Re: [Xen-devel] [PATCH] xl: Fix CHK_ERRNO

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [PATCH] xl: Fix CHK_ERRNO"):
> On 09/12/13 14:55, Ian Campbell wrote:
> >[Andrew Cooper:]
> >> Split the macro into two; CHK_ERRNO() for calls which return -1
> >> and set errno on error, and CHK_POSERRNO() for calls which return
> >> a positive errno.

This is a bit confusing.  Why do you write "a _positive_ errno"
(emph. mine) ?  errno values are always positive.  In the libxl LOG*
macros we call a style where an errno value is passed explicitly
"ERRNOVAL".

You propose:

    #define CHK_POSERRNO( call ) ({                                         \
            int chk_errno = (call);                                         \
            if (chk_errno > 0) {                                            \
                fprintf(stderr,"xl: fatal error: %s:%d: %s: %s\n",          \
                        __FILE__,__LINE__, strerror(chk_errno), #call);     \
                exit(-ERROR_FAIL);                                          \
            }                                                               \
        })

This is what I would call CHK_ERRNOVAL.  (But I think it should
abort() if the returned value is negative, not treat it as success!)

> > Would be better to call POSERRNO LIBXLERR or something, rather than
> > accidentally imply that it was related to "errno" somehow, I think.

I think there should be a CHK_LIBXL or something too, but that's not
needed right now because all the CHK_* call sites are either
(return -1, set errno) or (return errno value).

I think the former macro would better be called CHK_SYSCALL, because
it's the system call return convention.  CHK_ERRNO would do.

Ian.

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