Support read-only, hidden & system bits on files

[Kroc]

The flags byte for each directory entry currently has two bits for in-use and directory|file.

First, may I suggest that bit 6 is used for the directory|file bit as bits 7 & 6 are easy to read on 6502 but not bits 0-5 (should someone wish to implement a ZealFS driver on 6502). The 6502 has a very strange BIT instruction that ANDs the accumulator and sets the zero flag, but copies bit 6 & 7 from the parameter into the CPU flags (N&V). Madness, yet, but it means that bits 6&7 can be tested without using any registers. For the other bits the Accumulator is needed. The remaining flags can be in bits 0-5 (this also helps with processing as the bits could be popped off in order using shift-right).

• A read-only / write-lock flag is a must and would not cost much in implementation
• A hidden flag is a nice-to-have
• A system flag is used to convey some special status. If you wanted to mimic Linux then it could be used for executables so that a file extension is not required and the OS can identify what to do with the file quickly. If you go with an execute bit, it should be on bit 0 so that it's fastest to check given once entry-in-use and is-file has been determined