Re: constants for tar header offsets

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Apr 18, 2023 at 11:38 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> 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