GFS2: Add hints to directory leaf blocks

This patch adds four new fields to directory leaf blocks. The intent is not to use them in the kernel itself, although perhaps we may be able to use them as hints at some later date, but instead to provide more information for debug/fsck use. One new field adds a pointer to the inode to which the leaf belongs. This can be useful if the pointer to the leaf block has become corrupt, as it will allow us to know which inode this block should be associated with. This field is set when the leaf is created and never changed over its lifetime. The second field is a "distance from the hash table" field. The meaning is as follows: 0 = An old leaf in which this value has not been set 1 = This leaf is pointed to directly from the hash table 2+ = This leaf is part of a chain, pointed to by another leaf block, the value gives the position in the chain. The third and fourth fields combine to give a time stamp of the most recent directory insertion or deletion from this leaf block. The time stamp is not updated when a new leaf block is chained from the current one. The code is currently written such that the timestamp on the dir inode will match that of the leaf block for the most recent insertion/deletion. For backwards compatibility, any of these new fields which is zero should be considered to be "unknown".

SWSteven Whitehouse committed 12 years ago