>>> I've already recommended that iopmem not be a block device and >>> instead be a device-dax instance. I also don't think it should claim >>> the PCI ID, rather the driver that wants to map one of its bars this >>> way can register the memory region with the device-dax core. >>> >>> I'm not sure there are enough device drivers that want to do this to >>> have it be a generic /sys/.../resource_dmableX capability. It still >>> seems to be an exotic one-off type of configuration. >> >> >> Yes, this is essentially my thinking. Except I think the userspace >> interface should really depend on the device itself. Device dax is a >> good choice for many and I agree the block device approach wouldn't be >> ideal. I tend to agree here. The block device interface has seen quite a bit of resistance and /dev/dax looks like a better approach for most. We can look at doing it that way in v2. >> >> Specifically for NVME CMB: I think it would make a lot of sense to just >> hand out these mappings with an mmap call on /dev/nvmeX. I expect CMB >> buffers would be volatile and thus you wouldn't need to keep track of >> where in the BAR the region came from. Thus, the mmap call would just be >> an allocator from BAR memory. If device-dax were used, userspace would >> need to lookup which device-dax instance corresponds to which nvme >> drive. >> > > I'm not opposed to mapping /dev/nvmeX. However, the lookup is trivial > to accomplish in sysfs through /sys/dev/char to find the sysfs path of the > device-dax instance under the nvme device, or if you already have the nvme > sysfs path the dax instance(s) will appear under the "dax" sub-directory. > Personally I think mapping the dax resource in the sysfs tree is a nice way to do this and a bit more intuitive than mapping a /dev/nvmeX. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
