Thanks for clarifying this, John. Although everything seems to work fine, I'm a bit worried about the 'strict-aliasing' warnings my gcc compiler gives, like this one:
slpd_knownda.c:564: warning: dereferencing pointer ‘daaddr.53’ does break strict-aliasing rules With the used optimization levels, it is possible that modifying an 'alias' is optimized away completely, since the compiler assumes its value isn't used anymore. See e.g. http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html We could use the '-fno-strict-aliasing' compiler option, but I'd prefer to use a 'cleaner' way. I'm not sure if a 'double cast' through void* is good enough. BR, Roel On 05/25/2011 05:25 PM, John Calcote wrote: > This has been a minor sore point for decades in the socket interface - how > to refer to a structure that could hold any of a number of different address > types. Early on, it was decided just to refer to a sockaddr object - an > object of a well-known type and size - too small these days, but at least > useful for ipv4 addresses. This was done because void* was not actually > added to the C standard till 1989 when the C89 standard came out. Prior to > that, your only option was to typecast. > > In short, this is exactly the sort of thing for which void * was originally > introduced. You pass a generic pointer to the data structure, along with a > type discriminator and a buffer length. In this case, the type discriminator > is always at a well-known offset within the buffer referred to, and the size > is a separate argument. Had void* been available when the sockets interface > was being designed, I believe they would have used it instead of passing > sockaddr pointers around, because in the C language, you can automatically > cast to and from void (not so in C++, of course, but not relevant here), so > you can simply use a void* as if it were any of the sockaddr family of > structures. > > Is it type safe? Of course not. You can just as easily auto-cast it to the > wrong type of thing. But given the fact that the original socket spec has > you manually type-casting from one type of structure to another all over the > place, it's at least as safe, but much more convenient. > > John > > -----Original Message----- > From: Roel van de Kraats [mailto:rkra...@dds.nl] > Sent: Wednesday, May 25, 2011 6:06 AM > To: 'openslp-devel@lists.sourceforge.net' > Subject: Re: [Openslp-devel] Bug in libslp_knownda.c > > > > On 05/25/2011 01:18 PM, Morrell Richard (external) wrote: >> Hi Roel, >> >> The change in r1597 was only supposed to abstract the cache refresh >> code into a separate function, not change anything else, so the change >> to the address size in the second call was incorrect. Please go ahead >> with the update. > Done. See r1673. > > In my opinion it is a bit 'dangerous' to pass through void pointers like > this. Wouldn't it be better to explicitly use 'struct sockaddr_storage' > pointers? Or even use a union throughout the whole source tree to hold the > different 'sockaddr' types, like > http://svn.tartarus.org/sgt/putty/unix/uxnet.c?p2=%2Fputty%2Funix%2Fuxnet.c&; > p1=putty%2Funix%2Fuxnet.c&r1=8612&r2=8611&view=diff&pathrev=8612 > ? > > BR, > Roel >> Regards, >> >> Richard >> >> -----Original Message----- >> From: Roel van de Kraats [mailto:rkra...@dds.nl] >> Sent: 25 May 2011 11:34 >> To: 'openslp-devel@lists.sourceforge.net' >> Subject: [Openslp-devel] Bug in libslp_knownda.c >> >> >> Dear all, >> >> It seems that libslp_knownda.c has a bug on line 716 (see >> > http://openslp.svn.sourceforge.net/viewvc/openslp/trunk/openslp/libslp/libsl >> p_knownda.c?view=markup&pathrev=1672), >> because sizeof(struct in_addr) is too small to copy the whole address. >> This causes 'slptool findsrvtypes' to fail in case another host acts as >> DA. This was introduced in r1597 (see >> > http://openslp.svn.sourceforge.net/viewvc/openslp?view=revision&revision=159 >> 7). >> >> I guess it is safe to replace 'sizeof (struct in_addr)' with >> 'sizeof(struct sockaddr_storage)', but I'm not sure. If anyone can >> confirm this, I'll commit the fix. >> >> BR, >> Roel >> >> >> >> > ---------------------------------------------------------------------------- >> -- >> vRanger cuts backup time in half-while increasing security. >> With the market-leading solution for virtual backup and recovery, >> you get blazing-fast, flexible, and affordable data protection. >> Download your free trial now. >> http://p.sf.net/sfu/quest-d2dcopy1 >> _______________________________________________ >> Openslp-devel mailing list >> Openslp-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/openslp-devel >> >> This email, including any attachment, is a confidential communication >> intended solely for the use of the individual or entity to whom it is >> addressed. It contains information which is private and may be proprietary >> or covered by legal professional privilege. 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