linux-kernel - Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

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Message-ID: <20160623211845.GL3262@mtj.duckdns.org>
Date:	Thu, 23 Jun 2016 17:18:45 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, NeilBrown <neilb@...e.de>,
	stable@...r.kernel.org
Subject: Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

On Wed, Jun 22, 2016 at 09:42:16PM +0300, Konstantin Khlebnikov wrote:
> Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> byte at a time. Script gets 'i' instead of 'idle' when reads current action
> from /sys/block/$dev/md/sync_action and as a result does nothing.
> 
> This patch adds trivial implementation of partial read: generate whole
> string and move required part into buffer head.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> Cc: Stable <stable@...r.kernel.org> # v3.19+

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun