On Mon, Jan 23, 2017 at 10:03 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Mon, Jan 23, 2017 at 09:14:04AM -0800, Dan Williams wrote: >> The use case that we have now is distinguishing volatile vs persistent >> memory (brd vs pmem). > > brd is a development tool, so until we have other reasons for this > abstraction (which I'm pretty sure will show up rather sooner than later) > I would not worry about it too much. By "volatile" I also meant cases where pmem is fronting volatile memory, or more importantly when the platform has otherwise arranged for cpu caches to be flushed on a power loss event like I believe some existing storage appliances do. >> I took a look at mtd layering approach and the main difference is that >> layers above the block layer do not appear to know anything about mtd >> specifics. > > Or the block layer itself for that matter. And that's exactly where > I want DAX to be in the future. > >> For fs/dax.c we currently need some path to retrieve a dax >> anchor object through the block device. > > We have a need to retreiver the anchor object. We currently do it > though the block layer for historical reasons, but it doesn't have > to be that way. > >> > In the longer run I like your dax_operations, but they need to be >> > separate from the block layer. >> >> I'll move them from block_device_operations to dax data hanging off of >> the bdev_inode, or is there a better way to go from bdev-to-dax? > > I don't think that's any better. What we really want is a way > to find the underlying persistent memory / DAX / whatever we call > it node without going through a block device. E.g. a library function > to give that object for a given path name, where the path name could > be either that of the /dev/pmemN or the /dev/daxN device. > > If the file system for now still needs a block device as well it > will only accept the /dev/pmemN name, and open both the low-level > pmem device and the block device. Once that file system doesn't > need block code (and I think we could do that easily for XFS, > nevermind any new FS) it won't have to deal with the block > device at all. > > pmem.c then becomes a consumer of the dax_ops just like the file system. Ah ok, I'll take a look at a dax_by_path() capability. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
