Hello Heiko, On 21 November 2017 at 11:23, Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote: > 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. When you put it as above, the interface feels less odd. But, in that case, I think the return value should be documented more as you word it above. Something like: "On success the return value matches the condition code of the STHYI instructions, which is a value between 0-3 (that is: emulation succeeded)." Followed by an explanation of the meaning of 0 and any of the values > 0 that may be returned. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
