[openssl-dev] Backporting opaque struct getter/setter functions

[Viktor Dukhovni]

> On Jan 11, 2016, at 5:23 AM, Tomas Mraz <tmraz at redhat.com> wrote:
> 
> On Po, 2016-01-11 at 01:09 +0000, Peter Waltenberg wrote:
>> The point of using accessor FUNCTIONS is that the code doesn't break
>> if the structure size or offsets of fields in the underlying
>> structures change across binaries.
>> 
>> Where that mainly has an impact is updating the crypto/ssl libs
>> underneath existing binaries is more likely to just work.
>> 
>> #defines in the headers do not help at all here.
>> 
> 
> The point is in achieving reverse API compatibility between 1.1 and
> 1.0.2. No binary compatibility is expected between those branches.
> 
> I think that having the API compatibility would be really useful thing
> easing porting application code to 1.1 branch.

Yes, although in practice may users of 1.0.x will have previous releases
that don't have the accessors, so the issue is difficult to address
retroactively in OpenSSL.  In Postfix, I add the macros myself:

#if OPENSSL_VERSION_NUMBER < 0x10100000L
#define X509_up_ref(x) (CRYPTO_add(&x->references, 1, CRYPTO_LOCK_X509))
#endif

Which means that interestingly enough adding these to 1.0.x would break
my code and similar code elsewhere.

So on the whole forward-compatibility macros don't fully address the
problem, and may do as much harm as good.

I think that applications porting to 1.1.0 can and should implement
their own macros against a stable 1.0.x API that we don't change
at the last minute.  Providing your own forward-compatible glue
is easy enough...

-- 
	Viktor.