remarkable-linux/drivers/staging/ramster/tmem.c

/*
 * In-kernel transcendent memory (generic implementation)
 *
 * Copyright (c) 2009-2012, Dan Magenheimer, Oracle Corp.
 *
 * The primary purpose of Transcedent Memory ("tmem") is to map object-oriented
 * "handles" (triples containing a pool id, and object id, and an index), to
 * pages in a page-accessible memory (PAM).  Tmem references the PAM pages via
 * an abstract "pampd" (PAM page-descriptor), which can be operated on by a
 * set of functions (pamops).  Each pampd contains some representation of
 * PAGE_SIZE bytes worth of data. For those familiar with key-value stores,
 * the tmem handle is a three-level hierarchical key, and the value is always
 * reconstituted (but not necessarily stored) as PAGE_SIZE bytes and is
 * referenced in the datastore by the pampd.  The hierarchy is required
 * to ensure that certain invalidation functions can be performed efficiently
 * (i.e. flush all indexes associated with this object_id, or
 * flush all objects associated with this pool).
 *
 * Tmem must support potentially millions of pages and must be able to insert,
 * find, and delete these pages at a potential frequency of thousands per
 * second concurrently across many CPUs, (and, if used with KVM, across many
 * vcpus across many guests).  Tmem is tracked with a hierarchy of data
 * structures, organized by the elements in the handle-tuple: pool_id,
 * object_id, and page index.  One or more "clients" (e.g. guests) each
 * provide one or more tmem_pools.  Each pool, contains a hash table of
 * rb_trees of tmem_objs.  Each tmem_obj contains a radix-tree-like tree
 * of pointers, with intermediate nodes called tmem_objnodes.  Each leaf
 * pointer in this tree points to a pampd, which is accessible only through
 * a small set of callbacks registered by the PAM implementation (see
 * tmem_register_pamops). Tmem only needs to memory allocation for objs
 * and objnodes and this is done via a set of callbacks that must be
 * registered by the tmem host implementation (e.g. see tmem_register_hostops).
 */

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
#ifdef CONFIG_RAMSTER
#include <linux/delay.h>
#endif

#include "tmem.h"

/* data structure sentinels used for debugging... see tmem.h */
#define POOL_SENTINEL 0x87658765
#define OBJ_SENTINEL 0x12345678
#define OBJNODE_SENTINEL 0xfedcba09

/*
 * A tmem host implementation must use this function to register callbacks
 * for memory allocation.
 */
static struct tmem_hostops tmem_hostops;

static void tmem_objnode_tree_init(void);

void tmem_register_hostops(struct tmem_hostops *m)
{
	tmem_objnode_tree_init();
	tmem_hostops = *m;
}

/*
 * A tmem host implementation must use this function to register
 * callbacks for a page-accessible memory (PAM) implementation.
 */
static struct tmem_pamops tmem_pamops;

void tmem_register_pamops(struct tmem_pamops *m)
{
	tmem_pamops = *m;
}

/*
 * Oid's are potentially very sparse and tmem_objs may have an indeterminately
 * short life, being added and deleted at a relatively high frequency.
 * So an rb_tree is an ideal data structure to manage tmem_objs.  But because
 * of the potentially huge number of tmem_objs, each pool manages a hashtable
 * of rb_trees to reduce search, insert, delete, and rebalancing time.
 * Each hashbucket also has a lock to manage concurrent access and no
 * searches, inserts, or deletions can be performed unless the lock is held.
 * As a result, care must be taken to ensure tmem routines are not called
 * recursively; the vast majority of the time, a recursive call may work
 * but a deadlock will occur a small fraction of the time due to the
 * hashbucket lock.
 *
 * The following routines manage tmem_objs.  In all of these routines,
 * the hashbucket lock is already held.
 */

/* Search for object==oid in pool, returns object if found. */
static struct tmem_obj *__tmem_obj_find(struct tmem_hashbucket *hb,
					struct tmem_oid *oidp,
					struct rb_node **parent,
					struct rb_node ***link)
{
	struct rb_node *_parent = NULL, **rbnode;
	struct tmem_obj *obj = NULL;

	rbnode = &hb->obj_rb_root.rb_node;
	while (*rbnode) {
		BUG_ON(RB_EMPTY_NODE(*rbnode));
		_parent = *rbnode;
		obj = rb_entry(*rbnode, struct tmem_obj,
			       rb_tree_node);
		switch (tmem_oid_compare(oidp, &obj->oid)) {
		case 0: /* equal */
			goto out;
		case -1:
			rbnode = &(*rbnode)->rb_left;
			break;
		case 1:
			rbnode = &(*rbnode)->rb_right;
			break;
		}
	}

	if (parent)
		*parent = _parent;
	if (link)
		*link = rbnode;
	obj = NULL;
out:
	return obj;
}

static struct tmem_obj *tmem_obj_find(struct tmem_hashbucket *hb,
					struct tmem_oid *oidp)
{
	return __tmem_obj_find(hb, oidp, NULL, NULL);
}

static void tmem_pampd_destroy_all_in_obj(struct tmem_obj *, bool);

/* Free an object that has no more pampds in it. */
static void tmem_obj_free(struct tmem_obj *obj, struct tmem_hashbucket *hb)
{
	struct tmem_pool *pool;

	BUG_ON(obj == NULL);
	ASSERT_SENTINEL(obj, OBJ);
	BUG_ON(obj->pampd_count > 0);
	pool = obj->pool;
	BUG_ON(pool == NULL);
	if (obj->objnode_tree_root != NULL) /* may be "stump" with no leaves */
		tmem_pampd_destroy_all_in_obj(obj, false);
	BUG_ON(obj->objnode_tree_root != NULL);
	BUG_ON((long)obj->objnode_count != 0);
	atomic_dec(&pool->obj_count);
	BUG_ON(atomic_read(&pool->obj_count) < 0);
	INVERT_SENTINEL(obj, OBJ);
	obj->pool = NULL;
	tmem_oid_set_invalid(&obj->oid);
	rb_erase(&obj->rb_tree_node, &hb->obj_rb_root);
}

/*
 * Initialize, and insert an tmem_object_root (called only if find failed).
 */
static void tmem_obj_init(struct tmem_obj *obj, struct tmem_hashbucket *hb,
					struct tmem_pool *pool,
					struct tmem_oid *oidp)
{
	struct rb_root *root = &hb->obj_rb_root;
	struct rb_node **new = NULL, *parent = NULL;

	BUG_ON(pool == NULL);
	atomic_inc(&pool->obj_count);
	obj->objnode_tree_height = 0;
	obj->objnode_tree_root = NULL;
	obj->pool = pool;
	obj->oid = *oidp;
	obj->objnode_count = 0;
	obj->pampd_count = 0;
#ifdef CONFIG_RAMSTER
	if (tmem_pamops.new_obj != NULL)
		(*tmem_pamops.new_obj)(obj);
#endif
	SET_SENTINEL(obj, OBJ);

	if (__tmem_obj_find(hb, oidp, &parent, &new))
		BUG();

	rb_link_node(&obj->rb_tree_node, parent, new);
	rb_insert_color(&obj->rb_tree_node, root);
}

/*
 * Tmem is managed as a set of tmem_pools with certain attributes, such as
 * "ephemeral" vs "persistent".  These attributes apply to all tmem_objs
 * and all pampds that belong to a tmem_pool.  A tmem_pool is created
 * or deleted relatively rarely (for example, when a filesystem is
 * mounted or unmounted).
 */

/* flush all data from a pool and, optionally, free it */
static void tmem_pool_flush(struct tmem_pool *pool, bool destroy)
{
	struct rb_node *rbnode;
	struct tmem_obj *obj;
	struct tmem_hashbucket *hb = &pool->hashbucket[0];
	int i;

	BUG_ON(pool == NULL);
	for (i = 0; i < TMEM_HASH_BUCKETS; i++, hb++) {
		spin_lock(&hb->lock);
		rbnode = rb_first(&hb->obj_rb_root);
		while (rbnode != NULL) {
			obj = rb_entry(rbnode, struct tmem_obj, rb_tree_node);
			rbnode = rb_next(rbnode);
			tmem_pampd_destroy_all_in_obj(obj, true);
			tmem_obj_free(obj, hb);
			(*tmem_hostops.obj_free)(obj, pool);
		}
		spin_unlock(&hb->lock);
	}
	if (destroy)
		list_del(&pool->pool_list);
}

