[pacman-dev] [PATCH 2/3] Use OpenSSL MD5 crypto functions if available

[Allan McRae]

On 07/09/10 00:42, Dan McGee wrote:
> On Mon, Sep 6, 2010 at 9:34 AM, Allan McRae<allan at archlinux.org>  wrote:
>> On 05/09/10 22:10, Allan McRae wrote:
>>>
>>> On 04/09/10 19:16, Jürgen Hötzel wrote:
>>>>
>>>> Hi Dan,
>>>>
>>>> 2010/9/2 Dan McGee<dan at archlinux.org>:
>>>>>
>>>>> This does not remove the MD5 code from our codebase, but it does enable
>>>>> linking against OpenSSL to get their much faster implementation if it is
>>>>> available on whatever platform you are using. At configure-time, we will
>>>>> default to using it if it is available, but this can be easily
>>>>> changed by
>>>>> using the `--with-openssl` or `--without-openssl` arguments to
>>>>> configure.
>>>>
>>>> What about just replacing the current MD5 implementation with the
>>>> OpenSSL implementation?
>>>>
>>>> This would prevent conditional compilation and a direct OpenSSL
>>>> dependency in libalpm.
>>>
>>> Can we do that? Openssl is BSD code.
>>>
>>>
>>> Anyway, I have concerns... Think of an openssl upgrade. pacman is in
>>> SyncFirst and it pulls in all its deps. If that pulls in openssl with a
>>> soname bump, things may get interesting. I have not check, but I do not
>>> think --as-needed saves us there.
>>>
>>
>> My concern is lessened...   I just did an update on a year old install and
>> pacman pulled in openssl for the lib* updates.  I did another update and
>> nothing too bad happened.  So this may be fine.
>
> We already had this non-explicit dep chain anyway: pacman ->
> libarchive ->  openssl, or pacman ->  libfetch ->  openssl. Moving it up
> one level shouldn't affect a whole lot.
>
> The only thing that should break here is "everything else" on your
> system. E.g. if you are prompted to upgrade pacman first because it is
> in SyncFirst, and it pulls in an so-bump OpenSSL, then anything else
> on your system that links that library won't work until you complete a
> full -Syu. However, as I pointed out above, this was already happening
> as far as I can see before.

Pulling openssl only happened on an old system when updating pacman. 
The versioned dependencies used for Arch's pacman package are quite 
relaxed so updating pacman would only pull new libfetch and libarchive 
(and thus openssl) on a really old system.  Remember the multiple 
rebuilds of pacman when we were deciding if the libarchive and libfetch 
dependency versioning should force it to pull in the openssl update and 
it was finally decided it was best not to.

Anyway the choices are (with a openssl update)
1) update pacman + openssl followed by full update
2) full update with openssl  (initial pacman update only when pacman is 
out of date)

Stopping for whatever reason in the middle of 1) could be very painful. 
Think of a network outage...  and there is quite a scope for something 
bad to happen as it is the entire second transaction, including package 
download which may take some time.  With 2), the pain only occurs with 
stopping during the actual package install stage so is a much smaller 
scope to cause issues.

Anyway, I like the whole not reinventing the wheel being done here so 
overall I like the idea.  It just gives me this nagging concern...

Allan