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Date: Mon, 18 Mar 2002 05:08:02 -0500
From: Jeff Garzik <jgarzik@mandrakesoft.com>
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To: Jan Hudec <bulb@ucw.cz>
CC: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: fadvise syscall?
In-Reply-To: <3C945635.4050101@mandrakesoft.com> <5.1.0.14.2.20020317170621.00abd980@pop.cus.cam.ac.uk> <5.1.0.14.2.20020317190303.03289ec0@pop.cus.cam.ac.uk> <5.1.0.14.2.20020318000057.051d30e0@pop.cus.cam.ac.uk> <a73ujs$5mc$1@cesium.transmeta.com> <20020318085811.GA21981@artax.karlin.mff.cuni.cz>
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Jan Hudec wrote:

>>Followup to:  <5.1.0.14.2.20020318000057.051d30e0@pop.cus.cam.ac.uk>
>>By author:    Anton Altaparmakov <aia21@cam.ac.uk>
>>In newsgroup: linux.dev.fs.devel
>>
>>>Ok, so basically we want both fadvise() and open(2) semantics, with the 
>>>open(2) being a superset of the fadvise() capabilities (some things no 
>>>longer make sense to be specified once the file is open). They can of 
>>>course both be calling the same common helpers inside the kernel...
>>>
>>If they're open() flags, they should probably be controlled with
>>fcntl() rather than with a new system call.
>>
>
>Then posix_fadvise interface can be implemented in libc using fcntl.
>
Indeed it can be...  but it less flexible that way, unless you want to 
add another level of indirection.

It is far better for future-proofing the interface IMO if fadvise is 
implementing directly.  Hints are less important than open O_xxx flags 
or F_xxx flags, because an implementation can safely ignore 100% of the 
fadvise hints, if it so chooses.  One cannot say the same thing for 
open/fcntl flags.

So, different class of fd flags deserves a different syscall, IMO...

    Jeff






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