/*
 * A tmem_obj contains a radix-tree-like tree in which the intermediate
 * nodes are called tmem_objnodes.  (The kernel lib/radix-tree.c implementation
 * is very specialized and tuned for specific uses and is not particularly
 * suited for use from this code, though some code from the core algorithms has
 * been reused, thus the copyright notices below).  Each tmem_objnode contains
 * a set of pointers which point to either a set of intermediate tmem_objnodes
 * or a set of of pampds.
 *
 * Portions Copyright (C) 2001 Momchil Velikov
 * Portions Copyright (C) 2001 Christoph Hellwig
 * Portions Copyright (C) 2005 SGI, Christoph Lameter <clameter@sgi.com>
 */

struct tmem_objnode_tree_path {
	struct tmem_objnode *objnode;
	int offset;
};

/* objnode height_to_maxindex translation */
static unsigned long tmem_objnode_tree_h2max[OBJNODE_TREE_MAX_PATH + 1];

static void tmem_objnode_tree_init(void)
{
	unsigned int ht, tmp;

	for (ht = 0; ht < ARRAY_SIZE(tmem_objnode_tree_h2max); ht++) {
		tmp = ht * OBJNODE_TREE_MAP_SHIFT;
		if (tmp >= OBJNODE_TREE_INDEX_BITS)
			tmem_objnode_tree_h2max[ht] = ~0UL;
		else
			tmem_objnode_tree_h2max[ht] =
			    (~0UL >> (OBJNODE_TREE_INDEX_BITS - tmp - 1)) >> 1;
	}
}

static struct tmem_objnode *tmem_objnode_alloc(struct tmem_obj *obj)
{
	struct tmem_objnode *objnode;

	ASSERT_SENTINEL(obj, OBJ);
	BUG_ON(obj->pool == NULL);
	ASSERT_SENTINEL(obj->pool, POOL);
	objnode = (*tmem_hostops.objnode_alloc)(obj->pool);
	if (unlikely(objnode == NULL))
		goto out;
	objnode->obj = obj;
	SET_SENTINEL(objnode, OBJNODE);
	memset(&objnode->slots, 0, sizeof(objnode->slots));
	objnode->slots_in_use = 0;
	obj->objnode_count++;
out:
	return objnode;
}

static void tmem_objnode_free(struct tmem_objnode *objnode)
{
	struct tmem_pool *pool;
	int i;

	BUG_ON(objnode == NULL);
	for (i = 0; i < OBJNODE_TREE_MAP_SIZE; i++)
		BUG_ON(objnode->slots[i] != NULL);
	ASSERT_SENTINEL(objnode, OBJNODE);
	INVERT_SENTINEL(objnode, OBJNODE);
	BUG_ON(objnode->obj == NULL);
	ASSERT_SENTINEL(objnode->obj, OBJ);
	pool = objnode->obj->pool;
	BUG_ON(pool == NULL);
	ASSERT_SENTINEL(pool, POOL);
	objnode->obj->objnode_count--;
	objnode->obj = NULL;
	(*tmem_hostops.objnode_free)(objnode, pool);
}

/*
 * Lookup index in object and return associated pampd (or NULL if not found).
 */
static void **__tmem_pampd_lookup_in_obj(struct tmem_obj *obj, uint32_t index)
{
	unsigned int height, shift;
	struct tmem_objnode **slot = NULL;

