samba3 have built-in (without any patches) ability to run in foreground (smbd -
F) and to write log to stdout (smbd -FS). But realisation of logging to stdout 
is broken: only few first strings of log appears in stdout, all other strings 
of log are disappear.

You can simply check this: run "smbd -FS", connect clients, do some operations 
and watch log output to console. Then run smbd as usually (logging in syslog or 
log files), connect clients, do the same operations. Then compare stdout log 
and usual log. Stdout log is limited by few strings, when usual log is complete.

I investigated this problem since samba v2.2.8. In this version ability to run 
in foreground and logging to stdout was added by patches from Michael Handler 
(www.grendel.net). By the way, these patches was applied for samba3 source 
tree, so in samba3-release abilities to run in foreground and log to stdout are 
built-in.

For samba3 problem in file smbd/server.c, in call of procedure close_low_fds
(False) - it closing stdout and log disappears. By the way, "False" in calling 
of this procedure means not to close stderr (see lib/util.c). 

I noticed that in smbd/server.c procedure close_low_fds called 2 times, and 
both times with "False" argument. So, if we not closing stderr, maybe direct 
log to stderr will be more reasonable?

I do this by editing lib/debug.c. In fragment:
	if (interactive) {
		stdout_logging = True;
		dbf = x_stdout;
		x_setbuf( x_stdout, NULL );
	}
i replaced x_stdout to x_stderr. Then i run smbd daemon:
exec 2>&1
exec /usr/local/samba/bin/smbd -FS
logging to stdout works great!