Re: [PATCH v3 5/7] bdev: add open_finish.

[Christoph Hellwig]

Please make sure you CC linux-block if you add block device ops.

On Fri, Oct 25, 2019 at 01:21:42PM +0200, Michal Suchanek wrote:
> Opening a block device may require a long operation such as waiting for
> the cdrom tray to close. Performing this operation with locks held locks
> out other attempts to open the device. These processes waiting to open
> the device are not killable.
> 
> To avoid this issue and still be able to perform time-consuming checks
> at open() time the block device driver can provide open_finish(). If it
> does opening the device proceeds even when an error is returned from
> open(), bd_mutex is released and open_finish() is called. If
> open_finish() succeeds the device is now open, if it fails release() is
> called.
> 
> When -ERESTARTSYS is returned from open() blkdev_get may loop without
> calling open_finish(). On -ERESTARTSYS open_finish() is not called.
> 
> Move a ret = 0 assignment up in the if/else branching to avoid returning
> -ENXIO. Previously the return value was ignored on the unhandled branch.

Still a complete nack for splitting a fundamental operation over two
ops, especially just for working around a piece of buggy software.