Re: ODS5 and hardlinks

John E. Malmberg wrote:

....

A hard link on UNIX and an alias created by SET FILE/ENTER are close to the same. There are some differences that are important to some programs and quota management.

My increasingly-feeble powers of recollection just offered up one such. IIRC ODS-2 maintains up-pointers in each file header to each file's/directory's parent - but of course it has room for only one such (which I'd suspect is updated when the file/directory is renamed to another parent). With hard links enabled, presumably either that entry represents the initial parent (or a new parent renamed to from the initial parent) just as it does in non-hard-link systems where additional ENTER operations have been performed, and becomes irrelevant if the file is deleted from that parent, or is simply suppressed to avoid giving any parent unequal status.

I can't off-hand recall why the up-pointer was defined in the first place, save perhaps that it was possible without undue effort and might help reconstruct a directory hierarchy which had become damaged. The file name field in the file header (which IIRC is updated on RENAME operations to the original parent) is in the same boat when it comes to having multiple parents (hard-link-enabled or not), but I think may always have been defined as being merely informational in nature rather than being used by the system in any manner - save perhaps that the combination of the two fields could be used to determine whether a RENAME was being applied to the original parent entry (since there could have been additional entries even in that one parent directory) and hence whether the name should be updated.

- bill
.

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