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Diffstat (limited to 'ipc/kdbus/node.c')
-rw-r--r-- | ipc/kdbus/node.c | 897 |
1 files changed, 897 insertions, 0 deletions
diff --git a/ipc/kdbus/node.c b/ipc/kdbus/node.c new file mode 100644 index 000000000..89f58bc85 --- /dev/null +++ b/ipc/kdbus/node.c @@ -0,0 +1,897 @@ +/* + * Copyright (C) 2013-2015 Kay Sievers + * Copyright (C) 2013-2015 Greg Kroah-Hartman <gregkh@linuxfoundation.org> + * Copyright (C) 2013-2015 Daniel Mack <daniel@zonque.org> + * Copyright (C) 2013-2015 David Herrmann <dh.herrmann@gmail.com> + * Copyright (C) 2013-2015 Linux Foundation + * + * kdbus is free software; you can redistribute it and/or modify it under + * the terms of the GNU Lesser General Public License as published by the + * Free Software Foundation; either version 2.1 of the License, or (at + * your option) any later version. + */ + +#include <linux/atomic.h> +#include <linux/fs.h> +#include <linux/idr.h> +#include <linux/kdev_t.h> +#include <linux/rbtree.h> +#include <linux/rwsem.h> +#include <linux/sched.h> +#include <linux/slab.h> +#include <linux/wait.h> + +#include "bus.h" +#include "domain.h" +#include "endpoint.h" +#include "fs.h" +#include "handle.h" +#include "node.h" +#include "util.h" + +/** + * DOC: kdbus nodes + * + * Nodes unify lifetime management across exposed kdbus objects and provide a + * hierarchy. Each kdbus object, that might be exposed to user-space, has a + * kdbus_node object embedded and is linked into the hierarchy. Each node can + * have any number (0-n) of child nodes linked. Each child retains a reference + * to its parent node. For root-nodes, the parent is NULL. + * + * Each node object goes through a bunch of states during it's lifetime: + * * NEW + * * LINKED (can be skipped by NEW->FREED transition) + * * ACTIVE (can be skipped by LINKED->INACTIVE transition) + * * INACTIVE + * * DRAINED + * * FREED + * + * Each node is allocated by the caller and initialized via kdbus_node_init(). + * This never fails and sets the object into state NEW. From now on, ref-counts + * on the node manage its lifetime. During init, the ref-count is set to 1. Once + * it drops to 0, the node goes to state FREED and the node->free_cb() callback + * is called to deallocate any memory. + * + * After initializing a node, you usually link it into the hierarchy. You need + * to provide a parent node and a name. The node will be linked as child to the + * parent and a globally unique ID is assigned to the child. The name of the + * child must be unique for all children of this parent. Otherwise, linking the + * child will fail with -EEXIST. + * Note that the child is not marked active, yet. Admittedly, it prevents any + * other node from being linked with the same name (thus, it reserves that + * name), but any child-lookup (via name or unique ID) will never return this + * child unless it has been marked active. + * + * Once successfully linked, you can use kdbus_node_activate() to activate a + * child. This will mark the child active. This state can be skipped by directly + * deactivating the child via kdbus_node_deactivate() (see below). + * By activating a child, you enable any lookups on this child to succeed from + * now on. Furthermore, any code that got its hands on a reference to the node, + * can from now on "acquire" the node. + * + * Active References (or: 'acquiring' and 'releasing' a node) + * Additionally to normal object references, nodes support something we call + * "active references". An active reference can be acquired via + * kdbus_node_acquire() and released via kdbus_node_release(). A caller + * _must_ own a normal object reference whenever calling those functions. + * Unlike object references, acquiring an active reference can fail (by + * returning 'false' from kdbus_node_acquire()). An active reference can + * only be acquired if the node is marked active. If it is not marked + * active, yet, or if it was already deactivated, no more active references + * can be acquired, ever! + * Active references are used to track tasks working on a node. Whenever a + * task enters kernel-space to perform an action on a node, it acquires an + * active reference, performs the action and releases the reference again. + * While holding an active reference, the node is guaranteed to stay active. + * If the node is deactivated in parallel, the node is marked as + * deactivated, then we wait for all active references to be dropped, before + * we finally proceed with any cleanups. That is, if you hold an active + * reference to a node, any