 'control' byte is then added after.
)

You can also use the special SCSICommandField class to simply attach defaults, descriptions, and automatically compute sizes.

Command = SCSICommand(
        0x01,
        GroupCode.GROUP0,
        'Foo' / SCSICommandField('This is a field', default = 0, length = 3),
        'Bar' / SCSICommandField('This is also a field', length = 5)
)

Parameters:

opcode (int) – The operation code (opcode) for the given command.
group_code (GroupCode) – The specific SCSI group code for this command.
size (None, int) – The size of the command, if not provided, this is inferred from the group_code if possible. (default: None)
*subcons (list[construct.Subconstruct]) – The collection of construct construct.Subconstruct members representing the command.

Attributes:

group_code (GroupCode) – The SCSI commands group code.
size (int) – The total size of the SCSI command.

Note

The result of the sizeof() call returns the size of the SCSI command in bits. To get the size in bytes either call the len() method or divide the result of the sizeof() call by 8.

len() → int¶

Return structure length in bytes

Return type:: int

parse(data, **ctxkw)¶

Parse an in-memory buffer (often bytes object). Strings, buffers, memoryviews, and other complete buffers can be parsed with this method.

Whenever data cannot be read, ConstructError or its derivative is raised. This method is NOT ALLOWED to raise any other exceptions although (1) user-defined lambdas can raise arbitrary exceptions which are propagated (2) external libraries like numpy can raise arbitrary exceptions which are propagated (3) some list and dict lookups can raise IndexError and KeyError which are propagated.

Context entries are passed only as keyword parameters **contextkw.

Parameters:: **contextkw – context entries, usually empty
Returns:: some value, usually based on bytes read from the stream but sometimes it is computed from nothing or from the context dictionary, sometimes its non-deterministic
Raises:: ConstructError – raised for any reason

class squishy.scsi.command.SCSICommand6(opcode: int, *subcons, **subconmskw) → None¶

Six-byte SCSI Command

This is a specialization of the SCSICommand class that deals with six-byte SCSI commands. It automatically sets the group code to Group 0.

The rough layout of the six-byte SCSI commands are the opcode followed by four data bytes, and then the control byte.

Byte	7	6	5	4	3	2	1	0
`0`	`opcode`
`1`	`data`
`2`
`3`
`4`
`5`	`control`

Parameters:

opcode (int) – The operation code (opcode) for the given command.
*subcons (list[construct.Subconstruct]) –
The collection of construct construct.Subconstruct members representing the command.

Attributes:

group_code (GroupCode) – The SCSI commands group code.
size (int) – The total size of the SCSI command.

Note

The result of the sizeof() call returns the size of the SCSI command in bits. To get the size in bytes either call the len() method or divide the result of the sizeof() call by 8.

class squishy.scsi.command.SCSICommand10(opcode: int, *subcons, **subconmskw) → None¶

Ten-byte SCSI Command

This is a specialization of the SCSICommand class that deals with ten-byte SCSI commands. It automatically sets the group code to Group 1.

The rough layout of the ten-byte SCSI commands are the opcode followed by eight data bytes, and then the control byte.

Byte	7	6	5	4	3	2	1	0
`0`	`opcode`
`1`	`data`
`2`
`3`
`4`
`5`
`6`
`7`
`8`
`9`	`control`

Parameters:

opcode (int) – The operation code (opcode) for the given command.
*subcons (list[construct.Subconstruct]) –
The collection of construct construct.Subconstruct members representing the command.

Attributes:

group_code (GroupCode) – The SCSI commands group code.
size (int) – The total size of the SCSI command.

Note

The result of the sizeof() call returns the size of the SCSI command in bits. To get the size in bytes either call the len() method or divide the result of the sizeof() call by 8.

class squishy.scsi.command.SCSICommand12(opcode: int, *subcons, **subconmskw) → None¶

Twelve-byte SCSI Command

This is a specialization of the SCSICommand class that deals with twelve-byte SCSI commands. It automatically sets the group code to Group 5.

The rough layout of the ten-byte SCSI commands are the opcode followed by ten data bytes, and then the control byte.

Byte	7	6	5	4	3	2	1	0
`0`	`opcode`
`1`	`data`
`2`
`3`
`4`
`5`
`6`
`7`
`8`
`9`
`A`
`B`	`control`

Parameters:

opcode (int) – The operation code (opcode) for the given command.
*subcons (list[construct.Subconstruct]) –
The collection of construct construct.Subconstruct members representing the command.

Attributes:

group_code (GroupCode) – The SCSI commands group code.
size (int) – The total size of the SCSI command.

Note

The result of the sizeof() call returns the size of the SCSI command in bits. To get the size in bytes either call the len() method or divide the result of the sizeof() call by 8.

class squishy.scsi.command.SCSICommandField(description: str = '', default: Any = None, *, length: int | None = None) → None¶

SCSI Command Field

This is a wrapper construct.Subconstruct to allow for some metadata and automatic type deduction to be preformed based on the field name.

By default SCSI Command fields don’t have any type prefixing in their name, however this class allows for names with a prefix to automatically set the size and type.

The following table lists the field name prefixes and their type information:

Prefix	Type
`u8l`	`construct.Int8ul`
`u16l`	`construct.Int16ul`
`u24l`	`construct.Int24ul`
`u32l`	`construct.Int32ul`
`u64l`	`construct.Int64ul`
`s8l`	`construct.Int8sl`
`s16l`	`construct.Int16sl`
`s24l`	`construct.Int24sl`
`s32l`	`construct.Int32sl`
`s64l`	`construct.Int64sl`
`u8b`	`construct.Int8ub`
`u16b`	`construct.Int16ub`
`u24b`	`construct.Int24ub`
`u32b`	`construct.Int32ub`
`u64b`	`construct.Int64ub`
`s8b`	`construct.Int8sb`
`s16b`	`construct.Int16sb`
`s24b`	`construct.Int24bl`
`s32b`	`construct.Int32sb`
`s64b`	`construct.Int64sb`
`b#`	`construct.BitsInteger`

An example prefixed field name would be u8lAllocLen which would define an unsigned eight-bit unsigned little-endian integer called AllocLen.

However, if the length argument is passed, that will override the prefix calculated by the name if any is present.

Parameters:

description (str) – The description of this field. (default: '')
default (Any) – The default value for this field if any. (default: None)

Keyword Arguments:

length (int) – The length of the field in bits.

class squishy.scsi.command.CommandEmitter(command: SCSICommand) → None¶

Creates an emitter based on the specified SCSI command.

Given a SCSI command like the following:

Command = SCSICommand6(0x00,
        'Foo' / SCSICommandField(default = 0, length = 8),
        'Bar' / SCSICommandField(length = 8)
)

You are then able to construct an emitter and use it like so:

e = CommandEmitter(Command)
e.Bar = 0xab

# b'\x00\xab'
data = e.emit()

It is also possible to use it within a context like the following:

with CommandEmitter(Command) as cmd:
        cmd.Bar = 0x15

# b'\x00\x15'
cmd.emit()

Parameters:: command (SCSICommand) – The SCSICommand to wrap.

emit() → bytes¶

Emit bytes

Takes the assigned fields and generates a byte string from the specified format.

Warning

This method wraps the internal construct.Subconstruct in a construct.Bitwise() to serialize the structure to bytes.

Returns:: The byte string of the serialized command.
Return type:: bytes
Raises:: KeyError – If missing a required field for the command.