AmigaDOS Packets

This page is currently being updated to AmigaOS 4.x. Some of the information contained here may not yet be applicable in part or totally.

Introduction

Packet passing handles all communication performed by AmigaDOS between processes. The function diagram below shows how packets fit in with the other components of the Amiga operating system.

   +--------------+
   | User Process +-----------------------+
   +-------+------+                       |
           |                              |
           |                              |
    Function Calls                        |
           |                              |
          \|/                             |
 +---------+--------+                     |
 | AmigaDOS Open(), |                     |
 |   Close(), etc.  |                     |
 +---------+--------+                     |
           |                              |
           |                              |
      +-Packets---+--------+     +-----Packets--------+
      |           |        |     |        |           |
     \|/         \|/      \|/   \|/      \|/         \|/
 +----+----+ +----+----+ +-+--+--+-+ +----+----+ +----+----+
 | FFS/OFS | | FFS/OFS | | FFS/OFS | |   CON:  | |   CON:  |
 |   DH0:  | |   DF0:  | |   DF1:  | | Window1 | | Window2 |
 | Handler | | Handler | | Handler | | Handler | | Handler |
 | Process | | Process | | Process | | Process | | Process |
 +----+----+ +-------+-+ +----+----+ +----+----+ +----+----+
      |              |        |           |           |
     \|/            \|/      \|/         \|/         \|/
 +----+--------+  +--+--------+----+ +----+-----------+----+
 |Hddisk.device|  |Trackdisk.device| |    Console.device   |
 +-------------+  +----------------+ +---------------------+

A StandardPacket (defined in <dos/dosextens.h>) is used to send packet commands to a process's MsgPort. The StandardPacket structure contains an Exec Message structure and an AmigaDOS DOSPacket structure:

    struct StandardPacket
    {   struct Message   sp_Msg;
        struct DOSPacket sp_Pkt;
    };

This structure must be longword-aligned, and initialized to link the Message and DOSPacket sections to each other:

    packet->sp_Msg.mn_Node.ln_Name = (char *) &(packet->sp_Pkt);
    packet->sp_Pkt.dp_Link         = &(packet->sp_Msg);

Packets must also be initialized with a ReplyPort which is created with AllocSysObject():

    if (replyport = (struct MsgPort *) IExec->AllocSysObjectTags(ASOT_PORT, TAG_END))
        packet->sp_Pkt.dp_Port = replyport;

The DOSPacket portion of the StandardPacket structure is used to pass the packet type and arguments, and to receive the results of the packet. The argument types, number of arguments, and results vary for different packet types and are documented with each packet description. A DOSPacket must be longword-aligned and has the following general structure:

Type	Name	Description
struct Message*	dp_Link	Pointer back to Exec message structure
struct Message*	dp_Port	Reply port for the packet. Must be filled in each send
int32	dp_Type	Packet type
int32	dp_Res1	For filesystem calls this is the result that would have been returned by the function; eg. Write("W") returns actual length written.
int32	dp_Res2	For filesystem calls this is what would have been returned by IoErr()
int32	dp_Arg1	Argument 1 (depends on packet type)
int32	dp_Arg2	Argument 2 (depends on packet type)
int32	dp_Arg3	Argument 3 (depends on packet type)
int32	dp_Arg4	Argument 4 (depends on packet type)
int32	dp_Arg5	Argument 5 (depends on packet type)
int32	dp_Arg6	Argument 6 (depends on packet type)
int32	dp_Arg7	Argument 7 (depends on packet type)

The format of a specific packet depends on its type; but in all cases it contains a back-pointer to the Message structure, the MsgPort for the reply, and two result fields. When AmigaDOS sends a packet, the reply port is overwritten with the process ID of the sender so that the packet can be returned. Thus, when sending a packet to an AmigaDOS handler process, you must fill in the reply MsgPort each time; otherwise when the packet returns, AmigaDOS has overwritten the original port. AmigaDOS maintains all other fields except the result fields.

All AmigaDOS packets are sent to the message port created as part of a process; this message port is initialized so that arriving messages cause signal bit 8 to be set. An AmigaDOS process that is waiting for a message waits for signal 8 to be set. When the process wakes up because this event has occurred, GetMsg() takes the message from the message port and extracts the packet address. If the process is an AmigaDOS handler process, then the packet contains a value in the PktType field that indicates an action to be performed, such as reading some data. The argument fields contain specific information such as the size of the buffer where the characters go.

When the handler process has completed the work required to satisfy this request, the packet returns to the sender, using the same message structure. Both the message structure and the packet structure must be allocated by the client and not deallocated before the reply has been received. Normally AmigaDOS is called by the client to send the packet, such as when a call to Read() is made. However, there are cases where asynchronous I/O is required, and in this case the client may send packets to the handler process as required. The packet and message structures must be allocated, and the process ID field filled in with the message port where this packet must return. A call to PutMsg() then sends the message to the destination. Note that many packets may be sent out, returning to either the same or different message ports.

Packet Types

Packets sent to a filesystem or handler can be divided into several basic categories:

Basic Input/Output.

These actions deal with transferring data to and from objects controlled by the handler.

File/Directory Manipulation/Information.

These actions are used to gain access to and manipulate the high-level structures of the filesystem.

Volume Manipulation/Information.

These actions allow access to the specific volume controlled by the filesystem.

Handler Maintenance and Control.

These actions allow control over the handler/filesystem itself, independent of the actual volume or structure underneath.

Handler Internal.

These actions are never sent to the handler directly. Instead they are generally responses to I/O requests made by the handler. The handler makes these responses look like packets to simplify processing.

Obsolete Packets.

These packets are no longer valid for use by handlers and filesystems.

Console Only Packets.

These packets are specific to console handlers. Filesystems can ignore these packets.

Each packet type documented in this section is listed with its action name, its corresponding number, any AmigaDOS routines that use this packet, and the list of parameters that the packet uses. The C variable types for the packet parameters are one of the following types:

Type	Description
BPTR	This is a BCPL pointer (the address of the given object shifted right by 2). Note: This means that the object must be aligned on a longword boundary.
LOCK	This is a BPTR to a FileLock structure returned by a previous ACTION_LOCATE_OBJECT. A lock of 0 is legal, indicating the root of the volume for the handler.
BSTR	This is a BPTR to a string where the first byte indicates the number of characters in the string. A byte of this length is unsigned but because the information is stored in a byte, the strings are limited to 255 characters in length.
BOOL	A 32-bit boolean value either containing DOSTRUE (-1) or DOSFALSE (0). Note: Equality comparisons with DOSTRUE should be avoided.
CODE	A 32-bit error code as defined in the <dos/dos.h> include file. Handlers should not return error codes besides those defined in <dos/dos.h>.
ARG1	The FileHandle->fh_Arg1 field.
LONG	A 32-bit integer value.

