Re: [PATCH] floppy: remove floppy-specific O_EXCL handling

NeilBrown
2012-05-14T23:22:17Z

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

> On Mon, 14 May 2012, Tejun Heo wrote:
>
> > > Because since
> > >
> > > commit e525fd89d380c4a94c0d63913a1dd1a593ed25e7
> > > Author: Tejun Heo <tj@kernel.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@suse.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@suse.cz>
> Acked-by: Tejun Heo <tj@kernel.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@suse.de>

Thanks,
NeilBrown

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