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From: evans@ditsyda.oz (Bruce Evans)
Newsgroups: comp.os.minix
Subject: Re: Pipes in the Minix filesystem
Message-ID: <2178@ditsyda.oz>
Date: 6 Sep 89 18:20:38 GMT
References: <15116@ea.ecn.purdue.edu> <252@nikhefh.nikhef.nl>
Reply-To: evans@ditsyda.mq.oz (Bruce Evans)
Organization: CSIRO DIT Sydney, Australia
Lines: 34

In article <252@nikhefh.nikhef.nl> Schutte@nikhefh.nikhef.nl (Klamer Schutte) writes:
>Why not configuring at compile-time at which device the pipes should go?
>( at my system this should be RAM; but this also puts a constraint on the maximum
>  pipe size (512k on my system)).

Pipe sizes are limited to 7 blocks by the implementation of pipes using inodes.

I hate compile-time decisions (limitations). How about putting pipes on
/dev/pipe? It would be acceptable to cache the value found for the first
pipe open. I'm not sure if this would allow reconfiguring /dev/pipe just
after booting.

As Peter Housel pointed out, it is unreasonable to hold all pipes in the
cache (holding them on a disk delays the problem :-)). However, it would
be nice to avoid flushing discarded pipe blocks and inodes. Once a block
is marked dirty, it is normally only cleaned by writing. The same applies
to deleted files ...

The limitation of writing only 7K to pipes is very annoying (not device-
independent). In article <2234@nucleus.UUCP>, msm@nucleus.UUCP
(Michael S. Mattone) posted a fix. It didn't quite work for me. There
was a bug with skipping a block in the pipes. I only saw it while
writing a fairly complicated directory structure using PD-tar. It seemed
to have something to do with the extra i/o for system("mkdir").

This is the fate of many fixes posted to the newsgroup. There is not
enough feedback about source code and fixes. I'm not suggesting that
everyone follow up everything, but a few should send mail to the author
and the author should follow up after a few weeks. No mail is signifigant
and probably means no-one was interested; the newsgroup is not that big.

Bruce
-- 
Bruce Evans		evans@ditsyda.oz.au