	BUG_ON(obj == NULL);
	ASSERT_SENTINEL(obj, OBJ);
	BUG_ON(obj->pool == NULL);
	ASSERT_SENTINEL(obj->pool, POOL);

	height = obj->objnode_tree_height;
	if (index > tmem_objnode_tree_h2max[obj->objnode_tree_height])
		goto out;
	if (height == 0 && obj->objnode_tree_root) {
		slot = &obj->objnode_tree_root;
		goto out;
	}
	shift = (height-1) * OBJNODE_TREE_MAP_SHIFT;
	slot = &obj->objnode_tree_root;
	while (height > 0) {
		if (*slot == NULL)
			goto out;
		slot = (struct tmem_objnode **)
			((*slot)->slots +
			 ((index >> shift) & OBJNODE_TREE_MAP_MASK));
		shift -= OBJNODE_TREE_MAP_SHIFT;
		height--;
	}
out:
	return slot != NULL ? (void **)slot : NULL;
}

static void *tmem_pampd_lookup_in_obj(struct tmem_obj *obj, uint32_t index)
{
	struct tmem_objnode **slot;

	slot = (struct tmem_objnode **)__tmem_pampd_lookup_in_obj(obj, index);
	return slot != NULL ? *slot : NULL;
}

#ifdef CONFIG_RAMSTER
static void *tmem_pampd_replace_in_obj(struct tmem_obj *obj, uint32_t index,
					void *new_pampd, bool no_free)
{
	struct tmem_objnode **slot;
	void *ret = NULL;

	slot = (struct tmem_objnode **)__tmem_pampd_lookup_in_obj(obj, index);
	if ((slot != NULL) && (*slot != NULL)) {
		void *old_pampd = *(void **)slot;
		*(void **)slot = new_pampd;
		if (!no_free)
			(*tmem_pamops.free)(old_pampd, obj->pool,
						NULL, 0, false);
		ret = new_pampd;
	}
	return ret;
}
#endif

static int tmem_pampd_add_to_obj(struct tmem_obj *obj, uint32_t index,
					void *pampd)
{
	int ret = 0;
	struct tmem_objnode *objnode = NULL, *newnode, *slot;
	unsigned int height, shift;
	int offset = 0;

	/* if necessary, extend the tree to be higher  */
	if (index > tmem_objnode_tree_h2max[obj->objnode_tree_height]) {
		height = obj->objnode_tree_height + 1;
		if (index > tmem_objnode_tree_h2max[height])
			while (index > tmem_objnode_tree_h2max[height])
				height++;
		if (obj->objnode_tree_root == NULL) {
			obj->objnode_tree_height = height;
			goto insert;
		}
		do {
			newnode = tmem_objnode_alloc(obj);
			if (!newnode) {
				ret = -ENOMEM;
				goto out;
			}
			newnode->slots[0] = obj->objnode_tree_root;
			newnode->slots_in_use = 1;
			obj->objnode_tree_root = newnode;
			obj->objnode_tree_height++;
		} while (height > obj->objnode_tree_height);
	}
insert:
	slot = obj->objnode_tree_root;
	height = obj->objnode_tree_height;
	shift = (height-1) * OBJNODE_TREE_MAP_SHIFT;
	while (height > 0) {
		if (slot == NULL) {
			/* add a child objnode.  */
			slot = tmem_objnode_alloc(obj);
			if (!slot) {
				ret = -ENOMEM;
				goto out;
			}
			if (objnode) {

				objnode->slots[offset] = slot;
				objnode->slots_in_use++;
			} else
				obj->objnode_tree_root = slot;
		}
		/* go down a level */
		offset = (index >> shift) & OBJNODE_TREE_MAP_MASK;
		objnode = slot;
		slot = objnode->slots[offset];
		shift -= OBJNODE_TREE_MAP_SHIFT;
		height--;
	}
	BUG_ON(slot != NULL);
	if (objnode) {
		objnode->slots_in_use++;
		objnode->slots[offset] = pampd;
	} else
		obj->objnode_tree_root = pampd;
	obj->pampd_count++;
out:
	return ret;
}

static void *tmem_pampd_delete_from_obj(struct tmem_obj *obj, uint32_t index)
{
	struct tmem_objnode_tree_path path[OBJNODE_TREE_MAX_PATH + 1];
	struct tmem_objnode_tree_path *pathp = path;
	struct tmem_objnode *slot = NULL;
	unsigned int height, shift;
	int offset;

