🚀 go-pugleaf

In article <1992Dec29.012215.10632@ryn.mro4.dec.com> Peter.Mayne@cao.mts.dec.com writes:
[...]
>** I believe that you can also run into problems if you have
>** a signal handler that gets invoked, and resets errno in the period
>** between your successful system call and your test for success. It's
[...]
>Fixing this kind of problem would involve changing the model of "returning
>an error flag and a static errno". You could:
>
>- return an error status rather than an error flag
>- signal on errors
>- call a "callback" routine on errors
>- fill in a program-provided "status block" (non-static "errno" equivalent)
>
>Any one of these would probably be considered incompatible by a large number
>of UNIX style programmers (including DOS programmers and a lot of VMS
>programmers).

Yes, this is a big problem with the way Unix does error reporting.  However
you can kludge around it like this:

sighandler(...)
{
	int old_errno = errno;
	/* do stuff */
	errno = old_errno;
}

Note: you need to do this even if you exit()/abort() after any syscall failure.
I beleve that syscalls are allowed to alter errno even on a succesful return.

(also this doesn't magicly make all of libc rentrent, but it does mean that
if someone has a rentrent libc you can use it and not stomp errno...)
-- 
           stripes@pix.com              "Security for Unix is like
      Josh_Osborne@Real_World,The          Multitasking for MS-DOS"
      "The dyslexic porgramer"                  - Kevin Lockwood
We all agree on the necessity of compromise.  We just can't agree on
when it's necessary to compromise.       - Larry Wall