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

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

[Luiz Capitulino]

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>
---
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;
     }
-- 
1.7.1.231.gd0b16

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

[Markus Armbruster]

Luiz Capitulino <lcapitulino@redhat.com> writes:

> 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().

To error_report(), you mean.

> 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>

Looks good.

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

[Luiz Capitulino]

On Wed, 02 Jun 2010 20:26:58 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Luiz Capitulino <lcapitulino@redhat.com> writes:
> 
> > 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().
> 
> To error_report(), you mean.

 It's the original commit log.. Should this be fixed? If so, Michael,
could you resend?

> 
> > 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>
> 
> Looks good.
> 

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

[Markus Armbruster]

Luiz Capitulino <lcapitulino@redhat.com> writes:

> On Wed, 02 Jun 2010 20:26:58 +0200
> Markus Armbruster <armbru@redhat.com> wrote:
>
>> Luiz Capitulino <lcapitulino@redhat.com> writes:
>> 
>> > 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().
>> 
>> To error_report(), you mean.
>
>  It's the original commit log.. Should this be fixed? If so, Michael,
> could you resend?

Or maybe it could be fixed up on commit.

[...]

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

[Anthony Liguori]

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;
>       }
>