MDS Lock Value Block
^^^^^^^^^^^^^^^^^^^^
[[struct-lov-mds-md]]

The 'lov_mds_md' structure is a Lock Value Block (LVB) for layout
locks. In replies to lock requests and other situations requiring
layout information from an MDT the 'lov_mds_md' information provides
details about the layout of a file across the OSTs.

----
struct lov_mds_md {
	__u32 lmm_magic;
	__u32 lmm_pattern;
	struct ost_id	lmm_oi;
	__u32 lmm_stripe_size;
	__u16 lmm_stripe_count;
	__u16 lmm_layout_gen;
	struct lov_ost_data_v1 lmm_objects[0];
};
----

The 'lmm_magic' field is filled in with the value LOV_MAGIC
(0x0BD10BD0) when the structure is in use. If the structure is in a
buffer of an RPC without the magic number in place, then the rest of
the structure is ignored.

The 'lmm_pattern' field is only ever set to LOV_PATTERN_RAID0
(0x001).

The 'lmm_oi' field gives the LOV object ID for the first OST of the
layout. This is the OST where striping will begin.

The 'lmm_stripe_size' field give the stripe size for the object. This
is how many bytes will be on a particular OST before going to the next
stripe.

The 'lmm_stripe_count' field gives how many OSTs the file is striped
over.

The 'lmm_layout_gen' field ges updated as the layout of the obeject is
updated. This way out-of-date references to the layout can be
recognized.

The 'lmm_objects' array gives per-stripe data for more complex
(non-uniform) layouts.