Implement an memory-based OSD device with writeback support for Lustre.

It borrows lots of design from memory-based file systems such as tmpfs/ramfs.

The data is frist written into memory-based file system (called MemFS in short).

And then, the data can be flushed to the persistent storage in a delayed write-back manner.

TODO

• limiting for inodes and blocks.

• lprocfs support. Track OSD stats and access them via lprocfs.

• Use Maple Tree in new kernel to manage and access entries within a directory and Indexing access for FID seq and persistent node map setting, etc, al.

• Implement the functionalirty needed by LFSCK.

• Using a single storage target for a combined OST/MDT/MGT.

• Quota support.

• Writeback support with ldiskfs/ZFS or KV store as persistent backends.

• Add transcation support.