cpio -m does not preserve timestamps for symlinks

[Carl Edquist]

It seems that for a cpio archive that contains symlinks, the timestamps 
for those symlinks are not getting preserved, even with the '-m' option.

A quick strace shows that in '-m' mode, utimensat(2) gets called for all 
the regular files and directories, to restore their timestamps, but no 
attempt is made to restore it for symlinks (even though utimensat(2) does 
allow that with AT_SYMLINK_NOFOLLOW).

At first I was not sure if this was going to be a bug report or a feature 
request, so I took a look at the latest cpio-2.13 sources.

There is an inline wrapper function called 'lutimensat' around utimensat 
with AT_SYMLINK_NOFOLLOW, but it is never referenced anywhere else in the 
sources.  And there is a more complicated 'lutimens' function which 
contains some #ifdefs to try to do the right thing as best it can to set 
symlink timestamps if possible.

'lutimens' is defined in utimens.c and referenced in utimensat.c, which 
includes at-func.c, which is a maze of macros that's a bit hard to follow.

So it seems that the intention in cpio is to handle setting timestamps for 
symlinks.  But in any case that code path does not seem to get reached for 
me, even with the latest cpio-2.13.  (I'm using Linux kernel 4.15.0, gcc 
7.4.0, and gnu libc 2.27.)


Easy reproducer:

        $ ln -s . selfie
        $ touch -hd '2000-01-01 12:34:56' selfie
        $ echo selfie | cpio -o > selfie.cpio
        $ cpio -tv < selfie.cpio
        lrwxrwxrwx   1 root  root         1 Jan  1  2000 selfie -> .

        $ rm selfie
        $ cpio -im < selfie.cpio

        $ ls -l selfie
        lrwxrwxrwx 1 root root 1 Feb  3 18:10 selfie -> .


Note the timestamp of the 'selfie' symlink was not preserved.


Can the current maintainers confirm whether this might be broken?

Thanks,
Carl