GNU bug report logs - #12366
[gnu-prog-discuss] Writing unwritable files

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From: Paolo Bonzini <bonzini <at> gnu.org>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: gnu-prog-discuss <at> gnu.org, dwheeler <at> dwheeler.com, 12366 <at> debbugs.gnu.org, john <at> darrington.wattle.id.au
Subject: bug#12366: [gnu-prog-discuss] Writing unwritable files
Date: Thu, 06 Sep 2012 14:39:51 +0200

Il 06/09/2012 14:30, Pádraig Brady ha scritto:
>>
>> I consider "shuf foo -o foo" (on a read-write file) to be insecure.
>> Besides, it works by chance just because it reads everything in memory
>> first.  If it used mmap to process the input file, "shuf foo -o foo"
>> would be broken, and the only way to fix it would be to do the same as
>> "sed -i".
>>
>> shuf could in fact introduce a "shuf -i" mode that would be consistent
>> with the way "sed -i" works, including the ability to create a backup
>> file _and_ the breaking of hard links.
> 
> Well `sort` and `shuf` need to read all their input before
> generating output.

Yes, but they could use mmap instead of a single large buffer to cope
with files that are bigger than the available memory, but smaller than
the address space.

> This is traditional behavior and
> POSIX also states that -o can refer to one of the input files.

Interesting, thanks!

Paolo

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