Finally managed to optimize qmail-smtpd to load control files only once using dlopen()

One issue with qmail-smtpd has been bugging me for past many years.
Over the years the number of control files loaded by qmail-smtpd in
the function setup() have kept on increasing badmailfrom,
badmaipatterns, goodrcptto, badrcptto, accesslist, etc (around 36
control files in my case).

These files get loaded every time qmail-smtpd gets invoked by
tcpserver. This is not a issue for the unpatched qmail as it loads
only 6 control files.

This is something I have been working for the past few months.
Initially it was just a theory, but managed to put into practice by
using the dlopen() function. I did the following to achieve it

1. renamed main() function to qmail_smtpd(). in qmail-smtpd.c
2. used ifdef to conditionally compile qmail-smtpd with main()
3. use gcc -fPIC to generate qmail_smtpd.so with qmail_smtpd()
function and setup() function
4. use dlopen() in tcpserver.c parent to load qmail_smtpd.so and
execute setup() function
5. use dlsym() in the child to get the qmail_smtpd() function and
execute it instead of using execvp() on /var/qmail/bin/qmail-smtpd

Now I have a feature in tcpserver which allows you to load a .so file
and execute a function named as the basename of the .so file. It
allows be to load qmail_smtpd.so as well as rblsmtpd.so. e.g. my run
file is

exec /var/indimail/bin/softlimit -m 104857600 -o 1024
/var/indimail/bin/tcpserver \
-v -h -R -l 0 -x /var/indimail/etc/tcp.smtp.cdb \
-c /service/qmail-smtpd.25/variables/MAXDAEMONS -o -b 75 -u 555 -g 555 0 25 \
/var/indimail/plugins/rblsmtpd.so -rdnsbl-1.uceprotect.net -rzen.spamhaus.org \
/var/indimail/plugins/qmail_smtpd.so indimail.in /var/indimail/sbin/vchkpass \
/var/indimail/sbin/systpass /bin/false

Just thought of sharing this in case if it of any use to anyone.

In case you want to look at the git sources for indimail-mta -
tcpserver.c, tcpserver_plugin.c, load_shared.c, pathexec_run.c
at https://sourceforge.net/p/indimail/code/ci/master/tree/ucspi-tcp-0.88/

and qmail-smtpd.c, smtpd.c, Makefile at
https://sourceforge.net/p/indimail/code/ci/master/tree/qmail-1.03/

-- 
Regards Manvendra - http://www.indimail.org