Re: [PATCH] btrfs: Don't check for file->private_data on open(). It is set by the core.

[Chris Mason]

On Wed, Nov 12, 2014 at 11:38 AM, Martin Kepplinger <martink@xxxxxxxxx> 
wrote:
> The miscdevice core now sets file->private_data to the struct 
> miscdevice
> so don't fail when this is not NULL.
>
> Signed-off-by: Martin Kepplinger <martink@xxxxxxxxx>
> ---
> This is a question: what does this check provide and does overwriting
> file->private_data make any difference?
>
> Is miscdevice's open() by the user not allowed here, if 
> file->private_data
> is set?
>
> thanks!!

Btrfs uses this in the transaction start ioctl to record the 
transaction handle being started.  Ceph is the main user of the ioctl, 
and we could setup a hash table if needed.  But which call path in 
miscdevice is doing this?

With your patch in place, btrfs would end up overwriting the miscdevice 
private_data field, which would probably cause problems.

-chris

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