Important Note for AmigaOS 4 Developers

The following specification of AmigaDOS packet types dates back to the original documentation as provided by Commodore-Amiga in an AmigaMail article published concurrently with the release of OS2.0. Developers working on current versions of the Amiga Operating System need to refer to the SDK documentation and included AutoDocs as the following has not been updated to reflect changes in dos.library itself, nor changes to the implementation of FFS, nor to new packet types introduced alongside SFS or JXFS. The following specification is only provided as an additional reference and is to be updated to reflect changes introduced with Release 3 and Release 4 of the operating system.

Basic Input/Output

The Basic Input/Output actions are supported by both handlers and file systems. In this way, the application can get a stream level access to both devices and files. One difference that arises between the two is that a handler will not necessarily support an ACTION_SEEK while it is generally expected for a file system to do so.

These actions work based on a FileHandle which is filled in by one of the three forms of opens:

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FINDINPUT         1005    Open(..., MODE_OLDFILE) 
ACTION_FINDOUTPUT        1006    Open(..., MODE_NEWFILE)
ACTION_FINDUPDATE        1004    Open(..., MODE_READWRITE)
ARG1:   BPTR    FileHandle to fill in
ARG2:   LOCK    Lock on directory that ARG3 is relative to
ARG3:   BSTR    Name of file to be opened (relative to ARG1)

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

All three actions use the lock (ARG2) as a base directory location from which to open the file. If this lock is NULL, then the file name (ARG3) is relative to the root of the current volume. Because of this, file names are not limited to a single file name but instead can include a volume name (followed by a colon) and multiple slashes allowing the file system to fully resolve the name. This eliminates the need for AmigaDOS or the application to parse names before sending them to the file system. Note that the lock in ARG2 must be associated with the file system in question. It is illegal to use a lock from another file system.

The calling program owns the file handle (ARG1). The program must initialize the file handle before trying to open anything (in the case of a call to Open(), AmigaDOS allocates the file handle automatically and then frees it in Close() ). All fields must be zero except the fh_Pos and fh_End fields which should be set to -1. The Open() function fills in the fh_Type field with a pointer to the MsgPort of the handler process. Lastly, the handler must initialize fh_Arg1 with something that allows the handler to uniquely locate the object being opened (normally a file). This value is implementation specific. This field is passed to the READ/WRITE/SEEK/ END/TRUNCATE operations and not the file handle itself.

FINDINPUT and FINDUPDATE are similar in that they only succeed if the file already exists. FINDINPUT will open with a shared lock while FINDUPDATE will open it with a shared lock but if the file doesn't exist, FINDUPDATE will create the file. FINDOUTPUT will always open the file (deleting any existing one) with an exclusive lock.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_READ              'R'     Read(...)
ARG1:   ARG1    fh_Arg1 field of the opened FileHandle
ARG2:   APTR    Buffer to put data into
ARG3:   LONG    Number of bytes to read

RES1:   LONG    Number of bytes read.
       0 indicates EOF.
      -1 indicates ERROR
RES2:   CODE    Failure code if RES1 is -1

This action extracts data from the file (or input channel) at the current position. If fewer bytes remain in the file than requested, only those bytes remaining will be returned with the number of bytes stored in RES1. The handler indicates an error is indicated by placing a -1 in RES1 and the error code in RES2. If the read fails, the current file position remains unchanged. Note that a handler may return a smaller number of bytes than requested, even if not at the end of a file. This happens with interactive type file handles which may return one line at a time as the user hits return, for example the console handler, CON:.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_WRITE             'W'     Write(...)
ARG1:   ARG1    fh_Arg1 field of the opened file handle
ARG2:   APTR    Buffer to write to the file handle
ARG3:   LONG    Number of bytes to write

RES1:   LONG    Number of bytes written.
RES2:   CODE    Failure code if RES1 not the same as ARG3

This action copies data into the file (or output channel) at the current position. The file is automatically extended if the write passes the end of the file. The handler indicates failure by returning a byte count in RES1 that differs from the number of bytes requested in ARG3. In the case of a failure, the handler does not update the current file position (although the file may have been extended and some data overwritten) so that an application can safely retry the operation.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SEEK              1008    Seek(...)
ARG1:   ARG1    fh_Arg1 field of the opened FileHandle
ARG2:   LONG    New Position
ARG3:   LONG    Mode:   OFFSET_BEGINNING,OFFSET_END, or  OFFSET_CURRENT

RES1:   LONG    Old Position.   -1 indicates an error
RES2:   CODE    Failure code if RES1 = -1

This packet sets the current file position. The new position (ARG2) is relative to either the beginning of the file (OFFSET_BEGINNING), the end of the file (OFFSET_END), or the current file position (OFFSET_CURRENT), depending on the mode set in ARG3. Note that ARG2 can be negative. The handler returns the previous file position in RES1. Any attempt to seek past the end of the file will result in an error and will leave the current file position in an unknown location.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_END               1007    Close(...)
ARG1:   ARG1    fh_Arg1 field of the opened FileHandle

RES1:   LONG    DOSTRUE

This packet closes an open file handle. This function generally returns a DOSTRUE as there is little the application can do to recover from a file closing failure. If an error is returned under 2.0, DOS will not deallocate the file handle. Under 1.3, it does not check the result.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_LOCK_RECORD       2008    LockRecord(fh,pos,len,mod,tim)
ARG1:   BPTR    FileHandle to lock record in
ARG2:   LONG    Start position (in bytes) of record in the file
ARG3:   LONG    Length (in bytes) of record to be locked
ARG4:   LONG    Mode
                 0 = Exclusive
                 1 = Immediate Exclusive (timeout is ignored)
                 2 = Shared
                 3 = Immediate Shared (timeout is ignored)
ARG5:   LONG    Timeout period in AmigaDOS ticks (0 is legal)

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This function locks an area of a file in either a sharable (indicating read-only) or exclusive (indicating read/write) mode. Several sharable record locks from different file handles can exist simultaneously on a particular file area but only one file handle can have exclusive record locks on a particular area at a time. The exclusivity of an exclusive file lock only applies to record locks from other file handles, not to record locks within the file handle. One file handle can have any number of overlapping exclusive record locks. In the event of overlapping lock ranges, the entire range must be lockable before the request can succeed. The timeout period (ARG5) is the number of AmigaDOS ticks (1/50 second) to wait for success before failing the operation.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FREE_RECORD       2009    UnLockRecord(file,pos,len)
ARG1:   BPTR    FileHandle to unlock record in
ARG2:   LONG    Start position (in bytes) of record in the file
ARG3:   LONG    Length of record (in bytes) to be unlocked

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This function unlocks any previous record lock. If the given range does not represent one that is currently locked in the file, ACTION_FREE_RECORD returns an error. In the event of multiple locks on a given area, only one lock is freed.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SET_FILE_SIZE     1022    SetFileSize(file,off,mode)
ARG1:   BPTR    FileHandle of opened file to modify
ARG2:   LONG    New end of file location based on mode
ARG3:   LONG    Mode.  One of OFFSET_CURRENT, OFFSET_BEGIN, or OFFSET_END

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This function is used to change the physical size of an opened file. ARG2, the new end-of-file position, is relative to either the current file position (OFFSET_CURRENT), the beginning of the file (OFFSET_BEGIN), or the end of the file (OFFSET_END), depending on the mode set in ARG3. The current file position will not change unless the current file position is past the new end-of-file position. In this case, the new file position will move to the new end of the file. If there are other open file handles on this file, ACTION_SET_FILE_SIZE sets the end-of-file for these alternate file handles to either their respective current file position or to the new end-of-file position of the file handle in ARG1, whichever makes the file appear longer.

