SOLVED: lo0 not in ioctl( SIOCGIFCONF )

[Brooks Davis]

On Tue, Jul 22, 2008 at 07:16:24AM +0000, Jens Rehsack wrote:
> Brooks Davis wrote:
>> On Mon, Jul 21, 2008 at 10:36:34PM +0000, Jens Rehsack wrote:
>>> Brooks Davis wrote:
>>>> On Mon, Jul 21, 2008 at 09:30:39PM +0000, Jens Rehsack wrote:
>>>>> Brooks Davis wrote:
>>>>>>> Hi,
>>>>>>> 
>>>>>>> maybe this question is better asked in this list ...
>>>>>>> 
>>>>>>> I was searching why ports/net/p5-Net-Interface was not working as
>>>>>>> expected and found some reasons. Most of them I can answer by implementing
>>>>>>> some test code as attached, but now I'm wondering why em0 is shown twice
>>>>>>> and lo0 is not included.
>>>>>>> The same situation on another machine ..
>>>>>> The attachment didn't make it through.
>>>>>> 
>>>>>> -- Brooks
>>>>> Copy&Paste starts here ...
>>>>> #include <stdio.h>
>>>>> #include <stdlib.h>
>>>>> #include <sys/socket.h>
>>>>> #include <net/if.h>
>>>>> #include <errno.h>
>>>>> #include <strings.h>
>>>>> #include <sys/ioctl.h>
>>>>> #include <ifaddrs.h>
>>>>> 
>>>>> #ifndef _SIZEOF_ADDR_IFREQ
>>>>> #define	_SIZEOF_ADDR_IFREQ(ifr) \
>>>>> 	((ifr).ifr_addr.sa_len > sizeof(struct sockaddr) ? \
>>>>> 	 (sizeof(struct ifreq) - sizeof(struct sockaddr) + \
>>>>> 	  (ifr).ifr_addr.sa_len) : sizeof(struct ifreq))
>>>>> #endif
>>>>> 
>>>>> int
>>>>> main()
>>>>> {
>>>>>     struct ifconf ifc;
>>>>>     struct ifreq *ifr, *lifr;
>>>>>     int fd;
>>>>>     unsigned int n;
>>>>> 
>>>>>     fd = socket( AF_INET, SOCK_STREAM, 0 );
>>>>>     bzero(&ifc, sizeof(ifc));
>>>>>         n = 3;
>>>>>         ifr = calloc( ifc.ifc_len, sizeof(*ifr) );
>>>>>         do
>>>>>         {
>>>>>             n *= 2;
>>>>>             ifr = realloc( ifr, sizeof(*ifr) * n );
>>>>>             bzero( ifr, sizeof(*ifr) * n );
>>>>>             ifc.ifc_req = ifr;
>>>>>             ifc.ifc_len = n * sizeof(*ifr);
>>>>>         } while( ( ioctl( fd, SIOCGIFCONF, &ifc ) == -1 ) || ( 
>>>>> ifc.ifc_len == n * sizeof(*ifr)) );
>>>> There are several problems with this loop.  First, icoctl won't return
>>>> an error in the overflow case because that's not how SIOCGIFCONF works.
>>>> SIOCGIFCONF is badly designed in a number of ways, but that's how it
>>>> is.  Second, checking that the array is completely full isn't at all
>>>> reliable because what is returned is actually ifreq structures which
>>>> might or might not vary in length as they contain addresses.  Thus you
>>>> need <=.  Third, you should start by allocating a significant amount of
>>>> space.  Yes, your algorithm is O(sqrt(n)), but allocating a larger
>>>> value has effectively no cost so you might as well save some system calls
>>>> on average.
>>> Thanks - that was the information I miss. I'll try tomorrow (it's 
>>> slightly late here) and send back the result.
>>> Using <= should produce an endless loop, but maybe checking if 
>>> ifc.ifc_len <= (n/2) * sizeof(*ifr) could bring wanted results ...
>> 
>> Oops, you're right.  Actually, the condition to check is probably
>> (n*sizeof(*ifr) - ifc.ifc_len < sizeof(*ifr)).  Actually, since the size
>> of the returned values aren't actually a multiple of sizeof(*ifr), I'd
>> probably switch to allocating a multiple of 4k.
> 
> Actually, because there're very different sizes of sockaddr's (sockaddr_in, 
> sockaddr_in6, ...), I require at least a page must be left over.
> Because of other OS may support return of errors in overflow, I didn't 
> remove the check - finally it must run on AIX, Windows and Linux, too.
> 
>>>>>     lifr = (struct ifreq *)&ifc.ifc_buf[ifc.ifc_len];
>>>>> 
>>>>>     while (ifr < lifr) >     {
>>>>>         printf( "%s\n", ifr->ifr_name );
>>>>>         ifr = (struct ifreq *)(((char *)ifr) + _SIZEOF_ADDR_IFREQ(*ifr));
>>>>>     }
>>>> This loop has two problems.  First, the ifr's are variable length so you
>>>> immediately go off into the weeds.
>>> The _SIZEOF_ADDR_IFREQ macro should handle that correctly, shouldn't it?
>> 
>> Right here as well.
> 
> Finally - I must enhance this using SA_LEN if available to support systems 
> without sa_len member support. I'll try it in office with our linux 
> machines there, because I don't have any penguins at home ;)
> 
>>>>  Second, there is at least one per
>>>> interface and one per address so you to keep track of the last interface
>>>> name and not repeat them.
>>> Good point - if it's sure in this order, this is a good way to handle it.
>> 
>> It is in the current implementation and it's hard to imaging that we'd
>> break that.
> 
> By the way, because I'm looking for interfaces, I skip everything which is 
> no AF_LINK - should work, too (and does for my test-machines ...).
> 
> Final question: would it make sense to submit a patch against 
> ports/net/p5-Net-Interface using this knowledge to unbreak the port, or 

