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Re: [Nmh-workers] m_getfld

From: Jon Steinhart
Subject: Re: [Nmh-workers] m_getfld
Date: Mon, 10 Dec 2012 20:54:27 -0800

Paul Vixie writes:
> On 2012-12-11 4:32 AM, Ken Hornstein wrote:
> > Also ... maybe I'm just showing my age, but I always felt that mmap()
> > should be reserved for special-purpose uses, and this ain't one of them
> > (IMHO).
> there's no way to avoid string copy overhead if you use read(), unless
> you're on a rare kernel that will see a page aligned page sized buffer
> passed to it and do page flipping from the buffer cache. i love the fact
> that freebsd "cp" uses mmap when it can. looks like "ar", "cmp", and
> "tail" also do this. fun!
> but m_getfld isn't reading mail bodies, just headers. they fit in one
> page on almost all modern machines and all mail messages. i'd say
> there's no advantage to mmap if it's only saving us a 4K string copy
> from kernel to user mode. stdio doesn't prefetch all that much.
> paul

First of all, I'm pleased that at least folks are talking about getting
rid of m_getfld.  I like Paul's idea of just writing something new and
migrating over to it.

I would like to see a separation between parsing mail messages and reading
profiles and such.  Seems like the old code is really doing two completely
unrelated things, maybe to save a few bytes in the old days.

I don't quite agree with Paul on the "just headers" part of things.  I would
like any m_getfld replacement to have the ability to extract information
about MIME message parts which means finding headers in the middle of bodies.
As per postings some years ago, I would like to add code for reading attachments
that needs this feature.  Unfortunately I don't have time to do much more than
lurk at the moment.


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