On Wed, 2006-03-15 at 16:33 -0800, Aaron Stone wrote:
> On Wed, 2006-03-15 at 18:36 -0500, Geo Carncross wrote:
> > On Wed, 2006-03-15 at 14:30 -0800, Blake Mitchell wrote:
> > > Geo, I think you are confusing your forks. You are thinking fork as in
> > > run in the background by forking and then killing the parent. Where as
> > > Aaron is talking about forking child processes to handle each connection.
> >
> > If that's the case, then fine.
>
> Right -- What I mean by fork and detach are:
>
> fork: children to handle connections.
> detach: double fork away from console.
Yeah, except note use you the word fork in defining detach. Better to
say:
-P: [pre]fork processes for handling children
-D: detach from console by closing fds 0..93 inclusive after starting
-B: put dbmail in the background (because for some reason you're
starting dbmail from something that isn't a shell and you can't use &)
-G: start dbmail in its own process group (setpgid) so that stupid
programs (like pppd) don't kill it when a user disconnects- even more
useful if someone starts it from a serial console and has a SAK
-S: start dbmail in its own session (setsid)- implies -G, and requires
-D (and the operations performed by -D must be done before setsid())
I'm not married to these switches- anything is fine, but there is
something important about them: none of these definitions are negative;
none of these switches "stop" dbmail from doing something. That's
confusing.
If the "default" should be something else, I recommend using a wrapper
script as I described earlier.
> the -f option is already taken for alt. config file; that option runs
> across all of the command line programs and would be hard to change,
> needing to rearrange other options to make room in some cases.
>
> It would kinda neat if you ran 'dbmail-imapd' and the program returned
> "Dbmail-IMAPd ready to rock" and started speaking IMAP to you ;-) I'm
> not sure if I like this, though. I'll marinate with it some more.
Supporting imap preauth isn't such a bad idea- it makes it so people can
ssh-tunnel their IMAP mail without having to do port forwarding.
As a side note- there's a reason I listed fds 0..93 as should be closed
by -D; I'm sure everyone guesses 0 through 2 easily enough, but there
might be some pipelines, so close a bit further- fds 15 or 16 is usually
what I see.
The Bourne shell (the REAL one) uses file descriptor 19 internally for
reading scripts- we shouldn't close it in the parent- but after forking
(-P) because the script running dbmail might not end in:
exec dbmail-start ....
but instead expect to be able to do some things afterwards.
HP-UX uses file descriptor 59 instead of file descriptor 19, but for the
same reason.
I've heard reports of shells in this era using a descriptor as high as
92- but as you already know- I treat the detaching from the console as a
significantly system-dependant, and non-portable thing, such that I let
the administrator do it in the shell if they know they're using such a
beast.
Besides, THESE days, UNIX has close-on-exec (or ioctl FIOCLEX), so the
shell doesn't need to use magic file descriptors anymore.
so if -S is set and -D isn't,
if we have FIOCLEX defined, or FD_CLOEXEC,
setsid() will do the right thing
otherwise, we need to close all file descriptors 0..93
otherwise if -D is set,
we need to close all file descriptors 0..93
of course, if we DON'T have FD_CLOEXEC, then chances are we don't have
setsid() either (FD_CLOEXEC and setsid() are both in POSIX 1003)- so
really, this is more of a historical footnote- especially in case anyone
wants to port dbmail to a V7 machine :)
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