Directory/File Manipulation/Information

The directory/file actions permits an application to make queries about and modifications to handler objects. These packets perform functions such as creating subdirectories, resolving links, and filling in FileInfoBlock structures for specific files.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_LOCATE_OBJECT     8       Lock(...)
ARG1:   LOCK    Lock on directory to which ARG2 is relative
ARG2:   BSTR    Name (possibly with a path) of object to lock
ARG3:   LONG    Mode:   ACCESS_READ/SHARED_LOCK, ACCESS_WRITE/EXCLUSIVE_LOCK

RES1:   LOCK    Lock on requested object or 0 to indicate failure
RES2:   CODE    Failure code if RES1 = 0

The AmigaDOS function Lock() uses this action to create its locks. Given a name for the object, which may include a path, (ARG2) and a lock on a directory from which to look for the name (and path), ACTION_LOCATE_OBJECT will locate the object within the file system and create a FileLock structure associated with the object. If the directory lock in ARG1 is NULL, the name is relative to the root of the file handler's volume (a.k.a. :). The memory for the FileLock structure returned in RES1 is maintained by the handler and freed by an ACTION_FREE_LOCK. Although it's not a requirement, if an handler expects to support the pre-1.3 Format command, it must accept any illegal mode as ACCESS_READ.

A handler can create an exclusive lock only if there are no other outstanding locks on the given object. Once created, an exclusive lock prevents any other locks from being created for that object. In general, a handler uses the FileLock->fl_Key field to uniquely identify an object. Note that some applications rely on this (although a handler is not required to implement this packet).

The fl_Volume field of the returned FileLock structure should point to the DOS device list's volume entry for the volume on which the lock exists. In addition, there are several diagnostic programs that expect all locks for a volume to be chained together off the dl_LockList field in the volume entry. Note that relying on this chaining is not safe, and can cause serious problems including a system crash. No application should use it.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_COPY_DIR          19      DupLock(...)
ARG1:   LOCK    Lock to duplicate

RES1:   LOCK    Duplicated Lock or 0 to indicate failure
RES2:   CODE    Failure code if RES1 = 0

This action's name is misleading as it does not manipulate directories. Instead, it creates a copy of a shared lock. The copy is subsequently freed with an ACTION_FREE_LOCK. Note that it is valid to pass a NULL lock. Currently, the DupLock() call always returns 0 if passed a 0, although a handler is not required to return a 0.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FREE_LOCK         15      UnLock(...)
ARG1:   LOCK    Lock to free

RES1:   BOOL    TRUE

This action frees the lock passed to it. The AmigaDOS function Unlock() uses this packet. If passed a NULL lock, the handler should return success.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_EXAMINE_OBJECT    23      Examine(...)
ARG1:   LOCK    Lock of object to examine
ARG2:   BPTR    FileInfoBlock to fill in

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

This action fills in the FileInfoBlock with information about the locked object. The Examine() function uses this packet. This packet is actually used for two different types of operations. It is called to obtain information about a given object while in other cases, it is called to prepare for a sequence of EXAMINE_NEXT operations in order to traverse a directory.

This seemingly simple operation is not without its quirks. One in particular is the FileInfoBlock->fib_Comment field. This field used to be 116 bytes long, but was changed to 80 bytes in release 1.2. The extra 36 bytes lie in the fib_Reserved field. Another quirk of this packet is that both the fib_EntryType and the fib_DirEntryType fields must be set to the same value, as some programs look at one field while other programs look at the other.

File systems should use the same values for fib_DirEntryType as the ROM file system and ram-handler do. These are as follows:

ST_ROOT          1
ST_USERDIR       2
ST_SOFTLINK      3 NOTE: this Shows up as a directory unless checked for explicitly
ST_LINKDIR       4
ST_FILE         -3
ST_LINKFILE     -4

Also note that for directories, handlers must use numbers greater than 0, since some programs test to see if fib_DirEntryType is greater than zero, ignoring the case where fib_DirEntryType equals 0. Handlers should avoid using 0 because it is not interpreted consistently.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_EXAMINE_NEXT      24      ExNext(...)
ARG1:   LOCK    Lock on directory being examined
ARG2:   BPTR    BPTR FileInfoBlock

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

The ExNext() function uses this packet to obtain information on all the objects in a directory. ACTION_EXAMINE fills in a FileInfoBlock structure describing the first file or directory stored in the directory referred to in the lock in ARG1. ACTION_EXAMINE_NEXT is used to find out about the rest of the files and directories stored in the ARG1 directory. ARG2 contains a pointer to a valid FileInfoBlock field that was filled in by either an ACTION_EXAMINE or a previous ACTION_EXAMINE_NEXT call. It uses this structure to find the next entry in the directory. This packets writes over the old FileInfoBlock with information on the next file or directory in the ARG2 directory. ACTION_EXAMINE_NEXT returns a failure code of ERROR_NO_MORE_ENTRIES when there are no more files or directories left to be examined. Unfortunately, like ACTION_EXAMINE, this packet has its own peculiarities. Among the quirks that ACTION_EXAMINE_NEXT must account for are:

• The situation where an application calls ACTION_EXAMINE_NEXT one or more times and then stops invoking it before encountering the end of the directory.

• The situation where a FileInfoBlock passed to ACTION_EXAMINE_NEXT is not the same as the one passed to ACTION_EXAMINE or even the previous EXAMINE_NEXT operation. Instead, it is a copy of the FileInfoBlock with only the fib_DiskKey and the first 30 bytes of the fib_FileName fields copied over. This is now considered to be illegal and will not work in the future. Any new code should not be written in this manner.

• Because a handler can receive other packet types between ACTION_EXAMINE_NEXT operations, the ACTION_EXAMINE_NEXT function must handle any special cases that may result.

• The LOCK passed to ACTION_EXAMINE_NEXT is not always the same lock used in previous operations. It is however a lock on the same object.

