+/**
+ * \defgroup nrs Network Request Scheduler
+ * @{
+ */
+struct ptlrpc_nrs_policy;
+struct ptlrpc_nrs_resource;
+struct ptlrpc_nrs_request;
+
+/**
+ * NRS control operations.
+ *
+ * These are common for all policies.
+ */
+enum ptlrpc_nrs_ctl {
+ /**
+ * Activate the policy.
+ */
+ PTLRPC_NRS_CTL_START,
+ /**
+ * Reserved for multiple primary policies, which may be a possibility
+ * in the future.
+ */
+ PTLRPC_NRS_CTL_STOP,
+ /**
+ * Recycle resources for inactive policies.
+ */
+ PTLRPC_NRS_CTL_SHRINK,
+ /**
+ * Not a valid opcode.
+ */
+ PTLRPC_NRS_CTL_INVALID,
+ /**
+ * Policies can start using opcodes from this value and onwards for
+ * their own purposes; the assigned value itself is arbitrary.
+ */
+ PTLRPC_NRS_CTL_1ST_POL_SPEC = 0x20,
+};
+
+/**
+ * NRS policy operations.
+ *
+ * These determine the behaviour of a policy, and are called in response to
+ * NRS core events.
+ */
+struct ptlrpc_nrs_pol_ops {
+ /**
+ * Called during policy registration; this operation is optional.
+ *
+ * \param[in] policy The policy being initialized
+ */
+ int (*op_policy_init) (struct ptlrpc_nrs_policy *policy);
+ /**
+ * Called during policy unregistration; this operation is optional.
+ *
+ * \param[in] policy The policy being unregistered/finalized
+ */
+ void (*op_policy_fini) (struct ptlrpc_nrs_policy *policy);
+ /**
+ * Called when activating a policy via lprocfs; policies allocate and
+ * initialize their resources here; this operation is optional.
+ *
+ * \param[in] policy The policy being started
+ *
+ * \see nrs_policy_start_locked()
+ */
+ int (*op_policy_start) (struct ptlrpc_nrs_policy *policy);
+ /**
+ * Called when deactivating a policy via lprocfs; policies deallocate
+ * their resources here; this operation is optional
+ *
+ * \param[in] policy The policy being stopped
+ *
+ * \see nrs_policy_stop_final()
+ */
+ void (*op_policy_stop) (struct ptlrpc_nrs_policy *policy);
+ /**
+ * Used for policy-specific operations; i.e. not generic ones like
+ * \e PTLRPC_NRS_CTL_START and \e PTLRPC_NRS_CTL_GET_INFO; analogous
+ * to an ioctl; this operation is optional.
+ *
+ * \param[in] policy The policy carrying out operation \a opc
+ * \param[in] opc The command operation being carried out
+ * \param[in,out] arg An generic buffer for communication between the
+ * user and the control operation
+ *
+ * \retval -ve error
+ * \retval 0 success
+ *
+ * \see ptlrpc_nrs_policy_control()
+ */
+ int (*op_policy_ctl) (struct ptlrpc_nrs_policy *policy,
+ enum ptlrpc_nrs_ctl opc, void *arg);
+
+ /**
+ * Called when obtaining references to the resources of the resource
+ * hierarchy for a request that has arrived for handling at the PTLRPC
+ * service. Policies should return -ve for requests they do not wish
+ * to handle. This operation is mandatory.
+ *
+ * \param[in] policy The policy we're getting resources for.
+ * \param[in] nrq The request we are getting resources for.
+ * \param[in] parent The parent resource of the resource being
+ * requested; set to NULL if none.
+ * \param[out] resp The resource is to be returned here; the
+ * fallback policy in an NRS head should
+ * \e always return a non-NULL pointer value.
+ * \param[in] moving_req When set, signifies that this is an attempt
+ * to obtain resources for a request being moved
+ * to the high-priority NRS head by
+ * ldlm_lock_reorder_req().
+ * This implies two things:
+ * 1. We are under obd_export::exp_rpc_lock and
+ * so should not sleep.
+ * 2. We should not perform non-idempotent or can
+ * skip performing idempotent operations that
+ * were carried out when resources were first
+ * taken for the request when it was initialized
+ * in ptlrpc_nrs_req_initialize().
+ *
+ * \retval 0, +ve The level of the returned resource in the resource
+ * hierarchy; currently only 0 (for a non-leaf resource)
+ * and 1 (for a leaf resource) are supported by the
+ * framework.
