The vfio-ccw driver and the vfio parent device provided by it (parent) support just a single mdev_type, and this is not likely to change any time soon. To match the mdev interfaces nicely initially the choice was made that mdev_types (which gets passed into mdev_register_parent()) shall be an array of pointers to struct mdev_type with a single element, and to make things worse it ended up being the last member. Now the problem with that is that before C99 the usual way to get something similar to a flexible array member was to use a trailing array of size 0 or 1. This is what I called fake flex array. For a while now the community is trying to get rid of fake flex arrays. And while mdev_types was not a fake flex array but an array of size one, because it can easily be and probably was mistaken for a fake flex array it got converted into a real C99 flex array with a compile time known constant size of one. As per [1] it was established that "only fake flexible arrays should be transformed into C99 flex-array members". Since IMHO the entire point of flex arrays is being flexible about the array size at run time, a C99 flex array is a poor fit for mdev_types. But an array of a size one is a poor fit as well for the reason stated above, let us try to get rid of the flex array without introducing back the one sized array. So, lets make mdev_types a pointer to struct mdev_type and pass in the address of that pointer as the 4th formal parameter of mdev_register_parent(). [1] https://lore.kernel.org/lkml/85863d7a-2d8b-4c1b-b76a-e2f40834a7a8@xxxxxxxxxxxxxx/ Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx> Tested-by: Eric Farman <farman@xxxxxxxxxxxxx> --- I've also considered switching up the order in which the members mdev_types and mdev_type are defined in struct vfio_ccw_parent but decided against that because that could look to somebody like well known mistake that can be made when using fake flex arrays. --- drivers/s390/cio/vfio_ccw_drv.c | 6 +++--- drivers/s390/cio/vfio_ccw_private.h | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c index 914dde041675..6ff5c9cfb7ed 100644 --- a/drivers/s390/cio/vfio_ccw_drv.c +++ b/drivers/s390/cio/vfio_ccw_drv.c @@ -171,7 +171,7 @@ static int vfio_ccw_sch_probe(struct subchannel *sch) return -ENODEV; } - parent = kzalloc(struct_size(parent, mdev_types, 1), GFP_KERNEL); + parent = kzalloc(sizeof(*parent), GFP_KERNEL); if (!parent) return -ENOMEM; @@ -186,10 +186,10 @@ static int vfio_ccw_sch_probe(struct subchannel *sch) parent->mdev_type.sysfs_name = "io"; parent->mdev_type.pretty_name = "I/O subchannel (Non-QDIO)"; - parent->mdev_types[0] = &parent->mdev_type; + parent->mdev_types = &parent->mdev_type; ret = mdev_register_parent(&parent->parent, &sch->dev, &vfio_ccw_mdev_driver, - parent->mdev_types, 1); + &parent->mdev_types, 1); if (ret) goto out_unreg; diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h index b62bbc5c6376..0501d4bbcdbd 100644 --- a/drivers/s390/cio/vfio_ccw_private.h +++ b/drivers/s390/cio/vfio_ccw_private.h @@ -79,7 +79,7 @@ struct vfio_ccw_parent { struct mdev_parent parent; struct mdev_type mdev_type; - struct mdev_type *mdev_types[]; + struct mdev_type *mdev_types; }; /** -- 2.45.2