	BUG_ON(obj == NULL);
	ASSERT_SENTINEL(obj, OBJ);
	BUG_ON(obj->pool == NULL);
	ASSERT_SENTINEL(obj->pool, POOL);
	height = obj->objnode_tree_height;
	if (index > tmem_objnode_tree_h2max[height])
		goto out;
	slot = obj->objnode_tree_root;
	if (height == 0 && obj->objnode_tree_root) {
		obj->objnode_tree_root = NULL;
		goto out;
	}
	shift = (height - 1) * OBJNODE_TREE_MAP_SHIFT;
	pathp->objnode = NULL;
	do {
		if (slot == NULL)
			goto out;
		pathp++;
		offset = (index >> shift) & OBJNODE_TREE_MAP_MASK;
		pathp->offset = offset;
		pathp->objnode = slot;
		slot = slot->slots[offset];
		shift -= OBJNODE_TREE_MAP_SHIFT;
		height--;
	} while (height > 0);
	if (slot == NULL)
		goto out;
	while (pathp->objnode) {
		pathp->objnode->slots[pathp->offset] = NULL;
		pathp->objnode->slots_in_use--;
		if (pathp->objnode->slots_in_use) {
			if (pathp->objnode == obj->objnode_tree_root) {
				while (obj->objnode_tree_height > 0 &&
				  obj->objnode_tree_root->slots_in_use == 1 &&
				  obj->objnode_tree_root->slots[0]) {
					struct tmem_objnode *to_free =
						obj->objnode_tree_root;

					obj->objnode_tree_root =
							to_free->slots[0];
					obj->objnode_tree_height--;
					to_free->slots[0] = NULL;
					to_free->slots_in_use = 0;
					tmem_objnode_free(to_free);
				}
			}
			goto out;
		}
		tmem_objnode_free(pathp->objnode); /* 0 slots used, free it */
		pathp--;
	}
	obj->objnode_tree_height = 0;
	obj->objnode_tree_root = NULL;

out:
	if (slot != NULL)
		obj->pampd_count--;
	BUG_ON(obj->pampd_count < 0);
	return slot;
}

/* Recursively walk the objnode_tree destroying pampds and objnodes. */
static void tmem_objnode_node_destroy(struct tmem_obj *obj,
					struct tmem_objnode *objnode,
					unsigned int ht)
{
	int i;

	if (ht == 0)
		return;
	for (i = 0; i < OBJNODE_TREE_MAP_SIZE; i++) {
		if (objnode->slots[i]) {
			if (ht == 1) {
				obj->pampd_count--;
				(*tmem_pamops.free)(objnode->slots[i],
						obj->pool, NULL, 0, true);
				objnode->slots[i] = NULL;
				continue;
			}
			tmem_objnode_node_destroy(obj, objnode->slots[i], ht-1);
			tmem_objnode_free(objnode->slots[i]);
			objnode->slots[i] = NULL;
		}
	}
}

static void tmem_pampd_destroy_all_in_obj(struct tmem_obj *obj,
						bool pool_destroy)
{
	if (obj->objnode_tree_root == NULL)
		return;
	if (obj->objnode_tree_height == 0) {
		obj->pampd_count--;
		(*tmem_pamops.free)(obj->objnode_tree_root,
					obj->pool, NULL, 0, true);
	} else {
		tmem_objnode_node_destroy(obj, obj->objnode_tree_root,
					obj->objnode_tree_height);
		tmem_objnode_free(obj->objnode_tree_root);
		obj->objnode_tree_height = 0;
	}
	obj->objnode_tree_root = NULL;
#ifdef CONFIG_RAMSTER
	if (tmem_pamops.free_obj != NULL)
		(*tmem_pamops.free_obj)(obj->pool, obj, pool_destroy);
#endif
}

/*
 * Tmem is operated on by a set of well-defined actions:
 * "put", "get", "flush", "flush_object", "new pool" and "destroy pool".
 * (The tmem ABI allows for subpages and exchanges but these operations
 * are not included in this implementation.)
 *
 * These "tmem core" operations are implemented in the following functions.
 */