+ * \retval -ve error
+ *
+ * \see ptlrpc_nrs_req_initialize()
+ * \see ptlrpc_nrs_hpreq_add_nolock()
+ * \see ptlrpc_nrs_req_hp_move()
+ */
+ int (*op_res_get) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_request *nrq,
+ struct ptlrpc_nrs_resource *parent,
+ struct ptlrpc_nrs_resource **resp,
+ bool moving_req);
+ /**
+ * Called when releasing references taken for resources in the resource
+ * hierarchy for the request; this operation is optional.
+ *
+ * \param[in] policy The policy the resource belongs to
+ * \param[in] res The resource to be freed
+ *
+ * \see ptlrpc_nrs_req_finalize()
+ * \see ptlrpc_nrs_hpreq_add_nolock()
+ * \see ptlrpc_nrs_req_hp_move()
+ */
+ void (*op_res_put) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_resource *res);
+
+ /**
+ * Obtain a request for handling from the policy via polling; this
+ * operation is mandatory.
+ *
+ * \param[in] policy The policy to poll
+ *
+ * \retval NULL No erquest available for handling
+ * \retval valid-pointer The request polled for handling
+ *
+ * \see ptlrpc_nrs_req_poll_nolock()
+ */
+ struct ptlrpc_nrs_request *
+ (*op_req_poll) (struct ptlrpc_nrs_policy *policy);
+ /**
+ * Called when attempting to add a request to a policy for later
+ * handling; this operation is mandatory.
+ *
+ * \param[in] policy The policy on which to enqueue \a nrq
+ * \param[in] nrq The request to enqueue
+ *
+ * \retval 0 success
+ * \retval != 0 error
+ *
+ * \see ptlrpc_nrs_req_add_nolock()
+ */
+ int (*op_req_enqueue) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_request *nrq);
+ /**
+ * Removes a request from the policy's set of pending requests. Normally
+ * called after a request has been polled successfully from the policy
+ * for handling; this operation is mandatory.
+ *
+ * \param[in] policy The policy the request \a nrq belongs to
+ * \param[in] nrq The request to dequeue
+ *
+ * \see ptlrpc_nrs_req_del_nolock()
+ */
+ void (*op_req_dequeue) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_request *nrq);
+ /**
+ * Called before carrying out the request; should not block. Could be
+ * used for job/resource control; this operation is optional.
+ *
+ * \param[in] policy The policy which is starting to handle request
+ * \a nrq
+ * \param[in] nrq The request
+ *
+ * \pre spin_is_locked(&svcpt->scp_req_lock)
+ *
+ * \see ptlrpc_nrs_req_start_nolock()
+ */
+ void (*op_req_start) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_request *nrq);
+ /**
+ * Called after the request being carried out. Could be used for
+ * job/resource control; this operation is optional.
+ *
+ * \param[in] policy The policy which is stopping to handle request
+ * \a nrq
+ * \param[in] nrq The request
+ *
+ * \pre spin_is_locked(&svcpt->scp_req_lock)
+ *
+ * \see ptlrpc_nrs_req_stop_nolock()
+ */
+ void (*op_req_stop) (struct ptlrpc_nrs_policy *policy,
+ struct ptlrpc_nrs_request *nrq);
+ /**
+ * Registers the policy's lprocfs interface with a PTLRPC service.
+ *
+ * \param[in] svc The service
+ *
+ * \retval 0 success
+ * \retval != 0 error
+ */
+ int (*op_lprocfs_init) (struct ptlrpc_service *svc);
+ /**
+ * Unegisters the policy's lprocfs interface with a PTLRPC service.
+ *
+ * \param[in] svc The service
+ */
+ void (*op_lprocfs_fini) (struct ptlrpc_service *svc);
+};
+
+/**
+ * Policy flags
+ */
+enum nrs_policy_flags {
+ /**
+ * Fallback policy, use this flag only on a single supported policy per
+ * service. Do not use this flag for policies registering using
+ * ptlrpc_nrs_policy_register() (i.e. ones that are not in
+ * \e nrs_pols_builtin).
+ */
+ PTLRPC_NRS_FL_FALLBACK = (1 << 0),
+ /**
+ * Start policy immediately after registering.
+ */
+ PTLRPC_NRS_FL_REG_START = (1 << 1),
+ /**
+ * This is a polciy registering externally with NRS core, via
+ * ptlrpc_nrs_policy_register(), (i.e. one that is not in
+ * \e nrs_pols_builtin. Used to avoid ptlrpc_nrs_policy_register()
+ * racing with a policy start operation issued by the user via lprocfs.
