guy@sun.uucp (Guy Harris) (04/06/86)
> Remember that there are really two CPIO formats: > (1) binary headers, therefore machine-dependent format > (2) ASCII headers, therefore portable format > If your tape is the latter, you need to add the letter "c" to the > list of "cpio" options in order to read it. If your tape is the > former, it must be read on a machine with similar binary architecture > (unless you want to hack up a special version of "cpio") without using > the "c" option. What really annoys is that this requirement for a machine with a similar binary architecture is really totally unnecessary! All the "cpio" control information consists either of 1) 16-bit numbers (even the 32-bit numbers are made out of two 16-bit pieces) or 2) ASCII strings. The latter are totally unaffected by the byte-order of the machine (they are affected by stupidity in the tape controller, if it doesn't write out character strings in memory to consecutive frames on the tape, but to fix that you have to run the tape through "dd" with "conv=swab" and pipe that to "cpio" - the byte-swapping options of the System V "cpio" don't swap the bytes of *all* blocks, just blocks of file data or ASCII filename strings, i.e. exactly those bytes which should *not* be swapped), and the former can all be fixed by swapping their two bytes. "cpio" need merely look at the magic number, and if it looks like the normal "cpio" magic number with its bytes swapped, set a flag which tells it to swap the bytes of "cpio" headers (and nothing else). Yes, it works. I built such a version and tried reading a tape, which was made on a VAX, on a Sun. Is anybody from the USDL listening? If so, put this change in. (And, while you're at it, get rid of those idiotic error messages which print the *decimal value* of "errno"! NOBODY wants to see that number. They want to see something meaningful, like, say, "sys_errlist[errno]", assuming that element exists.) > One final note: really old versions of CPIO did not support ASCII > headers. Specifically, System III and earlier. -- Guy Harris {ihnp4, decvax, seismo, decwrl, ...}!sun!guy guy@sun.arpa (yes, really)