Because of these problems, ACTION_EXAMINE_NEXT is probably the trickiest action to write in any handler. Failure to handle any of the above cases can be quite disastrous.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_CREATE_DIR        22      CreateDir(...)
ARG1:   LOCK    Lock to which ARG2 is relative
ARG2:   BSTR    Name of new directory  (relative to ARG1)

RES1:   LOCK    Lock on new directory
RES2:   CODE    Failure code if RES1 = DOSFALSE

ACTION_DELETE_OBJECT     16      DeleteFile(...)
ARG1:   LOCK    Lock to which ARG2 is relative
ARG2:   BSTR    Name of object to delete (relative to ARG1)

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

ACTION_RENAME_OBJECT     17      Rename(...)
ARG1:   LOCK    Lock to which ARG2 is relative
ARG2:   BSTR    Name of object to rename (relative to ARG1)
ARG3:   LOCK    Lock associated with target directory
ARG4:   BSTR    Requested new name for the object

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

These three actions perform most of the work behind the AmigaDOS commands MakeDir, Delete, and Rename (for single files). These packets take as their parameters a lock describing where the file is and a name relative to that lock. It is the responsibility of the file system to ensure that the operation is not going to cause adverse effects. In particular, the RENAME_OBJECT action allows moving files across directory bounds and as such must ensure that it doesn't create hidden directory loops by renaming a directory into a child of itself.

For Directory objects, the DELETE_OBJECT action must ensure that the directory is empty before allowing the operation.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_PARENT            29      Parent(...)
ARG1:   LOCK    Lock on object to get the parent of

RES1:   LOCK    Parent Lock
RES2:   CODE    Failure code if RES1 = 0

This action receives a lock on an object and creates a shared lock on the object's parent. If the original object has no parent, then a lock of 0 is returned. Note that this operation is typically used in the process of constructing the absolute path name of a given object.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SET_PROTECT       21      SetProtection(...)
ARG1:   Unused
ARG2:   LOCK    Lock to which ARG3 is relative
ARG3:   BSTR    Name of object (relative to ARG2)
ARG4:   LONG    Mask of new protection bits

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

This action allows an application to modify the protection bits of an object. The 4 lowest order bits (RWED) are a bit peculiar. If their respective bit is set, that operation is not allowed (i.e. if a file's delete bit is set the file is not deleteable). By default, files are created with the RWED bits set and all others cleared. Additionally, any action which modifies a file is required to clear the A (archive) bit. See the dos/dos.h include file for the definitions of the bit fields.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SET_COMMENT       28      SetComment(...)
ARG1:   Unused
ARG2:   LOCK    Lock to which ARG3 is relative
ARG3:   BSTR    Name of object (relative to ARG2)
ARG4:   BSTR    New Comment string

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

This action allows an application to set the comment string of an object. If the object does not exist then DOSFALSE will be returned in RES1 with the failure code in RES2. The comment string is limited to 79 characters.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SET_DATE          34      SetFileDate(...) in 2.0
ARG1:   Unused
ARG2:   LOCK    Lock to which ARG3 is relative
ARG3:   BSTR    Name of Object (relative to ARG2)
ARG4:   CPTR    DateStamp

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = DOSFALSE

This action allows an application to set an object's creation date.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FH_FROM_LOCK      1026    OpenFromLock(lock)
ARG1:   BPTR    BPTR to file handle to fill in
ARG2:   LOCK    Lock of file to open

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 = NULL

This action open a file from a given lock. If this action is successful, the file system will essentially steal the lock so a program should not use it anymore. If ACTION_FH_FROM_LOCK fails, the lock is still usable by an application.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SAME_LOCK         40      SameLock(lock1,lock2)
ARG1:   BPTR    Lock 1 to compare
ARG2:   BPTR    Lock 2 to compare

RES1:   LONG    Result of comparison, one of
    DOSTRUE           if locks are for the same object
    DOSFALSE          if locks are on different objects
RES2:   CODE    Failure code if RES1 is LOCK_DIFFERENT

This action compares the targets of two locks. If they point to the same object, ACTION_SAME_LOCK should return LOCK_SAME.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_MAKE_LINK         1021    MakeLink(name,targ,mode)
ARG1:   BPTR    Lock on directory ARG2 is relative to
ARG2:   BSTR    Name of the link to be created (relative to ARG1)
ARG3:   BPTR    Lock on target object or name (for soft links).
ARG4:   LONG    Mode of link, either LINK_SOFT or LINK_HARD

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This packet causes the file system to create a link to an already existing file or directory. There are two kinds of links, hard links and soft links. The basic difference between them is that a file system resolves a hard link itself, while the file system passes a string back to DOS telling it where to find a soft linked file or directory. To the packet level programmer, there is essentially no difference between referencing a file by its original name or by its hard link name. In the case of a hard link, ARG3 is a lock on the file or directory that the link is linked to, while in a soft link, ARG3 is a pointer (CPTR) to a C-style string.

In an over-simplified model of the ROM file system, when asked to locate a file, the system scans a disk looking for a file header with a specific (file) name. That file header points to the actual file data somewhere on the disk. With hard links, more than one file header can point to the same file data, so data can be referenced by more than one name. When the user tries to delete a hard link to a file, the system first checks to see if there are any other hard links to the file. If there are, only the hard link is deleted, the actual file data the hard link used to reference remains, so the existing hard links can still use it. In the case where the original link (not a hard or soft link) to a file is deleted, the file system will make one of its hard links the new real link to the file. Hard links can exist on directories as well. Because hard links link directly to the underlying media, hard links in one file system cannot reference objects in another file system.

Soft links are resolved through DOS calls. When the file system scans a disk for a file or directory name and finds that the name is a soft link, it returns an error code (ERROR_IS_SOFT_LINK). If this happens, the application must ask the file system to tell it what the link the link refers to by calling ACTION_READ_LINK. Soft Links are stored on the media, but instead of pointing directly to data on the disk, a soft link contains a path to its object. This path can be relative to the lock in ARG1, relative to the volume (where the string will be prepended by a colon ':'), or an absolute path. An absolute path contains the name of another volume, so a soft link can reference files and directories on other disks.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_READ_LINK         1024  ReadLink(port,lck,nam,buf,len)
ARG1:   BPTR    Lock on directory that ARG2 is relative to
ARG2:   CPTR    Path and name of link (relative to ARG1).
                  NOTE: This is a C string not a BSTR
ARG3:   APTR    Buffer for new path string
ARG4:   LONG    Size of buffer in bytes

RES1:   LONG    Actual length of returned string, -2 if there isn't
                  enough space in buffer,or -1 for other errors
RES2:   CODE    Failure code

This action reads a link and returns a path name to the link's object. The link's name (plus any necessary path) is passed as a CPTR (ARG2) which points to a C-style string, not a BSTR. ACTION_READ_LINK returns the path name in ARG3. The length of the target string is returned in RES1 (or a -1 indicating an error).

