On Fri, Apr 26, 2019 at 05:45:53AM -0700, Christoph Hellwig wrote: > On Fri, Apr 26, 2019 at 04:28:16PM +1000, Dave Chinner wrote: > > i.e. go look at how xfs_pnfs.c works to hand out block mappings to > > remote pNFS clients so they can directly access the underlying > > storage. Basically, anyone wanting to map blocks needs a file layout > > lease and then to manage the filesystem state over that range via > > these methods in the struct export_operations: > > > > int (*get_uuid)(struct super_block *sb, u8 *buf, u32 *len, u64 *offset); > > int (*map_blocks)(struct inode *inode, loff_t offset, > > u64 len, struct iomap *iomap, > > bool write, u32 *device_generation); > > int (*commit_blocks)(struct inode *inode, struct iomap *iomaps, > > int nr_iomaps, struct iattr *iattr); > > Nipick: get_uuid isn't needed for the least itself, it just works > around the fact that the original pNFS/block protocol is braindead. > The pNFS/SCSI prototocol already switches to a device UUID, and other > users that work locally shouldn't need it either. Hmmm, this lease interface still doesn't support COW, right? (Right, xfs_pnfs.c bails out with -ENXIO for reflink files) It occurs to me that maybe we don't want Goldwyn's IOMAP_DAX_COW approach (hide the read address in the iomap->inline_data pointer); we just want two physical source addresses. Then the dax code can turn that into a memory pointer and file lessees can do sector accesses or whatever they need to do to write the range before calling ->commit_blocks. Oh, right, both of you commented about a dual iomap approach on the v2 btrfs dax support series. /me goes back to drinking coffee. --D
