Re: [Qemu-devel] [PATCH 2/2] qemu-nbd: Improve error reporting

[malc]

On Sat, 20 Mar 2010, Ryota Ozaki wrote:

> - use err(3) instead of errx(3) if errno is available
>   to report why failed
> - let fail prior to daemon(3) if opening a nbd file
>   is likely to fail after daemonizing to avoid silent
>   failure exit

I'm under impression that you and the original author of this
code is misunderstading how err[x] works, first argument is
what will be used to exit the process and has little to do
with POSIX/C error codes.

> ---
>  qemu-nbd.c |   16 +++++++++++-----
>  1 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index b89c361..5f10ff0 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -316,7 +316,7 @@ int main(int argc, char **argv)
>      if (disconnect) {
>          fd = open(argv[optind], O_RDWR);
>          if (fd == -1)
> -            errx(errno, "Cannot open %s", argv[optind]);
> +            err(errno, "Cannot open %s", argv[optind]);
>  
>          nbd_disconnect(fd);
>  
> @@ -333,23 +333,29 @@ int main(int argc, char **argv)
>      if (bs == NULL)
>          return 1;
>  
> -    if (bdrv_open(bs, argv[optind], flags) < 0)
> -        return 1;
> +    if ((ret = bdrv_open(bs, argv[optind], flags)) < 0) {
> +        errno = -ret;
> +        err(errno, "Failed to bdrv_open '%s'", argv[optind]);
> +    }
>  
>      fd_size = bs->total_sectors * 512;
>  
>      if (partition != -1 &&
>          find_partition(bs, partition, &dev_offset, &fd_size))
> -        errx(errno, "Could not find partition %d", partition);
> +        err(errno, "Could not find partition %d", partition);
>  
>      if (device) {
>          pid_t pid;
>          int sock;
>  
> +        /* want to fail before daemonizing */
> +        if (access(device, R_OK|W_OK) == -1)
> +            err(errno, "Could not access '%s'", device);
> +
>          if (!verbose) {
>              /* detach client and server */
>              if (daemon(0, 0) == -1) {
> -                errx(errno, "Failed to daemonize");
> +                err(errno, "Failed to daemonize");
>              }
>          }
>  
> 

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