Re: [PATCH 1/1] s390_sthyi.2: New page for s390-specific s390_sthyi(2)

[Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>]

On Tue, Nov 21, 2017 at 09:48:02AM +0100, Michael Kerrisk (man-pages) wrote:
> >> What does "On other cases" mean? When do those cases happen?
> >> Could you reword please.
> >
> > The case is:
> > If the STHYI facility is enabled and the system call fails to execute the
> > underlying
> > STHYI instruction, the value of condition code is returned, which currently
> > is only
> > 3 indicating "unsupported function code".
> > Is this OK to put it here?
> 
> Let me see if I understand correctly. There are three possible return
> values for this system call:
> 
> 0 ==> success
> -1 ==> failure (and errno is set)
> [condition code value is returned -- e,g,, 3]
> 
> This last case is a kind of failure in the system call, right?
> 
> If this is correct, this is a highly unusual--possibly even
> unique--model for the system call return value. Most (in fact, I think
> all) system calls indicate errors by returning -1. Values >= 0 always
> mean success. I think it may be worth revisiting this design, to make
> it more consistent with the usual conventions. For example, why not
> handle the last case by returning -1, setting errno to some value
> (maybe ENOTSUP), and return the condition code in *buffer?.

Well, I would have written this differently: on success the return value
matches the condition code of the STHYI instructions, which is a value
between 0-3 (that is: emulation succeeded). If a condition code, which is
not 0, is an error or not, may not be the same in the future, if the
instruction gets extended.

That being said, if you think this still doesn't make much sense, we might
have to reconsider the interface.

--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html