doc/doc-misc/LongTermIssues

   1 $Cambridge: exim/doc/doc-misc/LongTermIssues,v 1.1 2004/10/08 10:38:47 ph10 Exp $
   2
   3 Exim Long Term Issues
   4 ---------------------
   5
   6 I restarted this list from scratch for Exim 4. I amalgamated it with another
   7 list when creating the CVS repository (October 2004). But it still probably
   8 needs a substantial spring clean. Some of it is very old now.
   9
  10
  11 AUTOCONF
  12 --------
  13
  14 Somebody once tried to \(autoconf)\ Exim, but found it too big a job. I now
  15 have some experience with using \(autoconf)\ for PCRE, and I think maybe some
  16 use could be made of it. I don't, however, believe that \(all)\ Exim build-time
  17 configuration should be done that way. The reason is that, unlike something
  18 like PCRE, there is quite a lot of information that is "user choice". Giving it
  19 all as options to a \(configure)\ command does not seem the best way of doing
  20 things.
  21
  22 Whenever I build something that needs more than a couple of obvious options to
  23 \(configure)\, I always save them in a file anyway, so I know what I did for
  24 next time. Therefore, I think it is sensible to retain the current Local file
  25 structure for all the user choice configuration.
  26
  27 However, it might be helpful to use \(autoconf)\ to dig out various bits of
  28 information about the operating system. At present, the \(OS/Makefile-*)\ files
  29 have hard-wired settings, and maybe this information could be figured out by
  30 running \(autoconf)\, which would save having to keep maintaining these files.
  31
  32 I would arrange things so that \(configure)\ is run automatically the first
  33 time that \(make)\ is run, but it would be possible to run it manually first,
  34 to override defaults. (For example, if you have both \(cc)\ and \(gcc)\
  35 installed on your system, as I do, you need to be able to specify which to
  36 use.) I will need to do some experiments to see exactly how this would work.
  37
  38
  39 EXIMON and other utilities
  40 --------------------------
  41
  42 . Consider optionally making it possible to link with something other than
  43   Athena widgets - for example, gtk. Or indeed re-write the whole thing!
  44
  45
  46 GENERAL
  47 -------
  48
  49 . Convert os.c into a directory of separate functions, with the macro
  50   switches defined elsewhere. Then make it into a library.
  51
  52 . Use a pointer to an address structure for expanding $domain etc, to make it
  53   easier to save/restore this collection of variables. But note that $domain
  54   and $local_part aren't always in an address. Check out when these are set.
  55   Note also the new $address_data possibility.
  56
  57 . Spool_in and spool_out - speed up by using a table?
  58
  59 . Find a more compact way of encoding the options interpretation, and also of
  60   checking for incompatible options.
  61
  62 . Find a more compact way of passing an open SMTP channel without having
  63   to use options. What about the TLS state information? Could use a pipe to
  64   pass more data.
  65
  66 . Some people have suggested separately loadable modules. But do all systems
  67   have them? Is this going too far for just a few specialist users? In
  68   particular, people want to be able to replace the logging with his own code.
  69   Can we arrange this without going for the separately loaded modules? (cf the
  70   incoming checking code.)
  71
  72 . SIGHUP the daemon - don't close the sockets; instead pass a list of them
  73   somewhere for the new daemon to pick up. Iff started by exim or root, of
  74   course. There might be quite a long list of them - argv might not be the best
  75   idea. If this were done, then a non-setuid exim daemon could be SIGHUPped.
  76
  77 . Parallel deliveries. Currently dead host information doesn't get propagated
  78   between them very well. Is there anyway this could be improved?
  79
  80 . In some environments the use of gethostbyname() seems to cause problems.
  81   Check out its use, and see if having a "force DNS" option could be helpful.
  82   But people would have to know what they were doing.
  83
  84 . accept_max_per_host is a slow, linear search. If smtp_accept_max is large,
  85   this can be very slow. Is there some way we can speed this up? Some kind of
  86   index based on the IP address? Remember, this is in the daemon, so it must
  87   not consume store.
  88
  89 . Change the names of all the pcre_ stuff to, say, PCRE_ so that Exim can be
  90   linked with libraries or whatever that also use an external PCRE library.
  91
  92 . Look at code in pidentd for running Exim in wait mode from inetd and re-using
  93   the socket. This would allow it to run more tidily as non-root.
  94
  95 . Think up some scheme for checking for orphan files in the spool directories.
