在 2017/11/21 19:51, Heiko Carstens 写道:
Hello Michael
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.
Yes, I agree with you.
Thanks a lot and I'll change it accordingly.
--
Regards
QingFeng Hao
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