11 Apr
2019
11 Apr
'19
9:57 p.m.
When did the Unix filesystem add the semantics for
"files with holes" (large,
sparse files)?
It was there in the first edition:
https://www.bell-labs.com/usr/dmr/www/pdfs/man51.pdf
The FILE SYSTEM (V) man page includes a last paragraph identical to
that of FILSYS (V) in seventh edition:
If block b in a file exists, it is not necessary that all blocks
less than b exist. A zero block number either in the address words
of the the i-node or in an indirect block indicates that the
corresponding block has never been allocated. Such a missing block
reads as if it contained all zero words.
The first edition indirect blocks were a bit different though: if the
file was bigger than 8 blocks (4kB), all the blocks in the inode were
(singly) indirect.
-- Richard
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