Re: [PATCH 1/2] add option to set the offset of the archive

[Matteo Croce]

Il giorno gio 24 ott 2024 alle ore 20:26 Sergey Poznyakoff
<gray@gnu.org.ua> ha scritto:
>
> Hi Matteo,
>
> > Add a --offset option which allows to extract an archive which is
> > embedded in another file or it's not at the start of the device.
>
> What *practical* use do you envision for this?
>
> Regards,
> Sergey
>

Hi Sergey,

I'm developing a feature which aligns the file content to the
filesystem boundary by adding a PAX comment header.
This, along with, the --offset option will allow to extract a Debian
package (which is an an archive embedding a tar one),
by using under Linux the FICLONERANGE ioctl(), and extract the archive
without doing any IO.
Another advantage will be that the extracted files will not use any
disk space because of the data sharing, so it's possible to do distro
upgrades where there is limited space left on the root partition.
To actually work, the archive file descriptor needs to be a file and not a pipe.

I could share the code but, as is, it depends on --offset, it this is
not a problem.

Regards,

--
Matteo Croce

perl -e 'for($t=0;;$t++){print chr($t*($t>>8|$t>>13)&255)}' |aplay