11 Apr
2019
11 Apr
'19
5:57 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
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
11 Apr
11 Apr
9:09 p.m.
New subject: Unix filesystem semantics history - files with holes
Sparse files: “Thin Provisioning” way ahead of its time. Combined with the patented SUID:
The UNIX marvels never cease.
It just goes to show that all this marketing BS touted today has already been done before.
Bill Corcoran
On Apr 11, 2019, at 12:36 PM, Richard Tobin <richard(a)inf.ed.ac.uk> wrote:
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
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
9:49 p.m.
New subject: Unix filesystem semantics history - files with holes
On Apr 11, 2019, at 8:57 AM, Richard Tobin <richard(a)inf.ed.ac.uk> wrote:
You still had to read all those unallocated blocks as zeroes
if you wanted to copy such a "holey" file. I believe it was
Solaris (may be just for zfs?) that added SEEK_HOLE and
SEEK_DATA lseek whence values.
This could've been hidden if only mmap was allowed on files.
Or alternately read/write buffering was done by the kernel
or the {network,file}-server - which can avoid copying in
cases where it makes sense.
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
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participants (3)
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Bakul Shah -
Richard Tobin -
William Corcoran