On Mon, Jul 24, 2017 at 02:42:29PM +0200, David Sterba wrote:
> On Fri, Jul 21, 2017 at 01:29:07PM -0400, [email protected] wrote:
> > From: Josef Bacik <[email protected]>
> > 
> > We need to use file->private_data for readdir on directories, so just
> > don't allow user space transactions on directories.
> > 
> > Signed-off-by: Josef Bacik <[email protected]>
> > ---
> >  fs/btrfs/ioctl.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> > index bedeec6..ddb3811 100644
> > --- a/fs/btrfs/ioctl.c
> > +++ b/fs/btrfs/ioctl.c
> > @@ -3968,6 +3968,9 @@ static long btrfs_ioctl_trans_start(struct file *file)
> >     struct btrfs_trans_handle *trans;
> >     int ret;
> >  
> > +   if (S_ISDIR(inode->i_mode))
> > +           return -EINVAL;
> 
> You can't do this, starting a transaction on a directory needs to work.
> The most natural way to run the ioctl is on the mount point.
> 
> The file private data would need to be able to hold multipe values, so
> you can add
> 
> struct btrfs_inode {
>       ...
>       struct priv_data {
>               void *for_readdir;
>               void *for_tranc_ioctl;
>       };
>       ...
> };
> 
> then set file->file_private = &btrfs_inode->priv_data; and update all
> uses to check for the embedded pointers.

So this cannot be attached to the inode but to struct file itself,
otherwise this won't work for parallel readdir obviously.
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