resources that are bound to the "active" state + * are guaranteed to stay accessible until you release your reference. + * + * Active-references are very similar to rw-locks, where acquiring a node is + * equal to try-read-lock and releasing to read-unlock. Deactivating a node + * means write-lock and never releasing it again. + * Unlike rw-locks, the 'active reference' concept is more versatile and + * avoids unusual rw-lock usage (never releasing a write-lock..). + * + * It is safe to acquire multiple active-references recursively. But you + * need to check the return value of kdbus_node_acquire() on _each_ call. It + * may stop granting references at _any_ time. + * + * You're free to perform any operations you want while holding an active + * reference, except sleeping for an indefinite period. Sleeping for a fixed + * amount of time is fine, but you usually should not wait on wait-queues + * without a timeout. + * For example, if you wait for I/O to happen, you should gather all data + * and schedule the I/O operation, then release your active reference and + * wait for it to complete. Then try to acquire a new reference. If it + * fails, perform any cleanup (the node is now dead). Otherwise, you can + * finish your operation. + * + * All nodes can be deactivated via kdbus_node_deactivate() at any time. You can + * call this multiple times, even in parallel or on nodes that were never + * linked, and it will just work. The only restriction is, you must not hold an + * active reference when calling kdbus_node_deactivate(). + * By deactivating a node, it is immediately marked inactive. Then, we wait for + * all active references to be released (called 'draining' the node). This + * shouldn't take very long as we don't perform long-lasting operations while + * holding an active reference. Note that once the node is marked inactive, no + * new active references can be acquired. + * Once all active references are dropped, the node is considered 'drained'. Now + * kdbus_node_deactivate() is called on each child of the node before we + * continue deactivating our node. That is, once all children are entirely + * deactivated, we call ->release_cb() of our node. ->release_cb() can release + * any resources on that node which are bound to the "active" state of a node. + * When done, we unlink the node from its parent rb-tree, mark it as + * 'released' and return. + * If kdbus_node_deactivate() is called multiple times (even in parallel), all + * but one caller will just wait until the node is fully deactivated. That is, + * one random caller of kdbus_node_deactivate() is selected to call + * ->release_cb() and cleanup the node. Only once all this is done, all other + * callers will return from kdbus_node_deactivate(). That is, it doesn't matter + * whether you're the selected caller or not, it will only return after + * everything is fully done. + * + * When a node is activated, we acquire a normal object reference to the node. + * This reference is dropped after deactivation is fully done (and only iff the + * node really was activated). This allows callers to link+activate a child node + * and then drop all refs. The node will be deactivated together with the + * parent, and then be freed when this reference is dropped. + * + * Currently, nodes provide a bunch of resources that external code can use + * directly. This includes: + * + * * node->waitq: Each node has its own wait-queue that is used to manage + * the 'active' state. When a node is deactivated, we wait on + * this queue until all active refs are dropped. Analogously, + * when you release an active reference on a deactivated + * node, and the active ref-count drops to 0, we wake up a + * single thread on this queue. Furthermore, once the + * ->release_cb() callback finished, we wake up all waiters. + * The node-owner is free to re-use this wait-queue for other + * purposes. As node-management uses this queue only during + * deactivation, it is usually totally fine to re-use the + * queue for other, preferably low-overhead, use-cases. + * + * * node->type: This field defines the type of the owner of this node. It + * must be set during node initialization and must remain + * constant. The node management never looks at this value, + * but external users might use to gain access to the owner + * object of a node. + * It is totally up to the owner of the node to define what + * their type means. Usually it means you can access the + * parent structure via container_of(), as long as you hold an + * active reference to the node. + * + * * node->free_cb: