linux-ext4 - Re: [RFC] Heads up on sys

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Message-ID: <45EC32B2.1000802@redhat.com>
Date:	Mon, 05 Mar 2007 07:09:38 -0800
From:	Ulrich Drepper <drepper@...hat.com>
To:	Jörn Engel <joern@...ybastard.org>
CC:	Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, suparna@...ibm.com, cmm@...ibm.com,
	alex@...sterfs.com, suzuki@...ibm.com
Subject: Re: [RFC] Heads up on sys_fallocate()

Jörn Engel wrote:
> The bad news for posix_fallocate() is that even if libc is smart enough
> to write random data, mmap() can still cause problems.

This is not smart, quite to the contrary.  The standard guarantees that
all not-yet-written-to places in the file are zero.  And if a block has
already been written posix_fallocate cannot change it.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖


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