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Date: Fri, 23 Apr 2010 14:46:51 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] give some useful error messages when tap
	open fails
References: <20100422092826.EF03612B5C@gandalf.tls.msk.ru>
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To: Markus Armbruster <armbru@redhat.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>, qemu-devel@nongnu.org

Am 22.04.2010 11:52, schrieb Markus Armbruster:
> Michael Tokarev <mjt@tls.msk.ru> writes:
> 
>> 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>
>>
>> diff --git a/net/tap-linux.c b/net/tap-linux.c
>> index 6af9e82..dbcbe6f 100644
>> --- a/net/tap-linux.c
>> +++ b/net/tap-linux.c
>> @@ -39,7 +39,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
>>  
>>      TFR(fd = open("/dev/net/tun", O_RDWR));
>>      if (fd < 0) {
>> -        fprintf(stderr, "warning: could not open /dev/net/tun: no virtual network emulation\n");
>> +        qemu_error("could not open /dev/net/tun: %m\n");
>>          return -1;
>>      }
>>      memset(&ifr, 0, sizeof(ifr));
> 
> This might apply to the stable branch (I haven't tried), but I don't
> think it works on master.  There, it should look like this (untested):
> 
> +        error_report("could not open /dev/net/tun: %m");

I'm not sure where this %m is defined exactly (Linux specific? Maybe
BSDs, too?), but it doesn't seem to work with mingw.

Kevin