generic/556: Filter touch error message

generic/556: Filter touch error message

Coreutils commit d435cfc0bc55 ("touch: fix wrong
diagnostic (Bug#48106)"), released in coreutils v9.0, changed the error
reported by the tool when openat() fails with EINVAL.  Instead of
reporting a generic message for the failure of either openat() or the
following utimensat(), it now differentiates both failures with
different messages.

This change breaks generic/556, which relied on the parsing of that
message.  This test was originally developed by me on a Debian
Buster (coreutils v8.x), so I used the generic error message.  Now that
I tried to run it on a more modern distro, it reports a different error
message, which fails the test, as shown below:

  output mismatch (see /tmp/results/generic/556.out.bad)
      --- tests/generic/556.out	2022-05-20 13:15:00.447525770 -0400
      +++ /tmp/results/generic/556.out.bad	2022-05-20 13:15:24.988167427 -0400
      @@ -12,5 +12,5 @@
       # file: SCRATCH_MNT/xattrs/x/f1
       user.foo="bar"

      -touch: setting times of 'SCRATCH_MNT/strict/corac'$'\314\247\303': Invalid argument
      -touch: setting times of 'SCRATCH_MNT/strict/cora'$'\303\247\303': Invalid argument
      +touch: cannot touch 'SCRATCH_MNT/strict/corac'$'\314\247\303': Invalid argument
      +touch: cannot touch 'SCRATCH_MNT/strict/cora'$'\303\247\303': Invalid argument
      ...

The fix filters out the touch-specific parts of the touch error
messages, to prevent breakage from future changes, but preserves the
return code information, which is actually useful (and more stable).

There is no change in behavior on the kernel side, just a broken test.
On both older and new distros, the kernel correctly rejects this invalid
sequence with -EINVAL, as shown in the strace hunk below:

  [...]
  openat(AT_FDCWD, "/scratch_mnt/strict/corac\314\247\303", ...) = -1 EINVAL
  utimensat(AT_FDCWD, "/scratch_mnt/strict/corac\314\247\303", ...) = -1 EINVAL
  [...]

Tested on Debian sid (coreutils v8.32) and Fedora (coreutils 9.0).

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>