linux-kernel - Re: [PATCH 01/15] Introduce noop

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Message-Id: <200911211756.27596.arnd@arndb.de>
Date:	Sat, 21 Nov 2009 17:56:27 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Jan Blunck <jblunck@...e.de>
Cc:	Jamie Lokier <jamie@...reable.org>, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Linux-Kernel Mailinglist" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, jkacur@...hat.com,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH 01/15] Introduce noop_llseek()

On Friday 20 November 2009, Jan Blunck wrote:
> On Fri, Nov 20, Jamie Lokier wrote:
> 
> > Jan Blunck wrote:
> > > The noop_llseek() is a llseek() operation that filesystems can use that
> > > don't want to support seeking (leave the file->f_pos untouched) but still
> > > want to let the syscall itself to succeed.
> > 
> > This is weird behaviour: if you want to allow llseek() to succeed but
> > don't really support seeking, why does the device even care about the
> > value of file->f_pos?
> 
> The device itself does not care about it but it is userspace that is expecting
> the seek to succeed. There is a comment in osst that at least there seems to
> be a borken version of tar that wants to seek on the device even it that does
> not have any effect.

Looking at the question from the other side -- if the device and the user
don't care about file->f_pos, what's wrong with calling generic_file_llseek
instead of noop_llseek?

	Arnd <><
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