Re: [LSF/MM TOPIC] Direct block mapping through fs for device

Christoph Hellwig
2019-04-26T12:45:57Z

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.