+ */
+ PTLRPC_NRS_FL_REG_EXTERN = (1 << 2),
+};
+
+/**
+ * NRS queue type.
+ *
+ * Denotes whether an NRS instance is for handling normal or high-priority
+ * RPCs, or whether an operation pertains to one or both of the NRS instances
+ * in a service.
+ */
+enum ptlrpc_nrs_queue_type {
+ PTLRPC_NRS_QUEUE_REG,
+ PTLRPC_NRS_QUEUE_HP,
+ PTLRPC_NRS_QUEUE_BOTH,
+};
+
+/**
+ * NRS head
+ *
+ * A PTLRPC service has at least one NRS head instance for handling normal
+ * priority RPCs, and may optionally have a second NRS head instance for
+ * handling high-priority RPCs. Each NRS head maintains a list of available
+ * policies, of which one and only one policy is acting as the fallback policy,
+ * and optionally a different policy may be acting as the primary policy. For
+ * all RPCs handled by this NRS head instance, NRS core will first attempt to
+ * enqueue the RPC using the primary policy (if any). The fallback policy is
+ * used in the following cases:
+ * - when there was no primary policy in the
+ * ptlrpc_nrs_pol_state::NRS_POL_STATE_STARTED state at the time the request
+ * was initialized.
+ * - when the primary policy that was at the
+ * ptlrpc_nrs_pol_state::PTLRPC_NRS_POL_STATE_STARTED state at the time the
+ * RPC was initialized, denoted it did not wish, or for some other reason was
+ * not able to handle the request, by returning a non-valid NRS resource
+ * reference.
+ * - when the primary policy that was at the
+ * ptlrpc_nrs_pol_state::PTLRPC_NRS_POL_STATE_STARTED state at the time the
+ * RPC was initialized, fails later during the request enqueueing stage.
+ *
+ * \see nrs_resource_get_safe()
+ * \see nrs_request_enqueue()
+ */
+struct ptlrpc_nrs {
+ spinlock_t nrs_lock;
+ /** XXX Possibly replace svcpt->scp_req_lock with another lock here. */
+ /**
+ * Linkage into nrs_core_heads_list
+ */
+ cfs_list_t nrs_heads;
+ /**
+ * List of registered policies
+ */
+ cfs_list_t nrs_policy_list;
+ /**
+ * List of policies with queued requests. Policies that have any
+ * outstanding requests are queued here, and this list is queried
+ * in a round-robin manner from NRS core when obtaining a request
+ * for handling. This ensures that requests from policies that at some
+ * point transition away from the
+ * ptlrpc_nrs_pol_state::NRS_POL_STATE_STARTED state are drained.
+ */
+ cfs_list_t nrs_policy_queued;
+ /**
+ * Service partition for this NRS head
+ */
+ struct ptlrpc_service_part *nrs_svcpt;
+ /**
+ * Primary policy, which is the preferred policy for handling RPCs
+ */
+ struct ptlrpc_nrs_policy *nrs_policy_primary;
+ /**
+ * Fallback policy, which is the backup policy for handling RPCs
+ */
+ struct ptlrpc_nrs_policy *nrs_policy_fallback;
+ /**
+ * This NRS head handles either HP or regular requests
+ */
+ enum ptlrpc_nrs_queue_type nrs_queue_type;
+ /**
+ * # queued requests from all policies in this NRS head
+ */
+ unsigned long nrs_req_queued;
+ /**
+ * # scheduled requests from all policies in this NRS head
+ */
+ unsigned long nrs_req_started;
+ /**
+ * # policies on this NRS
+ * TODO: Can we avoid having this?
+ */
+ unsigned nrs_num_pols;
+ /**
+ * This NRS head is in progress of starting a policy
+ */
+ unsigned nrs_policy_starting:1;
+ /**
+ * In progress of shutting down the whole NRS head; used during
+ * unregistration
+ */
+ unsigned nrs_stopping:1;
+};
+
+#define NRS_POL_NAME_MAX 16
+
+/**
+ * NRS policy registering descriptor
+ *
+ * Is used to hold a description of a policy that can be passed to NRS core in
+ * order to register the policy with NRS heads in different PTLRPC services.
+ */
+struct ptlrpc_nrs_pol_desc {
+ /**
+ * Human-readable policy name
+ */
+ char pd_name[NRS_POL_NAME_MAX];
+ /**
+ * NRS operations for this policy
+ */
+ struct ptlrpc_nrs_pol_ops *pd_ops;
+ /**
+ * Service Compatibility function; this determines whether a policy is
+ * adequate for handling RPCs of a particular PTLRPC service.