/*
 * "Put" a page, e.g. associate the passed pampd with the passed handle.
 * Tmem_put is complicated by a corner case: What if a page with matching
 * handle already exists in tmem?  To guarantee coherency, one of two
 * actions is necessary: Either the data for the page must be overwritten,
 * or the page must be "flushed" so that the data is not accessible to a
 * subsequent "get".  Since these "duplicate puts" are relatively rare,
 * this implementation always flushes for simplicity.
 */
int tmem_put(struct tmem_pool *pool, struct tmem_oid *oidp, uint32_t index,
		bool raw, void *pampd_to_use)
{
	struct tmem_obj *obj = NULL, *objfound = NULL, *objnew = NULL;
	void *pampd = NULL, *pampd_del = NULL;
	int ret = -ENOMEM;
	struct tmem_hashbucket *hb;

	hb = &pool->hashbucket[tmem_oid_hash(oidp)];
	spin_lock(&hb->lock);
	obj = objfound = tmem_obj_find(hb, oidp);
	if (obj != NULL) {
		pampd = tmem_pampd_lookup_in_obj(objfound, index);
		if (pampd != NULL) {
			/* if found, is a dup put, flush the old one */
			pampd_del = tmem_pampd_delete_from_obj(obj, index);
			BUG_ON(pampd_del != pampd);
			(*tmem_pamops.free)(pampd, pool, oidp, index, true);
			if (obj->pampd_count == 0) {
				objnew = obj;
				objfound = NULL;
			}
			pampd = NULL;
		}
	} else {
		obj = objnew = (*tmem_hostops.obj_alloc)(pool);
		if (unlikely(obj == NULL)) {
			ret = -ENOMEM;
			goto out;
		}
		tmem_obj_init(obj, hb, pool, oidp);
	}
	BUG_ON(obj == NULL);
	BUG_ON(((objnew != obj) && (objfound != obj)) || (objnew == objfound));
	pampd = pampd_to_use;
	BUG_ON(pampd_to_use == NULL);
	ret = tmem_pampd_add_to_obj(obj, index, pampd);
	if (unlikely(ret == -ENOMEM))
		/* may have partially built objnode tree ("stump") */
		goto delete_and_free;
	(*tmem_pamops.create_finish)(pampd, is_ephemeral(pool));
	goto out;

delete_and_free:
	(void)tmem_pampd_delete_from_obj(obj, index);
	if (pampd)
		(*tmem_pamops.free)(pampd, pool, NULL, 0, true);
	if (objnew) {
		tmem_obj_free(objnew, hb);
		(*tmem_hostops.obj_free)(objnew, pool);
	}
out:
	spin_unlock(&hb->lock);
	return ret;
}

#ifdef CONFIG_RAMSTER
/*
 * For ramster only:  The following routines provide a two-step sequence
 * to allow the caller to replace a pampd in the tmem data structures with
 * another pampd. Here, we lookup the passed handle and, if found, return the
 * associated pampd and object, leaving the hashbucket locked and returning
 * a reference to it.  The caller is expected to immediately call the
 * matching tmem_localify_finish routine which will handles the replacement
 * and unlocks the hashbucket.
 */
void *tmem_localify_get_pampd(struct tmem_pool *pool, struct tmem_oid *oidp,
				uint32_t index, struct tmem_obj **ret_obj,
				void **saved_hb)
{
	struct tmem_hashbucket *hb;
	struct tmem_obj *obj = NULL;
	void *pampd = NULL;

	hb = &pool->hashbucket[tmem_oid_hash(oidp)];
	spin_lock(&hb->lock);
	obj = tmem_obj_find(hb, oidp);
	if (likely(obj != NULL))
		pampd = tmem_pampd_lookup_in_obj(obj, index);
	*ret_obj = obj;
	*saved_hb = (void *)hb;
	/* note, hashbucket remains locked */
	return pampd;
}

void tmem_localify_finish(struct tmem_obj *obj, uint32_t index,
			  void *pampd, void *saved_hb, bool delete)
{
	struct tmem_hashbucket *hb = (struct tmem_hashbucket *)saved_hb;

	BUG_ON(!spin_is_locked(&hb->lock));
	if (pampd != NULL) {
		BUG_ON(obj == NULL);
		(void)tmem_pampd_replace_in_obj(obj, index, pampd, 1);
		(*tmem_pamops.create_finish)(pampd, is_ephemeral(obj->pool));
	} else if (delete) {
		BUG_ON(obj == NULL);
		(void)tmem_pampd_delete_from_obj(obj, index);
	}
	spin_unlock(&hb->lock);
}

