We cannot just use %m, because strerror returns a confusing error message
for ESRCH or ENOEXEC. udev code was doing a good job, but the error handling
was very verbose. Let's encapsulate the customized error messages in a
helper.
No functional change, except that the error messages have a slightly different
form now. The old messages were a bit better, but we don't have as much
flexibility in the new scheme. "Failed to resolve user 'foo': Unknown user"
should be good enough.
This also makes shebang always use env command, and drops unnecessary
'bash -c' or 'sh -c' when a signle command is invoked in the shell,
like sleep or echo.
Otherwise, the result may point to outside of the root directory.
This also sets CONF_FILES_REGULAR and CONF_FILES_FILTER_MASKED, as the
callers will call fopen() or friends for the result, thus the enumerated
results must be non-empty regular files.
Zbigniew Jędrzejewski-Szmek
Yu Watanabe