PSF2 Virtual Filesystem

The PSF2 virtual filesystem is a directory hierarchy with filenames of up to 36 characters each.

Filenames are case-insensitive and must consist exclusively of characters in the ASCII 32-126 range, with the exception of the forward slash, backslash, and colon (/, \, :) characters. The total length of a path must be no longer than 255 bytes.

All quantities are stored in little-endian unsigned format. All offsets are relative to the beginning of the Reserved section.

Starting at offset 0 is the root directory.

Directory Format

A directory has the following format:

• First 4 bytes: Number of directory entries (N)
• Next 48*N bytes: N directory entries

N may be zero to indicate the directory is empty.

Directory Entries

The format of a directory entry is as follows:

• First 36 bytes: Filename
  • Must have nonzero length
  • Must be padded with null (0x00) bytes
  • Does not have to be null-terminated if it's exactly 36 characters
• Next 4 bytes: Offset (O) of the file data or subdirectory
• Next 4 bytes: Uncompressed size (U)
• Next 4 bytes: Block size (B)

If U, B, and O are all zero, then the entry describes a zero-length file. In this case, there is no data.

If U and B are zero and O is nonzero, the entry describes a subdirectory.

Otherwise, the entry describes a regular file.

File Data Format

File data is stored as a sequence of consecutive zlib compress()-format blocks.

• First 4*X bytes: Size table
  • Each entry contains the size of a compressed block
  • X = (U + B - 1) / B;
• Remainder of file data: Compressed blocks
  • The uncompressed size of all blocks (except the last) must equal B
  • The last block may have an uncompressed size less than or equal to B

Consistency

The offset of any subdirectory or file must be greater than the offset of its directory entry. This provides for easier consistency checks.

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CategoryPSF