COW Links
Posted Apr 3, 2004 1:31 UTC (Sat) by
iabervon (subscriber, #722)
Parent article:
COW Links
The question really comes down to whether this is supposed to be a
delayed copy operation or a kind of link; while the effect is much the
same, it is a serious semantic difference centered on whether the two
have the same identity or not. If it is supposed to be an actual copy
which the filesystem optimizes, then it makes sense for it to require a
special system call to determine that two things are necessarily the
same, and tar should probably include each copy individually (unless,
perhaps, it can similarly hack its file format to share the data between
the two names). If, on the other hand, they are a kind of link, then they
certainly can't be used for normal copies, since people expect
normally-copied files to behave normally.
Of course, the right thing may be to have both, such that you can create
links with explicit copy-on-write semantics, while normal copies look
like separate files (potentially even down to reserving space for them)
but share the actual storage (and share code with the link semantics).
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