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

Jiri Kosina
2012-05-15T06:16:04Z

On Tue, 15 May 2012, NeilBrown wrote:

> > 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>

Good point, thanks.

Andrew, could you please replace
floppy-remove-floppy-specific-o_excl-handling.patch in your tree with the
updated version below?

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>
Acked-by: NeilBrown <neilb@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
---
drivers/block/floppy.c | 18 ++++--------------
1 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index b0b00d7..87c3a6e 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3612,9 +3612,7 @@ static int floppy_release(struct gendisk *disk, fmode_t mode)

mutex_lock(&floppy_mutex);
mutex_lock(&open_lock);
- if (UDRS->fd_ref < 0)
- UDRS->fd_ref = 0;
- else if (!UDRS->fd_ref--) {
+ if (!UDRS->fd_ref--) {
DPRINT("floppy_release with fd_ref == 0");
UDRS->fd_ref = 0;
}
@@ -3650,13 +3648,7 @@ 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;

@@ -3719,10 +3711,8 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
mutex_unlock(&floppy_mutex);
return 0;
out:
- if (UDRS->fd_ref < 0)
- UDRS->fd_ref = 0;
- else
- UDRS->fd_ref--;
+ UDRS->fd_ref--;
+
if (!UDRS->fd_ref)
opened_bdev[drive] = NULL;
out2:

--
Jiri Kosina
SUSE Labs