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SubjectRe: [PATCH] btrfs: Don't check for file->private_data on open(). It is set by the core.
On Wed, Nov 12, 2014 at 11:38 AM, Martin Kepplinger <martink@posteo.de> 
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@posteo.de>
> ---
> 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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