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From: Bakul Shah <bakul@bitblocks.com>
To: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: Re: [TUHS] Unix filesystem semantics history - files with holes
Date: Thu, 11 Apr 2019 12:49:34 -0700
Message-ID: <D70410E5-4EFA-4C5A-A2A8-8BF00F7A4824@bitblocks.com> (raw)
In-Reply-To: <20190411155748.8791B255ADDC@macaroni.inf.ed.ac.uk>

On Apr 11, 2019, at 8:57 AM, Richard Tobin <richard@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

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. 

      parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-11  2:37 Erik E. Fair
2019-04-11  5:28 ` Ronald Natalie
2019-04-11 15:57 Richard Tobin
2019-04-11 19:09 ` William Corcoran
2019-04-11 19:49 ` Bakul Shah [this message]

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