Re: [Qemu-devel] [PATCH] give some useful error messages when tap open

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/02/2010 12:33 PM, Luiz Capitulino wrote:
> From: Michael Tokarev<mjt@tls.msk.ru>
>
> In net/tap-linux.c, when manipulation of /dev/net/tun fails, it prints
> (with fprintf) something like this:
>
>    warning: could not open /dev/net/tun: no virtual network emulation
>
> this has 2 issues:
>   1) it is not a warning really, it's a fatal error (kvm exits after
> that),
>   2) there's no indication as of what's actually wrong: printing errno there
>      is helpful.
>
> The patch below removes the "warning" prefix, uses %m (since it's linux,
> %m is available as format modifier), and changes fprintf() to %qemu_error().
> Now it prints something like this instead:
>
>   could not configure /dev/net/tun: Device or resource busy
>
> (there are 2 messages like that in the same function)
>
> This fixes Debian bug #578154, see
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=578154
>
> Signed-off-by: Michael Tokarev<mjt@tls.msk.ru>
> Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>
>    

Applied.  Thanks.

Regards,

Anthony Liguori
> ---
> IMPORTANT: this an old fix that got forgotten, probably because it was
>             submitted in the middle of thread. I've just compiled tested it.
>
>   net/tap-linux.c |    8 +++++---
>   1 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/tap-linux.c b/net/tap-linux.c
> index 03b8301..c92983c 100644
> --- a/net/tap-linux.c
> +++ b/net/tap-linux.c
> @@ -33,14 +33,16 @@
>   #include "qemu-common.h"
>   #include "qemu-error.h"
>
> +#define PATH_NET_TUN "/dev/net/tun"
> +
>   int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required)
>   {
>       struct ifreq ifr;
>       int fd, ret;
>
> -    TFR(fd = open("/dev/net/tun", O_RDWR));
> +    TFR(fd = open(PATH_NET_TUN, O_RDWR));
>       if (fd<  0) {
> -        fprintf(stderr, "warning: could not open /dev/net/tun: no virtual network emulation\n");
> +        error_report("could not open %s: %m", PATH_NET_TUN);
>           return -1;
>       }
>       memset(&ifr, 0, sizeof(ifr));
> @@ -71,7 +73,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
>           pstrcpy(ifr.ifr_name, IFNAMSIZ, "tap%d");
>       ret = ioctl(fd, TUNSETIFF, (void *)&ifr);
>       if (ret != 0) {
> -        fprintf(stderr, "warning: could not configure /dev/net/tun: no virtual network emulation\n");
> +        error_report("could not configure %s (%s): %m", PATH_NET_TUN, ifr.ifr_name);
>           close(fd);
>           return -1;
>       }
>