Re: [PATCH 11/13] libmultipath: Add support for block device IOCTL

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, Feb 25, 2026 at 03:32:23PM +0000, John Garry wrote:
> Add mpath_bdev_ioctl() as a multipath block device IOCTL handler. This
> handler calls into driver mpath_head_template.ioctl handler.
> 
> It is expected that the .ioctl handler will unlock the SRCU read lock,
> as this is what NVMe requires - see nvme_ns_head_ctrl_ioctl(). As such,
> export a handler to unlock, mpath_head_read_unlock().
> 
> The .compat_ioctl handler is given the standard handler.
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>  include/linux/multipath.h |  4 ++++
>  lib/multipath.c           | 42 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/include/linux/multipath.h b/include/linux/multipath.h
> index 3846ea8cfd319..40dda6a914c5f 100644
> --- a/include/linux/multipath.h
> +++ b/include/linux/multipath.h
> @@ -72,6 +72,9 @@ struct mpath_head_template {
>  	bool (*is_disabled)(struct mpath_device *);
>  	bool (*is_optimized)(struct mpath_device *);
>  	enum mpath_access_state (*get_access_state)(struct mpath_device *);
> +	int (*bdev_ioctl)(struct block_device *bdev, struct mpath_device *,
> +			blk_mode_t mode, unsigned int cmd, unsigned long arg,
> +			int srcu_idx);

I don't know that this API is going to work out. SCSI persistent
reservations need access to all the mpath_devices, not just one, and
they are commonly handled via SG_IO ioctls. Unless you want to disallow
SCSI persistent reservations via SG_IO, you need to be able to detect
them, and handle them using the persistent reservation code with the
mpath_head.

-Ben