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_CHANGE_MODE       1028    ChangeMode(type,obj,mode)
ARG1:   LONG    Type of object to change - either CHANGE_FH
                  or CHANGE_LOCK
ARG2:   BPTR    object to be changed
ARG3:   LONG    New mode for object - see ACTION_FINDINPUT,
                  and ACTION_LOCATE_OBJECT

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This action requests that the handler change the mode of the given file handle or lock to the mode in ARG3. This request should fail if the handler can't change the mode as requested (for example an exclusive request for an object that has multiple users).

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_COPY_DIR_FH       1030    DupLockFromFH(fh)
ARG1:   LONG    fh_Arg1 of file handle

RES1:   BPTR    Lock associated with file handle or NULL
RES2:   CODE    Failure code if RES1 = NULL

This action requests that the handler return a lock associated with the currently opened file handle. The request may fail for any restriction imposed by the file system (for example when the file handle is not opened in a shared mode). The file handle is still usable after this call, unlike the lock in ACTION_FH_FROM_LOCK.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_PARENT_FH         1031    ParentOfFH(fh)
ARG1:   LONG    fh_Arg1 of File handle to get parent of

RES1:   BPTR    Lock on parent of a file handle
RES2:   CODE    Failure code if RES1 = NULL

This action obtains a lock on the parent directory (or root of the volume if at the top level) for a currently opened file handle. The lock is returned as a shared lock and must be freed. Note that unlike ACTION_COPY_DIR_FH, the mode of the file handle is unimportant. For an open file, ACTION_PARENT_FH should return a lock under all circumstances.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_EXAMINE_ALL       1033    ExAll(lock,buff,size,type,ctl)
ARG1:   BPTR    Lock on directory to examine
ARG2:   APTR    Buffer to store results
ARG3:   LONG    Length (in bytes) of buffer (ARG2)
ARG4:   LONG    Type of request - one of the following:
           ED_NAME Return only file names
           ED_TYPE Return above plus file type
           ED_SIZE Return above plus file size
           ED_PROTECTION Return above plus file protection
           ED_DATE Return above plus 3 longwords of date
           ED_COMMENT Return above plus comment or NULL
ARG5:   BPTR    Control structure to store state information.  The control
                  structure must be allocated with AllocDosObject()!

RES1:   LONG    Continuation flag - DOSFALSE indicates termination
RES2:   CODE    Failure code if RES1 is DOSFALSE

This action allows an application to obtain information on multiple directory entries. It is particularly useful for applications that need to obtain information on a large number of files and directories.

This action fills the buffer (ARG2) with partial or whole ExAllData structures. The size of the ExAllData structure depends on the type of request. If the request type field (ARG4) is set to ED_NAME, only the ed_Name field is filled in. Instead of copying the unused fields of the ExAllData structure into the buffer, ACTION_EXAMINE_ALL truncates the unused fields. This effect is cumulative, so requests to fill in other fields in the ExAllData structure causes all fields that appear in the structure before the requested field will be filled in as well. Like the ED_NAME case mentioned above, any field that appears after the requested field will be truncated (see the ExAllData structure below). For example, if the request field is set to ED_COMMENT, ACTION_EXAMINE_ALL fills in all the fields of the ExAllData structure, because the ed_Comment field is last. This is the only case where the packet returns entire ExAllData structures.

struct ExAllData {
         struct ExAllData *ed_Next;
         UBYTE  *ed_Name;
         LONG    ed_Type;
         ULONG   ed_Size;
         ULONG   ed_Prot;
         ULONG   ed_Days;
         ULONG   ed_Mins;
         ULONG   ed_Ticks;
         UBYTE  *ed_Comment;     /* strings will be after last used field. */
 };

Each ExAllData structure entry has an ead_Next field which points to the next ExAllData structure. Using these links, a program can easily chain through the ExAllData structures without having to worry about how large the structure is. Do not examine the fields beyond those requested as they certainly will not be initialized (and will probably overlay the next entry).

The most important part of this action is the ExAllControl structure. It must be allocated and freed through AllocDosObject()/FreeDosObject(). This allows the structure to grow if necessary with future revisions of the operating and file systems. Currently, ExAllControl contains four fields:

• Entries - This field is maintained by the file system and indicates the actual number of entries present in the buffer after the action is complete. Note that a value of zero is possible here as no entries may match the match string.

• LastKey - This field must be initialized to 0 by the calling application before using this packet for the first time. This field is maintained by the file system as a state indicator of the current place in the list of entries to be examined. The file system may test this field to determine if this is the first or a subsequent call to this action.

• MatchString - This field points to a pattern matching string parsed by ParsePattern() or ParsePatternNoCase(). The string controls which directory entries are returned. If this field is NULL, then all entries are returned. Otherwise, this string is used to pattern match the names of all directory entries before putting them into the buffer. The default AmigaDOS pattern match routine is used unless MatchFunc is not NULL (see below). Note that it is not acceptable for the application to change this field between subsequent calls to this action for the same directory.

• MatchFunc - This field contains a pointer to an alternate pattern matching routine to validate entries. If it is NULL then the standard AmigaDOS wild card routines will be used. Otherwise, MatchFunc points to a hook function that is called in the following manner:

BOOL = MatchFunc(hookptr, data,typeptr)
                   A0      A1    A2
hookptr    Pointer to hook being called
data       Pointer to (partially) filled in ExAllData for item
             being checked.
typeptr    Pointer to longword indicating the type of the
             ExAll request (ARG4).

This function is expected to return DOSTRUE if the entry is acceptedand DOSFALSE if it is to be discarded.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_EXAMINE_FH        1034    ExamineFH(fh,fib)
ARG1:   BPTR    File handle on open file
ARG2:   BPTR    FileInfoBlock to fill in

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This function examines a file handle and fills in the FileInfoBlock (found in ARG2) with information about the current state of the file. This routine is analogous to the ACTION_EXAMINE_OBJECT action for locks. Because it is not always possible to provide an accurate file size (for example when buffers have not been flushed or two processes are writing to a file), the fib_Size field (see dos/dos.h) may be inaccurate.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_ADD_NOTIFY        4097    StartNotify(NotifyRequest)
ARG1:   BPTR    NotifyRequest structure

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This action asks a file system to notify the calling program if a particular file is altered. A file system notifies a program either by sending a message or by signaling a task.

struct NotifyRequest {
         UBYTE *nr_Name;
         UBYTE *nr_FullName;             /* set by dos - don't touch */
         ULONG nr_UserData;              /* for applications use */
         ULONG nr_Flags;
 
         union {
 
             struct {
                 struct MsgPort *nr_Port;        /* for SEND_MESSAGE */
             } nr_Msg;
 
             struct {
                 struct Task *nr_Task;           /* for SEND_SIGNAL */
                 UBYTE nr_SignalNum;             /* for SEND_SIGNAL */
                 UBYTE nr_pad[3];
             } nr_Signal;
         } nr_stuff;
 
         ULONG nr_Reserved[4];           /* leave 0 for now */
 
         /* internal use by handlers */
         ULONG nr_MsgCount;              /* # of outstanding msgs */
         struct MsgPort *nr_Handler;     /* handler sent to (for EndNotify) */
 };

To use this packet, an application needs to allocate and initialize a NotifyRequest structure (see above). As of this writing, NotifyRequest structures are not allocated by AllocDosObject(), but this may change in the future. The handler gets the watched file's name from the nr_FullName field. The current file system does not currently support wild cards in this field, although there is nothing to prevent other handlers from doing so.

