Re: [XEN PATCH v6] tools/lsevtchn: Use errno macro to handle hypercall error cases

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Mon, Jul 29, 2024 at 04:02:41PM +0100, Matthew Barnes wrote:
> diff --git a/tools/xcutils/lsevtchn.c b/tools/xcutils/lsevtchn.c
> index d1710613ddc5..29504c9d2077 100644
> --- a/tools/xcutils/lsevtchn.c
> +++ b/tools/xcutils/lsevtchn.c
> @@ -24,7 +25,28 @@ int main(int argc, char **argv)
>          status.port = port;
>          rc = xc_evtchn_status(xch, &status);
>          if ( rc < 0 )
> -            break;
> +        {
> +            switch ( errno )
> +            {
> +            case EACCES: /* Xen-owned evtchn */
> +                continue;
> +
> +            case EINVAL: /* Port enumeration has ended */
> +                rc = 0;
> +                break;
> +
> +            case ESRCH:
> +                perror("Domain ID does not correspond to valid domain");

I think this is going to print:
    "Domain ID does not correspond to valid domain: No such process"

> +                rc = ESRCH;

So, `rc` is going to be the value returned by main(), that is the exit
value of the program `lsevtchn`. Having different exit value might
be useful sometime to distinguish between different errors but that
would at least need to be written in some document. Can we just return
"1" here on error? (I mean "rc = 1")

> +                break;
> +
> +            default:
> +                perror(NULL);

It would be slightly more useful to print which function fails, simply
with:
    perror("xc_evtchn_status");


> +                rc = errno;

Same here, just "rc=1" should be good enough. Then if someone want to
know why `lsevtchn` failed, they can read the error messages.

At least, errno is likely to be between 0 and 255, but still, usually
not very useful as an exit value for a program.

> +                break;
> +            }
> +            goto out;
> +        }
>  
>          if ( status.status == EVTCHNSTAT_closed )
>              continue;
> @@ -58,7 +80,8 @@ int main(int argc, char **argv)
>          printf("\n");
>      }
>  
> + out:
>      xc_interface_close(xch);
>  
> -    return 0;
> +    return rc;
>  }

Thanks,

-- 

Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech