linux-kernel - Re: [PATCH] floppy: remove floppy-specific O

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Date:	Tue, 15 May 2012 09:22:01 +1000
From:	NeilBrown <neilb@...e.de>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] floppy: remove floppy-specific O_EXCL handling

On Mon, 14 May 2012 23:38:27 +0200 (CEST) Jiri Kosina <jkosina@...e.cz> wrote:

> On Mon, 14 May 2012, Tejun Heo wrote:
> 
> > > Because since
> > > 
> > > 	commit e525fd89d380c4a94c0d63913a1dd1a593ed25e7
> > > 	Author: Tejun Heo <tj@...nel.org>
> > > 	Date:   Sat Nov 13 11:55:17 2010 +0100
> > > 
> > > 	    block: make blkdev_get/put() handle exclusive access
> > > 
> > > mount of /dev/fd0 actually causes the fd0 block device be claimed with 
> > > _EXCL. Before this commit, you are able to mount /dev/fd0 and then open() 
> > > it afterward. After this commit you can't any more, because mounting 
> > > /dev/fd0 already passes O_EXCL to floppy_open(), and thus noone else can 
> > > open(/dev/fd0) any more.
> > > 
> > > My commit brings things back into shape, i.e. you can, equally to other 
> > > block devices, both mount it and open() it afterwards.
> > 
> > Ah, that makes sense.  Maybe it's a good idea to note why the change
> > is necessary in the commit message too?
> 
> Makes sense. Please find the updated patch below. Andrew, Jens, are you 
> going to pick it up, please?
> Thanks.
> 
> 
> 
> 
> From: Jiri Kosina <jkosina@...e.cz>
> Subject: [PATCH] floppy: remove floppy-specific O_EXCL handling
> 
> Block layer now handles O_EXCL in a generic way for block devices.
> 
> The semantics is however different for floppy and all other block devices,
> as floppy driver contains its own O_EXCL handling.
> 
> The semantics for all-but-floppy bdevs is "there can be at most one O_EXCL 
> open of this file", while for floppy bdev the semantics is "if someone has 
> the bdev open with O_EXCL, noone else can open it".
> 
> There is actual userspace-observable change in behavior because of this 
> since commit e525fd89d380c ("block: make blkdev_get/put() handle exclusive 
> access") -- on kernels containing this commit, mount of /dev/fd0 causes 
> the fd0 block device be claimed with _EXCL, preventing subsequent 
> open(/dev/fd0).
> 
> Bring things back into shape, i.e. make it possible, analogically to other 
> block devices, to mount the floppy and open() it afterwards -- remove the 
> floppy-specific handling and let the generic bdev code O_EXCL handling 
> take over.
> 
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> Acked-by: Tejun Heo <tj@...nel.org>
> ---
>  drivers/block/floppy.c |    8 +-------
>  1 files changed, 1 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index b0b00d7..fe694f8 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3650,13 +3650,7 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
>  		set_bit(FD_VERIFY_BIT, &UDRS->flags);
>  	}
>  
> -	if (UDRS->fd_ref == -1 || (UDRS->fd_ref && (mode & FMODE_EXCL)))
> -		goto out2;
> -
> -	if (mode & FMODE_EXCL)
> -		UDRS->fd_ref = -1;
> -	else
> -		UDRS->fd_ref++;
> +	UDRS->fd_ref++;
>  
>  	opened_bdev[drive] = bdev;
>  


As we not longer set fd_ref to -1, you should also remove:

	if (UDRS->fd_ref < 0)
		UDRS->fd_ref = 0;
	else 

from floppy_release(), and the 'out:' section of floppy_open().

With those changes:
   Acked-by: NeilBrown <neilb@...e.de>

Thanks,
NeilBrown

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