The string in nr_FullName must be an absolute path, including the name of the root volume (no assigns). The absolute path is necessary because the file or its parent directories do not have to exist when the notification is set up. This allows notification on files in directories that do not yet exist. Notification will not occur until the directories and file are created.

An application that uses the StartNotify() DOS call does not fill in the NotifyRequest's nr_FullName field, but instead fills in the nr_Name field. StartNotify() takes the name from the nr_Name field and uses GetDeviceProc() and NameFromLock() to expand any assigns (such as ENV:), storing the result in nr_FullName. Any application utilizing the packet level interface instead of StartNotify() must expand their own assigns. Handlers must not count on nr_Name being correct.

The notification type depends on which bit is set in the NotifyRequest.nr_Flags field. If the NRF_SEND_MESSAGE bit is set, an application receives notification of changes to the file through a message (see NotifyMessage from dos/notify.h). In this case, the nr_Port field must point to the message port that will receive the notifying message . If the nr_Flags NRF_SEND_SIGNAL bit is set, the file system will signal a task instead of sending a message. In this case, nr_Task points to the task and nr_SignalNum is the signal number. Only one of these two bits should be set!

When an application wants to limit the number of NotifyMessages an handler can send per NotifyRequest, the application sets the NRF_WAIT_REPLY bit in the nr_Flags field. This bit tells the handler not to send new NotifyMessages to a NotifyRequest's message port if the application has not returned a previous NotifyMessage. This pertains only to a specific NotifyRequest--if other NotifyRequests exist on the same file (or directory) the handler will still send NotifyMessages to the other NotifyRequest's message ports. The NRF_WAIT_REPLY bit only applies to message notification.

If an application needs to know if a file or directory exists at the time the application sets up notification on that file or directory, the application can set the NRF_NOTIFY_INITIAL bit in the nr_Flags field. If the file or directory exists, the handler sends an initial message or gives an initial signal.

Handlers should only perform a notification when the actual contents of the file have changed. This includes ACTION_WRITE, ACTION_SET_DATE, ACTION_DELETE, ACTION_RENAME_OBJECT, ACTION_FINDUPDATE, ACTION_FINDINPUT, and ACTION_FINDOUTPUT. It may also include other actions such as ACTION_SET_COMMENT or ACTION_SET_PROTECT, but this is not required (and may not be expected by the application as there is no need to reread the data).

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_REMOVE_NOTIFY     4098    EndNotify(NotifyRequest) 
ARG1:   BPTR    Pointer to previously added notify request

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This action cancels a notification (see ACTION_ADD_NOTIFY) . ARG1 is the NotifyRequest structure used to initiate the notification. The handler should abandon any pending notification messages. Note that it is possible for a file system to receive a reply from a previously sent notification message even after the notification has been terminated. It should accept these messages silently and throw them away.

Volume Manipulation/Information

The Volume Manipulation and Information actions are used to allow access to the underlying volume currently being manipulated by the file system.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_CURRENT_VOLUME    7       sendpkt only
RES1:   BPTR    Pointer to volume node of current volume

This action returns a pointer to the volume node (from the DOS device list) associated with the file system. As the volume node may be removed from the device list when the file system mounts a different volume (such as when directed to by an ACTION_INHIBIT) there is no guarantee that this pointer will remain valid for any amount of time. This action is generally used by AmigaDOS to provide the volume line of a requester.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_DISK_INFO         25      Info(...)
ARG1:   BPTR    Pointer to an InfoData structure to fill in

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)

ACTION_INFO              26      <sendpkt only>
ARG1:   LOCK    Lock
ARG2:   BPTR    Pointer to a InfoData Structure to fill in

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)

These actions are used to get information about the device and status of the file handler. ACTION_DISK_INFO is used by the info command to report the status of the volume currently in the drive. It fills in an InfoData structure about the volume the file system currently controls. This structure should be longword aligned. ACTION_INFO fills in an InfoData structure for the volume the lock (ARG1) is on instead of the volume currently in the drive. These actions are generally expected to return DOSTRUE.

The ACTION_DISK_INFO packet has a special meaning for console style handlers. When presented with this packet, a console style handler should return a pointer to the window associated with the open handle.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_RENAME_DISK      9       Relabel(...) in 2.0
ARG1:   BSTR    New disk name

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)

This action allows an application to change the name of the current volume. A file system implementing this function must also change the name stored in the volume node of the DOS device list.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FORMAT            1020    Format(fs,vol,type)
ARG1:   BSTR    Name for volume (if supported)
ARG2:   LONG    Type of format (file system specific)

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This packet tells a file system to perform any device or file system specific formatting on any newly initialized media. Upon receiving this action, a file system can assume that the media has already been low level formatted and should proceed to write out any high level disk structure necessary to create an empty volume.

Handler Maintenance and Control

A number of packets are defined to give an application some control over a file system:

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_DIE               5      sendpkt only
RES1:   BOOL    DOSTRUE

As its name implies, the ACTION_DIE packet tells a handler to quit. All new handlers are expected to implement this packet. Because of outstanding locks and the fact that the handler address is returned by the DeviceProc() routine, it is unlikely that the handler can disappear completely, but instead will have to release as many resources as possible and simply return an error on all packets sent to it.

In the future, the system may be able to determine if there are any outstanding DeviceProc() references to a handler, and therefore make it is safe to shut down completely.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_FLUSH             27     sendpkt only
RES1:   BOOL    DOSTRUE

This action causes the file system to flush out all buffers to disk before returning this packet. If any writes are pending, they must be processed before responding to this packet. This packet allows an application to make sure that the data that is supposed to be on the disk is actually written to the disk instead of waiting in a buffer.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_MORE_CACHE        18      AddBuffers(...) in 2.0
ARG1:   LONG    Number of buffers to add

RES1:   BOOL    DOSTRUE (-1L)
RES2:   LONG    New total number of buffers

This action allows an application to change the number of internal buffers used by the file system for caching. Note that a positive number increases the number of buffers while a negative number decreases the number of buffers. In all cases, the number of current buffers should be returned in RES2. This allows an application to inquire the number of buffers by sending in a value of 0 (resulting in no change). Note that the OFS and FFS in 1.3 do not accept a negative number of buffers.

