5 The 'lov_mds_md' structure contains the layout of a single file.
6 In replies to lock requests and other situations requiring
7 layout information from an MDT the 'lov_mds_md' information provides
8 details about the layout of a file across the OSTs. There may be
9 different types of layouts for different files, either 'lov_mds_md_v1'
10 or 'lov_mds_md_v3' as of Lustre 2.7, though they are very similar in
14 struct lov_mds_md_v1 {
18 __u32 lmm_stripe_size;
19 __u16 lmm_stripe_count;
21 struct lov_ost_data_v1 lmm_objects[0];
24 struct lov_mds_md_v3 {
28 __u32 lmm_stripe_size;
29 __u16 lmm_stripe_count;
31 char lmm_pool_name[16];
32 struct lov_ost_data_v1 lmm_objects[0];
36 The 'lmm_magic' field is filled in with the magic value that describes
37 the type of layout in use for a particular file. The rest of the layout
38 structure may vary depending on the magic value, but the 'lmm_magic'
39 value must be the first member of any valid file layout. The values
40 LOV_MAGIC_V1 (0x0BD10BD0) and LOV_MAGIC_V3 (0x0BD30BD0) are most
41 commonly used when the structure is in use. If the structure is in a
42 buffer of an RPC without the magic number in place, then the rest of
43 the structure is ignored.
45 The 'lmm_pattern' field describes the layout pattern within a particular
46 LOV_MAGIC layout type. Currently in Lustre 2.7 the most common pattern
47 is LOV_PATTERN_RAID0 (0x001). The high 16 bits of the 'lmm_pattern' field
48 may also contain flags that modify the layout. LOV_PATTERN_F_HOLE means
49 that there is a hole (missing object) within the layout, which is normally
50 caused by corruption or loss of the file layout that had to be rebuilt
51 by LFSCK. LOV_PATTERN_F_RELEASED is used by HSM to indicate that the
52 file data is not resident in the filesystem, but rather in an external
53 archive, so the layout is only a stub that describes the layout to use
54 when the file is restored.
56 The 'lmm_oi' field gives the identifier of the MDT object to which this
57 file belongs. See <<struct-ost-id>> for more details.
59 The 'lmm_stripe_size' field give the stripe size for the layout in bytes.
60 This is how many bytes will be on a particular OST object before going
63 The 'lmm_stripe_count' field gives how many OST objects the file is striped
66 The 'lmm_layout_gen' field is updated as the layout of the obeject is
67 updated. If the 'lmm_layout_gen' is modified, then clients can detect
68 the layout has changed when refreshing the layout after having lost the
71 The 'lmm_pool_name' field is only in LOV_MAGIC_V3 layouts, and contains
72 the name of the OST pool used during the creation of the layout.
74 For instantiated layouts, 'lmm_objects' array contains 'lmm_stripe_count'
75 'lov_ost_data_v1' structures with the per-stripe data for each OST object
76 in the layout. For uninstantiated layout templates, there will not be any
77 entries in the 'lmm_objects' array, which can be determined by the overall
81 struct lov_ost_data_v1 { /* per-stripe data structure (little-endian)*/
82 struct ost_id l_ost_oi; /* OST object ID */
83 __u32 l_ost_gen; /* generation of this l_ost_idx */
84 __u32 l_ost_idx; /* OST index in LOV (lov_tgt_desc->tgts) */
87 [[struct-lov-ost-data-v1]]
89 The 'lov_ost_data_v1' structure is used for both LOV_MAGIC_V1 and
90 LOV_MAGIC_V3 types to describe the OST objects allocated to this
91 layout, one per object.
93 'l_ost_id' identifies the object on the OST specified by 'l_ost_idx'.
94 It may contain a OST object ID or a FID as described in <<struct-ost-id>>.
95 The 'l_ost_gen' field is currently unused.