From: Christoph Hellwig [mailto:hch@xxxxxx] > On Sat, Jan 21, 2017 at 04:28:52PM +0000, Matthew Wilcox wrote: > > Of course, there may not be a backing device either! > > s/backing device/block device/ ? If so fully agreed. I like the dax_ops > scheme, but we should go all the way and detangle it from the block > device. I already brought up this issue with the fallback to direct I/O > on I/O error series. In the case of a network filesystem being used to communicate with a different VM on the same physical machine, there is no backing device, just a network protocol. > And both of them are wrong. The write_begin/write_end mistake > notwithstanding address_space ops are operations the VM can call without > knowing things like fs locking contexts. The above on the other hand > are device operations provided by the low-level driver, similar to > block_device operations. So what we need is to have a way to mount > a dax device as a file system, similar to how we support that for block > or MTD devices and can then call methods on it. For now this will > be a bit complicated because all current DAX-aware file systems also > still need block device for the metadata path, so we can't just say > you mount either a DAX or block device. But I think we should aim > for mounting a DAX device as the primary use case, and then deal > with block device emulation as a generic DAX layer thing, similarly > how we implement (bad in the rw case) block devices on top of MTD. I'm not terribly enthusiastic about creating a fake block device to sit on top of a network filesystem, but I suppose we could go that way if we had to. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
