linux-kernel - Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable

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Message-ID: <20090518094808.GA12041@shareable.org>
Date:	Mon, 18 May 2009 10:48:08 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Vitaly Mayatskikh <v.mayatskih@...il.com>,
	Josef Bacik <josef@...hat.com>, sandeen@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Perform check in iov_iter_fault_in_readable() by check_readable_bytes()

Alan Cox wrote:
> > System calls don't trigger SIGSEGVs so they can't rely on that when
> > calling read().  I'm not sure how they handle that.
> 
> Usually by touching the pages before the syscall.

Makes sense.

> (You can't rely on -EFAULT either in POSIX, its optional that it
> bothers to tell you and for example on MMUless it may well not)

On MMUless you wouldn't use page protection as a GC technique :-)
Is EFAULT really optional on systems with page protection?

-- Jamie
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