This document describes the new filesystem layout to be used with IDE64 and other systems. The expected behaviour for attributes, etc. is also explained.

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Most recent version available at http://singularcrew.hu/cfs/.

"Boot sector" layout

The disk starts with a "boot sector". This contains the identification string ("C64 CFS V 0.11B "), the global disklabel, a pointer to @Partition directory and it's backup, and the last sectors address. The default partition number (DP) is used to select which partition will be automatically selected after power on. Values of 0-15 are valid. The global disklabel is shown in partition listing. The @Last disk sector points to the last accessible sector on disk. If this pointer has the LBA bit set, this disk uses LBA addressing.

If there's a PC BIOS style partition table in the rest of the sector, then one of the partitions must cover all the C64 partitions. In this case use $CF as partition type.

Pointers (@...) usually have the following structure:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	0	LBA	0	0	HEAD / LBA HIGHEST
Byte 1	CYLINDER HIGH / LBA HIGH
Byte 2	CYLINDER LOW / LBA LOW
Byte 3	SECTOR / LBA LOWEST

If LBA=1 then this pointer is in LBA format.

The partition directory & backup

The partition directory is 1 sector long, and holds 16 entrys from the following 32 bytes long structure:

A partition entry:

OFFSET	0	1	2	3	4	5	6	7
$0000	Partition's name padded with $00 if shorter.
$0008
$0010	@Start of partition				@End of partition
$0018	Additional info (filesystem specific, see below)

First byte of @Start of partition has additional fields:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	VALID	LBA	HIDDEN	WRITEABLE	HEAD / LBAHIGHEST

If VALID=1 then this partition is valid.
If HIDDEN=1 then this partition won't show up in partition listing.
If WRITEABLE=0 then this partition is readonly.

First byte of @End of partition has additional fields:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	TYPE	LBA	TYPE		HEAD / LBAHIGHEST

TYPE is 4 bit number extracted by clearing the LBA bit, so 8 combinations are possible.
If TYPE=%0000 then partition is unformatted.
If TYPE=%0001 then filesystem is CFS.
If TYPE=%0010 then disk space is used by GEOS.
TYPE values of %0011-%1011 are reserved.

Additional info layout for CFS:

OFFSET	0	1	2	3	4	5	6	7
$0018	@Deleted directory				@Root directory

First byte of @Deleted directory has no additional fields:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	reserved (0)	LBA	reserved (0)		HEAD / LBAHIGHEST

First byte of @Root directory has additional fields:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	BITMAP	LBA	reserved (0)		HEAD / LBAHIGHEST

If BITMAP=0 then this CFS partition uses the #1 usage bitmap, otherwise the #2.

A CFS partition layout:

1st usage bitmap sector #1	4 0 9 6
1st usage bitmap sector #2
4094 data sectors
2nd usage bitmap sector #1	4 0 9 6
2nd usage bitmap sector #2
4094 data sectors
...etc...	.

A usage bitmap sector:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	0	0	1st-6th data sectors useage
Byte 1	7th-14th data sectors useage
...	...etc...
Byte 511	4087th-4094th data sectors useage

Each bit represents a free data sector (1) or used data sector (0).
If there aren't 4094 data sectors at the end of partition, all sectors not part of this partition must be marked as used.

CFS Directory sectors

A directory sector holds 16 file entrys and a pointer to @Next directory sector.
Filesize range is from 0 to 4294967295 bytes, for relative files max. 16711425 bytes.

"Empty entry / Directory separator" type

A "DEL" entry (FILETYPE=%000):

OFFSET	0	1	2	3	4	5	6	7
$0000	Filename padded with $00 if shorter.
$0008
$0010	$00	$00	$00	$00	@reserved
$0018	AT	$44	$45	$4C	Creation time

If CLOSED=0 then this is a free entry, can be reused next time. It's skipped in directory list.

If CLOSED=1 then this is a directory separator entry in this case:
The READABLE, WRITEABLE, EXECUTEABLE, bits must be always 0, these flags are not changeable!
A directory separator cannot hold real data, it's only a directory entry.
Should appear with filetype "DEL" in directory listing.

