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The AROS File System Interface

Bemerkung

This document is currently only a draft and as such will most likely change before it is accepted as an official specification. It might also be deprecated if a better approach has been found in the mean time, and doesn't necessarily correspond precisely with the current implementations.

Introduction

As an application programmer you don't have to worry about the file system interface -- you can do everything you want via simple calls to DOS. However you may need to know how to interface with a file system if you:

  • Need to write your own file system,
  • Wish to do asynchronous I/O,
  • Are writing a console driver,
  • Don't trust DOS.

Of the above the most useful of these would be doing asynchronous I/O, although it is in many cases better to use one of the publicly available libraries to do this, as that will hide from you the file systems' implementation details.

It's completely different

The interface to the file systems under AROS differs from that under AmigaOS in many ways:

  • File systems are exec devices, not process' message ports. This gives two main benefits -- it is possible to do some work on the callers schedule, which for simple requests can save two context switches; and it gives us a way to abort a request, which is an important feature for a network file system.
  • There is no difference between locks and file handles any more. This avoids requiring redundant methods such as ACTION_FH_FROM_LOCK.
  • No BCPL -- everything is a C data type or a string. A side effect of this is that there is no limit on string size which translates to no limit on filename size either.

Obviously this change renders the file system incompatible to the current AmigaOS file systems and DOS implementation. However it should be possible to build a bridge between the file systems if necessary.

File system devices

The major API-change of file systems is that they now use the Exec Device API. You can use the normal device functions (DoIO(), AbortIO(), etc.). The I/O Request structure is defined in dos/file systems.h:

/* IORequest from <exec/io.h> */
struct IORequest
{
    struct Message  io_Message;
    struct Device  *io_Device;  /* file system base pointer */
    struct Unit    *io_Unit;    /* file or directory handle */
    UWORD           io_Command; /* the command */
    UBYTE           io_Flags;   /* normal device flags (IOF_QUICK) */
    BYTE            io_Error;   /* error code from device functions */
};

struct IOFileSys
{
    struct IORequest IOFS;
    LONG             io_DosError; /* secondary error code (IoErr()) */
    union {}         io_Union;    /* arguments - command dependent */
};

The io_DosError field is used to return the secondary error code to the caller. This is the code that is returned by the dos.library function IoErr(). The io_Error`field of `struct IORequest should only be used to return a simple failure/success for file system commands, and should have the normal effect for the device open/close commands.

The io_Union field is an union containing different structures for each of the commands. This field has a variable length depending upon the command. The fields listed in the "Input" sections of the autodocs below refer to a specific member of this union.

Command documentation

OpenDevice()

Name

OpenDevice("*.handler", 0, iofs, 0);

Function

Mount a new file system. The IOFileSys structure passed in iofs to the handler should contain enough information for the handler to mount the file system.

If a volume is mounted in this device, it's the responsibility of the handler to add the required volume nodes to the DOS device list before returning to the caller. Note here, that the DOS device list is already locked, so you do not need to lock it yourself.

The file system must return a handle to the device in the io_Unit pointer of the struct IOFileSys. The io_Error and io_DosError fields should be set appropriately for success or failure.

Input

iofs

The union field io_OpenDevice is being used. Fill it with these values:

io_DeviceName
Name of the exec device to mount the file system upon. This device is the underlying hardware of the device. Note that this field may not be valid for some special types of handlers (for example network file systems or special devices AUX:, SER:).
io_Unit
Unit number for the exec device. Note this is the io_Union.io_DeviceName.io_Unit field, not io_Unit.
io_Environ
This is a pointer to the struct DosEnvec which describes this device.

Result

io_Device
device base pointer.
io_Unit
logical device handle.
io_Error
IOERR_OPENFAIL or 0 for no error.
io_DosError
DOS error code or 0 for no error.

CloseDevice()

Name

CloseDevice()

Function

Try to dismount a DOS device. If there are any mounted volumes in the device, the file system should remove them from the DOS device list. Note that the DOS device list will have already been locked by the caller, so you will not have to do this yourself.

You should not dismount the device if there are open files or outstanding locks remaining.

Input

io_Unit
logical device handle.

Result

The DOS device shall be dismounted if possible.

io_DosError
DOS error code or 0 for no error.

