At 8:31 PM -0700 9/24/01, Dan Harkless wrote:
>It looks to me like what's happening is that my scripts do a POP3 connect
>(which I do more often than anyone else, explaining why only _I_ have
>noticed mail loss), my spool is emptied out of /var/mail/<user> into
>/var/mail/.<user>.pop, the machine crashes, and then after the machine's
>back up again, my spool is zero-length and the temp_drop is overwritten by
>the first check.
>
>I didn't pore through the code exhaustively, but I couldn't find any code
>that would prevent this. Shouldn't there be code that would check for the
>pre-existence of the temp_drop file and merge its messages back into the
>spool before doing anything else??
There is such code, and has been for as long as I can recall. I've
hit it many times in testing.
An popper/pop_dropcopy.c:1532, we revert to non-server mode if the
temp drop isn't empty:
/*
* If the temporary popdrop is not empty, revert to regular mode.
*/
if ( mybuf.st_size != 0 )
p->server_mode = 0;
Then at line 1604 we deal with any left-over mail in the temp drop:
if ( mybuf.st_size != 0 ) { /* Mostly this is for regular mode. */
DEBUG_LOG2 ( p, "Temp drop %s not empty (%u octets)",
p->temp_drop, (unsigned) mybuf.st_size );
if ( init_dropinfo ( p, p->temp_drop, p->drop, time(0) ) != POP_SUCCESS ) {
/* Occurs on temp_drop corruption */
flock ( dfd, LOCK_UN );
close ( dfd );
return ( POP_FAILURE );
}
At this point, the file pointer is at the end of the temp drop,
following any left-over mail. We then lock the spool, append mail
from it to the temp drop (after any left-over mail), zero the spool,
and work out of the temp drop.
>As I understand things, the only way to prevent any possibility of
>overwriting an existing temp_drop file would be to do it atomically, with
>O_EXCL specified along with O_CREAT on the open() call.
I'm not sure why O_EXCL is needed. Qpopper always locks the temp
drop before doing anything, to make sure only one Qpopper process is
active for the user. It then checks if the file is non-empty, and
processes any left-over mail.
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