[ On Fri, June 7, 1996 at 16:27:49 (+0100), Philip Hazel wrote: ]
> Subject: Exim 0.52
>
> 1. The code I was using to find the maximum number of file descriptors
> didn't work on FreeBSD or NetBSD. It has been replaced.
Are you ready for GNU Autoconf yet? ;-)
> 2. I was suffering from a delusion that close() implied fsync() -- my
> ignorance of Unix is showing -- some explicit fsync() calls are now
> included to improve integrity.
Unix traditionally has only agreed to *schedule* writes of dirty
buffers, and not to actually do them, and of course it used the sync(2)
call to trigger this activity.
Most modern unix operating systems have O_SYNC option to open(2) that
ensures each write(2) will wait for the dirty buffers associated with
the file handle in question to be successfully written and the status
physically updated. This is somewhat equivalent to the 4.3bsd fsync(2)
system call (i.e. the same as calling "write(fd,...); fsync(fd);", but I
don't think fsync(2) is in POSIX-1003.1 or any other accepted standard.
I don't know if O_SYNC *is* in POSIX though. Neither NetBSD-1.2 nor
FreeBSD-2.1 have O_SYNC.
I think I've seen O_FSYNC somewhere too. Ah, yes, in 4.4bsd. They
don't document it though, and on a quick look through /usr/src/sys/kern
on NetBSD and FreeBSD I can't find it implemented anywhere. I would
guess that it *should* be equivalent to "fsync(fd); close(fd);".
Xenix, on the other hand, didn't let sync(2) return until all the dirty
buffers were written because it didn't have the newer O_SYNC or fsync(2).
Are you ready for GNU Autoconf yet? ;-)
> 3. I hadn't realized that some OS don't provide bi-directional pipes --
> Unix ignorance again -- and in one case had written and read from the
> "wrong" file descriptors.
I hadn't realized *any* unix-like OS ever provided bi-directional pipes! ;-)
> Have a good weekend!
You too! Thanks!
I hope to have a more serious look at exim soon, esp. now that I've
finally finished the release of smail-3.2.
--
Greg A. Woods
+1 416 443-1734 VE3TCP robohack!woods
Planix, Inc. <woods@???>; Secrets of the Weird <woods@???>