"Normal file" type

A normal file entry (FILETYPE=%001):

OFFSET	0	1	2	3	4	5	6	7
$0000	Filename padded with $00 if shorter.
$0008
$0010	Filesize				@Data tree
$0018	AT	Filetype padded with $00			Modification time

Filetype "D"/"DEL" is not valid, because it's an alias of "DEL", and it's handled elsewere.
Filetype "S" is not valid, because it's an alias of "SEQ".
Filetype "P" is not valid, because it's an alias of "PRG".
Filetype "U" is not valid, because it's an alias of "USR".
Filetype "L"/"R"/"REL" is not valid, because it's an alias of "REL", and it's handled elsewere.
Filetype "C"/"CBM" is not valid, because it's an alias of "CBM", and it's reserved.
Filetype "B"/"DIR" is not valid, because it's an alias of "DIR", and it's handled elsewere.
Filetype "J"/"LNK" is not valid, because it's an alias of "LNK", and it's handled elsewere.
Normal file type includes "SEQ", "PRG", "USR", and user defined filetypes.

Behaviour of flags:

If EXECUTEABLE=1, it's possible to load this file, otherwise it's skipped when searching (might be still openable!).
If READABLE=1, it's possible to open this file, otherwise error happens (might be still loadable!).

"Relative file" type

A "REL" entry (FILETYPE=%010):

OFFSET	0	1	2	3	4	5	6	7
$0000	Filename padded with $00 if shorter.
$0008
$0010	Filesize			RS	@Data tree
$0018	AT	$52	$45	$4C	Modification time

Traditionally used for random access files in CBM DOS.
RS is the record size, from 1 to 255. 0 is invalid.
Should appear with filetype "REL" in directory listing.

"Subdirectory / Directory label" type

A subdirectory entry (FILETYPE=%011):

OFFSET	0	1	2	3	4	5	6	7
$0000	Dirname padded with $00 if shorter.
$0008
$0010	$00	$00	$00	$00	@Sub directory
$0018	AT	$44	$49	$52	Creation time

If CLOSED=1 this entry is a regular subdirectory.

If CLOSED=0 this is a directory label.

The directory label must be always the first entry in the directory. It holds the @Parent directory and @This directory pointer. The name field will show up in directory listing as directory label.

A directory label entry (FILETYPE=%011):

OFFSET	0	1	2	3	4	5	6	7
$0000	Dirlabel padded with $20 if shorter.
$0008
$0010	@This directory				@Parent directory
$0018	AT	$44	$49	$52	Creation time

The DELETEABLE, EXECUTEABLE, WRITEABLE, READABLE, HIDDEN flags must be the same as for the directory entry for this dir in the parent directory. Name is changeable by user, defaults to it's "DIR" entry's name.

Behaviour of flags (for both):

If READABLE=0 if's not possible to list this dir.
If WRITEABLE=0 if's not possible to create/delete/rename file in dir.
If EXECUTEABLE=0 it's not possible to change to this dir.

"Link" type

A "LNK" entry (FILETYPE=%100):

OFFSET	0	1	2	3	4	5	6	7
$0000	Filename padded with $00 if shorter.
$0008
$0010	Pathlength		$00	$00	@Link sector
$0018	AT	$4C	$4E	$4B	Modification time

The Pathlength represents the size of the string in the link sector.
The link sector holds a string ending with $00. It is a relative path to a file from the current dir.
File cannot be longer than 1 sector.

"Reserved" types

FILETYPE=%101,%110,%111 are reserved for future use.

The attributes field:

All entrys have an 1 byte attribute field (AT) at the same position, which specifies flags and filetype.

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	CLOSED	DELETEABLE	READABLE	WRITEABLE	EXECUTEABLE	FILETYPE

Behaviour of flags:

If CLOSED=0 then this file cannot be accessed, because it wasn't closed (yet).
If DELETEABLE=0 then this file cannot be deleted.
If READABLE=0 then this file cannot be opened for reading. (might be still loadable)
If WRITEABLE=0 then this file is readonly.
If EXECUTEABLE=0 then this file cannot be loaded. (file is skipped for load)

Packed Creation / Modification time bits:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	Month HIGH		Second (0-59)
Byte 1	Month LOW		Minute (0-59)
Byte 2	Hour HIGH		Year (0-63)
Byte 3	Hour LOW			Day (1-31)

Month (1-12), Hour (0-23). Year begins from 1980, so 2001 is 21.

