On Mon, Feb 27, 2023 at 12:59:45PM +0100, Andreas Hindborg wrote: (snip) > >> +#else > >> +void ublk_set_nr_zones(struct ublk_device *ub); > >> +void ublk_dev_param_zoned_apply(struct ublk_device *ub); > >> +int ublk_revalidate_disk_zones(struct gendisk *disk); > > > > These are declarations, shouldn't they be dummy definitions instead? > > I looked at how nvme host defines nvme_revalidate_zones() when I did > this. The functions become undefined symbols but because the call sites > are optimized out they go away. Looking at e.g. nvme_revalidate_zones $ git grep nvme_revalidate_zones drivers/nvme/host/core.c: ret = nvme_revalidate_zones(ns); drivers/nvme/host/nvme.h:int nvme_revalidate_zones(struct nvme_ns *ns); drivers/nvme/host/zns.c:int nvme_revalidate_zones(struct nvme_ns *ns) The function is declared in nvme.h, but like you say, without any definition. zns.c provides a definition, but that file is only build if CONFIG_BLK_DEV_ZONED is set. > > https://github.com/torvalds/linux/blob/v6.2/fs/btrfs/Makefile#L39 > > https://github.com/torvalds/linux/blob/v6.2/drivers/block/null_blk/Makefile#L11 > > > > They have put the zoned stuff in a separate C file that is only compiled > > when CONFIG_BLK_DEV_ZONED is set. > > > > I'm not sure if a similar design is desired for ublk or not. > > > > However, if a similar design pattern was used, it could probably avoid > > some of these unpleasant dummy definitions altogether. > > This is the same as I do here, except I put the declarations in the c > file instead of a header. I did this for two reasons 1) there is no ublk > header besides the uapi header (I would add a header just for this), 2) > the declarations need only exist inside ublk_drv.c. For btrfs, null_blk, > nvme, the declarations go in a header file and the functions in question > do not have static linkage. > > I could move the function declarations out of the #else block, but then > they would need to be declared static and that gives a compiler warning > when the implementation is not present. I would love to hear someone else's opinion about this as well, but I do think that having #ifdef and #else with both a declaration and a definition in the C file is quite ugly. If having an internal only header (in the same directory as the C file), makes the C code easier to read, I'm all for it. It seems to work for nvme to only have a declaration in an internal header file, and only provide a definition if CONFIG_BLK_DEV_ZONED is set, presumably without giving a warning. Perhaps ublk can do the same? Kind regards, Niklas
