From: Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
To: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: open(2) says O_DIRECT works on 512 byte boundries?
Date: Wed, 28 Jan 2009 13:33:22 -0800 [thread overview]
Message-ID: <20090128213322.GA15789@kroah.com> (raw)
In looking at open(2), it says that O_DIRECT works on 512 byte boundries
with the 2.6 kernel release:
Under Linux 2.4, transfer sizes, and the alignment of the user
buffer and the file offset must all be multiples of the logical
block size of the file system. Under Linux 2.6, alignment to
512-byte boundaries suffices.
However if you try to access an O_DIRECT opened file with a buffer that
is PAGE_SIZE aligned + 512 bytes, it fails in a bad way (wrong data is
read.)
Is this just a mistake in the documentation? Or am I reading it
incorrectly?
I have a test program that shows this if anyone wants it.
thanks,
greg k-h
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WARNING: multiple messages have this Message-ID (diff)
From: Greg KH <greg@kroah.com>
To: mtk.manpages@gmail.com
Cc: linux-man@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: open(2) says O_DIRECT works on 512 byte boundries?
Date: Wed, 28 Jan 2009 13:33:22 -0800 [thread overview]
Message-ID: <20090128213322.GA15789@kroah.com> (raw)
In looking at open(2), it says that O_DIRECT works on 512 byte boundries
with the 2.6 kernel release:
Under Linux 2.4, transfer sizes, and the alignment of the user
buffer and the file offset must all be multiples of the logical
block size of the file system. Under Linux 2.6, alignment to
512-byte boundaries suffices.
However if you try to access an O_DIRECT opened file with a buffer that
is PAGE_SIZE aligned + 512 bytes, it fails in a bad way (wrong data is
read.)
Is this just a mistake in the documentation? Or am I reading it
incorrectly?
I have a test program that shows this if anyone wants it.
thanks,
greg k-h
next reply other threads:[~2009-01-28 21:33 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-28 21:33 Greg KH [this message]
2009-01-28 21:33 ` open(2) says O_DIRECT works on 512 byte boundries? Greg KH
[not found] ` <20090128213322.GA15789-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-01-29 0:41 ` Robert Hancock
2009-01-29 0:41 ` Robert Hancock
[not found] ` <4980FB4D.9090009-fVOoFLC7IWo@public.gmane.org>
2009-01-29 1:17 ` Greg KH
[not found] ` <20090129011758.GA26534-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-01-29 2:59 ` Michael Kerrisk
2009-01-29 2:59 ` Michael Kerrisk
2009-01-29 3:13 ` Greg KH
[not found] ` <20090129031349.GA23722-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-01-29 15:40 ` Jeff Moyer
2009-01-29 15:40 ` Jeff Moyer
[not found] ` <x49iqnyi0ih.fsf-RRHT56Q3PSP4kTEheFKJxxDDeQx5vsVwAInAS/Ez/D0@public.gmane.org>
2009-01-30 6:16 ` Greg KH
2009-01-30 6:16 ` Greg KH
2009-01-29 5:13 ` KAMEZAWA Hiroyuki
2009-01-29 5:13 ` KAMEZAWA Hiroyuki
[not found] ` <20090129141338.34e44a1f.kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
2009-01-29 7:10 ` KOSAKI Motohiro
2009-01-29 7:10 ` KOSAKI Motohiro
[not found] ` <20090129160826.701E.KOSAKI.MOTOHIRO-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
2009-01-30 6:17 ` Greg KH
2009-01-30 6:17 ` Greg KH
[not found] ` <20090130061714.GC31209-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-02-02 22:08 ` Andrea Arcangeli
2009-02-02 22:08 ` Andrea Arcangeli
2009-02-03 1:29 ` KAMEZAWA Hiroyuki
[not found] ` <20090203102920.684e7b67.kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
2009-02-03 2:31 ` Andrea Arcangeli
2009-02-03 2:31 ` Andrea Arcangeli
[not found] ` <20090203023147.GZ20323-ulAA2RpUuRJvbPj5LQlJ3g@public.gmane.org>
2009-02-03 2:55 ` KAMEZAWA Hiroyuki
2009-02-03 2:55 ` KAMEZAWA Hiroyuki
[not found] ` <20090203115540.86a01273.kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
2009-02-03 3:42 ` KAMEZAWA Hiroyuki
2009-02-03 3:42 ` KAMEZAWA Hiroyuki
2009-02-06 17:55 ` Andrea Arcangeli
2009-02-06 17:55 ` Andrea Arcangeli
[not found] ` <20090202220856.GY20323-ulAA2RpUuRJvbPj5LQlJ3g@public.gmane.org>
2009-02-03 3:50 ` Greg KH
2009-02-03 3:50 ` Greg KH
[not found] ` <20090203035012.GC1867-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-02-03 15:01 ` Andrea Arcangeli
2009-02-03 15:01 ` Andrea Arcangeli
2009-02-03 4:13 ` KAMEZAWA Hiroyuki
2009-02-03 4:13 ` KAMEZAWA Hiroyuki
2009-02-03 4:38 ` KAMEZAWA Hiroyuki
2009-02-03 4:38 ` KAMEZAWA Hiroyuki
[not found] ` <20090203133811.47324d80.kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
2009-02-03 15:08 ` Andrea Arcangeli
2009-02-03 15:08 ` Andrea Arcangeli
2009-02-04 23:41 ` Greg KH
2009-02-04 23:41 ` Greg KH
[not found] ` <20090204234153.GA32244-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2009-02-06 17:54 ` Andrea Arcangeli
2009-02-06 17:54 ` Andrea Arcangeli
[not found] ` <20090206175414.GQ14011-ulAA2RpUuRJvbPj5LQlJ3g@public.gmane.org>
2009-02-06 18:38 ` Andrea Arcangeli
2009-02-06 18:38 ` Andrea Arcangeli
2009-02-07 13:32 ` Izik Eidus
2009-02-07 13:32 ` Izik Eidus
[not found] ` <498D8D53.6030007-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2009-02-07 15:33 ` Andrea Arcangeli
2009-02-07 15:33 ` Andrea Arcangeli
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