give some useful error messages when tap open

From: Michael Tokarev <[email protected]>

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 <[email protected]>

Signed-off-by Luiz Capitulino <[email protected]>

Quoted 13 lines · Luiz Capitulino

From: Michael Tokarev <[email protected]>

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.

Quoted 2 lines

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.

Quoted 5 lines

Now it prints something like this instead:

could not configure /dev/net/tun: Device or resource busy

Quoted 7 lines

(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 <[email protected]>

Signed-off-by Luiz Capitulino <[email protected]>

Looks good.

Quoted 15 lines · On Wed, 02 Jun 2010 20:26:58 +0200 Markus Armbruster <[email protected]> wrote:

Quoted 13 lines · Luiz Capitulino

From: Michael Tokarev <[email protected]>

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.

Quoted 4 lines

Quoted 2 lines

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?

From: Michael Tokarev<[email protected]>

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<[email protected]>

Signed-off-by Luiz Capitulino<[email protected]>

---
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(-)

net/tap-linux.c +5 -3

index 03b8301..c92983c 100644
@@ -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;
      }