The Lustre Distributed Lock Manager
-----------------------------------
[[ldlm]]

The discussion of the LDLM is deferred for now. We'll get into it soon
enough.

LDLM Structures
~~~~~~~~~~~~~~~

Lock Modes
^^^^^^^^^^

----
typedef enum {
        LCK_MINMODE = 0,
        LCK_EX      = 1,
        LCK_PW      = 2,
        LCK_PR      = 4,
        LCK_CW      = 8,
        LCK_CR      = 16,
        LCK_NL      = 32,
        LCK_GROUP   = 64,
        LCK_COS     = 128,
        LCK_MAXMODE
} ldlm_mode_t;
----

LDLM Extent
^^^^^^^^^^^

----
struct ldlm_extent {
        __u64 start;
        __u64 end;
        __u64 gid;
};
----

LDLM Flock Wire
^^^^^^^^^^^^^^^

----
struct ldlm_flock_wire {
        __u64 lfw_start;
        __u64 lfw_end;
        __u64 lfw_owner;
        __u32 lfw_padding;
        __u32 lfw_pid;
};
----

LDLM Inode Bits
^^^^^^^^^^^^^^^

----
struct ldlm_inodebits {
        __u64 bits;
};
----

LDLM Wire Policy Data
^^^^^^^^^^^^^^^^^^^^^

----
typedef union {
        struct ldlm_extent l_extent;
        struct ldlm_flock_wire l_flock;
        struct ldlm_inodebits l_inodebits;
} ldlm_wire_policy_data_t;
----

Resource Descriptor
^^^^^^^^^^^^^^^^^^^

----
struct ldlm_resource_desc {
        ldlm_type_t lr_type;
        __u32 lr_padding;       /* also fix lustre_swab_ldlm_resource_desc */
        struct ldlm_res_id lr_name;
};
----

The 'ldlm_type_t' is given by one of these values:
----
typedef enum {
        LDLM_PLAIN     = 10,
        LDLM_EXTENT    = 11,
        LDLM_FLOCK     = 12,
        LDLM_IBITS     = 13
} ldlm_type_t;
----

Lock Descriptor
^^^^^^^^^^^^^^^

----
struct ldlm_lock_desc {
        struct ldlm_resource_desc l_resource;
        ldlm_mode_t l_req_mode;
        ldlm_mode_t l_granted_mode;
        ldlm_wire_policy_data_t l_policy_data;
};
----

Lock Request
^^^^^^^^^^^^

----
#define LDLM_LOCKREQ_HANDLES 2
struct ldlm_request {
        __u32 lock_flags;
        __u32 lock_count;
        struct ldlm_lock_desc lock_desc;
        struct lustre_handle lock_handle[LDLM_LOCKREQ_HANDLES];
};
----

Lock Reply
^^^^^^^^^^

----
struct ldlm_reply {
        __u32 lock_flags;
        __u32 lock_padding;     /* also fix lustre_swab_ldlm_reply */
        struct ldlm_lock_desc lock_desc;
        struct lustre_handle lock_handle;
        __u64  lock_policy_res1;
        __u64  lock_policy_res2;
};
----

Lock Value Block
^^^^^^^^^^^^^^^^

A lock value block is part of reply messages from servers when an
LDLM_ENQUEUE command has been issued. There are two varieties. Which
is chosen depends on the target.

----
struct ost_lvb_v1 {
    __u64        lvb_size;
    obd_time     lvb_mtime;
    obd_time     lvb_atime;
    obd_time     lvb_ctime;
    __u64        lvb_blocks;
};
struct ost_lvb {
    __u64        lvb_size;
    obd_time     lvb_mtime;
    obd_time     lvb_atime;
    obd_time     lvb_ctime;
    __u64        lvb_blocks;
    __u32        lvb_mtime_ns;
    __u32        lvb_atime_ns;
    __u32        lvb_ctime_ns;
    __u32        lvb_padding;
};
----