I'd suggest doing both.  We want it fixed in CPAN, but having it be useful on
FreeBSD would also be good.

-- Brooks

> /Jens

> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/socket.h>
> #include <net/if.h>
> #include <errno.h>
> #include <strings.h>
> #include <sys/ioctl.h>
> #include <ifaddrs.h>
> #include <machine/param.h>
> 
> /* FIXME use SA_LEN for systems like Linux */
> #ifndef _SIZEOF_ADDR_IFREQ
> #define	_SIZEOF_ADDR_IFREQ(ifr) \
> 	((ifr).ifr_addr.sa_len > sizeof(struct sockaddr) ? \
> 	 (sizeof(struct ifreq) - sizeof(struct sockaddr) + \
> 	  (ifr).ifr_addr.sa_len) : sizeof(struct ifreq))
> #endif
> 
> int
> main()
> {
>     struct ifconf ifc;
>     struct ifreq *ifr, *lifr;
>     int fd;
>     unsigned int n;
> 
>     fd = socket( AF_INET, SOCK_STREAM, 0 );
>     bzero(&ifc, sizeof(ifc));
>         n = 1;
>         ifr = calloc( ifc.ifc_len, sizeof(*ifr) );
>         do
>         {
>             n *= 2;
>             ifr = realloc( ifr, PAGE_SIZE * n );
>             bzero( ifr, PAGE_SIZE * n );
>             ifc.ifc_req = ifr;
>             ifc.ifc_len = n * PAGE_SIZE;
>         } while( ( ioctl( fd, SIOCGIFCONF, &ifc ) == -1 ) || ( ifc.ifc_len >= ( (n-1) * PAGE_SIZE)) );
> 
>     lifr = (struct ifreq *)&ifc.ifc_buf[ifc.ifc_len];
> 
>     while (ifr < lifr)
>     {
>         struct sockaddr *sa = &ifr->ifr_ifru.ifru_addr;
>         if( AF_LINK == sa->sa_family )
>         {
>             printf( "%s\n", ifr->ifr_name );
>         }
>         ifr = (struct ifreq *)(((char *)ifr) + _SIZEOF_ADDR_IFREQ(*ifr));
>     }
> 
>     return 0;
> }

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-net/attachments/20080722/80e0eccf/attachment.pgp