FFS (Amiga): Difference between revisions
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User directory blocks have type T.SHORT and secondary type ST.USERDIRECTORY. The six information words at the start of the block also indicate the block's own key (this is, the block number) as a consistency check and the size of the hash table. The 50 information words at the end of the block contain the date and time of creation, the name of the directory, a pointer to the next file or directory on the hash chain, and a pointer to the directory above.
To find a file or sub-directory, you must first apply a hash function to its name. This has function yields and offset in the hash table, which is the key of the first block on a chain linking those with the same hash value (or 0, if there are none). AmigaDOS reads
1.1.3 File Header Block
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There are as many file extension blocks as required to list the data blocks that make up the file. The layout of the block is very similar to that of a file header block, except that the type is different and the date and filename fields are not used.
=== Data Block (OFS) ===
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Normally, all data blocks except the last are full (that is, they have a blocksize = blocksize-6). The last data block has a forward pointer of 0.
=== Data Block (FFS) ===
FFS data blocks are different from OFS data blocks in that there are no metadata in the Former. The whole block is data. The lack of a checksum makes the file system more vulnerable to detect data corruption and there is no way to follow a linked list to get to the next data block in the sequence. The file header block will be the starting point to follow the list of blocks and extension blocks till 'bytesize' amount of bytes has been read, which should be in the last number of blocks indicated (HIGHEST SEQ). These lists of blocks are read in backwards order.
[[Category:Filesystems]]
[[Category:Amiga]]
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