FSA_OPEN

Name

FSA_OPEN

Function

Create a handle to an existing file or directory. You can use this handle to read directories or read/write files.

The filename io_Args[0] is relative to the path of the directory associated with the handle io_Unit. If io_Unit is NULL however, the filename should be taken as relative to the root directory of the device.

This command uses the io_Union.io_OPEN member.

Input

io_Unit
Handle to the current directory.
io_Filename
Relative file or directory name.
io_FileMode

Mode to open with:

FMF_LOCK
lock exclusively
FMF_READ
open for reading
FMF_WRITE
open for writing
FMF_EXECUTE
open to execute

Result

io_Unit
Freshly created handle.
io_DosError
DOS error code or 0 for success.

FSA_CLOSE

Name

FSA_CLOSE - close an open file

Function

Close a file or directory handle. You should write out any buffered data before returning. It is the responsibility of the file system to free the data pointed to by io_Unit.

Input

io_Unit
Handle to a file or directory.

Result

io_DosError
DOS error code or 0 for no error.

FSA_READ

Name

FSA_READ

Function

Try and read the requested number of bytes from the file handle. A handler will normally try and fulfil the request completely, but special handlers (such as the console) may return less than the requested number of bytes.

If you reach the end of the file, you should return the number of bytes read in the current attempt. On the next call you should return 0 for EOF. Any further attempts to read should result in a return of -1 with an error code.

This function uses the io_Union.io_READ_WRITE field.

Input

io_Unit
File handle.
io_Buffer
Pointer to byte buffer.
io_Length
Number of bytes to read from the file.

Result

The buffer io_Buffer should contain some data if it was possible to read any.

io_Length
Number of bytes read.
io_DosError
DOS error code or 0 for no error.

FSA_WRITE

Name

FSA_WRITE - Write to a file

Function

Try to write the requested number of bytes to the file handle. A handler should try and fulfil the request completely, but special handlers may write less than the requested number of bytes.

If you cannot write any bytes return 0 in io_Length.

This command uses the io_Union.io_READ_WRITE member.

Input

io_Unit
File handle.
io_Buffer
Byte buffer containing data to write.
io_Length
Number of bytes in buffer.

Result

The contents of the buffer should have been written to the stream.

io_Length
Number of bytes read.
io_DosError
DOS error code or 0 for no error.

FSA_SEEK

Name

FSA_SEEK - Seek within a file.

Function

This command shall change the position of the next read or write in the file. The command will also return the old position in the file.

FIXME: Error condition for seeking before the start, or after the end of file.

This command uses the io_Union.io_SEEK member.

Notes

A command with io_Offset == 0, and io_SeekMode == OFFSET_CURRENT is a NOP in terms of seeking and will simply return the current file position.

Input

io_Unit
file handle
io_Offset
offset
io_SeekMode

mode

OFFSET_BEGINNING
offset is relative to the beginning of the file
OFFSET_CURRENT
offset is relative to the current position
OFFSET_END
offset is relative to the end of the file

Result

io_Offset
old position
io_DosError
DOS error code or 0 for no error.

FSA_SET_FILE_SIZE

Name

FSA_SET_FILE_SIZE - Set the size of a file.

Function

Change the size of a file.

If the old file size is less than the new size, then the file is simply truncated. If the file is made larger, then the data contained in the new section is invalid.

This command uses the io_Union.io_SEEK member.

Input

io_Unit
file handle
io_Offset
offset
io_SeekMode

mode

OFFSET_BEGINNING
offset is relative to the beginning of the file
OFFSET_CURRENT
offset is relative to the current position
OFFSET_END
offset is relative to the end of the file

Result

The file will be the new size.

io_DosError
dos error code or 0 for success

Notes

Not all handlers will support this command.

FSA_WAIT_CHAR

Name

FSA_WAIT_CHAR - wait for a character to arrive

Function

This command will wait for a character to be ready for reading. You should only wait for a maximum of io_Timeout microseconds. If io_Timeout is 0, then you should wait indefinitely.

This command can be used on both plain files and interactive files. For plain files it should return immediately, unless for some reason there is no data available (a PIPE or a network file where there is no data yet).

This command uses the io_Union.io_WAIT_CHAR member.