callback after all references are dropped + * node->release_cb: callback during node deactivation + * These fields must be set by the node owner during + * node initialization. They must remain constant. If + * NULL, they're skipped. + * + * * node->mode: filesystem access modes + * node->uid: filesystem owner uid + * node->gid: filesystem owner gid + * These fields must be set by the node owner during node + * initialization. They must remain constant and may be + * accessed by other callers to properly initialize + * filesystem nodes. + * + * * node->id: This is an unsigned 32bit integer allocated by an IDA. It is + * always kept as small as possible during allocation and is + * globally unique across all nodes allocated by this module. 0 + * is reserved as "not assigned" and is the default. + * The ID is assigned during kdbus_node_link() and is kept until + * the object is freed. Thus, the ID surpasses the active + * lifetime of a node. As long as you hold an object reference + * to a node (and the node was linked once), the ID is valid and + * unique. + * + * * node->name: name of this node + * node->hash: 31bit hash-value of @name (range [2..INT_MAX-1]) + * These values follow the same lifetime rules as node->id. + * They're initialized when the node is linked and then remain + * constant until the last object reference is dropped. + * Unlike the id, the name is only unique across all siblings + * and only until the node is deactivated. Currently, the name + * is even unique if linked but not activated, yet. This might + * change in the future, though. Code should not rely on this. + * + * * node->lock: lock to protect node->children, node->rb, node->parent + * * node->parent: Reference to parent node. This is set during LINK time + * and is dropped during destruction. You must not access + * it unless you hold an active reference to the node or if + * you know the node is dead. + * * node->children: rb-tree of all linked children of this node. You must + * not access this directly, but use one of the iterator + * or lookup helpers. + */ + +/* + * Bias values track states of "active references". They're all negative. If a + * node is active, its active-ref-counter is >=0 and tracks all active + * references. Once a node is deactivaed, we subtract NODE_BIAS. This means, the + * counter is now negative but still counts the active references. Once it drops + * to exactly NODE_BIAS, we know all active references were dropped. Exactly one + * thread will change it to NODE_RELEASE now, perform cleanup and then put it + * into NODE_DRAINED. Once drained, all other threads that tried deactivating + * the node will now be woken up (thus, they wait until the node is fully done). + * The initial state during node-setup is NODE_NEW. If a node is directly + * deactivated without having ever been active, it is put into + * NODE_RELEASE_DIRECT instead of NODE_BIAS. This tracks this one-bit state + * across node-deactivation. The task putting it into NODE_RELEASE now knows + * whether the node was active before or not. + * + * Some archs implement atomic_sub(v) with atomic_add(-v), so reserve INT_MIN + * to avoid overflows if multiplied by -1. + */ +#define KDBUS_NODE_BIAS (INT_MIN + 5) +#define KDBUS_NODE_RELEASE_DIRECT (KDBUS_NODE_BIAS - 1) +#define KDBUS_NODE_RELEASE (KDBUS_NODE_BIAS - 2) +#define KDBUS_NODE_DRAINED (KDBUS_NODE_BIAS - 3) +#define KDBUS_NODE_NEW (KDBUS_NODE_BIAS - 4) + +/* global unique ID mapping for kdbus nodes */ +DEFINE_IDA(kdbus_node_ida); + +/** + * kdbus_node_name_hash() - hash a name + * @name: The string to hash + * + * This computes the hash of @name. It is guaranteed to be in the range + * [2..INT_MAX-1]. The values 1, 2 and INT_MAX are unused as they are reserved + * for the filesystem code. + * + * Return: hash value of the passed string + */ +static unsigned int kdbus_node_name_hash(const char *name) +{ + unsigned int hash; + + /* reserve hash numbers 0, 1 and >=INT_MAX for magic directories */ + hash = kdbus_strhash(name) & INT_MAX; + if (hash < 2) + hash += 2; + if (hash >= INT_MAX) + hash = INT_MAX - 1; + + return hash; +} + +/** + * kdbus_node_name_compare() - compare a name with a node's name + * @hash: hash of the string to compare the node with + * @name: name to compare the node with + * @node: node to compare the name with + * + * Return: 0 if @name and @hash exactly match the information in @node, or + * an integer less than or greater than zero if @name is found, respectively, + * to be less than or be greater than the string stored in @node. + */ +static int