[Bug-cpio] Order in cpio archive doesn't match the given list of files

[Reuti]

Hi,

I have no real found bug in `cpio`, but I decided to ask on this list first 
before further investigation.

I saved same files in a `cpio` archive an checked afterwards whether all files 
are included. I was astonished, that all files were there, but for 5 out of 
several thousands in the complete archive the order was different. One time two 
were swapped and one time 3 were rotated by one.

What I did:

$ cpio --version
cpio (GNU cpio) 2.11

- create a list of files with: $ find home/reuti -depth -print0 > mylist
- create the archive: $ cpio --null --quiet -o -c -B -a < mylist > 
archive.cpio.null 
- create a list of file in the archive: $ cpio -t -I archive.cpio.null  > 
archive.cpio.null.list
- translate \0 to \n in the original list: $ tr '\0' '\n' < mylist > mylist.txt
- compare them: $ diff mylist.txt archive.cpio.null.list

Out of 976626 files there are some discrepancies:

657136,657137d657135
< home/reuti/local/gcc-4.7.3/bin/g++
< home/reuti/local/gcc-4.7.3/bin/c++
657138a657137,657138
> home/reuti/local/gcc-4.7.3/bin/c++
> home/reuti/local/gcc-4.7.3/bin/g++
657147d657146
< home/reuti/local/gcc-4.7.3/bin/gcc
657149,657150c657148
< home/reuti/local/gcc-4.7.3/bin/gcc-ar
< home/reuti/local/gcc-4.7.3/bin/gcc-nm
---
> home/reuti/local/gcc-4.7.3/bin/gcc
657151a657150
> home/reuti/local/gcc-4.7.3/bin/gcc-ar
657152a657152
> home/reuti/local/gcc-4.7.3/bin/gcc-nm

These are plain files, but with hard links. But neither all links to these 
files were swapped, nor do all files with hard links show this behavior.

The home directory wasn't touched during the procedure and I can reproduce it 
again in exactly the same way. If either non or 95% were in a different order I 
would assume it's just the way it is. But this hand full of files makes me 
wondering about it.

The question I have is: is it a known behavior that the order of files is 
changed by `cpio` while either the list of files is read or the archive 
created? Under what circumstances does this happen?

-- Reuti