  96   Perhaps -bp should always do it, but it would be nice to have it done
  97   automatically now and again. Maybe we just leave this for a cron job? Perhaps
  98   a new -bx, e.g. -bpck or something. Better, perhaps, is a separate Perl
  99   script. Orphan = a file that is over 24h old (or 1s when test harness) and
 100   either doesn't end in -D or -H, or is a -D without a matching -H (or vice
 101   versa).
 102
 103 . Make set_process_info buffer bigger, and put the overflowed message at the
 104   end, thereby leaving the start.
 105
 106 . Swamping with delays in checking for reserved hosts - the connections are
 107   counted in the total allowed. Can we improve on this somehow? Maybe shared
 108   memory can help here. Think about different states and different limits.
 109
 110 . Lists that must use colons: can we check for other cases, and fix them up
 111   before passing them on? Is it worth it?
 112
 113 . Linux for S/390 - create configuration?
 114
 115 . Process receiving error message fails - can we get more info, such as the
 116   stdout/stderr?
 117
 118 . dbmbuild - if renaming one of .dir/.pag fails, reinstate the other. Should
 119   there be a lock?
 120
 121 . Write a script to check for format problems in the source - formats that are
 122   not fixed strings and are built from outside code.
 123
 124 . freeze_tell: Don't if message is a bounce message containing From: the local
 125   machine - even if the bounce comes from another host.
 126
 127 . Add additional data into the "frozen" log message at end of delivery, e.g. if
 128   remote host was the local host or whatever. At least some cross referencing.
 129
 130 . Someone had a requirement to install the Exim binary in a different place to
 131   the utilities, etc. Also, for different builds on the same host and
 132   architecture.
 133
 134 . Include (part of?) the ppid in the message id? Or a random number?
 135
 136 . Re-implement the code in readconf that reads error names for retry rules.
 137   Make it use a table for most of the error types. Then see if we can usefully
 138   add any additional error types.
 139
 140 . Should there be "exim -bP acls" etc? It would mean inventing some kind of
 141   "hide" facility within the ACL syntax.
 142
 143 . VERY LONG TERM: the message ID is too small now, with the recent changes to
 144   cram in the sub-second time. It would be a big project to extend it; Exim
 145   would have to recognize both forms for a while, and become stable, before
 146   generating the new form. Probably a runtime switch needed. The new form needs
 147   at least microsecond time (or more?) and should probably cope with 64-bit
 148   pids, just to be safe (or leave expansion space that could be used for that).
 149   It should also be able to hold big enough things in base 36.
 150
 151 . Take a look at libexec.
 152
 153 . Sort out the stcncpy/strlcpy issue once and for all. Time things.
 154
 155 . Error in transport filter. See test 407. All 3 processes see errors - which
 156   one should be noticed? Transport_filter_temp_errors may be needed.
 157
 158 . Think about 5xx thresholds -- too many and you're out. What about 4xx?
 159
 160 . autoreply - should it call /usr/sbin/sendmail? Provide a way of not passing
 161   -C and -D when creating the message ('cause it won't be privileged).
 162
 163 . Strings containing \000 - anything we can do?
 164
 165 . OpenSSL - can we pass an opened file for certificate? Repeatedly?
 166   Otherwise pre-initialize while root? There do seem to be functions for
 167   manipulating certificates, but documentation is scarce. Can we just load the
 168   certificate in as root in the server?
 169
 170 . Consider using poll() to close unwanted fds. Is this efficient? Perhaps it
 171   doesn't matter for the daemon.
 172
 173 . On a 64-bit system there are some cast warnings for casting addresses to
 174   ints. Either we must find a way of not warning, or we'll have to use unions
 175   to get round it.
 176
 177 . Run splint on the source?
 178
 179 . It has been suggested that rejection because not authenticated should use
 180   530 and not 550, but this is hard to detect because of the way ACLs work.
 181
 182 . When there is a sender verify failure, $acl_verify_message contains "sender
 183   verify failed", not the details of the failure. Should this change? Some of
 184   the waffly details are added later in smtp_in.c. In the ACL that text is in
 185   sender_verified_failed->user_message.
 186
 187 . An empty string for a transport filter currently causes an error. Should it
 188   ignore? Tricky because of special expansion rules for commands.
 189
 190 . GFDL for documentation (www.gnu.org/licenses/fdl.html)? The 1.2 version of
 191   this licence is still quite new (it is dated November 2002) so I think
 192   waiting for reaction/opinion is the best plan. There are Debian concerns
 193   about this licence. At very least, no Invariant Sections and no Cover Texts
 194   can be used.
 195
 196 . Allow $recipients in other places. Not clear what this value should be if,
 197   say, the system filter has overridden them. Default would be envelope
 198   recipients, as now.
 199
 200 End