Note that there is a bug in the ROM file system in both Release 2.04 and Release 3.0 that jumbles its return values for this packet. The file system erroneously returns the new number of buffers in RES1 instead of RES2 (it returns a failure code in RES2). To work around this bug when using this packet, test RES1 to see if it is DOSTRUE (-1L). If it is, look at RES2 for the number of buffers, otherwise RES1 should contain the new total number of buffers.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_INHIBIT           31     Inhibit(...) in 2.0
ARG1:   BOOL    DOSTRUE = inhibit,      DOSFALSE = uninhibit

RES1:   BOOL    Success/failure (DOSTRUE/DOSFALSE)

This action is probably one of the most dangerous that a file system has to handle. When inhibited (ARG1 = DOSTRUE), the file system must not access any underlying media and return an error code on all attempts to access the device. Once uninhibited (ARG1 = DOSFALSE), the file system must assume that the medium has been changed. The file system must flush the buffers before the ACTION_INHIBIT, popping up a requester demanding that the user put back the current disk, if necessary. The handler may choose to reject an inhibit request if any objects are open for writing.

Although it's not required, a handler should nest inhibits. Prior to 2.0, the system handlers did not keep a nesting count and were subject to some obscure race conditions. The 2.0 ROM filing system introduced a nesting count.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_WRITE_PROTECT     1023    sendpkt only
ARG1:   BOOL    DOSTRUE/DOSFALSE (write protect /un-write protect)
ARG2:   LONG    32 Bit pass key

RES1:   BOOL    DOSTRUE/DOSFALSE

This is a new packet defined for the Fast File System. This packet allows an application to change the write protect flag of a disk (if possible - applications cannot write to floppies that have their write-protect tabs set). This packet is primarily intended to allow write-protecting non-removable media such as hard disks. The value in ARG1 toggles the write status. The 32-bit passkey allows a program to prevent other programs from unwrite-protecting a disk. To unlock a disk, ARG2 must match the passkey of the packet that locked the disk, unless the disk was locked with a passkey of 0. In this case, no passkey is necessary to unlock the disk.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_IS_FILESYSTEM     1027    IsFileSystem(devname)

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

Through this function, a handler can indicates whether or not it is a file system (whether or not it can support separate files for storing information). Programs will assume a handler can create multiple, distinct files through calls to Open() if the handler returns this packet with a DOSTRUE value. A handler does not need to support directories and subdirectories in order to qualify as a file system. It does have to support the Examine()/ExNext() calls.

Note that the AmigaDOS routine IsFileSystem() will attempt to use Lock(":",SHARED_ACCESS) if this packet returns ERROR_ACTION_NOT_KNOWN.

Handler Internal

There are several actions that are generally used by handlers to allow messages returning from requested services (typically an Exec device) to look like incoming request packets. This allows the handler to request an asynchronous operation but be notified of the completion. For example, a handler sends the serial.device a request for a read, but instead of sending a plain IO request, it sends a DOS packet disguised as an IO request. The serial.device treats the packet like a normal IO request, returning it to the handler when it is finished. When the handler gets back its disguised DOS packet, it knows that the read has completed.

ACTION_NIL               0       internal

Although not specifically an action, many returns look like this value because the action field has not been filled in.

ACTION_READ_RETURN       1001    internal

Generally used to indicate the completion of an asynchronous read request.

ACTION_WRITE_RETURN      1002    internal

Generally used to indicate the completion of an asynchronous write request.

ACTION_TIMER             30     internal

Used to indicate the passage of a time interval. Many handlers have a steady stream of ACTION_TIMER packets so that they can schedule house keeping and flush buffers when no activity has occurred for a given time interval.

Obsolete Packets

There are several packet types that are documented within the system include files that are obsolete. A file system is not expected to handle these packets and any program which sends these packets can not expect them to work:

ACTION_DISK_CHANGE      33      Obsolete

ACTION_DISK_TYPE        32      Obsolete

ACTION_EVENT             6      Obsolete

ACTION_GET_BLOCK         2      Obsolete

ACTION_SET_MAP           4      Obsolete

Of particular note here is ACTION_DISK_CHANGE. The DiskChange command uses the ACTION_INHIBIT packet to accomplish its task.

Console Only Packets

The remaining packets are only used for console handlers and do not need to be implemented by a file system.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_SCREEN_MODE       994    SetMode() in 2.0+
ARG1:   LONG    Mode (zero or one)

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

Switch the console to and from RAW mode. An ARG1 of one indicates the unprocessed, raw mode while an ARG1 of zero indicates the processed, cooked mode.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_CHANGE_SIGNAL     995    sendpkt only
ARG1:   LONG    The fh_Arg1 of the console file handle
ARG2:   APTR    MsgPort of the process to signal
ARG3:   LONG    Reserved, currently this must be zero

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

This packet redirects what process the console handler signals when the user hits Control-C, Control-D, Control-E, or Control-F. Normally the process that opened the file handle receives the break signal.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_WAIT_CHAR         20     WaitForChar()
ARG1:   ULONG   Timeout in microseconds

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)
RES2:   CODE    Failure code if RES1 is DOSFALSE

Performs a timed read of a character. The WaitForChar() function uses this packet.

Packet Mnemonic          ID      Function Syntax
======================== ======= ==========================
ACTION_DISK_INFO         25      sendpkt only
ARG1:   BPTR    Pointer to an InfoData structure to fill in

RES1:   BOOL    Success/Failure (DOSTRUE/DOSFALSE)

The ACTION_DISK_INFO packet has a special meaning for console style handlers. When presented with this packet, a console style handler should return a pointer to the window associated with the open handle in the InfoData structure's id_VolumeNode field (the InfoData structure is defined in <dos/dos.h>). Note that some consoles can return a NULL Window pointer (for example, an AUTO CON: or a AUX: console). The Amiga's standard console handler, CON:, also returns a pointer to the console handler's IO request in the id_InUse field. In some cases, the IO request's io_Unit field (which normally point to a ConUnit structure) will be NULL. See also the ACTION_DISK_INFO packet in the Volume Manipulation/Information section.

Summary of Defined Packet Numbers

The following text was copied from an AmigaMail issue which coincided with the release of OS 2.0. The packet IDs may have changed and will be updated here to reflect new/changed packet IDs/actions as of OS 4.1.

This is a listing of all the DOS packets defined by Commodore with the release of OS 2.0. Packets 0-1999 are reserved for use by Commodore. Unless otherwise noted, packets 2050-2999 are reserved for use by third party developers (see chart below). The remaining packets are reserved for future expansion (Note: packets 2008, 2009, 4097, and 4098 are in use by Commodore).