/*
 * For ramster only.  Helper function to support asynchronous tmem_get.
 */
static int tmem_repatriate(void **ppampd, struct tmem_hashbucket *hb,
				struct tmem_pool *pool, struct tmem_oid *oidp,
				uint32_t index, bool free, char *data)
{
	void *old_pampd = *ppampd, *new_pampd = NULL;
	bool intransit = false;
	int ret = 0;

	if (!is_ephemeral(pool))
		new_pampd = (*tmem_pamops.repatriate_preload)(
				old_pampd, pool, oidp, index, &intransit);
	if (intransit)
		ret = -EAGAIN;
	else if (new_pampd != NULL)
		*ppampd = new_pampd;
	/* must release the hb->lock else repatriate can't sleep */
	spin_unlock(&hb->lock);
	if (!intransit)
		ret = (*tmem_pamops.repatriate)(old_pampd, new_pampd, pool,
						oidp, index, free, data);
	if (ret == -EAGAIN) {
		/* rare I think, but should cond_resched()??? */
		usleep_range(10, 1000);
	} else if (ret == -ENOTCONN || ret == -EHOSTDOWN) {
		ret = -1;
	} else if (ret != 0 && ret != -ENOENT) {
		ret = -1;
	}
	/* note hb->lock has now been unlocked */
	return ret;
}

/*
 * For ramster only.  If a page in tmem matches the handle, replace the
 * page so that any subsequent "get" gets the new page.  Returns 0 if
 * there was a page to replace, else returns -1.
 */
int tmem_replace(struct tmem_pool *pool, struct tmem_oid *oidp,
			uint32_t index, void *new_pampd)
{
	struct tmem_obj *obj;
	int ret = -1;
	struct tmem_hashbucket *hb;

	hb = &pool->hashbucket[tmem_oid_hash(oidp)];
	spin_lock(&hb->lock);
	obj = tmem_obj_find(hb, oidp);
	if (obj == NULL)
		goto out;
	new_pampd = tmem_pampd_replace_in_obj(obj, index, new_pampd, 0);
	/* if we bug here, pamops wasn't properly set up for ramster */
	BUG_ON(tmem_pamops.replace_in_obj == NULL);
	ret = (*tmem_pamops.replace_in_obj)(new_pampd, obj);
out:
	spin_unlock(&hb->lock);
	return ret;
}
#endif

/*
 * "Get" a page, e.g. if a pampd can be found matching the passed handle,
 * use a pamops callback to recreated the page from the pampd with the
 * matching handle.  By tmem definition, when a "get" is successful on
 * an ephemeral page, the page is "flushed", and when a "get" is successful
 * on a persistent page, the page is retained in tmem.  Note that to preserve
 * coherency, "get" can never be skipped if tmem contains the data.
 * That is, if a get is done with a certain handle and fails, any
 * subsequent "get" must also fail (unless of course there is a
 * "put" done with the same handle).
 */
int tmem_get(struct tmem_pool *pool, struct tmem_oid *oidp, uint32_t index,
		char *data, size_t *sizep, bool raw, int get_and_free)
{
	struct tmem_obj *obj;
	void *pampd = NULL;
	bool ephemeral = is_ephemeral(pool);
	int ret = -1;
	struct tmem_hashbucket *hb;
	bool free = (get_and_free == 1) || ((get_and_free == 0) && ephemeral);
	bool lock_held = false;
	void **ppampd;