kdbus_node_name_compare(unsigned int hash, const char *name, + const struct kdbus_node *node) +{ + if (hash != node->hash) + return hash - node->hash; + + return strcmp(name, node->name); +} + +/** + * kdbus_node_init() - initialize a kdbus_node + * @node: Pointer to the node to initialize + * @type: The type the node will have (KDBUS_NODE_*) + * + * The caller is responsible of allocating @node and initializating it to zero. + * Once this call returns, you must use the node_ref() and node_unref() + * functions to manage this node. + */ +void kdbus_node_init(struct kdbus_node *node, unsigned int type) +{ + atomic_set(&node->refcnt, 1); + mutex_init(&node->lock); + node->id = 0; + node->type = type; + RB_CLEAR_NODE(&node->rb); + node->children = RB_ROOT; + init_waitqueue_head(&node->waitq); + atomic_set(&node->active, KDBUS_NODE_NEW); +} + +/** + * kdbus_node_link() - link a node into the nodes system + * @node: Pointer to the node to initialize + * @parent: Pointer to a parent node, may be %NULL + * @name: The name of the node (or NULL if root node) + * + * This links a node into the hierarchy. This must not be called multiple times. + * If @parent is NULL, the node becomes a new root node. + * + * This call will fail if @name is not unique across all its siblings or if no + * ID could be allocated. You must not activate a node if linking failed! It is + * safe to deactivate it, though. + * + * Once you linked a node, you must call kdbus_node_deactivate() before you drop + * the last reference (even if you never activate the node). + * + * Return: 0 on success. negative error otherwise. + */ +int kdbus_node_link(struct kdbus_node *node, struct kdbus_node *parent, + const char *name) +{ + int ret; + + if (WARN_ON(node->type != KDBUS_NODE_DOMAIN && !parent)) + return -EINVAL; + + if (WARN_ON(parent && !name)) + return -EINVAL; + + if (name) { + node->name = kstrdup(name, GFP_KERNEL); + if (!node->name) + return -ENOMEM; + + node->hash = kdbus_node_name_hash(name); + } + + ret = ida_simple_get(&kdbus_node_ida, 1, 0, GFP_KERNEL); + if (ret < 0) + return ret; + + node->id = ret; + ret = 0; + + if (parent) { + struct rb_node **n, *prev; + + if (!kdbus_node_acquire(parent)) + return -ESHUTDOWN; + + mutex_lock(&parent->lock); + + n = &parent->children.rb_node; + prev = NULL; + + while (*n) { + struct kdbus_node *pos; + int result; + + pos = kdbus_node_from_rb(*n); + prev = *n; + result = kdbus_node_name_compare(node->hash, + node->name, + pos); + if (result == 0) { + ret = -EEXIST; + goto exit_unlock; + } + + if (result < 0) + n = &pos->rb.rb_left; + else + n = &pos->rb.rb_right; + } + + /* add new node and rebalance the tree */ + rb_link_node(&node->rb, prev, n); + rb_insert_color(&node->rb, &parent->children); + node->parent = kdbus_node_ref(parent); + +exit_unlock: + mutex_unlock(&parent->lock); + kdbus_node_release(parent); + } + + return ret; +} + +/** + * kdbus_node_ref() - Acquire object reference + * @node: node to acquire reference to (or NULL) + * + * This acquires a new reference to @node. You must already own a reference when + * calling this! + * If @node is NULL, this is a no-op. + * + * Return: @node is returned + */ +struct kdbus_node *kdbus_node_ref(struct kdbus_node *node) +{ + if (node) + atomic_inc(&node->refcnt); + return node; +} + +/** + * kdbus_node_unref() - Drop object reference + * @node: node to drop reference to (or NULL) + * + * This drops an object reference to @node. You must not access the node if you + * no longer own a reference. + * If the ref-count drops to 0, the object will be destroyed (->free_cb will be + * called). + * + * If you linked or activated the node, you must deactivate the node before you + * drop your last reference! If you didn't link or activate the node, you can + * drop any reference you want. + * + * Note that this calls into ->free_cb() and thus _might_ sleep. The ->free_cb() + * callbacks must not acquire any outer locks, though. So you can safely drop + * references while holding locks. + * + * If @node is NULL, this is a no-op. + * + * Return: This always returns NULL + */ +struct kdbus_node *kdbus_node_unref(struct kdbus_node *node) +{ + if (node && atomic_dec_and_test(&node->refcnt)) { + struct kdbus_node safe = *node; + + WARN_ON(atomic_read(&node->active) != KDBUS_NODE_DRAINED); + WARN_ON(!RB_EMPTY_NODE(&node->rb)); + + if (node->free_cb) + node->free_cb(node); + if (safe.id > 0) + ida_simple_remove(&kdbus_node_ida, safe.id); + + kfree(safe.name); + + /* + * kdbusfs relies on the parent to be available even after the + * node was deactivated