linux-kernel - Re: [PATCH, RFC] xfs: batched discard support

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Message-ID: <20090820011004.GC14005@shareable.org>
Date:	Thu, 20 Aug 2009 02:10:04 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	xfs@....sgi.com, linux-fsdevel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	liml@....ca, jens.axboe@...cle.com
Subject: Re: [PATCH, RFC] xfs: batched discard support

Christoph Hellwig wrote:
> > So i'm torn about the 'syscall versus ioctl' issue, i'd 
> > like to avoid making interface design mistakes and i'd 
> > like to solicit some opinions about this. I've attached 
> > the perfcounters ioctl patch below.
> 
> Only add a syscall if it has _one_ clear defined purpose,
> which has kernel-wide meaning.

One clear defined purpose which comes to mind is a "trim" or "punch"
system call, for making holes in files as well as trimming block
devices.  Several other OSes have that capability on files.

I don't remember - does TRIM guarantee the blocks read zeros afterwards?

It would be tidy if it does, as it could have the same meaning with files.

-- Jamie

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