ldb error codes

[tridge at samba.org]

Simo (and other interested parties),

I've just been discussing ldb error codes a bit with Andrew
Bartlett and wanted to get your opinion on how to fix it. 

As you know, the current situation is a bit of a mess. When I first
wrote ldb I screwed up by paying very little attention to error
codes. We were able to recover OK for most ldb calls, as we just
defined the return value as being a LDB_ERR* value, or LDB_SUCCESS. We
still haven't fixed all the places that need to set these values, but
at least the major ones are fixed.

The tricky one is ldb_search(). In the ldap API equivalent
ldap_search_s() returns an error code and then uses functions like
ldap_count_messages() to count the replies.  Our ldb_search() function
returns a message count directly, which leaves no room for an error
code.

So I have a few possible proposals for fixing this:

 1) change the sign of the LDB_ERR* values, and make all functions
    then return a ldb error value. For ldb_search() if the value is >=
    0 then its a search count, if its < 0 then its an error code. Not
    pretty, but requires very little code modification.

 2) change ldb_search() to only return a error code, and add a
    ldb_count_messages() function. This requires changing all existing
    calls to ldb_search(). We'd also have to ensure that all backends
    NULL terminate the result list, as otherwise ldb_count_messages()
    would not be possible to implemenet.

 3) we could have a ldb_errorcode() function that returns the last
    error code. 

I know you are also working towards the new ldb_request() API, and
that won't have this problem, but I think we should also keep the
current API working, which means we need to fix this anyway.

Do you have a preference? Metze and Andrew, any comments?

Cheers, Tridge