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Bug#894294: Comment in the source of unmkinitramfs is ambiguous

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On Wed, 28 Mar 2018 21:18:54 +0900 Osamu Aoki <osamu@debian.org> wrote:
> Source: initramfs-tools
> Version: 0.130
> Severity: wishlist
> 
> The line 56-59 of unmkinitramfs goes:
> 
>  # There may be a prepended uncompressed archive.  cpio
>  # won't tell us the true size of this so we have to
>  # parse the headers and padding ourselves.  This is
>  # very roughly based on linux/lib/earlycpio.c
> 
> The claim "cpio won't tell us the true size of this ..." doesn't have
> any explicit reference to substantiate its claim while my uneducated
> simple use of cpio telling me the true file size without the tailing
> garbage ;-)
>
> For example:
> 
> $ cpio -i -t </initrd.img >/dev/null
> 48 blocks
> 
> So the uncompressed cpio file size is 512*48 BYTES.  With some simple
> experimentation with cpio, I realize cpio always create file size in
> multiple of 512 bytes and it treat 512 bytes as a block.  I can extract
> tailing basic initrd image file as subinitrd.img with:
> 
> $ dd if=/initrd.img of=subinitrd.img bs=512 skip=48
> 
> At least on my recent Debian system, this subinitrd.img is a nicely
> extracted gzipped cpio archive.
[...]

This code started life in bug #717805 and you can see there that
various people found different behaviour.

Ben.

-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

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Bug#894294: Comment in the source of unmkinitramfs is ambiguous Osamu Aoki <osamu@debian.org> - 2018-03-28 14:30 +0200
  Bug#894294: Comment in the source of unmkinitramfs is ambiguous Ben Hutchings <ben@decadent.org.uk> - 2019-02-04 03:50 +0100

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