linux-kernel - Re: Bug in BLKBSZSET/GET ioctl ?

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Date:	Thu, 29 Dec 2011 12:40:59 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Wanlong Gao <gaowanlong@...fujitsu.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Bug in BLKBSZSET/GET ioctl ?

On Thu, Dec 29, 2011 at 12:28:44PM +0800, Wanlong Gao wrote:
> On 12/29/2011 12:20 PM, Wu Fengguang wrote:
> 
> > On Thu, Dec 29, 2011 at 11:51:45AM +0800, Wanlong Gao wrote:
> >> Hi all:
> >>
> >> This is first reported to *libguestfs*: https://bugzilla.redhat.com/show_bug.cgi?id=624335
> >>
> >> Then, I looked into upstream util-linux and it seems nothing wrong. I'm not convinced that it's a kernel bug.
> >>
> >> produce:
> >>
> >> ---
> >> # ./util-linux/disk-utils/blockdev --getbsz /dev/sda6
> >> 4096
> >> # ./util-linux/disk-utils/blockdev --setbsz 2048 /dev/sda6
> >> # ./util-linux/disk-utils/blockdev --getbsz /dev/sda6
> >> 4096
> >> # ./util-linux/disk-utils/blockdev --setbsz 512 /dev/sda6
> >> # ./util-linux/disk-utils/blockdev --getbsz /dev/sda6
> >> 4096
> > 
> > I think each blockdev invocation is working on a *new* bdev object.
> 
> 
> But the address of *new* bdev is the same?
> I did printk, and they all returned the same address.

Then the block size value should be reset in one of the bd_set_size()
calls in __blkdev_get().

> > You'll get consistent results if somehow keep it referenced, for
> 
> 
> But isn't it a bug? It seems that the setbsz has no effect?

Yeah, it does look like unexpected behavior to the end user..

Thanks,
Fengguang
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