Input

io_Unit
File handle to wait on
io_Timeout
number of microseconds to wait for input

Result

io_Success
set to TRUE if a character arrived in time.
io_DosError
set to the DOS error code, or 0 for no error

FSA_FILE_MODE

Name

FSA_FILE_MODE - set the mode of a file

Function

Apply a new mode to the file. This command uses a mask to define which of the modes should be changed. Supplying a mask of 0 will return the current set of modes.

This command uses the io_Union.io_FILE_MODE member.

Input

io_Unit
File handle to change mode on
io_FileMode
new modes to apply to the file
io_Mask
mask of modes which are to be changed.

Result

The modes should be set to those described by the mask and mode flags.

io_FileMode
the new set of file modes
io_DosError
the DOS error code on failure, or 0 for success

FSA_IS_INTERACTIVE

Name

FSA_IS_INTERACTIVE - is this file a terminal

Function

Query the file system as to whether this file is a interactive terminal.

This function uses the io_Union.io_IS_INTERACTIVE member.

Input

io_Unit
File handle to query

Result

io_IsInteractive
TRUE if the file is interactive, FALSE otherwise
io_DosError
dos error code, or 0 for success.

FSA_SAME_LOCK

Name

FSA_SAME_LOCK - are two locks the same?

Function

This function will compare two locks, and return whether the refer to the same object in the file system.

This command uses the io_Union.io_SAME_LOCK member.

Input

io_Lock[0]
lock 1
io_Lock[1]
lock 2

Result

io_Same
set to LOCK_DIFFERENT or LOCK_SAME depending upon the result of the comparison.
io_DosError
DOS error code, or 0 for success.

FSA_EXAMINE

Name

FSA_EXAMINE - examine a file or directory

Function

This command will obtain information about the current file or directory and return it in the ExAllData structure passed in.

Passing file systems the FileInfoBlock structure is not supported, as that has limits upon the size of paths. The AROS dos.library will handle the translation between the two structures.

You need only return the information requested, which is determined by the value in io_Mode.

This command uses the io_Union.io_EXAMINE.

Input

io_Unit
Handle of a file or directory
io_ead
struct ExAllData to be filled.
io_Size
size of the buffer in bytes.
io_Mode
type of information to obtain.

Result

io_DosError
one of the DOS error codes, or 0 for success.

FSA_EXAMINE_ALL

Name

FSA_EXAMINE_ALL - Examine the contents of a directory

Function

Read the directory information of the current file or directory. If the handle is for a file, then you need only fill in the information for that file. You need only fill in the information requested by the caller.

You should continue filling in information in the buffer until you run out of space. The ed_Next fields of the ExAllData structure are used to link the entries together. The last entry should have ed_Next = NULL. Entries should be aligned to the size of the system pointer datatype.

If io_DosError != 0, then the contents of the buffer is undefined. If you need space to store filenames, comments strings, etc. these should be placed at the end of the buffer.

Input

io_Unit
Handle of a file or directory
io_ead
struct ExAllData[] buffer to be filled
io_Size
size of the buffer in bytes
io_Mode
type of information to get

Result

io_DosError
dos error code or 0 for success.

FSA_EXAMINE_ALL_END

Name

FSA_EXAMINE_ALL_END - Finish examining a number of files.

Function

Finish examining a number of objects in the file system. This is used to reset the file systems internal state if required.

This command does not use the io_Union field.

Input

io_Unit
File handle

Result

io_DosError
DOS error code, or 0 for success.

FSA_OPEN_FILE

Name

FSA_OPEN_FILE

Function

Open a handle for a file, creating the file if necessary. This command only works on files, not directories.

Function

Open a handle for a file, creating the file if necessary. Thee io_Filename field gives the name of the file, which is relative to the handle passed in io_Unit. If the io_Unit handle is NULL, then the file is relative to the root of the directory tree.

This command also allows you to change the protection bits of the file.

Input

io_Unit
Handle of the current directory.
io_Filename
filename relative to io_Unit.
io_FileMode

mode to open with:

FMF_LOCK
lock exclusively
FMF_READ
open for reading
FMF_WRITE
open for writing
FMF_EXECUTE
open to execute
FMF_CREATE
create the file if it doesn't exist
FMF_CLEAR
delete the file before opening
FMF_RAW
open cooked console in raw mode (and vice versa).
io_Protection
The protection bits for the file.

Result

io_Unit
pointer to the newly created handle.
io_DosError
dos error code or 0 for success.

FSA_CREATE_DIR

Name

FSA_CREATE_DIR - Create a new directory

Function

This command tells the file system to create a new directory, lock it, and return a handle to the lock. The directory should be created with the modes given in io_Args[1].

FIXME: Is the lock read or write?

The lock should be relative to the handle in io_Unit, or to the root directory if io_Unit == NULL.

Input

io_Unit
Handle of the current directory or NULL.
io_Filename
relative name of directory to create
io_Protection
protection flags for the new directory

Result

The requested directory exists, if it could be created.

io_Unit
handle to the new directory
io_DosError
dos error code or 0 for success

FSA_CREATE_HARDLINK

Name

FSA_CREATE_HARDLINK - Create a hard link to a file.

Function

Create a hard link to a file. There is no difference between a hard link and its original file. If the original file is deleted, the data will still exist because of the link.

Hard links can not point across devices.

This command uses the io_Union.io_CREATE_HARDLINK member.

Input

io_Unit
Handle of the current directory or NULL.
io_Filename
filename of the hard link.
io_OldFile
file to make the hard link towards.

Result

A hard link will have been created, if possible.

io_DosError
DOS error code, or 0 for success.

FSA_CREATE_SOFTLINK

Name

FSA_CREATE_SOFTLINK - Create a soft link to a file.

Function

Create a soft link to a file. There is a difference between a soft link and its original file. If the original file is deleted, the soft link will no longer be valid (but it will not be deleted).

As soft links are stored as the filename of the link to file, they can be used across devices. This means that the filename stored must be an absolute filename, as the current directory will be unknown at read time.

This command uses the io_Union.io_CREATE_SOFTLINK member.

Input

io_Unit
Handle of the current directory or NULL.
io_Filename
filename of the soft link to create.
io_Reference
filename to make the soft link point towards.

Result

A soft link will have been created if possible.

io_DosError
DOS error code, or 0 for success.

FSA_RENAME

Name

FSA_RENAME - Rename an object in the file system

Function

Rename an object in the file system. This function may be called on a file which doesn't exist. The filenames specified should be considered relative to io_Unit which specifies the current directory (or NULL for the root directory).

Renaming a directory is equivalent to moving the entire contents of the directory.

This command uses the io_Union.io_RENAME member.

Input

io_Unit
Handle of the current directory or NULL.
io_Filename
old filename
io_NewName
new filename

Result

io_DosError
DOS error code, or 0 for success.

FSA_READ_SOFTLINK

Name

FSA_READ_SOFTLINK - Read the name of a soft-linked file.

Function

This command will read the name of the file referenced by file io_Unit. The filename returned is an absolute filename.

This command uses the io_Union.io_READ_SOFTLINK member.

Input

io_Unit
Handle of the file to resolve the soft link from.
io_Buffer
buffer to fill with the pathname
io_Size
size of the buffer. Return ERROR_LINE_TOO_LONG if the buffer is not large enough.

Result

The buffer io_Buffer will contain the absolute filename that this link refers to.

io_DosError
DOS error code, or 0 for success.

FSA_DELETE_OBJECT

Name

FSA_DELETE_OBJECT - Delete an object from the file system

Function

Delete a given file or directory. It is illegal to try and delete a directory which contains files - you should return ERROR_DIRECTORY_NOT_EMPTY if an attempt is made.

Files with outstanding handles cannot be deleted.

If the io_Unit handle is NULL, the file to delete is relative to the root of the file system.

Input

io_Unit
Handle of the current directory or NULL.
io_Filename
relative filename

Result

io_DosError
dos error code or 0

FSA_SET_COMMENT

Name

FSA_SET_COMMENT - Set the comment of an object

Function

Set a new comment for a file or directory. The maximum length for a comment has historically been 80 characters (including NULL termination).