Decimal	Hex	Action #define
0	0x0000	ACTION_NIL
1		<Reserved>
2	0x0002	ACTION_GET_BLOCK
3		<Reserved>
4	0x0004	ACTION_SET_MAP
5	0x0005	ACTION_DIE
6	0x0006	ACTION_EVENT
7	0x0007	ACTION_CURRENT_VOLUME
8	0x0008	ACTION_LOCATE_OBJECT
9	0x0009	ACTION_RENAME_DISK
10-14		<Reserved>
15	0x000F	ACTION_FREE_LOCK
16	0x0010	ACTION_DELETE_OBJECT
17	0x0011	ACTION_RENAME_OBJECT
18	0x0012	ACTION_MORE_CACHE
19	0x0013	ACTION_COPY_DIR
20	0x0014	ACTION_WAIT_CHAR
21	0x0015	ACTION_SET_PROTECT
22	0x0016	ACTION_CREATE_DIR
23	0x0017	ACTION_EXAMINE_OBJECT
24	0x0018	ACTION_EXAMINE_NEXT
25	0x0019	ACTION_DISK_INFO
26	0x001A	ACTION_INFO
27	0x001B	ACTION_FLUSH
28	0x001C	ACTION_SET_COMMENT
29	0x001D	ACTION_PARENT
30	0x001E	ACTION_TIMER
31	0x001F	ACTION_INHIBIT
32	0x0020	ACTION_DISK_TYPE
33	0x0021	ACTION_DISK_CHANGE
34	0x0022	ACTION_SET_DATE
35-39		<Reserved>
40	0x0028	ACTION_SAME_LOCK
41-81		<Reserved>
82	0x0052	ACTION_READ
83-86		<Reserved>
87	0x0057	ACTION_WRITE
88-993		<Reserved>
994	0x03E2	ACTION_SCREEN_MODE
995	0x03E3	ACTION_CHANGE_SIGNAL
996-1000		<Reserved>
1001	0x03E9	ACTION_READ_RETURN
1002	0x03EA	ACTION_WRITE_RETURN
1003		<Reserved>
1004	0x03EC	ACTION_FINDUPDATE
1005	0x03ED	ACTION_FINDINPUT
1006	0x03EE	ACTION_FINDOUTPUT
1007	0x03EF	ACTION_END
1008	0x03F0	ACTION_SEEK
1009-1019		<Reserved>
1020	0x03FC	ACTION_FORMAT
1021	0x03FD	ACTION_MAKE_LINK
1022	0x03FE	ACTION_SET_FILE_SIZE
1023	0x03FF	ACTION_WRITE_PROTECT
1024	0x0400	ACTION_READ_LINK
1025		<Reserved>
1026	0x0402	ACTION_FH_FROM_LOCK
1027	0x0403	ACTION_IS_FILESYSTEM
1028	0x0404	ACTION_CHANGE_MODE
1029		<Reserved>
1030	0x0406	ACTION_COPY_DIR_FH
1031	0x0407	ACTION_PARENT_FH
1032		<Reserved>
1033	0x0409	ACTION_EXAMINE_ALL
1034	0x040A	ACTION_EXAMINE_FH
1035-2007		<Reserved>
2008	0x07D8	ACTION_LOCK_RECORD
2009	0x07D9	ACTION_FREE_RECORD
2010-2049		<Reserved>
2050-2999		<Reserved for 3rd Party Handlers>
4097	0x1001	ACTION_ADD_NOTIFY
4098	0x1002	ACTION_REMOVE_NOTIFY
4099-		<Reserved>

Using Packets Directly

AmigaDOS contains many features that can only be accessed by sending a packet directly to a process. For example, the ACTION_DISK_INFO packet may be used to find the Intuition window pointer of a CON: or RAW: window. This is useful for redirecting system requesters so that they appear where the user can see them (see "Redirecting System Requesters" above). The Window pointer will be returned in the ID_VolumeNode field, and a pointer to the console's I/O request will be returned in the ID_InUse field. Note that auxiliary consoles (AUX:) can return a NULL Window pointer, and also may have no ConUnit (io_Unit) associated with their I/O request block. Be careful to check for these possibilities when you use this packet. If your application runs in a CLI window, a user may be running you in an auxiliary (AUX:) CLI.

Another example is the ACTION_SCREENMODE_MODE packet which can be sent to the handler process of a CON: window to put the console into raw or cooked mode.

By default, CON: provides mapped keyboard input which is filtered, buffered, and automatically echoed. Many of the special key escape sequences (such as those generated by the function, cursor, and help keys) are filtered out; all strokes are buffered and held back from the reader until the user hits the RETURN key; and the nonfiltered keypresses (such as alphanumeric keys and backspace) are automatically echoed to the CON: window. This "cooked" mode is perfect for general line input from a user because it provides automatic line editing features (same as in the Shell command line).

Sometimes, however, an application needs to get individual keys immediately from a CON: window, or control its own echoing, or receive the escape strings that the keymap generates for special keys such as the Help key or cursor keys.

In this case, an ACTION_SCREEN_MODE packet with the argument DOSTRUE (-1) may be sent to the MsgPort of a CON: window to put the CON: into "raw" mode. In raw mode, a CON: behaves much like a RAW: window. Keyboard console input is not automatically filtered, buffered, or echoed. When reading a CON: which has been set to "raw" mode, each keypress can be read immediately as the ASCII value or string to which the key is mapped by the keymap.

For some applications, it may be convenient to toggle a CON: window between cooked and raw modes, to use cooked mode for use line input, and raw mode when keypresses should cause immediate actions.

ACTION_SCREEN_MODE with the argument DOSFALSE (0L) will place a CON: window in cooked mode. Note that the ACTION_SCREEN_MODE packet may also be used on auxiliary (AUX:) consoles.

The handler MsgPort of most named AmigaDOS devices (like DF0:) can be found with the DeviceProc() function. Note that DeviceProc() cannot be used to find a CON: or RAW: handler because there may be many handlers for each of these. The handler MsgPort (ProcessID) of a CON: or RAW: window is in its FileHandle structure (fh_Type). The MsgPort of a CLI process's "*" window is process->pr_ConsoleTask.

Here's how to find the MsgPort of a handler process (in all cases make sure that port is non-NULL before using it):

Finding the MsgPort of a unique named handler process such as "DF0:":

    port = (struct MsgPort *) IDOS->DeviceProc("DF1:");

Finding the MsgPort of the handler process for an open file:

    fh = IDOS->Open("CON:0/40/640/140/Test", MODE_NEWFILE);
    if ((fh) && (fh->Type))
    {   /* if Open() succeeded and fh_Type is non-NULL */
        port = (struct MsgPort *)
               (((struct FileHandle *) (fh << 2))->fh_Type);
    }

Finding the MsgPort of your process's console handler:

    struct Task* task = IExec->FindTask(NULL);
    if (task->tc_Node.ln_Type == NT_PROCESS)
    {   /* port may be NULL - check before using! */
        port = ((struct Process *) task)->pr_ConsoleTask;
    }

Packets are sent by initializing a longword-aligned StandardPacket structure and sending the packet to the MsgPort of a handler process.

The dos.library provides simple functions for sending and replying to packets:

SendPkt()	asynchronously send your initialized packet
WaitPkt()	wait for asynchronous packet to complete
ReplyPkt()	reply a packet which has been sent to you
DoPkt()	creates and sends a packet, and waits for completion