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From: jas@llama.Ingres.COM (Jim Shankland)
Newsgroups: comp.unix.internals
Subject: Re: What does sync() _really_ do?
Message-ID: <1990Dec21.231437.2703@ingres.Ingres.COM>
Date: 21 Dec 90 23:14:36 GMT
References: <52328@mcdchg.chg.mcd.mot.com> <1635@lot.ACA.MCC.COM> <5156@segue.segue.com> <4670@pkmab.se> <5258@segue.segue.com> <1969@necisa.ho.necisa.oz.au>
Reply-To: jas@llama.Ingres.COM (Jim Shankland)
Organization: The Eddie Group
Lines: 27

In article <1969@necisa.ho.necisa.oz.au> boyd@necisa.ho.necisa.oz.au (Boyd Roberts) writes:
>In article <5258@segue.segue.com> jim@segue.segue.com (Jim Balter) writes:
>>Even if sync waited on dirty block writes, that would be a 1-deep "sync queue",
>>not the fabled 2-deep queue.
>
>There is no `sync queue'.

No, no, you're all wrong.

There is a "sync protocol" that goes as follows:

Programmer:  sync <cr>
Kernel:  (Hears you, but doesn't want to be bothered, thus ignores you)
Programmer:  sync <cr>
Kernel:  (Knows you really want those blocks synched, but is busy doing other
stuff.  Puts your request on a queue, to do "when I get around to it."
Programmer:  sync <cr>
Kernel:  (Now understands you're not going to back down, and it's going to
be in big trouble if it doesn't sync those blocks RIGHT NOW; does so.)

Coincidentally, my mother used to use a similar protocol with me when
I was an adolescent.  Third request always had the I_MEAN_IT_YOUNG_MAN flag,
too.

jas

(Hey, it's no sillier than the other explanations that have been posted.)