Input

io_Unit
Handle of the current directory.
io_Filename
relative filename
io_Comment
pointer to a C string (STRPTR)

Result

The object will have a new comment.

io_DosError
dos error code or 0 for success

FSA_SET_PROTECT

Name

FSA_SET_PROTECT - Set protection bits for a file

Function

Set the protection bits on a file or directory. Note that there are four groups of protection bits:

  • Owner read, write, execute, delete
  • Group read, write, execute, delete
  • Other read, write, execute, delete
  • Pure, Script, Archived

You should note that the owner bits are handled a bit strangely as they are active low (i.e. 0 means enabled/set).

Note that if io_Unit is valid (i.e. non-NULL) and io_Args[0] is NULL, then you should change the mode of the object described by the io_Unit handle.

Input

io_Unit
Handle of the current directory.
io_Filename
relative filename
io_Protection
new protection bits

Result

The object will have new protection bits.

io_DosError
dos error code or 0 for success.

FSA_SET_OWNER

Name

FSA_SET_OWNER - Set the owner of a file

Function

This command allows a user to set the ownership of files. The file should be changed to reflect the new owner of the directory.

The owner and group fields in the arguments are interpreted as 32-bit values, however in general, they will only be 16-bit values. If the values are outside the 16-bit range, and you are unable to handle the values then you can return an error. The ERROR_BAD_NUMBER appears to be the most appropriate error number.

Special User ID's:

0 root/Supervisor
-1 No owner (0x0000FFFF or 0xFFFFFFFF)

Special Group ID's:

0 wheel/Supergroup
-1 No group (0x0000FFFF or 0xFFFFFFFF)

Typically AmigaOS file systems have had little multi-user support, and it should be expected that few file systems will actually support this command. For security reasons, only the superuser or the owner of a file should be allowed to change the ownership.

Input

io_Unit
Handle of the current directory.
io_Filename
relative filename
io_UID
new user ID
io_GID
new group ID

Result

The file will now be owned by a different user.

io_DosError
dos error code or 0 or success.

FSA_SET_DATE

Name

FSA_SET_DATE - Set the date of a file/directory

Function

Set the modification date of a file or directory. If the file system does not support the date, for example if it's too old, then you should return ERROR_BAD_NUMBER. It should not be possible to set the creation date of an object (except by creating it).

Input

io_Unit
Handle of the current directory
io_Filename
relative filename
io_Date
struct DateStamp describing new date.

Result

The modification date will have been changed.

io_DosError
dos error code or 0 for success.

FSA_IS_FILESYSTEM

Name

FSA_IS_FILESYSTEM - Ask the file system handler whether it's a file system

Function

Query the file system as to whether it is a proper file system. An example of something that is not a file system is a device handler, like PAR:.

This command uses the io_Union.io_IS_FILESYSTEM member.

Input

None.

Result

io_IsFilesystem
TRUE if this is a file system, FALSE otherwise.
io_DosError
DOS error code, or 0 for success.

FSA_MORE_CACHE

Name

FSA_MORE_CACHE - Add more cache buffers to the file system.

Function

Add the number io_NumBuffers of cache buffers to the file system. The size of the buffer should have been given during the initial file system open.

If the number of buffers is negative, then the result will be to remove buffers from the device. You can not have less than 0 buffers.

This command uses the io_Union.io_MORE_CACHE member.

Input

io_NumBuffers
The number of buffers to add/remove.

Result

The number of buffers will have been altered if possible.

io_NumBuffers
The new number of buffers in the file system. This should be returned, even on failure.
io_DosError
DOS error code, or 0 for success.

FSA_FORMAT

Name

FSA_FORMAT - Initialise a file system

Function

Initialise a device to be used by this file system. The device media should have already been initialised, and this command simply gets the file system to write its own data.

This command uses the io_Union.io_FORMAT member.

Input

io_VolumeName
the new name for the volume.
io_DosType
the new type of the volume. This is file system-specific.

Result

The file system will have been initialised, and is ready for mounting.

io_DosError
DOS error code, or 0 for success.

FSA_MOUNT_MODE

Name

FSA_MOUNT_MODE

Function

Change or read the mount modes of the volume passed in io_Unit. The mask is used to select which modes are to be changed.

This command uses the io_Union.io_MOUNT_MODE member.

Input

io_MountMode
The new mount mode of the file system.
io_Mask
The mask of flags to change in the mount mode.
io_Password
The password which is required for MMF_LOCKED. It is a good idea not to store this password as plain text.

Result

io_MountMode
The new mount modes of the file system.

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