+ *
+ * XXX:This should give the same result during policy
+ * registration and unregistration, and for all partitions of a
+ * service; so the result should not depend on temporal service
+ * or other properties, that may influence the result.
+ */
+ bool (*pd_compat) (struct ptlrpc_service *svc,
+ const struct ptlrpc_nrs_pol_desc *desc);
+ /**
+ * Optionally set for policies that support a single ptlrpc service,
+ * i.e. ones that have \a pd_compat set to nrs_policy_compat_one()
+ */
+ char *pd_compat_svc_name;
+ /**
+ * Bitmask of nrs_policy_flags
+ */
+ unsigned pd_flags;
+ /**
+ * Link into nrs_core::nrs_policies
+ */
+ cfs_list_t pd_list;
+};
+
+/**
+ * NRS policy state
+ *
+ * Policies transition from one state to the other during their lifetime
+ */
+enum ptlrpc_nrs_pol_state {
+ /**
+ * Not a valid policy state.
+ */
+ NRS_POL_STATE_INVALID,
+ /**
+ * For now, this state is used exclusively for policies that register
+ * externally to NRS core, i.e. ones that do so via
+ * ptlrpc_nrs_policy_register() and are not part of nrs_pols_builtin;
+ * it is used to prevent a race condition between the policy registering
+ * with more than one service partition while service is operational,
+ * and the user starting the policy via lprocfs.
+ *
+ * \see nrs_pol_make_avail()
+ */
+ NRS_POL_STATE_UNAVAIL,
+ /**
+ * Policies are at this state either at the start of their life, or
+ * transition here when the user selects a different policy to act
+ * as the primary one.
+ */
+ NRS_POL_STATE_STOPPED,
+ /**
+ * Policy is progress of stopping
+ */
+ NRS_POL_STATE_STOPPING,
+ /**
+ * Policy is in progress of starting
+ */
+ NRS_POL_STATE_STARTING,
+ /**
+ * A policy is in this state in two cases:
+ * - it is the fallback policy, which is always in this state.
+ * - it has been activated by the user; i.e. it is the primary policy,
+ */
+ NRS_POL_STATE_STARTED,
+};
+
+/**
+ * NRS policy information
+ *
+ * Used for obtaining information for the status of a policy via lprocfs
+ */
+struct ptlrpc_nrs_pol_info {
+ /**
+ * Policy name
+ */
+ char pi_name[NRS_POL_NAME_MAX];
+ /**
+ * Current policy state
+ */
+ enum ptlrpc_nrs_pol_state pi_state;
+ /**
+ * # RPCs enqueued for later dispatching by the policy
+ */
+ long pi_req_queued;
+ /**
+ * # RPCs started for dispatch by the policy
+ */
+ long pi_req_started;
+ /**
+ * Is this a fallback policy?
+ */
+ unsigned pi_fallback:1;
+};
+
+/**
+ * NRS policy
+ *
+ * There is one instance of this for each policy in each NRS head of each
+ * PTLRPC service partition.
+ */
+struct ptlrpc_nrs_policy {
+ /**
+ * Linkage into the NRS head's list of policies,
+ * ptlrpc_nrs:nrs_policy_list
+ */
+ cfs_list_t pol_list;
+ /**
+ * Linkage into the NRS head's list of policies with enqueued
+ * requests ptlrpc_nrs:nrs_policy_queued
+ */
+ cfs_list_t pol_list_queued;
+ /**
+ * Current state of this policy
+ */
+ enum ptlrpc_nrs_pol_state pol_state;
+ /**
+ * Bitmask of nrs_policy_flags
+ */
+ unsigned pol_flags;
+ /**
+ * # RPCs enqueued for later dispatching by the policy
+ */
+ long pol_req_queued;
+ /**
+ * # RPCs started for dispatch by the policy
+ */
+ long pol_req_started;
+ /**
+ * Usage Reference count taken on the policy instance
+ */
+ long pol_ref;
+ /**
+ * The NRS head this policy has been created at
+ */
+ struct ptlrpc_nrs *pol_nrs;
+ /**
+ * NRS operations for this policy; points to ptlrpc_nrs_pol_desc::pd_ops
+ */
+ struct ptlrpc_nrs_pol_ops *pol_ops;
+ /**
+ * Private policy data; varies by policy type
+ */
+ void *pol_private;
+ /**
+ * Human-readable policy name; point to ptlrpc_nrs_pol_desc::pd_name
+ */
+ char *pol_name;
+};
+
+/**
+ * NRS resource
+ *
+ * Resources are embedded into two types of NRS entities:
+ * - Inside NRS policies, in the policy's private data in
+ * ptlrpc_nrs_policy::pol_private
+ * - In objects that act as prime-level scheduling entities in different NRS
+ * policies; e.g. on a policy that performs round robin or similar order
+ * scheduling across client NIDs, there would be one NRS resource per unique
+ * client NID. On a policy which performs round robin scheduling across
+ * backend filesystem objects, there would be one resource associated with
+ * each of the backend filesystem objects partaking in the scheduling
+ * performed by the policy.
+ *
+ * NRS resources share a parent-child relationship, in which resources embedded
+ * in policy instances are the parent entities, with all scheduling entities
+ * a policy schedules across being the children, thus forming a simple resource
+ * hierarchy. This hierarchy may be extended with one or more levels in the
+ * future if the ability to have more than one primary policy is added.
+ *
+ * Upon request initialization, references to the then active NRS policies are
+ * taken and used to later handle the dispatching of the request with one of
+ * these policies.
+ *
+ * \see nrs_resource_get_safe()
+ * \see ptlrpc_nrs_req_add()
+ */
+struct ptlrpc_nrs_resource {
+ /**
+ * This NRS resource's parent; is NULL for resources embedded in NRS
+ * policy instances; i.e. those are top-level ones.
+ */
+ struct ptlrpc_nrs_resource *res_parent;
+ /**
+ * The policy associated with this resource.
+ */
+ struct ptlrpc_nrs_policy *res_policy;
+};
+
+enum {
+ NRS_RES_FALLBACK,
+ NRS_RES_PRIMARY,
+ NRS_RES_MAX
+};
+
+/* \name fifo
+ *
+ * FIFO policy
+ *
+ * This policy is a logical wrapper around previous, non-NRS functionality.
+ * It dispatches RPCs in the same order as they arrive from the network. This
+ * policy is currently used as the fallback policy, and the only enabled policy
+ * on all NRS heads of all PTLRPC service partitions.
+ * @{
+ */
+
+/**
+ * Private data structure for the FIFO policy
+ */
+struct nrs_fifo_head {
+ /**
+ * Resource object for policy instance.
+ */
+ struct ptlrpc_nrs_resource fh_res;
+ /**
+ * List of queued requests.
+ */
+ cfs_list_t fh_list;
+ /**
+ * For debugging purposes.
+ */
+ __u64 fh_sequence;
+};
+
+struct nrs_fifo_req {
+ /** request header, must be the first member of structure */
+ cfs_list_t fr_list;
+ __u64 fr_sequence;
+};
+
+/** @} fifo */
+
+/**
+ * NRS request
+ *
+ * Instances of this object exist embedded within ptlrpc_request; the main
+ * purpose of this object is to hold references to the request's resources
+ * for the lifetime of the request, and to hold properties that policies use
+ * use for determining the request's scheduling priority.
+ * */
+struct ptlrpc_nrs_request {
+ /**
+ * The request's resource hierarchy.
+ */
+ struct ptlrpc_nrs_resource *nr_res_ptrs[NRS_RES_MAX];
+ /**
+ * Index into ptlrpc_nrs_request::nr_res_ptrs of the resource of the
+ * policy that was used to enqueue the request.
+ *
+ * \see nrs_request_enqueue()
+ */
+ unsigned nr_res_idx;
+ unsigned nr_initialized:1;
+ unsigned nr_enqueued:1;
+ unsigned nr_dequeued:1;
+ unsigned nr_started:1;
+ unsigned nr_finalized:1;
+ cfs_binheap_node_t nr_node;
+
+ /**
+ * Policy-specific fields, used for determining a request's scheduling
+ * priority, and other supporting functionality.
+ */
+ union {
+ /**
+ * Fields for the FIFO policy
+ */
+ struct nrs_fifo_req fifo;
+ } nr_u;
+ /**
+ * Externally-registering policies may want to use this to allocate
+ * their own request properties.
+ */
+ void *ext;
+};
+
+/** @} nrs */
+
+/**
+ * Basic request prioritization operations structure.
+ * The whole idea is centered around locks and RPCs that might affect locks.
+ * When a lock is contended we try to give priority to RPCs that might lead
+ * to fastest release of that lock.
+ * Currently only implemented for OSTs only in a way that makes all
+ * IO and truncate RPCs that are coming from a locked region where a lock is
+ * contended a priority over other requests.
+ */