and unlinked. Therefore, we pin it + * until a node is destroyed. + */ + kdbus_node_unref(safe.parent); + } + + return NULL; +} + +/** + * kdbus_node_is_active() - test whether a node is active + * @node: node to test + * + * This checks whether @node is active. That means, @node was linked and + * activated by the node owner and hasn't been deactivated, yet. If, and only + * if, a node is active, kdbus_node_acquire() will be able to acquire active + * references. + * + * Note that this function does not give any lifetime guarantees. After this + * call returns, the node might be deactivated immediately. Normally, what you + * want is to acquire a real active reference via kdbus_node_acquire(). + * + * Return: true if @node is active, false otherwise + */ +bool kdbus_node_is_active(struct kdbus_node *node) +{ + return atomic_read(&node->active) >= 0; +} + +/** + * kdbus_node_is_deactivated() - test whether a node was already deactivated + * @node: node to test + * + * This checks whether kdbus_node_deactivate() was called on @node. Note that + * this might be true even if you never deactivated the node directly, but only + * one of its ancestors. + * + * Note that even if this returns 'false', the node might get deactivated + * immediately after the call returns. + * + * Return: true if @node was already deactivated, false if not + */ +bool kdbus_node_is_deactivated(struct kdbus_node *node) +{ + int v; + + v = atomic_read(&node->active); + return v != KDBUS_NODE_NEW && v < 0; +} + +/** + * kdbus_node_activate() - activate a node + * @node: node to activate + * + * This marks @node as active if, and only if, the node wasn't activated nor + * deactivated, yet, and the parent is still active. Any but the first call to + * kdbus_node_activate() is a no-op. + * If you called kdbus_node_deactivate() before, then even the first call to + * kdbus_node_activate() will be a no-op. + * + * This call doesn't give any lifetime guarantees. The node might get + * deactivated immediately after this call returns. Or the parent might already + * be deactivated, which will make this call a no-op. + * + * If this call successfully activated a node, it will take an object reference + * to it. This reference is dropped after the node is deactivated. Therefore, + * the object owner can safely drop their reference to @node iff they know that + * its parent node will get deactivated at some point. Once the parent node is + * deactivated, it will deactivate all its child and thus drop this reference + * again. + * + * Return: True if this call successfully activated the node, otherwise false. + * Note that this might return false, even if the node is still active + * (eg., if you called this a second time). + */ +bool kdbus_node_activate(struct kdbus_node *node) +{ + bool res = false; + + mutex_lock(&node->lock); + if (atomic_read(&node->active) == KDBUS_NODE_NEW) { + atomic_sub(KDBUS_NODE_NEW, &node->active); + /* activated nodes have ref +1 */ + kdbus_node_ref(node); + res = true; + } + mutex_unlock(&node->lock); + + return res; +} + +/** + * kdbus_node_deactivate() - deactivate a node + * @node: The node to deactivate. + * + * This function recursively deactivates this node and all its children. It + * returns only once all children and the node itself were recursively disabled + * (even if you call this function multiple times in parallel). + * + * It is safe to call this function on _any_ node that was initialized _any_ + * number of times. + * + * This call may sleep, as it waits for all active references to be dropped. + */ +void kdbus_node_deactivate(struct kdbus_node *node) +{ + struct kdbus_node *pos, *child; + struct rb_node *rb; + int v_pre, v_post; + + pos = node; + + /* + * To avoid recursion, we perform back-tracking while deactivating + * nodes. For each node we enter, we first mark the active-counter as + * deactivated by adding BIAS. If the node as children, we set the first + * child as current position and start over. If the node has no + * children, we drain the node by waiting for all active refs to be + * dropped and then releasing the node. + * + * After the node is released, we set its parent as current position + * and start over. If the current position was the initial node, we're + * done. + * + * Note that this function can be called in parallel by multiple + * callers. We make sure that each node is only released once, and any + * racing caller will wait until the other thread fully released that + * node. + */ + + for (;;) { + /* + * Add BIAS to node->active to mark it as inactive. If it was + * never active before, immediately mark it as RELEASE_INACTIVE + * so we remember this state. + * We cannot remember v_pre as we might iterate into the + * children, overwriting v_pre, before we can release our node. + */ + mutex_lock(&pos->lock); + v_pre = atomic_read(&pos->active); + if (v_pre >= 0) + atomic_add_return(KDBUS_NODE_BIAS, &pos->active); + else if (v_pre == KDBUS_NODE_NEW) + atomic_set(&pos->active, KDBUS_NODE_RELEASE_DIRECT); + mutex_unlock(&pos->lock); + + /* wait until all active references were dropped */ + wait_event(pos->waitq, + atomic_read(&pos->active) <= KDBUS_NODE_BIAS); + + mutex_lock(&pos->lock); + /* recurse into first child if any */ + rb = rb_first(&pos->children); + if (rb) { + child = kdbus_node_ref(kdbus_node_from_rb(rb)); + mutex_unlock(&pos->lock); + pos = child; + continue; + } + + /* mark object as RELEASE */ + v_post = atomic_read(&pos->active); + if (v_post == KDBUS_NODE_BIAS || + v_post == KDBUS_NODE_RELEASE_DIRECT) + atomic_set(&pos->active, KDBUS_NODE_RELEASE); + mutex_unlock(&pos->lock); + + /* + * If this is the thread that marked the object as RELEASE, we + * perform the actual release. Otherwise, we wait until the + * release is done and the node is marked as DRAINED. + */ + if (v_post == KDBUS_NODE_BIAS || + v_post == KDBUS_NODE_RELEASE_DIRECT) { + if (pos->release_cb) + pos->release_cb(pos, v_post == KDBUS_NODE_BIAS); + + if (pos->parent) { + mutex_lock(&pos->parent->lock); + if (!RB_EMPTY_NODE(&pos->rb)) { + rb_erase(&pos->rb, + &pos->parent->children); + RB_CLEAR_NODE(&pos->rb); + } + mutex_unlock(&pos->parent->lock); + } + + /* mark as DRAINED */ + atomic_set(&pos->active, KDBUS_NODE_DRAINED); + wake_up_all(&pos->waitq); + + /* drop VFS cache */ + kdbus_fs_flush(pos); + + /* + * If the node was activated and someone subtracted BIAS + * from it to deactivate it, we, and only us, are + * responsible to release the extra ref-count that was + * taken once in kdbus_node_activate(). + * If the node was never activated, no-one ever + * subtracted BIAS, but instead skipped that state and + * immediately went to NODE_RELEASE_DIRECT. In that case + * we must not drop the reference. + */ + if (v_post == KDBUS_NODE_BIAS) + kdbus_node_unref(pos); + } else { + /* wait until object is DRAINED */ + wait_event(pos->waitq, + atomic_read(&pos->active) == KDBUS_NODE_DRAINED); + } + + /* + * We're done with the current node. Continue on its parent + * again, which will try deactivating its next child, or itself + * if no child is left. + * If we've reached our initial node again, we are done and + * can safely return. + */ + if (pos == node) + break; + + child = pos; + pos = pos->parent; + kdbus_node_unref(child); + } +} + +/** + * kdbus_node_acquire() - Acquire an active ref on a node + * @node: The node + * + * This acquires an active-reference to @node. This will only succeed if the + * node is active. You must release this active reference via + * kdbus_node_release() again. + * + * See the introduction to "active references" for more details. + * + * Return: %true if @node was non-NULL and active + */ +bool kdbus_node_acquire(struct kdbus_node *node) +{ + return node && atomic_inc_unless_negative(&node->active); +} + +/** + * kdbus_node_release() - Release an active ref on a node + * @node: The node + * + * This releases an active reference that was previously acquired via + * kdbus_node_acquire(). See kdbus_node_acquire() for details. + */ +void kdbus_node_release(struct kdbus_node *node) +{ + if (node && atomic_dec_return(&node->active) == KDBUS_NODE_BIAS) + wake_up(&node->waitq); +} + +/** + * kdbus_node_find_child() - Find child by name + * @node: parent node to search through + * @name: name of child node + * + * This searches through all children of @node for a child-node with name @name. + * If not found, or if the child is deactivated, NULL is returned. Otherwise, + * the child is acquired and a new reference is returned. + * + * If you're done with the child, you need to release it and drop your + * reference. + * + * This function does not acquire the parent node. However, if the parent was + * already deactivated, then kdbus_node_deactivate() will, at some point, also + * deactivate the child. Therefore, we can rely on the explicit ordering during + * deactivation. + * + * Return: Reference to acquired child node, or NULL if not found / not active. + */ +struct kdbus_node *kdbus_node_find_child(struct kdbus_node *node, + const char *name) +{ + struct kdbus_node *child; + struct rb_node *rb; + unsigned int hash; + int ret; + + hash = kdbus_node_name_hash(name); + + mutex_lock(&node->lock); + rb = node->children.rb_node; + while (rb) { + child = kdbus_node_from_rb(rb); + ret = kdbus_node_name_compare(hash, name, child); + if (ret < 0) + rb = rb->rb_left; + else if (ret > 0) + rb = rb->rb_right; + else + break; + } + if (rb && kdbus_node_acquire(child)) + kdbus_node_ref(child); + else + child = NULL; + mutex_unlock(&node->lock); + + return child; +} + +static struct kdbus_node *node_find_closest_unlocked(struct kdbus_node *node, + unsigned int hash, + const char *name) +{ + struct kdbus_node *n, *pos = NULL; + struct rb_node *rb; + int res; + + /* + * Find the closest child with ``node->hash >= hash'', or, if @name is + * valid, ``node->name >= name'' (where '>=' is the lex. order). + */ + + rb = node->children.rb_node; + while (rb) { + n = kdbus_node_from_rb(rb); + + if (name) + res = kdbus_node_name_compare(hash, name, n); + else + res = hash - n->hash; + + if (res <= 0) { + rb = rb->rb_left; + pos = n; + } else { /* ``hash > n->hash'', ``name > n->name'' */ + rb = rb->rb_right; + } + } + + return pos; +} + +/** + * kdbus_node_find_closest() - Find closest child-match + * @node: parent node to search through + * @hash: hash value to find closest match for + * + * Find the closest child of @node with a hash greater than or equal to @hash. + * The closest match is the left-most child of @node with this property. Which + * means, it is the first child with that hash returned by + * kdbus_node_next_child(), if you'd iterate the whole parent node. + * + * Return: Reference to acquired child, or NULL if none found. + */ +struct kdbus_node *kdbus_node_find_closest(struct kdbus_node *node, + unsigned int hash) +{ + struct kdbus_node *child; + struct rb_node *rb; + + mutex_lock(&node->lock); + + child = node_find_closest_unlocked(node, hash, NULL); + while (child && !kdbus_node_acquire(child)) { + rb = rb_next(&child->rb); + if (rb) + child = kdbus_node_from_rb(rb); + else + child = NULL; + } + kdbus_node_ref(child); + + mutex_unlock(&node->lock); + + return child; +} + +/** + * kdbus_node_next_child() - Acquire next child + * @node: parent node + * @prev: previous child-node position or NULL + * + * This function returns a reference to the next active child of @node, after + * the passed position @prev. If @prev is NULL, a reference to the first active + * child is returned. If no more active children are found, NULL is returned. + * + * This function acquires the next child it returns. If you're done with the + * returned pointer, you need to release _and_ unref it. + * + * The passed in pointer @prev is not modified by this function, and it does + * *not* have to be active. If @prev was acquired via different means, or if it + * was unlinked from its parent before you pass it in, then this iterator will + * still return the next active child (it will have to search through the + * rb-tree based on the node-name, though). + * However, @prev must not be linked to a different parent than @node! + * + * Return: Reference to next acquired child, or NULL if at the end. + */ +struct kdbus_node *kdbus_node_next_child(struct kdbus_node *node, + struct kdbus_node *prev) +{ + struct kdbus_node *pos = NULL; + struct rb_node *rb; + + mutex_lock(&node->lock); + + if (!prev) { + /* + * New iteration; find first node in rb-tree and try to acquire + * it. If we got it, directly return it as first element. + * Otherwise, the loop below will find the next active node. + */ + rb = rb_first(&node->children); + if (!rb) + goto exit; + pos = kdbus_node_from_rb(rb); + if (kdbus_node_acquire(pos)) + goto exit; + } else if (RB_EMPTY_NODE(&prev->rb)) { + /* + * The current iterator is no longer linked to the rb-tree. Use + * its hash value and name to find the next _higher_ node and + * acquire it. If we got it, return it as next element. + * Otherwise, the loop below will find the next active node. + */ + pos = node_find_closest_unlocked(node, prev->hash, prev->name); + if (!pos) + goto exit; + if (kdbus_node_acquire(pos)) + goto exit; + } else { + /* + * The current iterator is still linked to the parent. Set it + * as current position and use the loop below to find the next + * active element. + */ + pos = prev; + } + + /* @pos was already returned or is inactive; find next active node */ + do { + rb = rb_next(&pos->rb); + if (rb) + pos = kdbus_node_from_rb(rb); + else + pos = NULL; + } while (pos && !kdbus_node_acquire(pos)); + +exit: + /* @pos is NULL or acquired. Take ref if non-NULL and return it */ + kdbus_node_ref(pos); + mutex_unlock(&node->lock); + return pos; +} |