First byte of @file pointers (at offset $0014) have additional meaning:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	HIDDEN	LBA	NEXTS		HEAD / LBAHIGHEST

If HIDDEN=1 this file is hidden, so it won't show up in directory listing.
The @Next directory sector pointer is sliced in 16 parts, and the parts are in the NEXTS fields.

@Next directory sector slicing:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	in 13rd entry		in 14th entry		in 15th entry		in 16th entry
Byte 1	in 9th entry		in 10th entry		in 11th entry		in 12th entry
Byte 2	in 5th entry		in 6th entry		in 7th entry		in 8th entry
Byte 3	in 1st entry		in 2nd entry		in 3rd entry		in 4th entry

If all 4 bytes of @Next directory sector pointer are 0s. we reachd end of directory.

Deleted directory sector

It holds the last 15 deleted files, and is usually placed in first data sector of partition.
It has the same structure as a normal directory, but is only 1 sector long, so the NEXTS field is now called AGE, and it contain the age of entrys instead of next directory sector pointer's slices. Same filenames with same type are eliminated by replacing the first character of an older file's name with a character from "A" to "N". It's directory label is "%DELETED  FILES%", directory label flags: CLOSED=0, DELETEABLE=0, EXECUTEABLE=1, WRITEABLE=0, READABLE=1, HIDDEN=1,

Root directory

It's like any other normal directory, but this is the starting point of directory stucture. It's usually begins in the second data sector (after the deleted directory sector). The root directory label is usually the same as the partition's name, but is changeable. Directory label flags: CLOSED=0, DELETEABLE=0, EXECUTEABLE=1, WRITEABLE=1, READABLE=1, HIDDEN=0,
After the label there's usually a "%DELETED  FILES%" directory entry with flags CLOSED=1, DELETEABLE=0, EXECUTEABLE=1, WRITEABLE=0, READABLE=1, HIDDEN=1, it's pointer points to deleted directory sector.

Data tree sectors

Data sector pointers are organised in balanced tree for fast seeking. Here's a table about amount of sectors to read to search to a position in file:

Tree sector layout

OFFSET	0	1	2	3	4	5	6	7
$0000	@Data sector #1				@Data sector #2
...	...etc...
$01F8	@Data sector #127				@Data sector #128

Each node is 1 sector, and holds 8 @Next tree pointers, and 128 @Data sector pointers.

First byte of pointers have additional meaning:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	reserved (0)	LBA	SLICE		HEAD / LBAHIGHEST

@Next tree sector pointers 1-8 are sliced and are in 2 bit pieces (SLICE) in @Data sector pointers. (#1 in 1-16, #2 in 17-32 ...) Same slicing method is used as for @Next directory sector.

The following special @Data sector or @Next tree pointer is used to indicate a hole in file or tree:

Byte / Bit	7	6	5	4	3	2	1	0
Byte 0	reserved (0)	0	SLICE		0	0	0	0
Byte 1	0	0	0	0	0	0	0	0
Byte 2	0	0	0	0	0	0	0	0
Byte 3	0	0	0	0	0	0	0	0

Holes are sectors filled with $00, or for relative files $FF at record beginnings and $00 everywhere else. This way unused parts of relative/normal files do not eat up disk space.

Summary

Advantages over 0.02 filesystem:

• Filesystem up to 128Gb, file to 4Gb/16Mb ;)
• Allows seeking in files fast, and deleting is faster.
• Validating is faster (only directories and data trees are scanned)
• Partitions for more robustness.
• Multiple sector transfers speeds up read/write. (Now we'll know which sectors are comming)
• It's easy to get back recently deleted files.
• New filetypes/flags, customable filetypes.
• Able to share disk with other systems using special bootloader and PC BIOS type partition entrys in boot sector. (use type $CF for CFS disk area)
• Holes in files for database/imagefile handling.

Disadvantages:

• Incompatiple with the old filesystem. (converting would be painfull)
• Not easy to implement
• Small files use more space. (data+data tree)

-Soci/Singular-

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