ocfs2 has a system file called "slot_map". A "slot" is a collection of files local to particular mounted node, including the journal and allocators that node is using. The slot map converts the slot number to a node number, so when a node dies, ocfs2 knows which slot to recover. The old ocfs2 slot map is a very limited. It has a physical maximum of 254 entries - specifically, it must fit within one disk block. It only allows node numbers up to 254, and cannot be extended past INT16_MAX (32767). This is a problem in the world of userspace cluster stacks, where the node numbers are often sparse and can be up to UINT32_MAX. It also has the structural problem that empty slots are signified by a magic number. That number happens to be -1 (0xFFFF). It makes for code that isn't as obvious as one would like. Thus, we introduce a new slot map format, referred to hence as the "extended slot map". The extended slot map is allocated as regular file space, and so is bound by i_size. The new format adds a "valid" field, distinct from the node number. Finally, it has room for extension should it be needed. The kernel code is available on the 'new-slot-map' branch of my git repository. View: http://oss.oracle.com/git/?p=jlbec/linux-2.6.git;a=shortlog;h=new-slot-map Pull: git pull git://oss.oracle.com/git/jlbec/linux-2.6.git new-slot-map The tools code is also available via git, in the 'new-slot-map' branch as well. View: http://oss.oracle.com/git/?p=ocfs2-tools.git;a=shortlog;h=new-slot-map Pull: git pull git://oss.oracle.com/git/ocfs2-tools.git new-slot-map -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
