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From: Tom Lane <[email protected]>
To: Robert Haas <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: constants for tar header offsets
Date: Tue, 18 Apr 2023 12:06:09 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+TgmoZniAFyu-UOt-OtbGnVnc00BhGbN6sMjH_tX+XNoj1a_w@mail.gmail.com>
References: <CA+TgmoZNbLwhmCrNtkJAvi8FLkwFdMeVU3myV2HQQpA5bvbRZg@mail.gmail.com>
	<[email protected]>
	<CA+TgmoZniAFyu-UOt-OtbGnVnc00BhGbN6sMjH_tX+XNoj1a_w@mail.gmail.com>

Robert Haas <[email protected]> writes:
> On Tue, Apr 18, 2023 at 11:38 AM Tom Lane <[email protected]> wrote:
>> 2. The header size is defined as 512 bytes, but this doesn't sum to 512:
>> +       TAR_OFFSET_PREFIX = 345         /* 155 byte string */

> I think that what happened is that whoever designed the original tar
> format decided on 512 byte blocks. And the header did not take up the
> whole block. The USTAR format is an extension of the original format
> which uses more of the block, but still not all of it.

Hmm, you're right: I checked the POSIX.1-2018 spec as well, and
it agrees that the prefix field is 155 bytes long.  Perhaps just
add another comment line indicating that 12 bytes remain unassigned?

			regards, tom lane

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