Re: [Xenomai] [PATCH] demo/alchemy/cross-link: Properly handle syscall errors

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Mon, Feb 22, 2016 at 05:42:28PM -0600, Michael Welling wrote:
> Update cross link demo to properly handle errors returned from syscalls.
> 
> Signed-off-by: Michael Welling <mwelling@ieee.org>
> ---
>  demo/alchemy/cobalt/cross-link.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/demo/alchemy/cobalt/cross-link.c b/demo/alchemy/cobalt/cross-link.c
> index 8c0f53f..dceb928 100644
> --- a/demo/alchemy/cobalt/cross-link.c
> +++ b/demo/alchemy/cobalt/cross-link.c
> @@ -23,6 +23,7 @@
>  #include <stdio.h>
>  #include <signal.h>
>  #include <unistd.h>
> +#include <errno.h>
>  #include <sys/mman.h>
>  #include <alchemy/task.h>
>  #include <alchemy/timer.h>
> @@ -78,8 +79,8 @@ static int close_file( int fd, char *name)
>  	do {
>  		i++;
>  		err = close(fd);
> -		switch (err) {
> -		case -EAGAIN:
> +		switch (errno) {
> +		case EAGAIN:

This looks incorrect. errno has a meaningful value only if err is
-1. You could get away with setting errno to 0 before calling close,
this would probably work, but for a more complex service which calls
several syscalls under the hoold, this would not even work.

So, you should probably just add:
err = err < 0 ? -errno : 0;

-- 
					    Gilles.
https://click-hack.org