	do {
		hb = &pool->hashbucket[tmem_oid_hash(oidp)];
		spin_lock(&hb->lock);
		lock_held = true;
		obj = tmem_obj_find(hb, oidp);
		if (obj == NULL)
			goto out;
		ppampd = __tmem_pampd_lookup_in_obj(obj, index);
		if (ppampd == NULL)
			goto out;
#ifdef CONFIG_RAMSTER
		if ((tmem_pamops.is_remote != NULL) &&
		     tmem_pamops.is_remote(*ppampd)) {
			ret = tmem_repatriate(ppampd, hb, pool, oidp,
						index, free, data);
			/* tmem_repatriate releases hb->lock */
			lock_held = false;
			*sizep = PAGE_SIZE;
			if (ret != -EAGAIN)
				goto out;
		}
#endif
	} while (ret == -EAGAIN);
	if (free)
		pampd = tmem_pampd_delete_from_obj(obj, index);
	else
		pampd = tmem_pampd_lookup_in_obj(obj, index);
	if (pampd == NULL)
		goto out;
	if (free) {
		if (obj->pampd_count == 0) {
			tmem_obj_free(obj, hb);
			(*tmem_hostops.obj_free)(obj, pool);
			obj = NULL;
		}
	}
	if (free)
		ret = (*tmem_pamops.get_data_and_free)(
				data, sizep, raw, pampd, pool, oidp, index);
	else
		ret = (*tmem_pamops.get_data)(
				data, sizep, raw, pampd, pool, oidp, index);
	if (ret < 0)
		goto out;
	ret = 0;
out:
	if (lock_held)
		spin_unlock(&hb->lock);
	return ret;
}

/*
 * If a page in tmem matches the handle, "flush" this page from tmem such
 * that any subsequent "get" does not succeed (unless, of course, there
 * was another "put" with the same handle).
 */
int tmem_flush_page(struct tmem_pool *pool,
				struct tmem_oid *oidp, uint32_t index)
{
	struct tmem_obj *obj;
	void *pampd;
	int ret = -1;
	struct tmem_hashbucket *hb;

	hb = &pool->hashbucket[tmem_oid_hash(oidp)];
	spin_lock(&hb->lock);
	obj = tmem_obj_find(hb, oidp);
	if (obj == NULL)
		goto out;
	pampd = tmem_pampd_delete_from_obj(obj, index);
	if (pampd == NULL)
		goto out;
	(*tmem_pamops.free)(pampd, pool, oidp, index, true);
	if (obj->pampd_count == 0) {
		tmem_obj_free(obj, hb);
		(*tmem_hostops.obj_free)(obj, pool);
	}
	ret = 0;

out:
	spin_unlock(&hb->lock);
	return ret;
}

/*
 * "Flush" all pages in tmem matching this oid.
 */
int tmem_flush_object(struct tmem_pool *pool, struct tmem_oid *oidp)
{
	struct tmem_obj *obj;
	struct tmem_hashbucket *hb;
	int ret = -1;

	hb = &pool->hashbucket[tmem_oid_hash(oidp)];
	spin_lock(&hb->lock);
	obj = tmem_obj_find(hb, oidp);
	if (obj == NULL)
		goto out;
	tmem_pampd_destroy_all_in_obj(obj, false);
	tmem_obj_free(obj, hb);
	(*tmem_hostops.obj_free)(obj, pool);
	ret = 0;

out:
	spin_unlock(&hb->lock);
	return ret;
}

/*
 * "Flush" all pages (and tmem_objs) from this tmem_pool and disable
 * all subsequent access to this tmem_pool.
 */
int tmem_destroy_pool(struct tmem_pool *pool)
{
	int ret = -1;

	if (pool == NULL)
		goto out;
	tmem_pool_flush(pool, 1);
	ret = 0;
out:
	return ret;
}

static LIST_HEAD(tmem_global_pool_list);

/*
 * Create a new tmem_pool with the provided flag and return
 * a pool id provided by the tmem host implementation.
 */
void tmem_new_pool(struct tmem_pool *pool, uint32_t flags)
{
	int persistent = flags & TMEM_POOL_PERSIST;
	int shared = flags & TMEM_POOL_SHARED;
	struct tmem_hashbucket *hb = &pool->hashbucket[0];
	int i;

	for (i = 0; i < TMEM_HASH_BUCKETS; i++, hb++) {
		hb->obj_rb_root = RB_ROOT;
		spin_lock_init(&hb->lock);
	}
	INIT_LIST_HEAD(&pool->pool_list);
	atomic_set(&pool->obj_count, 0);
	SET_SENTINEL(pool, POOL);
	list_add_tail(&pool->pool_list, &tmem_global_pool_list);
	pool->persistent = persistent;
	pool->shared = shared;
}